Allied Telesis AT-MCF2000, Руководство по установке

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Chapter 3: AT-MCF2012LC, AT-MCF2012LC/1 and AT-MCF2032SP Modules
38 Section I: Features
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 network 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 network 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 network 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 assume that it still had 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, even though no remote traffic is received.
In the example, the initial loss of a link in a channel occurred on the
twisted pair port. But the mode operates in the same fashion when the
initial loss of a link is on the fiber optic port. Here, the mode disables the
transmitter on the twisted pair port to notify the node connected to that port
of the loss of the link on the fiber optic port.
The Link LEDs of the ports in a channel that are running in this mode
always operate in tandem, as shown in Table 9 on page 45. They are both
on or off. Both Link LEDs of the ports of a channel remain off until both
ports can establish links with their network devices.
This operating mode is primarily used on a channel when the network
devices can react to the loss of a link on a port, such as managed Fast
Ethernet switches that are running a spanning tree protocol. Conversely,
the MissingLink mode should not be used on a channel if the two ports are
connected to network devices that cannot react to a lost link. Instead, you
might set the channel to the Link Test mode.
Furthermore, Allied Telesis does not recommend using the MissingLink
mode when you’re trying to troubleshoot a network problem that might
have its roots with a link problem. This is because the MissingLink mode
does not allow you to use the Link LEDs of the ports in a channel to