May 16, 2005

Review

• Syllabus
• Home page for the course
• Description of the project - deadlines

Topics

• Using the Internet and the Web
  • being involved as a consumer
  • get involved as a producer
• Basic Internet Concepts and Terminology
  • Internet Basics
    • Two basic protocols used are Internet Protocol or IP and Transmission Control Protocol or TCP . You often see them referred to together as TCP/IP.
    • Each network on the Internet has a unique address, called the IP address , and each of the computer systems making up a network have an IP address based on the network's IP address.
    • Packets of characters, like envelopes holding messages, are used to carry information on the Internet.
    • Each computer system with a direct connection to the Internet has to have the hardware and/or software to allow it to work with packets. It's up to the individual computer systems to take care of sending and receiving packets.
• Web Basics
  • HTTP is the protocol used on the Web. It is based on TCP/IP.
  • A URL contains the protocol used, the domain name, and other information about the data being requested. For example: http://lcweb2.loc.gov/ammem/alhtml/alrel.html and ftp://garbo.uwasa.fi/pc/gifcraft/sat5a.gif
  • URLs sometimes have a different format when they reference the result of an application or service. - do a search at alltheweb.com
• Web Browsers and Web Servers, the Client/Server Model
  • A browser and the Web server work together according to a client/server relationship.
  • From the point of view of the Web browser, the client, the interaction with a Web server is this:
    • The client formulates an HTTP request to the server.
    • The system where the client resides sends the request to the system hosting the server via the Internet.
    • If communication is possible then the server will analyze the request and responds with a response code and accompanying information when it is appropriate.
  • There may be some problems:
    • The remote system can't be located. It could be that the domain name in the URL is incorrect, or the network where the remote host resides is unreachable. For example, http://users.ume.edu/~ernie/cpsc370k
    • The server doesn't respond within a certain amount of time. Perhaps the server software isn't running on the remote system or it is too busy to respond in a fixed amount of time.
  • More about client/server relationship
    • Client-side
      • The client sends an HTTP GET request for the file index.html to the server hosted on the system with domain name trierra.org.
    • Server-side
      • The server parses or analyzes the request. Since the file exists in an appropriate directory on the remote system, and since the permissions on the remote system were set so the server could read the file, the server sends the response code 200 and the type of the file followed by the contents of the file to the client. The server follows the protocol defined by HTTP in doing this.
    • Client-side
      • The client reads the response code, 200, and since that indicates the request was satisfied, the browser then interprets the HTML/XHTML on the rest of the transmission and eventually renders or displays the Web page.
    • Response codes Take a look at these using Web-Sniffer
      • 404 - Not Found http://people.umw.edu/~ernie/bobo.html
      • 401 - Unauthorized http://webliminal.com/cgi-bin/cpsc104/admin
      • 403 - Forbidden http://webliminal.com/bobo.html
      • 500 - Failed Script http://webliminal.com/cgi-bin/trymail.cgi

Home Work -

• Turn in Tuesday, May 17, 2005.
  • Page 1.12. Exercise 2 in the section Short Answer
  • Page 1.12. Exercise 5 in the section Short Answer
  • Page 1.12. Exercise 3 in the section Projects/Essay

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