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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP Interactive and Remote Application Protocols

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TCP/IP Interactive and Remote Application Protocols
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Telnet Overview, History and Standards
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Telnet Protocol

In the very earliest days of internetworking, one of the most important problems that computer scientists needed to solve was how to allow someone operating one computer to access and use another as if he or she were connected to it locally. The protocol created to meet this need was called Telnet, and the effort to develop it was tied closely to that of the Internet and TCP/IP as a whole. Even though most Internet users today never invoke the Telnet protocol directly, they use some of its underlying principles indirectly all the time. Every time you send a piece of e-mail, use FTP to transfer a file, or load a Web page, you are using technology based on Telnet. For this reason, the Telnet protocol can made a valid claim to the title of the most historically important application protocol in TCP/IP.

In this section, I describe the operation of the Telnet protocol. I begin with an overview and history of the protocol and a discussion of the standards that define it. I describe the general operation of Telnet clients and servers and how connections are made and maintained. I then explain the important concept of the Network Virtual Terminal (NVT), Telnet’s protocol commands, and how interrupts are handled using Telnet’s special synch function. I conclude with a detailed look at Telnet’s options and how they are negotiated.

Background Information: A basic comprehension of the Transmission Control Protocol (TCP), especially its sliding window mechanism and flow control feature, will be helpful in understanding this section.


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Telnet Overview, History and Standards
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