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Unformatted text preview: boxes in Figure 26.1 to note that the terminal and pseudoterminal
drivers, along with the TCP/IP implementation, are normally part of the operating
system kernel. The Telnet client and server, however, are often user applications.
We show the login shell on the server host to reiterate that we have to login to the
server. We must have an account on that system to login to it, using either Telnet or
Rlogin. It is interesting to compare the complexity of Telnet and Rlogin by looking at the number
of lines of source code required to implement the client and server for each. Figure 26.2
shows these counts for the standard Telnet and Rlogin client and server, as distributed in
different versions from Berkeley (Figure 1.10). Figure 26.2 Comparison of Telnet/Rlogin/client/server, number of lines of source code.
It is the continuing addition of new options to Telnet that causes its implementation to
grow, while Rlogin remains simple and stable.
Remote login is not a high-volume data transfer application. As we've mentioned earlier, file:///D|/Documents%20and%20Settings/bigini/Documenti/homenet2run/tcpip/tcp-ip-illustrated/telnet.htm (2 of 26) [12/09/2001 14.47.45] Chapter 26. Telnet and Rlogin: Remote Login lots of small packets are normally exchanged between the two end systems. [Paxson 1993]
found that the ratio of bytes sent by the client (the user typing at the terminal) to the
number of bytes sent back by the server is about 1:20. This is because we type short
commands that often generate lots of output. 26.2 Rlogin Protocol
Rlogin appeared with 4.2BSD and was intended for remote login only between Unix hosts.
This makes it a simpler protocol than Telnet, since option negotiation is not required when
the operating system on the client and server are known in advance. Over the past few
years, Rlogin has also been ported to several non-Unix environments.
RFC 1282 [Kantor 1991] specifies the Rlogin protocol. As with the Routing Information
Protocol (RIP) RFC, however, this one was written after Rlogin had been in use for many
years. Chapter 15 of [Stevens 1990] describes programming remote login clients and
servers, and provides the complete source code for the Rlogin client and server. Chapters
25 and 26 of [Comer and Stevens 1993] provide the implementation details and source
code for a Telnet cl...
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