Allied Telesis AT-S99 - Manual (Page 44)

Chapter 2: AT-CM and AT-CV Media Converter Line Cards
44
and their status in the management software will be Online. If one or both
ports cannot establish a link, then the Link LEDs will be off and their status
in the management software will be Offline.
This operating mode is useful when the network devices connected to the
ports of a line card can react to a loss of a link on a port, such as managed
Fast Ethernet switches running SNMP or a spanning tree protocol.
Conversely, the MissingLink mode will be of little value if the network
devices of a line card cannot react to a lost link. In the latter scenario, the
Link Test mode would probably be a better operating mode for a line card
during normal network operations.
Furthermore, Allied Telesis does not recommend using the MissingLink
mode when troubleshooting a network problem that may have its roots
with a link problem. The MissingLink mode will not allow you to use the
port’s Link LEDs or the management software to diagnose the problem,
since neither port will show a link. Rather, the Link Test and the Smart
MissingLink modes are more useful when troubleshooting a link problem.
Smart
MissingLink
Mode
The Smart MissingLink mode is nearly identical to the MissingLink mode.
it, too, enables the two ports on a media converter line card to share the
link status of their connections. This mode is different in that it does not
completely shut off the transmitter of a port on a line card when the
companion port loses its link. Rather, this operating mode pulses the
port’s transmitter and flashes the port’s Link LED once a second to signal
that the port can still establish a link to its network device and that the loss
of the link originated on the companion port on the line card.
The advantage of this operating mode over the MissingLink mode is that
you can use the Link LEDs on a line card to troubleshoot a link failure with
the ports. As an example, assume that the fiber optic port on a media
converter line card operating in the Smart MissingLink operating mode lost
its link to its network device. The mode would respond by pulsing the
transmitter on the twisted pair port and flashing the port’s Link LED about
once a second to signal that the failure originated on the fiber optic port.
When the connection is reestablished on the fiber optic port, the twisted
pair port would automatically resume normal operations to permit the two
ports to forward traffic again.
The operating mode functions the same if the failure starts on the twisted
pair port. Here, the mode pulses the transmitter on the fiber optic port.
As with the other operating modes, this mode does not interfere with the
flow of network traffic through the ports of a line card during normal
network operations of a media converter line card. However, Allied Telesis
recommends limiting its use to diagnosing link failures, particularly if the
network devices connected to the ports are managed devices. The pulsing
of the transmitter on a port and the constantly changing status of a link
could prove problematic for some managed devices. For example, the
device might send a constant stream of SNMP traps or, if the device is