1. ITIS 1210 Introduction to Web-Based Information Systems Chapter 23 How Web Host Servers Work

2. Introduction  Websites need a place to live – a host  Websites are hosted on a server  Stored  Distributed  Server  Manages communications protocols  Houses the Web pages themselves  Supporting software

3. Introduction  Server software  Delivers the pages requested by clients  Acts on other requests from servers  Handles the HTTP requests  Communicates with the host’s OS  Which handles the TCP/IP functions

4. How Web Host Servers Work  Different types of server software handle different kinds of requests from clients  Database servers  FTP requests  Network servers  Mail servers  Web servers are HTTP servers  Sends HTML documents using HTTP

5. How Web Host Servers Work  Most of the time, the client requests an HTML page  Server receives request  Locates the.html file  Sends it back to the requesting client  Can do more however  Passes requests to run CGI scripts to CGI applications

6. How Web Host Servers Work  These scripts run external mini-programs  Database lookup  Process and interactive form  Server sends script to CGI  In a standardized format  CGI communicates with external program  Receives results back from external program  Formats & returns results

7. How Web Host Servers Work  Basic problem with IP addresses:  They are limited in scope because of their 0- 255 format  IP addresses allow you to contact a specific computer  But how does that computer know which program you are using?

8. How Web Host Servers Work  The answer is port numbers  Value from 0 to 65535  Think of it as the extension of a telephone number  A complete data transfer always includes a port number:

9. How Web Host Servers Work 213.153.38.220:80