Post on 21-Dec-2015
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 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