Department of Computer Science amp EngineeringYCCE Nagpur

Seminaron

WWW(World Wide Web)

Presented ByMr Pratik R Tambekar

Roll No-19MTech II Sem(CSE)

The World Wide Web (WWW) can be viewed as a huge distributed system with millions of clients and servers for accessing linked documents

Servers maintain collections of documents while clients provide users an easy-to-use interface for presenting and accessing those documents

A document is fetched from a server transferred to a client and presented on the screen To a user there is conceptually no difference between a document stored locally or in another part of the world

2

INTRODUCTION

CONThellip

Now Web has become more than just a simple document based system

With the emergence of Web services it is becoming a system of distributed services rather than just documents offered to any user or machine

What can we get from WWW Read news listen to music and watch videoBuy or sell goods such as books airline ticketsMake reservations on hotel room rental car restaurant etcPay bills and transfer money from one bank account to anotherhellip

3

TRADITIONAL WEB-BASED SYSTEMS

4

Many Web-based systems are still organized as simple client-server architectures

The core of a Web site a process that has access to a local file system storing documents

How to refer to a documentURL (Uniform Resource Locator)Example

httpwwwcseunledu~ylucsce855notesweb- systemppt

A client interacts with Web servers through a special application known as browser

Whatrsquos the key function of a browserResponsible for displaying documents

5

The World Wide Web (WWW) can be viewed as a huge distributed system with millions of clients and servers for accessing linked documents

Servers maintain collections of documents while clients provide users an easy-to-use interface for presenting and accessing those documents

A document is fetched from a server transferred to a client and presented on the screen To a user there is conceptually no difference between a document stored locally or in another part of the world

2

INTRODUCTION

CONThellip

Now Web has become more than just a simple document based system

With the emergence of Web services it is becoming a system of distributed services rather than just documents offered to any user or machine

What can we get from WWW Read news listen to music and watch videoBuy or sell goods such as books airline ticketsMake reservations on hotel room rental car restaurant etcPay bills and transfer money from one bank account to anotherhellip

3

TRADITIONAL WEB-BASED SYSTEMS

4

Many Web-based systems are still organized as simple client-server architectures

The core of a Web site a process that has access to a local file system storing documents

How to refer to a documentURL (Uniform Resource Locator)Example

httpwwwcseunledu~ylucsce855notesweb- systemppt

A client interacts with Web servers through a special application known as browser

Whatrsquos the key function of a browserResponsible for displaying documents

5

CONThellip

Now Web has become more than just a simple document based system

With the emergence of Web services it is becoming a system of distributed services rather than just documents offered to any user or machine

What can we get from WWW Read news listen to music and watch videoBuy or sell goods such as books airline ticketsMake reservations on hotel room rental car restaurant etcPay bills and transfer money from one bank account to anotherhellip

3

TRADITIONAL WEB-BASED SYSTEMS

4

Many Web-based systems are still organized as simple client-server architectures

The core of a Web site a process that has access to a local file system storing documents

How to refer to a documentURL (Uniform Resource Locator)Example

httpwwwcseunledu~ylucsce855notesweb- systemppt

A client interacts with Web servers through a special application known as browser

Whatrsquos the key function of a browserResponsible for displaying documents

5

TRADITIONAL WEB-BASED SYSTEMS

4

Many Web-based systems are still organized as simple client-server architectures

The core of a Web site a process that has access to a local file system storing documents

How to refer to a documentURL (Uniform Resource Locator)Example

httpwwwcseunledu~ylucsce855notesweb- systemppt

A client interacts with Web servers through a special application known as browser

Whatrsquos the key function of a browserResponsible for displaying documents

5

The core of a Web site a process that has access to a local file system storing documents

How to refer to a documentURL (Uniform Resource Locator)Example

httpwwwcseunledu~ylucsce855notesweb- systemppt

A client interacts with Web servers through a special application known as browser

Whatrsquos the key function of a browserResponsible for displaying documents

5

Document Model

A Web document does not only contain text but it can include all kinds of dynamic features such as audio video animations etc

