3Com LINKBUILDER 3C18500 User Manual page 99

Resilient Links 6-3
might be lost. If a spare link could pick up where the broken link left
off, the network would appear to function normally to the outside
observer. At worst, a few frames would be corrupted or lost.
This is the concept of resilience as applied to ports. One port is on
stand-by waiting to take over if the main port fails.
You may set up 16 resilient pairs of ports on one chassis. A pair may be
on the same module or on different modules. Each port in the pair can
be attached to different media. Each resilient pair consists of a main
port and a stand-by port. When the pair is operating normally, the
main port carries data to and from the segment attached to the port.
However, if the management module detects a loss of link (link test
pulse for twisted pair medium) or loss of light (idle signal for fiber optic
medium), this main port is disabled and the stand-by port takes over.
To keep you informed of what is happening on the network, an event
or trap will be sent to the Network Manager informing you that a main
port has been disabled and a stand-by port has taken over. If you then
rectify the fault on the main port, or the fault clears, the operation will
switch back automatically to the main port.
It is important to ensure that the repeater module with the standby
port has the hardware link in the correct position, i.e.: in the 'Resilience
Enable' configuration (also known as the 'disabled on power-up'). If you
are unsure of how to do this, consult the guide that came with the
repeater module. Setting the link correctly will avoid creating a loop
when the power is first applied. The management module will
re-configure the ports after power-up.
The Resilience feature is available from VT100, Transcend or another
SNMP Manager. Details of how to use the Resilience screen are given in
Chapter 8, "Resilience" on page 8-17.
The management facility can only recognize loss of link/light on a local
port.
Suitable application of an alarm can bring into play the resilience
feature. If a port is receiving a number of errors, an alarm set on the
error counter can trigger change-over to its resilient partner. See
Chapter 8.
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