Cabletron Systems MMAC-5FNB, Networking Manual

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Description 6-7
Token Ring
Station D, having received eight consecutive beacon frames which identify it as
the NAUN, removes itself from the ring by closing the relay at the MAU. Station
D then enters a self-testing state, checking the operation of its own interface.
Determining that it is not at fault, Station D reattaches itself to the ring by opening
the relay at the MAU.
Figure 6-9. Beacon Recovery Process
In Figure 6-9, above, Station A has transmitted a number of beacons and has not
seen anything coming from its NAUN, Station D. Station A removes itself from
the ring to perform the self-testing process. Station D, having completed its
self-test, reattaches and rejoins the ring, which is now operating properly.
Ideally, Station A will determine that its receive port is at fault and will not
attempt to reattach to the now-operating Token Ring.
The case may also arise where a station is not, itself, at fault for error conditions
on a ring. This may occur when a cable develops a fault. A depiction of this
situation follows:
In Figure 6-10, below, the Token Ring network has completed the processes
shown in Figures 6-8 and 6-9, with Stations A and D each removing themselves
and testing. In the previous example, however, once Station A removed itself from
the ring, the error condition ended and data was able to freely circulate through
the remaining stations. In the figure below, Station A has removed itself from the
ring and Station B is now not receiving data. This indicates that there may be a
cable error in the ring.
self-
testing
?
A
B
C
D
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