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<h3>IP Multicast Channel</h3>
<p><b>Syntax</b></p>
<p><tt>dp_connect ipm -group </tt><em><tt>ipAddr</tt></em><tt>
-myport </tt><em><tt>myPort</tt></em><tt> -ttl </tt><em><tt>numHops</tt></em></p>
<p><b>Comments</b></p>
<p>IPM is the multicast version of UDP. It allows any
number of machines to join a group and if a message is sent to
the group address, all the machines will hear it.</p>
<ul>
<li><i>ipAddr</i> is the IP address of the group.
This <b>must</b> be an multicast address in the range of
224.0.0.0 to 239.255.255.255.</li>
<li><i>myPort</i> is the local port and is optional.</li>
<li><i>numHops</i> is the Time To Live value. The
multicast packets will only cross <i>numHops</i>-1
routers after which they are discarded by the
router. To keep all multicast data on the local
subnet, use a ttl value of 1. Proper netiquette
maintains that this number be as low as possible.
It is optional and defaults to 1.</li>
</ul>
<hr>
<p>One can add and drop IPM group memberships using the
fconfigure -group command. See below for examples and please note
the use of the plus and minus symbol to signify add or drop. An
IPM channel can be a member of any number of multicast groups
(although it is usually limited by the OS to 20) so it is not
necessary to drop a group in order to add a new one.</p>
<hr>
<p><b>Examples</b></p>
<dl>
<dt><tt>dp_connect ipm -group 224.76.0.119</tt></dt>
<dt><tt>dp_connect ipm -group 225.23.120.87 -ttl 3</tt></dt>
<dt><tt>dp_connect ipm -group 238.1.1.1 -port 1905 -ttl 255</tt></dt>
<dt><tt>fconfigure $ipmChan -group +226.54.3.2</tt></dt>
<dt><tt>fconfigure $ipmChan -group -232.56.198.6</tt></dt>
</dl>
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