What happens when you retrieve a Web page?

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What happens when you retrieve a Web page?
Skills none IT concepts client, server,
network service, network connection, URL, Tiny
URL, Web client (browser), Web server,
peer-to-peer
This work is licensed under a Creative Commons
Attribution-Noncommercial-Share Alike 3.0
License.
2
Where does this topic fit?

• Internet concepts
• Applications
• Technology
• Implications
• Internet skills
• Application development
• Content creation

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Two computers connected to a network
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One running Internet client softwareThe other
running Internet server software
Server
Client
5
You enter a uniform resource locator (URL) into
the address bar of the Web client program
What happens next?
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Establish a temporary connection between the
client and the server
Server
Client
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The client program sends a page request
Request
Server
Client
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The server program sends the page
Server
document
Client
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The client displays the page
Client
Server
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The page comes from server storage
Client
Server
Request
Web server program
Web client program
Document
Memory
Memory
Requested page
Requested page
The Internet
Storage
Display
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The client-server conversation
Client
Server
Open a connection
Opens the connection
OK
GET ltfile locationgt
Sends the docuemnt or an error message
Display the response
Close the connection
OK
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What if the page is not on the server?
If the server finds the page, it sends it back to
the client otherwise, it sends back an error
message.
The client is programmed to display whatever the
server sends.
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request
page
Server
Client

• Establish a temporary connection between the
  client and server (dotted line)
• Client sends the request to the server
• The server returns the requested page or an error
  message
• The client displays whatever the server returns
• Disconnect

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User clicks on a link to a second page
1. Get first page
Server 1
2. Get second page
Client
Server 2
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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.
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Mobile Web clients
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Web clients in things
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The parts of a URL
http//bpastudio.csudh.edu/fac/lpress/shortbio.htm

• 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
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Tiny URLs which do you prefer?
http//www.csudh.edu/studentaffairs/financialaid/f
aq.shtmlapply_for_scholarships
http//tinyurl.com/DHscholarship
http//preview.tinyurl.com/DHscholarship
(Made at http//www.tinyurl.com)
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Advertising business model
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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?

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Do the terms client and server refer to hardware
or software?
Dont continue until you think you have the
answer and can explain it.
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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

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A short video on the same topic
World Wide Web in plain English
http//www.commoncraft.com/world-wide-web
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request
page
Server
Client
Without looking back, can you recall the five
steps we discussed in retrieving a Web
page? 1. 2. 3. 4. 5.
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What happens when you retrieve a Web page?
Skills none IT concepts client, server,
network service, network connection, URL, Tiny
URL, Web client (browser), Web server,
peer-to-peer
This work is licensed under a Creative Commons
Attribution-Noncommercial-Share Alike 3.0
License.