In many cases special helper applications (interpreters) are needed and they are integrated into the browser Eg Windows Media Player and QuickTime Player for playing

streaming content

The variety of document types forces browser to be extensible As a result plug-ins are required to follow a standard interfaces so that they can be easily integrated with the browsers 6

CONThellip

User data comes from an HTML form specifying the program and parameters

Server-side scripting technologies are used to generate dynamic contentMicrosoft Active Server Pages (ASPNET)Sun Java Server Pages (JSP)Netscape JavaScriptFree Software Foundation PHP

7

8

ltHTMLgt lt- Start of HTML document --gtltBODYgt lt- Start of the main body --gtltH1gtHello WorldH1gt lt- Basic text to be displayed --gtltPgt lt- Start of a new paragraph --gtltSCRIPT type = textjavascriptgt lt- identify scripting language --gt documentwriteln (ltH1gtHello WorldltH1gt Write a line of textltSCRIPTgt lt- End of scripting section--gtltPgt lt- End of paragraph section --gtltBODYgt lt- End of main body--gtltHTMLgt lt- End of HTML section--gtbull A simple Web page embedding a script written in JavaScript

Document Model (1)

When a web page is loaded the browser creates a Document Object Model of the pageThe HTML DOM model is constructed as a tree of Objects

9

Document Model (2)

10

(1) ltELEMENT article (title author+journal)gt(2) ltELEMENT title (PCDATA)gt(3) ltELEMENT author (name affiliation)gt(4) ltELEMENT name (PCDATA)gt(5) ltELEMENT affiliation (PCDATA)gt(6) ltELEMENT journal (jname volume number month pages year)gt(7) ltELEMENT jname (PCDATA)gt(8) ltELEMENT volume (PCDATA)gt(9) ltELEMENT number (PCDATA)gt(10) ltELEMENT month (PCDATA)gt(11) ltELEMENT pages (PCDATA)gt(12) ltELEMENT year (PCDATA)gt

bull An XML definition for referring to a journal article

11

(1) ltxml = version 10gt(2) ltDOCTYPE article SYSTEM articledtdgt(3) ltarticlegt(4) lttitlegt Prudent Engineering Practice for Cryptographic Protocolslttitlegt(5) ltauthorgtltnamegtM Abadiltnamegtltauthorgt(6) ltauthorgtltnamegtR Needhamltnamegtltauthorgt(7) ltjournalgt(8) ltjnamegtIEEE Transactions on Software Engineeringltjnamegt(9) ltvolumegt22ltvolumegt(10) ltnumbergt12ltnumbergt(11) ltmonthgtJanuaryltmonthgt(12) ltpagesgt6 ndash 15ltpagesgt(13) ltyeargt1996ltyeargt(14) ltjournalgt(15) ltarticlegt

bull An XML document using the XML definitions from previous slide

Document Types

12

Type Subtype Description

Text Plain Unformatted text

HTML Text including HTML markup commands

XML Text including XML markup commands

Image GIF Still image in GIF format

JPEG Still image in JPEG format

Audio Basic Audio 8-bit PCM sampled at 8000 Hz

Tone A specific audible tone

Video MPEG Movie in MPEG format

Pointer Representation of a pointer device for presentations

Application Octet-stream An uninterrupted byte sequence

Postscript A printable document in Postscript

PDF A printable document in PDF

Multipart Mixed Independent parts in the specified order

Parallel Parts must be viewed simultaneously

bull Six top-level MIME types and some common subtypes

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

CONThellip

User data comes from an HTML form specifying the program and parameters

Server-side scripting technologies are used to generate dynamic contentMicrosoft Active Server Pages (ASPNET)Sun Java Server Pages (JSP)Netscape JavaScriptFree Software Foundation PHP

