chap 15 application layer
DESCRIPTION
Chap 15 Application Layer. Andres, Wen-Yuan Liao Department of Computer Science and Engineering De Lin Institute of Technology [email protected] http://www.cse.dlit.edu.tw/~andres. Overview. Client-Server Redirectors Domain Name System E-mail/Telnet/FTP/HTTP. - PowerPoint PPT PresentationTRANSCRIPT
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Chap 15 Application Layer
Andres, Wen-Yuan Liao
Department of Computer Science and Engineering
De Lin Institute of Technology
http://www.cse.dlit.edu.tw/~andres
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OverviewClient-Server
Redirectors
Domain Name System
E-mail/Telnet/FTP/HTTP
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Basics of the Application Layer
Application processes
Direct network applications
Indirect network support Making and breaking a connection
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Application processes
Supports the communicating component of an application
The OSI layer closest to the end system
Does not provide services to any other OSI layer
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Direct interface Browser, e-mail, FTP, Telnet
Indirect interface Word processors, spreadsheets, presentation managers with a network redirector
Application processes
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Direct network applications
Client-server applications (most)
FTP, web browsers, and e-mail
The client side On the local computer The requestor of the services
The server side On a remote computerProvides services
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WWW
Browsers (NN and IE) are probably the most commonly used network applications
An easy way to understand a Web browser is to compare it to a television remote control
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Indirect network support
If a client wants to save a file from a word processor to a network server, the redirector enables the word processing application to become a network client
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RedirectorA protocol that works with computer operating systems and network clients instead of specific application programs
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Redirectors
Apple File Protocol NetBIOS Extended User Interface (NetBEUI) Novell IPX/SPX protocols Network File System (NFS) of the TCP/IP protocol suite
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Redirector
Allows a network administrator to assign remote resources to logical names on the local client (F:, G:, … )
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Advantages
The applications on the client never have to recognize the networkExpand the capabilities of non-network software
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Making/breaking a connection
Web The connection was maintained just
long enough to download the current Web page
PrinterThe connection was maintained just
long enough to send the document to the print server
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Domain Name System
Problems with using IP addresses
The domain name server
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Problems with using IP addresses
A domain is a group of computers that are associated by their geographical location or their business type
A domain name is a string of characters and/or numbers
More than 200 top-level domains
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Generic names
.edu - educational sites
.com - commercial sites
.gov - government sites
.org - non-profit sites
.net - network service
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The domain name server
Domain name -> IP address
The DNS system is set up in a hierarchy that creates different levels of DNS servers
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Network Applications
Internet applications
E-mail message
DNS function
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Internet applications
The WWW uses the HTTP protocol
Remote access programs : Telnet protocol
E-mail programs : POP3 application layer protocol for electronic mail
File utility programs : FTP protocol
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E-mail message
The first is to send the e-mail to the user’s post office
The second is to deliver the e-mail from that post office to the user’s e-mail client
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Application Layer Examples
Telnet
File transfer protocol
Hypertext transfer protocol
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TelnetAll processing and storage take place on the remote computerWorks mainly at the top three layers of the OSI model Application, presentation , session layers
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FTP
Be designed to download files (e.g. receive from the Internet) or upload files (e.g. send to the Internet)
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Hypertext transfer protocol
The fastest growing and most used part of the Internet
A Web browser is a client-server applicationRequires both a client and a
server component in order to function
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Hyperlink
A hyperlink is an object (word, phrase, or picture) on a Web page that, when clicked, transfers you to a new Web page
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Summary
Direct and indirect network applications
The domain name system
Telnet, FTP and HTTP