o  buffer unavailable error

    Generated each time a frame is discarded because there is no
    receive buffer available.

 o  link down

    Generated each time the entity is disabled.

 o  link up

    Generated each time the entity is enabled.

 o  pdu receive overrun

    Generated each time the Physical layer entity reports a receive
    overrun.

 o  pdu transmit failed

    Generated each time an attempt to send a frame fails.  Argument:

    pdu transmit   Failure reason received from the Physical layer
    failed         entity.
    reason
                   disabled    The network manager has disabled the
                               line.

                   line down   The line is in the failed state.

                   no service  The Physical layer service is not
                               available.