7

8

ltHTMLgt lt- Start of HTML document --gtltBODYgt lt- Start of the main body --gtltH1gtHello WorldH1gt lt- Basic text to be displayed --gtltPgt lt- Start of a new paragraph --gtltSCRIPT type = textjavascriptgt lt- identify scripting language --gt documentwriteln (ltH1gtHello WorldltH1gt Write a line of textltSCRIPTgt lt- End of scripting section--gtltPgt lt- End of paragraph section --gtltBODYgt lt- End of main body--gtltHTMLgt lt- End of HTML section--gtbull A simple Web page embedding a script written in JavaScript

Document Model (1)

When a web page is loaded the browser creates a Document Object Model of the pageThe HTML DOM model is constructed as a tree of Objects

9

Document Model (2)

10

(1) ltELEMENT article (title author+journal)gt(2) ltELEMENT title (PCDATA)gt(3) ltELEMENT author (name affiliation)gt(4) ltELEMENT name (PCDATA)gt(5) ltELEMENT affiliation (PCDATA)gt(6) ltELEMENT journal (jname volume number month pages year)gt(7) ltELEMENT jname (PCDATA)gt(8) ltELEMENT volume (PCDATA)gt(9) ltELEMENT number (PCDATA)gt(10) ltELEMENT month (PCDATA)gt(11) ltELEMENT pages (PCDATA)gt(12) ltELEMENT year (PCDATA)gt

bull An XML definition for referring to a journal article

11

(1) ltxml = version 10gt(2) ltDOCTYPE article SYSTEM articledtdgt(3) ltarticlegt(4) lttitlegt Prudent Engineering Practice for Cryptographic Protocolslttitlegt(5) ltauthorgtltnamegtM Abadiltnamegtltauthorgt(6) ltauthorgtltnamegtR Needhamltnamegtltauthorgt(7) ltjournalgt(8) ltjnamegtIEEE Transactions on Software Engineeringltjnamegt(9) ltvolumegt22ltvolumegt(10) ltnumbergt12ltnumbergt(11) ltmonthgtJanuaryltmonthgt(12) ltpagesgt6 ndash 15ltpagesgt(13) ltyeargt1996ltyeargt(14) ltjournalgt(15) ltarticlegt

bull An XML document using the XML definitions from previous slide

Document Types

12

Type Subtype Description

Text Plain Unformatted text

HTML Text including HTML markup commands

XML Text including XML markup commands

Image GIF Still image in GIF format

JPEG Still image in JPEG format

Audio Basic Audio 8-bit PCM sampled at 8000 Hz

Tone A specific audible tone

Video MPEG Movie in MPEG format

Pointer Representation of a pointer device for presentations

Application Octet-stream An uninterrupted byte sequence

Postscript A printable document in Postscript

PDF A printable document in PDF

Multipart Mixed Independent parts in the specified order

Parallel Parts must be viewed simultaneously

bull Six top-level MIME types and some common subtypes

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

8

ltHTMLgt lt- Start of HTML document --gtltBODYgt lt- Start of the main body --gtltH1gtHello WorldH1gt lt- Basic text to be displayed --gtltPgt lt- Start of a new paragraph --gtltSCRIPT type = textjavascriptgt lt- identify scripting language --gt documentwriteln (ltH1gtHello WorldltH1gt Write a line of textltSCRIPTgt lt- End of scripting section--gtltPgt lt- End of paragraph section --gtltBODYgt lt- End of main body--gtltHTMLgt lt- End of HTML section--gtbull A simple Web page embedding a script written in JavaScript

Document Model (1)

When a web page is loaded the browser creates a Document Object Model of the pageThe HTML DOM model is constructed as a tree of Objects

9

Document Model (2)

10

(1) ltELEMENT article (title author+journal)gt(2) ltELEMENT title (PCDATA)gt(3) ltELEMENT author (name affiliation)gt(4) ltELEMENT name (PCDATA)gt(5) ltELEMENT affiliation (PCDATA)gt(6) ltELEMENT journal (jname volume number month pages year)gt(7) ltELEMENT jname (PCDATA)gt(8) ltELEMENT volume (PCDATA)gt(9) ltELEMENT number (PCDATA)gt(10) ltELEMENT month (PCDATA)gt(11) ltELEMENT pages (PCDATA)gt(12) ltELEMENT year (PCDATA)gt

