61 lines
3.1 KiB
HTML
61 lines
3.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<TITLE> Modem-HOWTO: Appendix D: Terminal Server Connection</TITLE>
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<H2><A NAME="s24">24.</A> <A HREF="Modem-HOWTO.html#toc24">Appendix D: Terminal Server Connection</A></H2>
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<P> This section was adapted from Text-Terminal-HOWTO.</P>
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<P>A terminal server is something like an intelligent switch that can
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connect many modems (or terminals) to one or more computers. It's
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not a mechanical switch so it may change the speeds and protocols of
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the streams of data that go thru it. A number of companies make
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terminal servers: Xyplex, Cisco, 3Com, Computone, Livingston, etc.
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There are many different types and capabilities. Another HOWTO is
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needed to compare and describe them (including the possibility of
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creating your own terminal server with a Linux PC). Most are used for
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modem connections rather than directly connected terminals.</P>
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<P>One use for them is to connect many modems (or terminals) to a high
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speed network which connects to host computers. Of course the
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terminal server must have the computing power and software to run
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network protocols so it is in some ways like a computer. The
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terminal server may interact with the user and ask what computer to
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connect to, etc. or it may connect without asking. One may sometimes
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send jobs to a printer thru a terminal server.</P>
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<P>A PC today has enough computing power to act like a terminal server
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except that each serial port should have its own hardware interrupt.
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PC's only have a few spare interrupts for this purpose and since they
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are hard-wired you can't create more by software. A solution is to
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use an advanced multiport serial card which has its own system of
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interrupts (or on lower cost models, shares one of the PC's interrupts
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between a number of ports). See Serial-HOWTO for more info. If such
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a PC runs Linux with getty running on many serial ports it might be
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thought of as a terminal server. It is in effect a terminal server if
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it's linked to other PC's over a network and if its job is mainly to
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pass thru data and handle the serial port interrupts every 14 (or so)
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bytes. Software called "radius" is sometimes used.</P>
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<P>Today real terminal servers serve more than just terminals. They also
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serve PC's which emulate terminals, and are sometimes connected to a
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bank of modems connected to phone lines. Some even include built-in
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modems. If a terminal (or PC emulating one) is connected directly to
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a modem, the modem at the other end of the line could be connected to
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a terminal server. In some cases the terminal server by default
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expects the callers to use PPP packets, something that real text
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terminals don't generate.</P>
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