Hypertext Transfer Protocol (HTTP)

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Hypertext Transfer Protocol (HTTP)
Madhusri Nayak CISC 856 TCP/IP and Upper Layer
Protocols Fall 2004
Thanks to Dr. Amer, UDEL for some of the slides
used in this presentation Thanks to Forouzan for
some slides used in this presentation
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Motivation ?
Tim-Berners Lee

• Created by Tim Berners-Lee at CERN (Centre
  European pour Rechearche Nucleaire)
• physicists, not computer scientists
• to share data from physics experiments
• because ftp was too heavy
• Standardized and much expanded by IETF

Aerial View of CERN
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Basic HTTP Protocol
HTTP
HTTP
TCP
TCP
IP
IP
Link
Link
Physical

• Goal transfer data
• Stateless, Application-layer protocol
• Request-Response Protocol, uses TCP port 80

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HTTP Version
HTTP/ltmajorgt.ltminorgt
HTTP/0.9 HTTP/1.0 HTTP/1.1
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Overview of a browser
TCP connection
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(No Transcript)
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Request Message
A-PDU

• 3 request methods
• GET, HEAD, POST

GET /pub/index.html HTTP/1.0 Date Wed, 20 Mar
2002 100002 GMT From amer_at_udel.edu User-Agent
Mozilla/4.03
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Response Message
HTTP/1.1 200 OK Date Tue, 08 Oct 2002 003135
GMT Server Apache/1.3.27 tomcat/1.0 Last-Modified
7Oct2002 234001 GMT Accept-Ranges
bytes Content-Length 27723 Keep-Alive
timeout5, max300 Connection Keep-Alive Content-
Type text/html
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Status Codes

• 200 OK
• 201 Created
• 202 Accepted
• 204 No Content
• 301 Moved Permanently
• 302 Moved Temporarily
• 304 Not Modified
• 400 Bad Request
• 401 Unauthorized
• 403 Forbidden
• 404 Not Found
• 500 Internal Server Error
• 501 Not Implemented
• 502 Bad Gateway
• 503 Service Unavailable

Classes 1xx Informational - not used, reserved
for future 2xx Success - action was
successfully received, understood, and
accepted 3xx Redirection - further action
needed to complete request 4xx Client Error -
request contains bad syntax or cannot be
fulfilled 5xx Server Error - server failed to
fulfill an apparently valid request
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Headers
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Example Of Request/Response
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Performance Issues
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FTP vs. HTTP
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FTP vs. HTTP (contd)
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HTTP/1.0 Nonpersistent Connections
Server
Client
SYN
SYN-ACK
3-way handshake
ACK
GET URI HTTP/1.0
URL
ACK
ACK
web page
web page transferred
client parses HTML web page
connection close
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HTTP/1.0 Nonpersistent (contd)
Client
Server
SYN
SYN-ACK
3-Way Handshake
ACK
URL
GET URI HTTP/1.0
ACK
ACK
Web Page with Image1
Web page transfer
Client parses HTML web page
connect close
HTML file gets parsed GET Image 1 will be
issued
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Nonpersistent with parallel Connections (a.k.a.
Parallel Connections Hack)
Client initiates new TCP connections for each
embedded object after parsing the HTML file
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HTTP Delay Estimation
assume web page with 2 images
Non Persistent with Parallel Connections
Non Persistent
Client
Server
Client
Server
Time Delay in RTTs 4
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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Potential HTTP 1.0 Inefficiencies

• v1.0 fetches single URL per TCP connection

• Mean size of responses only a few thousand bytes
  ? inefficient use of available network bandwidth

• Server resources wasted

• User perceived latency is high
• TCP congestion control not used due to short
  transfers

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HTTP/1.1 Default Persistent Connections
GET image 3
Client parses HTML GET image 1
Conn. timeout
GET image 2

• Either client or server can close the connection

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Why Persistent Connections?

• CPU time is saved in routers and hosts
• Reduced Network Congestion fewer packets
• Reduced perceived latency on subsequent requests

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Persistent with pipelining
GET Image 2
Client parses HTML
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HTTP Delay Estimation (contd)
Persistent w/o pipelining
Persistent with pipelining
Server
Client
Server
Client
Time Delay in RTTs 3
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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Quantifying TCP connection overhead
Throughput (bits/second)
Connection Length (bytes)
Figure 3-2 Throughput vs. connection length, RTT
70 msec
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Experimental Results
(NP HTTP/1.0)
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)
Network Latency (seconds)
Number of in lined images
Figure 6-2 Latencies for a remote server, image
size 45566 bytes
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TCP-PDUs and round-trip times for HTTP/1.0
Client
Server
SYN
Client opens TCP connection
SYN-ACK
ACK
DAT
Client sends HTTP GET request for /index.html
ACK
DAT
FIN
ACK
ACK
Client parses /index.html
FIN
SYN
Client Opens TCP Connection
ACK
SYN-ACK
ACK
Client Sends HTTP Request for image
DAT
ACK
DAT
Image Begins to Arrive
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TCP-PDUs for HTTP/1.1 (persistent connections)
Client
Server
SYN
Client opens TCP connection
SYN-ACK
ACK
DAT
Client Sends HTTP GET request for /index.html
ACK
DAT
ACK
Client Parses HTML
DAT
Client Sends HTTP Request for image 1-n
ACK
DAT
Image Begins to Arrive
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TCP-PDUs for HTTP/1.1 (persistent connections
with pipelining)
Client
Server
SYN
Client opens TCP connection
SYN-ACK
ACK
DAT
Client Sends HTTP GET request for /index.html
ACK
DAT
ACK
Client Parses HTML
GET Image-1
Client Sends HTTP Request for image 1-n
GET Image-2
GET Image-3
ACK
DAT
Image Begins to Arrive
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Questions?