bull An XML definition for referring to a journal article

11

(1) ltxml = version 10gt(2) ltDOCTYPE article SYSTEM articledtdgt(3) ltarticlegt(4) lttitlegt Prudent Engineering Practice for Cryptographic Protocolslttitlegt(5) ltauthorgtltnamegtM Abadiltnamegtltauthorgt(6) ltauthorgtltnamegtR Needhamltnamegtltauthorgt(7) ltjournalgt(8) ltjnamegtIEEE Transactions on Software Engineeringltjnamegt(9) ltvolumegt22ltvolumegt(10) ltnumbergt12ltnumbergt(11) ltmonthgtJanuaryltmonthgt(12) ltpagesgt6 ndash 15ltpagesgt(13) ltyeargt1996ltyeargt(14) ltjournalgt(15) ltarticlegt

bull An XML document using the XML definitions from previous slide

Document Types

12

Type Subtype Description

Text Plain Unformatted text

HTML Text including HTML markup commands

XML Text including XML markup commands

Image GIF Still image in GIF format

JPEG Still image in JPEG format

Audio Basic Audio 8-bit PCM sampled at 8000 Hz

Tone A specific audible tone

Video MPEG Movie in MPEG format

Pointer Representation of a pointer device for presentations

Application Octet-stream An uninterrupted byte sequence

Postscript A printable document in Postscript

PDF A printable document in PDF

Multipart Mixed Independent parts in the specified order

Parallel Parts must be viewed simultaneously

bull Six top-level MIME types and some common subtypes

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

When a web page is loaded the browser creates a Document Object Model of the pageThe HTML DOM model is constructed as a tree of Objects

9

Document Model (2)

10

(1) ltELEMENT article (title author+journal)gt(2) ltELEMENT title (PCDATA)gt(3) ltELEMENT author (name affiliation)gt(4) ltELEMENT name (PCDATA)gt(5) ltELEMENT affiliation (PCDATA)gt(6) ltELEMENT journal (jname volume number month pages year)gt(7) ltELEMENT jname (PCDATA)gt(8) ltELEMENT volume (PCDATA)gt(9) ltELEMENT number (PCDATA)gt(10) ltELEMENT month (PCDATA)gt(11) ltELEMENT pages (PCDATA)gt(12) ltELEMENT year (PCDATA)gt

bull An XML definition for referring to a journal article

11

(1) ltxml = version 10gt(2) ltDOCTYPE article SYSTEM articledtdgt(3) ltarticlegt(4) lttitlegt Prudent Engineering Practice for Cryptographic Protocolslttitlegt(5) ltauthorgtltnamegtM Abadiltnamegtltauthorgt(6) ltauthorgtltnamegtR Needhamltnamegtltauthorgt(7) ltjournalgt(8) ltjnamegtIEEE Transactions on Software Engineeringltjnamegt(9) ltvolumegt22ltvolumegt(10) ltnumbergt12ltnumbergt(11) ltmonthgtJanuaryltmonthgt(12) ltpagesgt6 ndash 15ltpagesgt(13) ltyeargt1996ltyeargt(14) ltjournalgt(15) ltarticlegt

bull An XML document using the XML definitions from previous slide

Document Types

12

Type Subtype Description

Text Plain Unformatted text

HTML Text including HTML markup commands

XML Text including XML markup commands

Image GIF Still image in GIF format

JPEG Still image in JPEG format

Audio Basic Audio 8-bit PCM sampled at 8000 Hz

Tone A specific audible tone

Video MPEG Movie in MPEG format

Pointer Representation of a pointer device for presentations

Application Octet-stream An uninterrupted byte sequence

Postscript A printable document in Postscript

PDF A printable document in PDF

Multipart Mixed Independent parts in the specified order

Parallel Parts must be viewed simultaneously

bull Six top-level MIME types and some common subtypes

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Document Model (2)

