1. 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

2. 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

3. 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

4. HTTP Version HTTP/0.9 HTTP/1.0 HTTP/1.1
HTTP/<major>.<minor>
HTTP/0.9
HTTP/1.0
HTTP/1.1

5. Overview of a browser HTTP request TCP connection HTTP response
URL
User-Agent (browser/client)
Origin Server
DNS Server
DNS query
DNS response
HTTP request
TCP connection
HTTP response
optional TCP connections

7. Request Message 3 request methods: A-PDU GET, HEAD, POST request line
headers
blank line
body
3 request methods:
GET, HEAD, POST
GET /pub/index.html HTTP/1.0
Date: Wed, 20 Mar :00:02 GMT
From:
User-Agent: Mozilla/4.03
GET: Retrieves resource indicated by URI
HEAD: Retrieves ONLY metadata indicated by URI
POST: Pushes the resource in place of the URI (or creates a new one) or inputs the entity (data part) to the program(ex: CGI script) pointed by the URI

8. Response Message status line headers blank line body HTTP/1.1 200 OK
Date: Tue, 08 Oct :31:35 GMT
Server: Apache/ tomcat/1.0
Last-Modified: 7Oct :40:01 GMT
Accept-Ranges: bytes
Content-Length: 27723
Keep-Alive: timeout=5, max=300
Connection: Keep-Alive
Content-Type: text/html
Why a human readeable phrase?
To make extensibility easier. You can add new status codes without waiting for a protocol standard

9. Status Codes Classes: 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
404, 403, 200, 304

10. Headers Request Line A Blank Line Body Entity Headers Request Headers
General Headers
Status Line
A Blank Line
Body
Entity Headers
Response Headers
General Headers

11. Example Of Request/Response

12. Performance Issues

13. FTP vs. HTTP

14. FTP vs. HTTP (cont’d)

15. HTTP/1.0 Nonpersistent Connections
Client
Server
SYN
SYN-ACK
3-way handshake
ACK
GET URI HTTP/1.0
URL
ACK OK
ACK
ACK
DATA
web page
web page transferred
client parses HTML web page
ACK
Nonpersistent Connection (short-lived connection)
-- use a new TCP connection for each request;
-- seldom get past the “slow-start” region.
-- fail to maximize their use of the available bandwidth
FIN
connection close
FIN
ACK
ACK

16. HTTP/1.0 Nonpersistent (cont’d)
Client
Server
SYN
3-Way Handshake
SYN-ACK
ACK
URL
GET URI HTTP/1.0 OK
ACK
ACK
DATA
ACK
Web Page with Image1
Web page transfer
ACK
Client parses HTML web page
FIN
connect close
FIN
ACK
ACK
HTML file gets parsed GET Image 1 will be issued
SYN
SYN-ACK
ACK
GET IMAGE1 HTTP/1.0 OK
FIN
image 1 transfer
connect close
3-Way Handshake
URL
DATA
image1

17. Nonpersistent with parallel Connections (a. k. a
Nonpersistent with parallel Connections (a.k.a. Parallel Connections Hack)
SYN
SYN-ACK
ACK
Client
Server
GET URI HTTP/1.0 OK
FIN
DATA Transfer
CONN. Close
3-Way Handshake
URL
DATA
Client initiates new TCP connections for each embedded object after parsing the HTML file
SYN
SYN-ACK
ACK
Client
Server
GET URI HTTP/1.0 OK
FIN
DATA Transfer
CONN. Close
3-Way Handshake
URL
DATA
SYN
SYN-ACK
ACK
Client
Server
GET URI HTTP/1.0 OK
FIN
DATA Transfer
CONN. Close
3-Way Handshake
URL
DATA
Increases network congestion, burstiness
Is not fair for well-behaved connections

18. HTTP Delay Estimation Non Persistent
assume web page with 2 images
Non Persistent
Non Persistent with Parallel Connections
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

19. 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

20. HTTP/1.1 Default: Persistent Connections
SYN
SYN-ACK
ACK
Client
Server
3-Way Handshake
GET URI HTTP/1.0
OK-ACK
ACK
DATA
DATA Transfer
URL
GET image 3
GET URI HTTP/1.0
OK-ACK
ACK
DATA
DATA Transfer
URL
Client parses HTML GET image 1
Conn. timeout
GET URI HTTP/1.0
OK-ACK
ACK
DATA
DATA Transfer
URL
FIN
CONN. Close
ACK
GET image 2
GET URI HTTP/1.0
OK-ACK
ACK
DATA
DATA Transfer
URL
Either client or server can close the connection

21. Why Persistent Connections?
CPU time is saved in routers and hosts
Reduced Network Congestion – fewer packets
Reduced perceived latency on subsequent requests

22. Persistent with pipelining
SYN
SYN-ACK
ACK
Client
Server
3-Way Handshake
GET Image 1
OK-ACK
URL Image 1
GET Image 2
GET URI HTTP/1.0
OK-ACK
ACK
DATA
DATA Transfer
URL
OK-ACK
URL Image 2
ACK
DATA Transfer
Image 1
DATA
Client parses HTML
ACK
DATA
Image 2
DATA Transfer
FIN
CONN. Close
ACK

23. HTTP Delay Estimation (cont’d)
Persistent w/o pipelining
Persistent with pipelining
Client
Server
Client
Server
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

24. Quantifying TCP connection overhead
Throughput (bits/second)
Connection Length (bytes)
Figure 3-2: Throughput vs. connection length, RTT = 70 msec

25. Experimental Results Network Latency (seconds)
(NP HTTP/1.0)
Network Latency (seconds)
Number of in lined images
Figure 6-1: Latencies for a remote server, image size = 2544 bytes

26. 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 = bytes

27. Questions?