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Ring monitors are associated with each port and can be switched from upstream
to downstream of that port. When the ring monitor detects a Beacon MAC frame
on the ring, it calls in the Recovery ASIC to perform beacon recovery and isolate
the faulty port (station). The following sections describe the beacon recovery
procedures employed in the module switching modules and the per-port
switching modules.
8.9.4 Beacon Recovery on the Module Switching Modules
As described in 8.9.1, “Introduction” on page 151, when a ring station detects a
failure of token-claiming following a hard error, it transmits a Beacon MAC
frame. The Beacon MAC frame can be one of the following types:
•
Type 2
•
Type 3
•
Type 4
The Downstream Recovery ASIC (DRA) is normally operating in ″MAC frame
monitor″ mode, but as soon as it detects one of the above beacon frames, it
enters ″frame transmit″ mode and starts transmitting Beacon Type 1 MAC
frames.
Note
If DRA sees a Beacon Type 1 (that is, a Beacon MAC frame issued by a DRA
on another module) it will remain in ″MAC frame monitor″ mode and will not
issue its own Beacon Type 1 MAC frames. This happens when a beaconing
condition is encountered on another module which is attached to the same
ring as this module.
The Beacon Type 1 MAC frames issued by DRA will first go onto the backplane
and then through all the other token-ring modules and lobes that make up the
beaconing ring. If the Beacon frames reach the Upstream Recovery ASIC (URA)
on this module, two conclusions can be made:
1. The rest of the ring is complete and operating normally and
2. The fault must be somewhere in this module or the stations attached to this
module or on the trunks
At this point, the module is wrapped from the backplane and Recovery ASIC
begins wrapping ports sequentially, starting with the first active port upstream of
DRA. The wrapping of the ports continues until the normal operation of the ring
is restored. The normal operation of the ring is detected when the DRA starts
receiving its own Beacon Type 1 MAC frames. At this point, the Recovery ASIC,
has isolated the beacon fault domain to two ports (the last two ports which are
wrapped) on this module.
To determine which one of the two ports is causing the beaconing condition, it
now wraps all the ports on the module and then tests each of the two ports in
the fault domain individually. The faulty port will be wrapped permanently and
the remaining ports of the module will be unwrapped and the module will be
inserted back into the backplane ring.
For example, in Figure 97 on page 159, if a beaconing condition is caused by
station ″B″ attached to module 1, the downstream station (station ″C″), will
158 8260 Multiprotocol Intelligent Switching Hub