10

(1) ltELEMENT article (title author+journal)gt(2) ltELEMENT title (PCDATA)gt(3) ltELEMENT author (name affiliation)gt(4) ltELEMENT name (PCDATA)gt(5) ltELEMENT affiliation (PCDATA)gt(6) ltELEMENT journal (jname volume number month pages year)gt(7) ltELEMENT jname (PCDATA)gt(8) ltELEMENT volume (PCDATA)gt(9) ltELEMENT number (PCDATA)gt(10) ltELEMENT month (PCDATA)gt(11) ltELEMENT pages (PCDATA)gt(12) ltELEMENT year (PCDATA)gt

bull An XML definition for referring to a journal article

11

(1) ltxml = version 10gt(2) ltDOCTYPE article SYSTEM articledtdgt(3) ltarticlegt(4) lttitlegt Prudent Engineering Practice for Cryptographic Protocolslttitlegt(5) ltauthorgtltnamegtM Abadiltnamegtltauthorgt(6) ltauthorgtltnamegtR Needhamltnamegtltauthorgt(7) ltjournalgt(8) ltjnamegtIEEE Transactions on Software Engineeringltjnamegt(9) ltvolumegt22ltvolumegt(10) ltnumbergt12ltnumbergt(11) ltmonthgtJanuaryltmonthgt(12) ltpagesgt6 ndash 15ltpagesgt(13) ltyeargt1996ltyeargt(14) ltjournalgt(15) ltarticlegt

bull An XML document using the XML definitions from previous slide

Document Types

12

Type Subtype Description

Text Plain Unformatted text

HTML Text including HTML markup commands

XML Text including XML markup commands

Image GIF Still image in GIF format

JPEG Still image in JPEG format

Audio Basic Audio 8-bit PCM sampled at 8000 Hz

Tone A specific audible tone

Video MPEG Movie in MPEG format

Pointer Representation of a pointer device for presentations

Application Octet-stream An uninterrupted byte sequence

Postscript A printable document in Postscript

PDF A printable document in PDF

Multipart Mixed Independent parts in the specified order

Parallel Parts must be viewed simultaneously

bull Six top-level MIME types and some common subtypes

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

11

(1) ltxml = version 10gt(2) ltDOCTYPE article SYSTEM articledtdgt(3) ltarticlegt(4) lttitlegt Prudent Engineering Practice for Cryptographic Protocolslttitlegt(5) ltauthorgtltnamegtM Abadiltnamegtltauthorgt(6) ltauthorgtltnamegtR Needhamltnamegtltauthorgt(7) ltjournalgt(8) ltjnamegtIEEE Transactions on Software Engineeringltjnamegt(9) ltvolumegt22ltvolumegt(10) ltnumbergt12ltnumbergt(11) ltmonthgtJanuaryltmonthgt(12) ltpagesgt6 ndash 15ltpagesgt(13) ltyeargt1996ltyeargt(14) ltjournalgt(15) ltarticlegt

