The H Command
.............

master: `H'
     This is used by the master to hang up the connection.  The slave
     will respond with an `H' command response.

    `HY'
          The slave agrees to hang up the connection.  In this case the
          master sends another `HY' command.  In some UUCP packages the
          slave will then send a third `HY' command.  At this point the
          protocol is shut down, and the final handshake is begun.

    `HN'
          The slave does not agree to hang up.  In this case the master
          and the slave exchange roles.  The next command will be sent
          by the former slave, which is the new master.  The roles may
          be reversed several times during a single connection.