Web a HTTP

1
Web ?a? HTTP

• ???? ???????a
• ???e Web se??da ap?te?e?ta? ap? a?t??e?µe?a
  (objects)
• O? a?t??e?µe?? µp??e? ?a ?e????e? ??a HTML
  a??e??, ??a a??e?? e????a?, ???? ? video, ??p???
  Java applet ?t?...
• ??a Web se??da µp??e? ?a pe???aµß??e? d??f??a
  a?t??e?µe?a, ta ?p??a ap??a????ta? ?a? referenced
  objects
• ???e a?t??e?µe?? d?e????s??d?te?ta? ap? ??a URL
  (Uniform Resource Locator)
• Example URL

2
HTTP Hyper-Text Transfer Protocol

• HTTP Hyper-Text Transfer Protocol
• Application layer protocol
• client/server model
• client browser that requests, receives,
  displays Web objects
• server Web server sends objects in response to
  requests
• HTTP 1.0 RFC 1945
• HTTP 1.1 RFC 2068

HTTP request
PC running Internet Explorer
HTTP response
HTTP request
Server running Apache Web server
HTTP response
Mac running Navigator
3
HTTP

• ???s? TCP
• ? client e????e? ??a TCP connection (d?µ?????e?
  ?a? s??d?eta? d??ad? µe socket) st?? server, st?
  port 80
• ? server d??eta? t? TCP connection t?? client
• ????µata HTTP (application-layer protocol
  µ???µata) a?ta??????ta? µeta?? t?? browser (HTTP
  client) ?a? t?? Web server (HTTP server)
• ?????, ??e??e? t? TCP connection

• HTTP is stateless
• ? server de? s????ate? p????f???a ?at?stas?? ??a
  ta pa?a??te?a requests t?? client (ap?? ???p???s?)

a?t???t??

• ?a p??t?????a efa?µ???? p?? d?at?????
  p????f???a ?at?stas?? e??a? s???eta!
• ???pe? ?a d?at??e?ta? ? pa??? ?at?stas?
• ?? ??a ap? ta d?? µ??? (server ? client)
  ap???pe?, ? ?at?stas? t?? d?? µe??? p??pe? ?a
  a?a?t??e? ap? t?? a??? se t?t???? e?d???
  p??t?????a

4
HTTP s??d?se??

• Persistent HTTP
• (ep?µ??e?) s??d?se??
• ????ap?? a?t??e?µe?a µp????? ?a sta???? p??? ap?
  µ?a TCP s??des? µeta?? e??? client ?a? e???
  server
• ?? HTTP/v.1.1 ???s?µ?p??e? persistent connections
  se default mode

• Non-persistent HTTP
• (µ? ep?µ??e?) s??d?se??
• ??a t? p??? a?t??e?µe?? µp??e? ?a sta?e? p??? ap?
  µ?a TCP s??des? µeta?? e??? client ?a? e???
  server
• ?? HTTP/v.1.0 ???s?µ?p??e? non-persistent HTTP

5
Non-persistent HTTP
(?st? ep?s?? ?t? t? URL pe????e? text ?a?
references se 10 jpeg e????e?)

• ?st? ?t? ? ???st?? ep???µe? t? URL
  www.someSchool.edu/someDepartment/index.html

• 1a. ? HTTP client e????e? ??a TCP connection st??
  HTTP server (1 process st? socket)
  www.someSchool.edu st? port 80

1b. ? HTTP server www.someSchool.edu ß??s?eta? se
?at?stas? a?aµ???? pe??µ????ta? ??a TCP
connection st? port 80. ???eta? t?? a?t?s? ??a
s??des? (connection) ?a? e?d?p??e? t?? client
2. ? HTTP client st???e? ??a HTTP request message
(p?? pe????e? t? URL) st? socket t?? TCP
connection. ?? message ?p?de????e? ?t? ? client
ep???µe? t? object someDepartment/index.html
3. ? HTTP server ?aµß??e? t? request message,
s????te? t? response message p?? pe????e? t?
??t??µe?? a?t??e?µe?? (object) ?a? st???e? t?
message a?t? st? socket
time
6
Non-persistent HTTP

• 4b. ? HTTP client ?aµß??e? t? µ???µa
• ap????s?? (response message) p??
• pe????e? t? html a??e?? ?a? t? eµfa???e?.
• ?at? t?? epe?e??as?a t?? html file,
• ß??s?e? 10 s?et???µe?a a?t??e?µe?a t?p?? jpeg