bull An XML document using the XML definitions from previous slide

Document Types

12

Type Subtype Description

Text Plain Unformatted text

HTML Text including HTML markup commands

XML Text including XML markup commands

Image GIF Still image in GIF format

JPEG Still image in JPEG format

Audio Basic Audio 8-bit PCM sampled at 8000 Hz

Tone A specific audible tone

Video MPEG Movie in MPEG format

Pointer Representation of a pointer device for presentations

Application Octet-stream An uninterrupted byte sequence

Postscript A printable document in Postscript

PDF A printable document in PDF

Multipart Mixed Independent parts in the specified order

Parallel Parts must be viewed simultaneously

bull Six top-level MIME types and some common subtypes

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Document Types

12

Type Subtype Description

Text Plain Unformatted text

HTML Text including HTML markup commands

XML Text including XML markup commands

Image GIF Still image in GIF format

JPEG Still image in JPEG format

Audio Basic Audio 8-bit PCM sampled at 8000 Hz

Tone A specific audible tone

Video MPEG Movie in MPEG format

Pointer Representation of a pointer device for presentations

Application Octet-stream An uninterrupted byte sequence

Postscript A printable document in Postscript

PDF A printable document in PDF

Multipart Mixed Independent parts in the specified order

Parallel Parts must be viewed simultaneously

bull Six top-level MIME types and some common subtypes

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Architectural Overview

13

bull The principle of using server-side CGI programs

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

14

(1) ltHTMLgt(2) ltBODYgt(3) ltPgtThe current content of ltpregtdatafiletxtltPREgtisltPgt(4) ltPgt(5) ltSERVER type = textjavascript)(6) clientFile = new File(datafiletxt)(7) if(clientFileopen(r))(8) while (clientFileeof())(9) documentwriteln(clientFilereadln())(10) clientFileclose()(11) (12) ltSERVERgt(13) ltPgt(14) ltPgtThank you for visiting this siteltPgt(15) ltBODYgt(16) ltHTMLgt

bull An HTML document containing a JavaScript to be executed by the server

CONThelliphelliphellip

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

bull Architectural details of a client and server in the Web

CONThelliphelliphellip

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

HTTPAll communication between clients and servers is based

on HTTP Servers listen on port 80HTTP is a simple protocol a client sends a request to a

server and waits for a responseHTTP is stateless it does not have any concept of open

connection and does not require a server to maintain information on its clients (Can use HTTP cookies to store session information)

HTTP is based on TCP whenever a client issues a request to a server it first sets up a TCP connection and sends the message on that connection The same connection is used for receiving the response

One of the problems with the first versions of HTTP was its inefficient use of TCP connectionsHTTP 10 vs HTTP 11

16

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

HTTP CONNECTIONS

A Web document is constructed from a collection of different files from the same server

In HTTP version 10 and older each request to a server required setting up a separate connection When server had responded the connection was broken down These connections are referred as nonpersistent

In HTTP version 11 several requests and their responses can be issued without the need for a separate connection These connections are referred as persistent

Furthermore a client can issue several requests in a row without waiting for the response to the first request which is referred as pipelining

17

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

CONThelliphelliphellip

18(a) Using non-persistent connections (b) Using persistent connections

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

HTTP Methods

19

Operation Description

Head Request to return the header of a document

Get Request to return a document to the client

Put Request to store a document

Post Provide data that is to be added to a document (collection)

Delete Request to delete a document

bull Operations supported by HTTP

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

HTTP Messages

20bull HTTP request message

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

21bull HTTP response message

CONThelliphelliphellip

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

22

Header Source Contents

Accept Client The type of documents the client can handle

Accept-Charset Client The character sets are acceptable for the client

Accept-Encoding Client The document encodings the client can handle

Accept-Language Client The natural language the client can handle

Authorization Client A list of the clients credentials

WWW-Authenticate Server Security challenge the client should respond to

Date Both Date and time the message was sent

ETag Server The tags associated with the returned document

Expires Server The time how long the response remains valid

From Client The clients e-mail address

Host Client The TCP address of the documents server

If-Match Client The tags the document should have

If-None-Match Client The tags the document should not have

If-Modified-Since ClientTells the server to return a document only if it has been modified since the specified time

If-Unmodified-Since ClientTells the server to return a document only if it has not been modified since the specified time

Last-Modified Server The time the returned document was last modified

Location ServerA document reference to which the client should redirect its request

Referer Client Refers to clients most recently requested document

Upgrade Both The application protocol the sender wants to switch to

Warning Both Information about the status of the data in the message

bull Some HTTP message headers

CONThelliphelliphellip

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Processes

A plug-in is a small program that can be dynamically loaded into a browser for handling a specific document type

When a browser encounters a document type for which it needs a plug-in it loads the plug-in locally and creates an instance

The plug-in is removed from the browser when it isno longer needed

23

1Clients

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

24bull Using a plug-in in a Web browser

CONThelliphelliphellip

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

CONThelliphellip

25

bull Using a Web proxy when the browser does not speak FTP

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Important The majority of Web servers is a configured Apache server which breaks down each HTTP request handling into eight phases This approach allows flexible configuration of servers

26

2Servers

bull General organization of the Apache Web server

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

In order to invoke the appropriate handler at the right time processing HTTP requests is broken down into sevral phases

