Transcript What happens when you request a Web page?

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-NoncommercialShare Alike 3.0 License.
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
You enter a uniform resource locator (URL)
into the address bar of the Web client program
What happens next?
Establish a temporary connection between
the client and the server
Client
Server
The client program sends a page request
Request
Client
Server
The server program sends the page
Client
document
Server
The client displays the page
Client
Server
The page comes from server storage
Client
Web
client
program
Server
Request
Web
server
program
Document
Memory
Requested
page
Display
Memory
The Internet
Requested
page
Storage
The client-server conversation
Client
Server
Open a connection
Opens the connection
OK
GET <file location>
Sends the docuemnt
or an error message
Display the response
Close the connection
OK
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.
request
page
Client
1.
2.
3.
4.
5.
Server
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
User clicks on a link to a second page
1. Get first page
Client
Server 1
Server 2
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
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
“Tiny” URLs – which do you prefer?
http://www.csudh.edu/studentaffairs/financial
aid/faq.shtml#apply_for_scholarships
http://tinyurl.com/DHscholarship
http://preview.tinyurl.com/DHscholarship
(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
World Wide Web in plain English
http://www.commoncraft.com/world-wide-web
request
page
Client
Server
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?
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-NoncommercialShare Alike 3.0 License.