Allied Telesis AT-MCF2012LC/1 - Manual (Page 32)

Chapter 1: Overview
32
transmitter on the companion port. This notifies the
networking device connected to the port of the loss of the
link on the other channel port.
Without the MissingLink mode, a networking device
connected to a port on the media converter will not be
aware of a loss of a link on a companion port in the channel,
because its link to the media converter would be unaffected.
When the link is reestablished on a port of a channel, the
MissingLink mode automatically reactivates the transmitter
on the companion port so that the two networking devices
can again forward traffic to each other through the two ports
of the media converter channel.
The value to this type of fault notification is that some
networking devices, such as managed Fast Ethernet
switches, can respond to the loss of a link on a port by
performing a specific action. For example, the networking
device might send a trap to a network management station,
and so alert the network administrator of the problem. Or, if
the device is running a spanning tree protocol, it might seek
a redundant path to a disconnected node.
Here is an example of how the MissingLink mode works.
Assume that the two ports of a channel are connected to
two Fast Ethernet switches, one local and the other remote.
Switch A, the local switch, is connected to the twisted pair
port of the channel, while Switch B, the remote device, is
connected to the fiber optic port.
If the link to Switch A is lost on the twisted pair cable, the
media converter disables the transmitter on the fiber optic
port in the same channel to signal Switch B of the loss of
the link to Switch A. This notifies Switch B of the problem so
that it too, along with Switch A, can take remedial action,
such as activating a redundant path if it is running a
spanning tree protocol or sending an SNMP trap to a
management workstation if it is using SNMP. Without the
MissingLink mode, switch B would continue to assume that
it still has a valid link to the remote device on the other side
of the media converter channel since its link to the port on
the channel is still valid, though no remote traffic is
received.
In the example, the initial loss occurred on the twisted pair
port. But the mode operates the same when the initial loss
of the link is on the fiber optic port of a channel. Here, the
transmitter on the twisted pair port is disabled to notify the