What happens when you retrieve a Web page?

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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 softwareThe 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

Client Server

The page comes from server storage

Webserverprogram

Memory

Storage

Requestedpage

Webclientprogram

Memory

Display

Requestedpage

Client ServerRequest

Document

The Internet

The client-server conversation

Client Server

Close the connection

Open a connection

GET <file location>

Display the response

OK

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 server3. The server returns the requested page or an error message4. The client displays whatever the server returns5. 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

http://bpastudio.csudh.edu/fac/lpress/shortbio.htm

Domain name = the unique name of a computer on the Internet

http://www.csudh.edu/studentaffairs/financialaid/faq.shtml#apply_for_scholarships

http://tinyurl.com/DHscholarship

http://preview.tinyurl.com/DHscholarship

“Tiny” URLs – which do you prefer?

(Made at http://www.tinyurl.com)

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

http://www.commoncraft.com/world-wide-web

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?

1.2.3.4.5.

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