HyperText Transfer Protocol

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• HyperText Transfer Protocol
• (HTTP)
• Deepti Kulkarni
• CISC 856 TCP/IP and Upper Layer Protocols
• Fall 2008
• Acknowledgements
• Professor Amer Richi Gupta

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Motivation ?

• Single informational network
• Light protocol
• Speed

Tim-Berners Lee Director of the W3C
HTTP Versions
Format HTTP/ltmajorgt.ltminorgt

• HTTP/0.9 No RFC
• HTTP/1.0 RFC 1945
• HTTP/1.1 RFC 2616

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Position of HTTP in the TCP/IP Protocol suite
HTTP
Application-layer
TCP
Transport layer

IGMP
ICMP
Network layer
IP
ARP
RARP
Data link layer

Underlying LAN or WAN
Physical layer

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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)

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Client-Server protocol
Server running Apache Web server

HTTP Request/Response are over TCP connections
HTTP Response
HTTP Request
PC running Explorer/MAC running Navigator
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A-PDU format
Note Each line ends with cr lf control
characters.
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A-PDU format (contd)
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A-PDU format (contd)
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)
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Variations of HTTP

• Nonpersistent connections
• with serial connections
• with parallel connections
• Persistent connections
• without pipelining
• with pipelining

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Nonpersistent (HTTP /1.0 default)
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Client
Server
SYN
SYN-ACK
3-way handshake
ACK
Get web page
Web page
Web page transferred
Client parses HTML web page
Ack
Data
1.Found referenced object Image 1 2.
Found referenced object Image 2
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Nonpersistent (contd)
Ack
Data
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Key points

• Connection does not persist for other objects
• Connections are sequential

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Rough calculation for number of RTTS
Client
Server
Web Page
Can we reduce the number of RTTS?
Image 1
Image 2
Delay due to connection request/handshake
Delay Due to HTML Page Request
Time delay in RTTs 6
Delay Due to Object Request
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• Nonpersistent with parallel connections( browser
  dependent)

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Client parses HTML web page
1. Referenced object Image 1 2.
Referenced object Image 2
Parallel connections
Ack
Data
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Rough calculation
Client
Server
Web page
Image1 Image2
Time delay in RTTs 4
Delay due to connection request/handshake
Delay due to HTML page request
Delay due to object request
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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

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Persistent without pipelining
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Ack
Data
Note 1) Requests are sequential 2)
Timer is at application layer
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Rough calculation
Client
Server
Web page
Image1
Image2
Time delay in RTTs 4
Delay due to connection request/handshake
Delay due to HTML page request
Delay due to object request
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Persistent with pipelining
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Back to back requests
Client parses web page Gets Image 1 Gets Image
2
Note Requests are serviced in order
Ack
Data
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Rough calculation
Client
Server
Web page
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Image1 Image2

Time delay in RTTs 3
Delay due to connection request/handshake
Delay due to HTML page request
Delay due to object request
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• 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

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Experimental Results
(NP HTTP/1.0) without parallel connections
(Persistent without pipelining)
(Persistent with pipelining)
Network Latency (seconds)
Number of in lined images
Figure 6-1 Latencies for a remote server, image
size 2544 bytes
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Experimental Results (contd)
(NP HTTP/1.0) without parallel connections
(Persistent without pipelining)
(Persistent with pipelining)
Network Latency (seconds)
Number of in lined images
Figure 6-2 Latencies for a remote server, image
size 45566 bytes
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Questions?
Thanks
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Example Of Request/Response

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