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Unformatted text preview: tems. Telnet uses option
negotiation between the client and server to determine what features each end can
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
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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- Spring '12