What happens when you retrieve a Web page? This work is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 License. Skills: none IT concepts: client, server, network service, network connection, URL, “Tiny” URL, Web client (browser), Web server, peer-to-peer

Where does this topic fit? Internet concepts –Applications –Technology –Implications Internet skills –Application development –Content creation

Two computers connected to a network

One running Internet client software The other running Internet server software Client Server

What happens next? You enter a uniform resource locator (URL) into the address bar of the Web client program

Establish a temporary connection between the client and the server Client Server

The client program sends a page request Client Server Request

The server program sends the page Client Serverdocument

The client displays the page ClientServer

The page comes from server storage Web server program Memory Storage Requested page Web client program Memory Display Requested page ClientServer Request Document The Internet

The client-server conversation ClientServer Close the connection Open a connection GET Display the response OK Sends the docuemnt or an error message Opens the connection

If the server finds the page, it sends it back to the client; otherwise, it sends back an error message. What if the page is not on the server? The client is programmed to display whatever the server sends.

1.Establish a temporary connection between the client and server (dotted line) 2.Client sends the request to the server 3.The server returns the requested page or an error message 4.The client displays whatever the server returns 5.Disconnect Client Server request page

User clicks on a link to a second page Client Server 1 Server 2 1. Get first page 2. Get second page

Peer-to-peer applications One computer can run both a client program and a server program For example File sharing Internet phone calls Internet service providers discourage home users from operating servers by charging more or limiting upstream speed.

Mobile Web clients

Web clients in things

The parts of a URL This request is for a Web (http) server The server program is running on a computer with the domain name bpastudio.csudh.edu Look in a subdirectory called fac/lpress If there is a file called shortbio.htm, send it back to the client to be displayed; if not, send an error message back to the client Domain name = the unique name of a computer on the Internet

aid/faq.shtml#apply_for_scholarships “Tiny” URLs – which do you prefer? (Made at

Advertising business model

A few URL questions When opening the connection to the server, which part of the URL does the client use? When retrieving a page from a server, which part of the URL does the server use? What happens if you misspell the name of a file in a URL? What happens if you misspell the domain name in a URL?

Do the terms client and server refer to hardware or software? Don’t continue until you think you have the answer and can explain it.

The big picture A client is a computer running a client program A server is a computer running a server program A server offers a service to clients on the network Clients use (geeks may say “consume”) those services

A short video on the same topic World Wide Web in plain English

Client Server request page Without looking back, can you recall the five steps we discussed in retrieving a Web page?

What happens when you retrieve a Web page? This work is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 License. Skills: none IT concepts: client, server, network service, network connection, URL, “Tiny” URL, Web client (browser), Web server, peer-to-peer