A module can register a handler for a specific phase Whenever a phase is reached the core module inspects which handlers have been registered for that phase and invoke one of them

27

1 Resolving document reference to local file name2 Client authentication3 Client access control4 Request access control5 MIME type determination of the response6 General phase for handling leftovers7 Transmission of the response8 Logging data on the processing of the request

CONThelliphellip

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

28

bull Essence To improve performance and availability WWW servers are often clustered in a way that is transparent to clients

Server Clusters

bull The principle of using a cluster of workstations to implement a Web service

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

bull Problem The front end may easily get overloaded so that special measures need to be taken

bull Transport-layer switching Front end simply passes the TCP request to one of the servers taking some performance metric into account

bull Content-aware distribution Front end reads the content of the HTTP request and then selects the best server

bull A crucial aspect of this organization is the the design of the front end as it can easily become a serious performance bottleneck 29

CONThelliphellip

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

30

CONThelliphellip

(a) The principle of TCP handoff

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

CONThelliphellip

31(b) A scalable content-aware cluster of Web servers

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

1URL(Uniform Resource Locators)

Uniform Resource Locator tells how and where to access a resource

32

Naming

bull Often-used structures for URLsa) Using only a DNS nameb) Combining a DNS name with a port numberc) combining an IP address with a port number

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

33

CONThelliphellip

Name Used for Example

http HTTP httpwwwcsvunl80globe

ftp FTP ftpftpcsvunlpupminxREADME

file Local file fileedubookworkchp1111

data Inline data datatextplaincharset=iso-8859-7e1e2e3

telnet Remote login telnetflitscsvunl

tel Telephone tel+31201234567

modem Modem modem+31201234567type=v32

Examples of URLs

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

2URN(Uniform Resource Names)

URNs are location-independent references to documents

34

The general structure of a URN

bull A typical example of a URN is the one used for identifying books by means of their ISBN such as urnisbn0-13-349945-6

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Synchronization WebDAV

bull Problem There is a growing need for collaborative auditing of Web documents but bare-bones HTTP canrsquot help here

bull Solution Web Distributed Authoring and Versioning

bull Supports exclusive and shared write locks which operate on entire documents

bull A lock is passed by means of a lock token the server registers the client(s) holding the lock

bull Clients modify the document locally and post it back to the server along with the lock token

bull Note There is no specific support for crashed clients holding a lock

35

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Caching and Replication

bull Basic idea Sites install a separate proxy server that handles all outgoing requests Proxies subsequently cache incoming documents Cache-consistency protocolsbull Always verify validity by contacting serverbull Age-based consistency

Texpire = α(Tcached ndash Tlast_modified) + Tcached

bull Cooperative caching by which you first check your neighbors on a cache miss

36

Web Proxy Caching

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

CONThelliphelliphellip

37The principle of cooperative caching

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

bull A nontransparent form of replication that is widely deployed is to make an entire copy of a web site available at a different server This approach is also called Mirroring

bull Content Delivery Network CDNs act as Web hosting services to replicate documents across the Internet providing their customers guarantees on high availability and performance (example Akamai)

38

Server Replication

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

CONThellip

39The principle working of the Akami CDN

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

bull Transport Layer Security Modern version of the the Secure Socket Layer (SSL) which ldquositsrdquo between transport layer and application protocols Relatively simple protocol that can support mutual authentication using certificates

40

Security

The position of TLS in the Internet protocol stack

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Conthelliphellip

41TLS with mutual authentication

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

CONThelliphellip

1first The client informs the server of the cryptographic algorithms it can handle as well as any compression methods it supports

2In the second phase authentication takes place The server is always required to authenticate itself for which reason it passes the client a certificate containing its public key signed by a certification authority CA

3If server requires that the client be authenticated the client will have to send a certificate to the server

4The client generates a random number that will be used by both sides for constructing a session key and sends this number to the server encrypted with the serverrsquos public key

5If client authenticated is required the client signs the number with its private key

42

Thank You

43

Thank You

43