<appendix id="X-087-2-appendix.cables"><title>Useful Cable Configurations</title>
<para>
If you wish to connect two computers together and you don't have an Ethernet
network, you will need either a serial null modem cable, or a PLIP parallel
cable.
</para>

<para>
These cables can be bought off the shelf, but are much cheaper and fairly
simple to make yourself.
</para>

<sect1 id="X-087-2-cable.plip"><title>A PLIP Parallel Cable</title>
<para>
<indexterm><primary>PLIP (Parallel Line IP) protocol</primary><secondary>null printer cable for</secondary></indexterm> 
To make a parallel cable to use for PLIP, you will need two 25-pin
connectors (called DB-25) and a cable with at least eleven conductors.
The cable must not be any longer than 15 meters (50 feet). The cable may or may
not have a shield, but if you are building a long cable, it is probably
a good idea to have one.
</para>

<para>
If you look at the connector, you should be able to read tiny numbers
at the base of each pin&mdash;from 1 for the pin at the top left (if you hold 
the broader side up) to 25 for the pin at the bottom right. For the null 
printer cable, you have to connect the following pins of both connectors
with each other, as shown in <xref linkend="X-087-2-cable.plip.diagram">.
</para>


<para>
All remaining pins remain unconnected. If the cable is shielded, the
shield should be connected to the DB-25's metallic shell on just 
<emphasis>one</emphasis> end.
</para>

</sect1>

<sect1 id="X-087-2-cable.serial"><title>A Serial NULL Modem Cable</title>
<para>
<indexterm><primary>SLIP (Serial Line IP) protocol</primary><secondary>null modem cable for</secondary></indexterm> 
<indexterm><primary>PPP (Point-to-Point Protocol)</primary><secondary>null modem cable for</secondary></indexterm> 
A serial null modem cable will work for both SLIP and PPP. Again, you
will need two DB-25 connectors. This time your cable requires only
eight conductors.
</para>

<para>
You may have seen other NULL modem cable designs, but this one allows you
to use hardware flow control&mdash;which is far superior to XON/XOFF
flow control&mdash;or none at all. The conductor configuration is
shown in <xref linkend="X-087-2-cable.nullmodem.diagram">:
</para>

<para>
Again, if you have a shield, you should connect it to the first pin at one 
end only.
</para>

<figure id="X-087-2-cable.plip.diagram">
<title>Parallel PLIP cable</title>
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<para>
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</para>

<figure id="X-087-2-cable.nullmodem.diagram">
<title>Serial NULL-Modem cable</title>
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<para>
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</para>


</sect1>

</appendix>
