HyperText Transfer Protocol (HTTP) Deepti Kulkarni CISC 856: TCP/IP and Upper Layer Protocols Fall...

transcript

HyperText Transfer Protocol (HTTP)

Deepti KulkarniCISC 856: TCP/IP and Upper Layer Protocols

Fall 2008

AcknowledgementsProfessor Amer Richi Gupta

Motivation ?

Single informational network

Light protocol

SpeedTim-Berners LeeDirector of the W3CHTTP Versions

Format : HTTP/<major>.<minor> HTTP/0.9 – No RFC

HTTP/1.0 – RFC 1945

HTTP/1.1 – RFC 2616

Position of HTTP in the TCP/IP Protocol suite

Application-layer

Transport layer

Network layer

Data link layer

Physical layer

IGMP ICMP

ARP RARPIP

Underlying LAN or WAN

Quick overview of HTTP

• Generic protocol for communication

• Stateless protocol

• In-band protocol• control information is sent in-band (unlike FTP)

• Pull protocol • pulls information from the server (unlike SMTP which is push

protocol)

Client-Server protocol

HTTP Request

HTTP Response

PC running Explorer/MAC running Navigator

Server running Apache Web server

HTTP Request/Response are over TCP connections

A-PDU format

Request Line

A Blank Line

Entity Headers

Request Headers

General Headers

Request Message

Status Line

A Blank Line

Entity Headers

Response Headers

General Headers

Response Message

Note: Each line ends with ‘cr lf ‘ control characters.

GET , HEAD, POST, PUT , TRACE , CONNECT , OPTION

URL HTTP version

space space

Request Line Request Type

Request Type

Header Name Header format : Header

General Header Date , Pragma, Cache control ,Connection, MIME-version, Upgrade, Transfer encoding

Request Header From, Referer, User-agent, Authorization, If-Modified-Since, Accept

Entity Header Content-length, Content-type, Content- encoding, Last-modified, Expires, Upgrade

Response Header Location, Age, Retry-after, Server

A-PDU format (cont’d)

1xx: Informational Continue (100) , Switching Protocols(101)

2xx: Success - action was successfully received, understood, and accepted Created (201), Accepted (202), No Content (204), OK (200)

3xx: Redirection - further action needed to complete request Moved Permanently (301) , Moved Temporarily (302), Not Modified (304)

4xx: Client Error - request contains bad syntax or cannot be fulfilled Bad Request (400), Unauthorized (401), Forbidden (403), Not Found (404)

5xx: Server Error - server failed to fulfill an apparently valid request Internal Server Error (500), Not Implemented (501), Bad Gateway (502),

Service Unavailable (503)

Status Code

Status Phrase

HTTP VersionStatus Line

space spaceA-PDU format (cont’d)…

Variations of HTTP

• Nonpersistent connections• with serial connections• with parallel connections

• Persistent connections• without pipelining• with pipelining

Nonpersistent (HTTP /1.0 default)

SYN-ACK

Client Server

GET web page HTTP/1.0

Web page transferred

3-way handshake

Connection close

Get web page

Web page

Client parses HTML web page

1.Found referenced object “Image 1”2. Found referenced object “Image 2”

Nonpersistent (cont’d)

SYNSYN-ACK

Client Server

GET image1 HTTP/1.0

Image 1 Transferred

Connection close

3-Way Handshake Get image1

FINACK

Image1

SYNSYN-ACK

Client Server

GET image2 HTTP/1.0

Image 2

Transferred

Connection close

3-Way Handshake Get image2

FINACK

Image2

Key points Connection does not persist for other objects

Connections are sequential

Rough calculation for number of RTTSClient Server

Delay due to connection request/handshake

Delay Due to HTML Page Request

Delay Due to Object Request

Time delay in RTTs = 6

Can we reduce the number of RTTS?

Web Page

Image 1

Image 2

Nonpersistent with parallel connections( browser dependent)

Parallel connections

SYN-ACKACK

Client Server

Web page Transferred

Connection close

3-Way Handshake

Get web page

FINACK

Web page

SYN-ACK

Client Server

GET image1 HTTP/1.0

Image 1 Transferred

Connection close

3-Way Handshake

Get image1

FINACK

Image1

SYN-ACKACK

Client Server

GET image2 HTTP/1.0

Image 2

Transferred

Connection close

3-Way Handshake

Get image2

FINACK

Image2

Client parses HTML web page

1. Referenced object “Image 1”2. Referenced object “Image 2”

Rough calculation

Client Server

Time delay in RTTs = 4 Delay due to connection request/handshake

Delay due to HTML page request

Delay due to object request

Web page

Image1 & Image2

Disadvantages:

• Overhead of multiple TCP connections.

• A busy server could end up with lots of connections in the ‘TIME-WAIT’ state

• Rarely does each connection get past the ‘slow-start’ region • Failure to use the full end-to-end available bandwidth

• Extra time opening connections increases user-perceived latency

Persistent without pipelining

Connection close

ACKFIN

Time Out

SYNSYN-ACK

Client Server

OKWeb page Transferred

3-Way Handshake Get web page

Web page

GET image2 HTTP/1.1

OK Image 2 Transferred

Get image2

Image2

GET image1 HTTP/1.1

OK Image 1 Transferred

Get image1

Image1

Note: 1) Requests are sequential 2) Timer is at application layer

Timer started

Timer startedTimer started

Rough calculation

Client Server

Time delay in RTTs = 4Delay due to connection request/handshake

Web page

Image1

Image2

Persistent with pipelining

Client parses

web page;

Gets Image 1

Gets Image 2

Connection close FIN

Back to back requests

SYNSYN-ACK

Client Server

GET webpage HTTP/1.1

OKWeb page Transferred

3-Way Handshake Get web

Web page

Image 2

OK Image 2

Get image1Get image2

GET image1 HTTP/1.1

GET image2 HTTP/1.1ACKACK

Image 1

Image 1OK

Time Out

Timer started

Timer startedNote: Requests are serviced in order

Rough calculation

Client Server

Time delay in RTTs = 3

Delay due to connection request/handshake

Web page

Image1 & Image2

Advantages:

• Fewer connections • Reduced network traffic • CPU time is saved in routers and hosts• Less overhead for the servers

• Reduced perceived latency for clients on subsequent requests

• Either client or server can close the connection

Disadvantages:

• Connections stay open longer at the server

Figure 6-1: Latencies for a remote server, image size = 2544 bytes

Experimental Results

(NP HTTP/1.0) without parallel connections

Number of in lined images

(Persistent without pipelining)

(Persistent with pipelining)

Figure 6-2: Latencies for a remote server, image size = 45566 bytes

Experimental Results (cont’d)

Number of in lined images

(Persistent without pipelining)

(Persistent with pipelining)

(NP HTTP/1.0) without parallel connections

Questions?

Thanks

Example Of Request/Response

Lets have a live demo!• telnet cis.poly.edu 80• GET /~ross/ HTTP/1.1 Host: cis.poly.edu

HyperText Transfer Protocol (HTTP) Deepti Kulkarni CISC 856: TCP/IP and Upper Layer Protocols Fall...

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