TCP IP Illustrated

Figure 261 shows the typical arrangement of the

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Unformatted text preview: tems. Telnet uses option negotiation between the client and server to determine what features each end can provide. 2. Rlogin is from Berkeley Unix and was developed to work between Unix systems only, but it has been ported to other operating systems also. In this chapter we look at both Telnet and Rlogin. We start with Rlogin because it's simpler. Telnet is one of the oldest of the Internet applications, dating back to 1969 on the ARPANET. Its name is actually an acronym that stands for "telecommunications network protocol." Remote login uses the client-server paradigm. Figure 26.1 shows the typical arrangement of the Telnet client and server. (We could draw a similar picture for an Rlogin client and server.) Figure 26.1 Overview of Telnet client-server. There are numerous points in this figure. 1. The Telnet client interacts with both the user at the terminal and the TCP/IP file:///D|/Documents%20and%20Settings/bigini/Documenti/homenet2run/tcpip/tcp-ip-illustrated/telnet.htm (1 of 26) [12/09/2001 14.47.45] Chapter 26. Telnet and Rlogin: Remote Login 2. 3. 4. 5. protocols. Normally everything we type is sent across the TCP connection, and everything received from the connection is output to our terminal. The Telnet server often deals with what's called a pseudo-terminal device, at least under Unix systems. This makes it appear to the login shell that's invoked on the server, and to any programs run by the login shell, that they're talking to a terminal device. Some applications, such as full-screen editors, assume they're talking to a terminal device. Indeed, making the login shell on the server think that it's talking to a terminal is often one of the hardest programming aspects involved in writing a remote login server. Only a single TCP connection is used. Since there are times when the Telnet client must talk to the Telnet server (and vice versa) there needs to be some way to delineate commands that are sent across the connection, versus user data. We'll see how both Telnet and Rlogin handle this. We show dashed...
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