+ BYE,<comments>
+
+Command sent to all connections when the software is shutting down. This is sent
+by the node just before shutdown occurs. This is really only used to help the
+network prune its routing tables. It isn't a requirement. The <comment> field
+is optional.
+
+=item B<DISC>
+
+ DISC,<node name>,<comments>
+
+Command sent when a node has disconnected from this node. This message is sent when
+an interface shuts down. It need not be sent if a L<BYE> from an interface for
+that node has just been received. This command should be broadcast.
+
+The <node name> is mandatory and is the name of the interface that has just
+disconnected.
+
+=item B<PING>
+
+ PING,<ping id>
+
+Command to send a ping to a node or user. This command is used both by the software
+and users to determine a) whether a node or user exists and b) how good the path is
+between them.
+
+The <ping id> is a unique string which is usually the hexadecimal equivalent of an
+integer that is incremented every time it is used. But it can be anything that
+will identify this ping using the tuple (L<Origin>,<ping id>) as unique.
+
+=item B<PONG>
+
+ PONG,<ping id>,<no of hops on ping>
+
+Command to reply to a ping. This is sent as a reply to an incoming ping command.
+The <ping id> is the one supplied and the <no of hops on ping> is the number of
+hops it took for the ping to arrive.
+
+=item B<T>
+
+ T,<text>
+
+All implementations must be able to send "text" (encoded as specified in
+L</Fields>). There would be little point in doing all this otherwise!
+
+=back