4a. ? HTTP server ??e??e? t? TCP connection
time
5. ?a ß?µata 1-4 epa?a?aµß????ta? ??a ???e ??a
ap? ta 10 jpeg objects
7
Response time modeling

• RTT (Round Trip Time) ? ?????? p?? apa?te?ta?
  ??a t?? ap?st??? e??? µ????? pa??t?? ??a ?a
  d?a??se? t?? ap?stas? ap? t?? client st?? server
  ?a? p?s?
• Response time
• one RTT to initiate TCP connection
• one RTT for HTTP request and first few bytes of
  HTTP response to return
• file transmission time
• ?otal 2RTT?ransmit ?ime

8
Persistent HTTP

• Non-persistent HTTP issues
• ?pa?te? 2 RTTs a?? ??a a?t??e?µe??
• ?? ?e?t??????? s?st?µa p??pe? ?a apas???e?ta?
  s??e??? ??a t?? e?t?p?sµ? resources ??a ???e TCP
  s??des? (af?? ??e??e? ? s??des?)
• ?µ?? ?? browsers s???? a??????? pa??????a TCP
  connections p??? ta d??f??a a?t??e?µe?a
• Persistent HTTP
• ? server af??e? a????t? t? s??des? af?? ste??e?
  t? response message
• ?ts? ta epa??????a HTTP messages µeta?? t??
  ?d??? client/server a?ta???ss??ta? ap? t?? ?d?a
  s??des?

• Persistent ????? pipelining
• ? client µp??e? ?a ???e? ??? request a? ?a? µ???
  a? ??e? ??ße? t? p??????µe?? response
• Synchronous
• ??????? apa?te?ta? ??a RTT ??a ???e a?t??e?µe??
• Persistent µe pipelining
• Default st? HTTP/v.1.1
• ? client µp??e? ?a ste??e? ??a requests ??a ??a
  objects, ????? ?a ??e? ??ße? a??µa ap??t?s? ??a
  p??????µe?a requests
• Asynchronous
• Te???t??? µp??e? ??????? se ??a RTT ?a a?t??e?
  (?a ste??e? requests) ??a ??a ta a?t??e?µe?a

9
HTTP request message

• ??a??????µe HTTP messages d?? t?p?? request,
  response
• HTTP request message
• ASCII (human-readable format)

request line (GET, POST, HEAD commands)
GET /somedir/page.html HTTP/1.1 Host
www.someschool.edu User-agent
Mozilla/1.1 Connection close Accept
text/html,image/jpg,image/gif Accept-languagefr
(extra carriage return, line feed)
header lines
Carriage return, line feed indicates end of
message
10
HTTP request message general format
11
????µata ???? (v1.0 ?a? v.1.1)

• HTTP/1.0
• GET
• POST
• G?a ap?st??? p????f???a? ap? t?? p?e??? t??
  client (p.?. S?µp????s? st???e??? ??e?t???????
  f??µa?)
• HEAD
• ?a?ap??s?? µe t? µ???µa GET, µe t? s?µa?t??? ?µ??
  d?af??? ?t? ?pa? ?a? ? client ste??e? µ???µa
  HEAD, ? server ??? ?????? ?a pe????e? ?????? µ?sa
  st? message body t?? response µ???µat??
  (???s?µ?p??e?ta? ??a testing)

• HTTP/1.1
• GET, POST, HEAD
• PUT
• ???e? upload t? a??e?? p?? µetaf??e? st? entity
  body t?? µ???µat??, st? path p?? a?af??e? t? URL
  ped?? t?? µ???µat??
• DELETE
• ??a???fe? t? a??e?? p?? pe?????feta? st? URL
  ped?? t?? µ???µat??

12
HTTP response message
status line (protocol status code status phrase)
HTTP/1.1 200 OK Connection close Date Thu, 22
Dec 2006 120015 GMT Server Apache/1.3.0
(Unix) Last-Modified Mon, 22 Jun 2004 ...
Content-Length 6821 Content-Type text/html
data data data data data ...
header lines
data, e.g., requested HTML file
13
HTTP response status codes

• 200 OK
• request succeeded, requested object later in this
  message
• 306 No content
• The request clients message (e.g. PUT or POST)
  didnt contain any content
• 301 Moved Permanently
• requested object moved, new location specified
  later in this message (Location)
• 400 Bad Request
• request message not understood by server
• 404 Not Found
• requested document not found on this server
• 505 HTTP Version Not Supported