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Session Layer

Posted on 1999-01-08
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Last Modified: 2013-12-23
Dear all,
    I have a very confusing question to ask... about the session layer of the OSI model.
    if I run ls& on unix, will it go thru telnet (the application layer), the presentation layer and the session layer to the transport layer? If I run another ls program on the same machine, will another seperated session layer be created?.. or both ls will run under one 'session' mechanism.

Thanks

The confused
Jacky
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Question by:whluk
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yoren earned 50 total points
ID: 1582868
Jacky,

The OSI model refers not so much to the specifics of an implementation as to the concept of how two computers communicate. There's no specific "OSI session" mechanism. When you run 2 "ls&" commands, UNIX creates 2 processes. That has nothing to do with OSI. The OSI model can, however, be used to describe what happens when you type "ls".

Application: You type "ls" into your telnet program
Presentation: Your message is interpreted using the ASCII character set.
Session: Send this message to TCP/IP port 23, since that is the port for Telnet
Transport: TCP (part of TCP/IP): make sure the message gets there
Network: IP: route the message across the Internet to the UNIX box
Link: Use Ethernet
Physical: the actual wire it goes across
Link: Use Ethernet
Network: IP: receive the message
Transport: TCP: let your computer know the message arrived
Session: Receive the message from port 23 (not exactly accurate, but conceptually right)
Application: Your UNIX shell receives the command "ls"

Yuval
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