27.1 Chapter 27 WWW and HTTP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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27.1
Chapter 27
WWW and HTTP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
27.2
27-1 ARCHITECTURE27-1 ARCHITECTURE
The The WWWWWW today is a distributed client/server service, today is a distributed client/server service, in which a client using a browser can access a service in which a client using a browser can access a service using a server. However, the service provided is using a server. However, the service provided is distributed over many locations called sites.distributed over many locations called sites.
Client (Browser)ServerUniform Resource LocatorCookies
Topics discussed in this section:Topics discussed in this section:
The WWW was originally designed as a stateless entity.
Cookies are needed for extending functionalities of the Web, such as: To remember past client in order to show a
customized webpage.
27.6
Cookies
When a server receives a request from a client, it stores information about the client in a file or a string.
The server includes the cookie in the response that it sends to the client.
When the client receives the response, the browser stores the cookie in the cookie directory.
27.7
Cookies: Creation and storage
27.8
27-2 WEB DOCUMENTS27-2 WEB DOCUMENTS
The documents in the WWW can be grouped into three The documents in the WWW can be grouped into three broad categories: broad categories: staticstatic, , dynamicdynamic, and , and activeactive. The . The category is based on the time at which the contents of category is based on the time at which the contents of the document are determined.the document are determined.
Static DocumentsDynamic DocumentsActive Documents
Topics discussed in this section:Topics discussed in this section:
27.11
Figure 27.7 Beginning and ending tags
Example: <a href="Chapter3-part3.ppt">Chapter3-
part3</a> <img src="../images/smallUCF.gif" width="200"
border="0" height="76">
27.18
27-3 HTTP27-3 HTTP
The Hypertext Transfer Protocol (HTTP) is a protocol The Hypertext Transfer Protocol (HTTP) is a protocol used mainly to access data on the World Wide Web. used mainly to access data on the World Wide Web.
HTTP TransactionPersistent Versus Nonpersistent Connection
Topics discussed in this section:Topics discussed in this section:
Trying out HTTP (client side) for yourself
1. Telnet to your favorite Web server:
Opens TCP connection to port 80(default HTTP server port) at cs.ucf.edu.Anything typed in sent to port 80 at www.cs.ucf.edu
telnet www.cs.ucf.edu 80
2. Type in a GET HTTP request:GET /~czou/CNT3004/example.html HTTP/1.1Host: www.cs.ucf.edu
By typing this in (hit carriagereturn twice), you sendthis minimal (but complete) GET request to HTTP server
3. Look at response message sent by HTTP server!
27.32
Web Browser’s Operation
First, get the basis static HTML file /~czou/CNT3004/example.html
Second, interpret HTML to find all contained “objects” Images, java applets, flash,….
<img src="../images/smallUCF.gif“ > <img
src=“http://upload.wikimedia.org/wikipedia/commons/6/63/Wikipedia-logo.png” >
Third, get those objects via HTTP
27.33
Let’s look at HTTP in action
Telnet example “GET” must be Capital letters! Must have “host” header!
For web proxy reason A proxy can know where to forward the GET
request
What if type in “HTTP/1.0” ? Wireshark example
27.34
Persistent vs Nonpersistent Connection In a nonpersistent connection, one
TCP connection is made for each request/response.
In a persistent connection, the server leaves the connection open for more requests after sending a response.
The server can close the connection at the request of a client or if a time-out has been reached.
27.36 Wireshark example
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