Protocol(TCP/IP, HTTP)

송준화조경민

2001/03/13

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Layering of TCP/IP-based protocols

HTTP FTP TELNETNFSRP C DNS SNMP

TC P UDP

IP

transportlayer

Networklayer

data linklayer

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TCP Characteristic

TCP is connection-oriented 3-way handshake is used for connection setup/teardown

TCP provides a stream-of-bytes service. TCP is reliable

Acknowledgements indicate delivery of data. Checksums are used to detect corrupted data. Sequence numbers detect missing, or mis-sequenced data. Corrupted data is retransmitted after a timeout. Mis-sequenced data is re-sequenced. (Window-based) Flow control prevents over-run of receiver.

TCP uses congestion control to share network capacity among users.

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TCP is connection-oriented

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Connection Establishment/Close telnet address port

Active open telnet> quit equivalent to “close”

Makes the system to send “FIN” for “active close”

Time Wait State (2MSL state) On “active close” side MSL: maximum segment lifetime Two effects:

lost ACK Port reuse

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TCP segment header

20 bytes

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(some) TCP Header Fields URG: urgent bit

One end tells the other that “urgent data” of some form has been placed into the normal stream of data

Works with 16 bit “urgent pointer” field ACK: PSH: RST: SYN: FIN:

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IP characteristic

Connectionless mis-sequencing

Unreliable may drop packets

Best Effort

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IP : Internet Protocol

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The IP Datagram

20 bytes

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(some) IP Header Fields TOS:

3 bit precedence (ignored) 4 bit TOS :

(minimize delay, maximize throughput, maximize reliability, minimize monetary cost)

Only one bit can be “on” Usually call bits “off”

ID: unique id for each datagram from a sender

TTL: upper bound for # of hops

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HTTP

HTTP Stateless protocol

Not include the concept of a session or interaction beyond delivery of the requested document.

Do not need to keep track of who the clients are or what requests were serviced in the past.

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HTTP 1.0 vs. HTTP 1.1(1)

HTTP 1.0 For each additional request, a new

TCP connection must be established. The system incurs again in a

connection setup overhead. HTTP 1.1

Persistent connection Pipeline of requests

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HTTP 1.0 vs. HTTP 1.1(2)

HTTP 1.1 Persistent connection

Avoids many round trip delays Improving performance Reducing the number of packets

exchanged Pipeline of requests

Allows multiple requests to be sent without waiting for a response.

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HTTP interaction

HTTP 1.0 HTTP 1.1

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Anatomy of an HTTP transaction

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(Network) System Overview

TC P

routeredge router

core router

edge router

router

BrowserTC PIP

ethernet card

C lient

DBfront end

ws

ws

ws

Internet

The main issue is how we can improve networksystem performance at each component.

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Where are the delays?(1)

Browser The end user clicks on a hyperlink and

requests a document. In the case of a hit, returns the requested

document in the local cache. In the case of a miss

mapping the server hostname to an IP address. The clients opens a TCP connection to the server. The clients sends an HTTP request to the server.

The browser formats and displays the document and renders the associated images.

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Where are the delays?(2)

Network The network imposes delays to

deliver information from the client to server and back from the server to client.

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Where are the delays?(3)

Server A request arrives from the client. The server parses the request, according to

the HTTP protocol. The server executes the method requested. The server reads the contents of the file

from disk or from its main memory cache and writes it to the network port.

Close the connection Service time and waiting time at the various

components of the server, such as processor, disk, and network

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QoS(Quality of Service)(1)

Customers want to have good services available at any time.

Customers do not care about site failures, traffic jams, network bandwidth, or other indicators of system activities.

Besides contents and aesthetics, online users want performance and security.

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QoS(Quality of Service)(2)

Users perceive Web services through performance metrics such as: Response time Availability

The percentage of time a site is available during an observation period.

Reliability Measuring the occurrence of failures during the

processing or services. Predictability Cost

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QoS(Quality of Service)(3)

Compounding the need for high reliability and availability is the dynamic nature of the Web, which internal and external customers rely on for up-to-date business, professional, and personal information.

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QoS(Quality of Service)(4)

Unpredictable For example, in a large trade show company, 250,000 hits a week during normal weeks A million hits a day at the peak of its largest Fall

show. Companies must measure traffic, performance,

and usage patterns in order to monitor the quality of service of their Web sites.

Management has to decide if additional capacity is needed to stay ahead of customer demands.