CSCI-235 Micro-Computer Applications The Internet

CSCI-235CSCI-235Micro-Computer ApplicationsMicro-Computer Applications

The InternetThe Internet

Communications and NetworkingCommunications and Networking

LAN (Local Area Network)LAN (Local Area Network)WAN (Wide Area Network)WAN (Wide Area Network)

The The InternetInternet is a global, interconnected computer is a global, interconnected computer network in which every computer connected to it can network in which every computer connected to it can exchange data with any other connected computerexchange data with any other connected computer

History of InternetHistory of InternetThe The ARPANetARPANet (precursor to the Internet) became a (precursor to the Internet) became a reality in 1969reality in 1969

• Advanced Research Project AgencyAdvanced Research Project Agency ((ARPAARPA))• Intended to connect only military installations and Intended to connect only military installations and

universities participating in government projectsuniversities participating in government projects• It employed dedicated cables, buried undergroundIt employed dedicated cables, buried underground• The data transfer was 56K bits/sec, roughly the same The data transfer was 56K bits/sec, roughly the same

as dial-up services todayas dial-up services today

By 1980, close to 100 sites were connected to the By 1980, close to 100 sites were connected to the ARPANetARPANet

• Satellite connections provided links to select cities Satellite connections provided links to select cities outside the continental U.S.outside the continental U.S.

Internet GrowthInternet Growth

© Prentice-Hall, Inc

A Quick TimelineA Quick Timeline

http://www.internet-story.com/index.htmhttp://www.internet-story.com/index.htm


The Future of the InternetThe Future of the Internet Key changes in the Internet need to take Key changes in the Internet need to take

place to handle the growing number of place to handle the growing number of users and the speed of the connectionsusers and the speed of the connections

Future changes include:Future changes include: More bandwidthMore bandwidth

• Internet 2 (I2)Internet 2 (I2) is being developed and tested to establish is being developed and tested to establish gigabits per second Points of Presence (gigaPOP)gigabits per second Points of Presence (gigaPOP)


The Internet and Web: What’s The Internet and Web: What’s the Difference?the Difference?

The Internet is the physical connection of The Internet is the physical connection of millions of networksmillions of networks

The Web uses the Internet for its existenceThe Web uses the Internet for its existence The Web consists of hypertext embedded on The Web consists of hypertext embedded on

Web pages that are hosted on Web sitesWeb pages that are hosted on Web sites


Web SiteWeb Site A A Web siteWeb site is a is a

collection of related collection of related Web documents that Web documents that are made available to are made available to the publicthe public

The The index pageindex page, or , or home pagehome page, is the first , is the first page of a Web sitepage of a Web site

Web pagesWeb pages are are individual Web individual Web documentsdocuments


Tim Berners-LeeTim Berners-Lee

Worked at CERN lab in GenevaWorked at CERN lab in Geneva Thought his work would be easier if he Thought his work would be easier if he

could link to colleagues’ computerscould link to colleagues’ computers Envisioned a network of computers Envisioned a network of computers

much like a spider webmuch like a spider web Used links to transfer data from one Used links to transfer data from one

site to another locationsite to another location

CERN site considered the CERN site considered the birthplace of the World Wide Webbirthplace of the World Wide Web

http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Tim_Berners-LeeTim_Berners-Lee


Marc AndreessenMarc Andreessen

Developed the first graphical Developed the first graphical browserbrowser Called Called MosaicMosaic Led to Led to Netscape NavigatorNetscape Navigator


Web Browsers and ServersWeb Browsers and Servers

Web browsersWeb browsers display a Web document and display a Web document and enable users to link to other Web pagesenable users to link to other Web pages The first browsers were text-onlyThe first browsers were text-only MosaicMosaic was the first graphical browser was the first graphical browser

Web serversWeb servers respond to the requests of respond to the requests of browsers. They find and send requested browsers. They find and send requested resources back to the browserresources back to the browser

Architecture of WWW

Browser


Web addresses are an addressing system Web addresses are an addressing system that identifies where a Web resource is that identifies where a Web resource is locatedlocated

The The uniform resource locatoruniform resource locator ( (URLURL) is the ) is the standard used to identify Web resourcesstandard used to identify Web resources

The URL consists of:The URL consists of:

URL

Web Addresses (URLs)Web Addresses (URLs)

http://

Protocol identifies the means of access

www.yahoo.com/

Server contains the domain name of the Web server

help/shop/

Path identifies the

location of the document

shop-01.html

Resource specifies the

filename of the resource


HTML Document

Web Page DesignWeb Page Design

Authors use a markup language called Authors use a markup language called Hypertext Hypertext Markup LanguageMarkup Language ( (HTMLHTML) to create Web pages) to create Web pages

The markup language consists of codes that The markup language consists of codes that identify portions and special effectsidentify portions and special effects in the in the documentdocument


Page CreatedHTML DocumentHTML DocumentClick to view an HTML document and the page that it Click to view an HTML document and the page that it

creates.creates.

Click again


IP AddressesIP Addresses

IP addressIP address – Each computer connected to the – Each computer connected to the Internet is given an address composed of Internet is given an address composed of numbers and periods. Example: numbers and periods. Example: 209.234.456.8209.234.456.8

Every machine on the Internet has a unique IP Every machine on the Internet has a unique IP addressaddress

Windows command Windows command WINIPCFG.EXEWINIPCFG.EXE ((IPCONFIG.EXEIPCONFIG.EXE for Windows 2000/XP) for Windows 2000/XP)

http://www.whatismyip.com/http://www.whatismyip.com/

19.19

Dotted-decimal notation and binary notation for an IPv4 address

Find the error, if any, in the following IPv4 addresses.

