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detect this and will issue Beacon MAC frames. These Beacon MAC frames will
be repeated by each station (station ″D″ in this case) until they arrive in the DRA
in module 1. Upon seeing these Beacon MAC frames, the URA on module 1 will
issue Beacon Type 1 MAC frames. The Beacon Type 1 MAC frames will be
repeated by every station on module 2 (including the URA and DRA on module 2)
until they arrive in the URA in module 1. At this point, the Recovery ASIC on
module 1 concludes that the rest of the ring (that is module 2 and its attached
stations as well as the backplane) is operational, therefore, the beaconing
condition must be on this module.
Recovery ASIC on module 1 starts taking recovery action by isolating module 1
from the backplane and deactivating its ports starting with the one upstream of
its DRA (station ″D″) and checking for the status of the ring. After the port
attaching station ″D″, the port attaching station ″C″ will be deactivated and so
on. As soon as it deactivates the port attaching station ″B″, the beacon
condition is removed; therefore, the fault domain is between station ″B″ and
station ″C″. The Recovery ASIC will then deactivate all the ports on module 1
and then check station ″B″ and station ″C″ individually, and when it finds that
station ″B″ is the source of problem, it deactivates the port attaching station ″B″
permanently and then reactivates all the other ports and inserts the module back
into the backplane.
Figure 97. Beacon Recovery on the Module Switching Modules
8.9.5 Beacon Recovery on the Per-port Switching Modules
The per-port switching module might have stations attached to 11 token-ring
segments consisting of the 10 different rings on the backplane and 11 isolated
rings on the module. Therefore, the Recovery ASIC (of which we have only one
on each module) is not connected to any rings under normal operating
conditions. Instead, the Ring Monitor function (which is implemented on each
port) is used to assist the Recovery ASIC with the beacon recovery process in
the per-port switching modules.
Under normal operating conditions, the Ring Monitor is located upstream of its
associated port. When a Ring Monitor detects the presence of a beaconing
condition, by noticing Beacon MAC frames, it alerts the Recovery ASIC. The
Recovery ASIC will then be inserted into the ring to which the reporting Ring
Chapter 8. 8260 Token-Ring Support 159