Example

Solutiona. There must be no leading zero (045).b. There can be no more than four numbers.c. Each number needs to be less than or equal to 255.d. A mixture of binary notation and dotted-decimal notation is not allowed.

Finding the classes in binary and dotted-decimal notation

Find the class of each address.a. 00000001 00001011 00001011 11101111b. 11000001 10000011 00011011 11111111c. 14.23.120.8d. 252.5.15.111

Example

Solutiona. The first bit is 0. This is a class A address.b. The first 2 bits are 1; the third bit is 0. This is a class C address.c. The first byte is 14; the class is A.d. The first byte is 252; the class is E.

19.23

Default masks for classful addressing

Two levels of hierarchy in an IPv4 address

A frame in a character-oriented protocol


Domain Name

Domain NamesDomain Names

Domain Name SystemDomain Name System ( (DNSDNS) – Enables users to ) – Enables users to type names of Web sites and Web pages as well type names of Web sites and Web pages as well as IP addressesas IP addresses

UNIX command UNIX command nslookupnslookup

http://www.iana.orghttp://www.iana.org

Port addresses


PortsPorts

Any server machine makes its services available Any server machine makes its services available to the Internet using numbered to the Internet using numbered portsports, one for , one for each service that is available on the server each service that is available on the server

Clients connect to a service at a specific IP Clients connect to a service at a specific IP address and on a specific portaddress and on a specific port

If a firewall is not protecting the port, you can If a firewall is not protecting the port, you can connect to the port from anywhere on the connect to the port from anywhere on the Internet and use the serviceInternet and use the service


PortsPorts If you were to set up your own machine and load If you were to set up your own machine and load

Web server software on it, you could put the Web Web server software on it, you could put the Web server on port server on port 918918, or any other unused port, if , or any other unused port, if you wanted to you wanted to

Then, if your machine were known as Then, if your machine were known as xxx.yyy.comxxx.yyy.com, someone on the Internet could , someone on the Internet could connect to your server with the URL connect to your server with the URL http://xxx.yyy.com:918http://xxx.yyy.com:918. The . The ":918"":918" explicitly explicitly specifies the port number specifies the port number

When no port is specified, the browser simply When no port is specified, the browser simply assumes that the server is using the well-known assumes that the server is using the well-known port port 8080


HTTP ProtocolHTTP Protocol Every Web server on the Internet conforms to the Every Web server on the Internet conforms to the

HTTP protocolHTTP protocol, summarized nicely in The Original , summarized nicely in The Original HTTP as defined in 1991 HTTP as defined in 1991

The most basic form of the protocol understood by The most basic form of the protocol understood by an HTTP server involves just one command: an HTTP server involves just one command: GETGET

""GET filenameGET filename," the server will respond by ," the server will respond by sending you the contents of the named file and sending you the contents of the named file and then disconnectingthen disconnecting

telnet www.cnn.com 80telnet www.cnn.com 80


Putting It All TogetherPutting It All Together http://www.stfx.ca/athletics/schedules.htmlhttp://www.stfx.ca/athletics/schedules.html

The browser breaks the URL into three parts: The browser breaks the URL into three parts: The The protocolprotocol ("http") ("http") The The server nameserver name ("www.stfx.ca") ("www.stfx.ca") The The file namefile name (“athletics/schedules.html") (“athletics/schedules.html")

The browser communicates with a name server The browser communicates with a name server to translate the server name, "www.stfx.ca," into to translate the server name, "www.stfx.ca," into an an IP addressIP address, which it uses to connect to that , which it uses to connect to that server machine server machine


Putting It All TogetherPutting It All Together

The browser then forms a connection to the Web The browser then forms a connection to the Web server at that server at that IP addressIP address on port on port 8080

Following the Following the HTTP protocolHTTP protocol, the browser sends , the browser sends a a GETGET request to the server, asking for the file request to the server, asking for the file

The server sends the The server sends the HTML textHTML text for the Web for the Web page to the browserpage to the browser

The browser reads the HTML tags and formats The browser reads the HTML tags and formats the page onto your screenthe page onto your screen

Static document

Dynamic document using CGI

Dynamic document using server-site script

Active document using Java applet

Active document using client-site script

Electronic Mail (E-mail)Electronic Mail (E-mail)

E-mail is sending messages via computerE-mail is sending messages via computer Business is using more e-mail and fax Business is using more e-mail and fax To access you must have a mail server and To access you must have a mail server and

softwaresoftware Each person has a username and passwordEach person has a username and password All mail programs allow you to Send, All mail programs allow you to Send,

Compose, Reply and Forward, DeleteCompose, Reply and Forward, Delete

Internet Address

[email protected]

Username Host Computer

Next-level domain

Highest-leveldomain

A valid Internet Address must contain the @ symbol

E-mail Protocols

POP Client --Post Office Protocol•Mail is read composed and stored locally•Can work off-lineIMAP --Messages stored remotely•Stored on a server•Download for local storageSMTP --Simple Mail Transfer Protocol•The protocol required to send mail messages through the Internet

Documents

CSCI-235 Micro-Computer Applications The Internet