Understanding the network.pdf - Back to Home

and the physical ring segment that separates the two stations. Isolating error's can
be often be attributed to a specific ring station within the fault domain, because the
nature of the soft error is such that it is detected by the next station in the ring's
logical order, which detects and sends the error report. Alternatively, Non-isolating
soft errors (NSE) can be detected by any station on the ring, making fault isolation
difficult. However, form a error reporting standpoint NSE are handled in a manor
similar to ISE, where the detecting station collects error data, and generates and
transmits an error report to REM.
NOTE
Almost all references to Ethernet frame sizes do not include the frame preamble
when calculating the minimum and maximum Ethernet frame sizes. Hence, the
standard minimum and maximum packet sizes are cited as 64 bytes and 1,518
bytes. Technically, however, although the frame preamble information is discarded
when the frame reaches its destination, it is part of the frame when it travels across
the wire. Therefore, when measuring the performance of the segment in terms of
transmission utilization and time, the entire frame must be accounted in the
calculation.
Not all ISE's and NSE's soft errors impact the rings performance equaly. The soft
errors severity dictates level of level of the ring recovery effort needed to stabilize
the ring. There are three soft error ring recovery procedure's, Type 1, Type 2, and
Type 3:
• Type 1—Do not require any ring recovery effort, aside from reporting. A Type
1 error might result in an ULP retransmission of the data contained in
packets that might be lost as a result of the error. A high rate of Type 1 errors
associated with a particular station are an indication of a faulty NIC, a bad
lobe connector, a bad horizontal, or patch cabling.
• Type 2—Type 2 soft errors require a ring-purge procedure to be invoked by
the Active Monitor as a recovery effort. The ring-purge procedure attempts
to reset the ring back to normal repeat mode. It is initiated by the active
monitor on the detection of a lost token, frame, or a disruption in the ring's
timing. The active monitor sends the ring-purge frame and awaits its return.
If it returns, it checks the ring-purge frame for errors and, if there are none,
generates a free token. If an error is detected, it transmits another
ring-purge frame and checks it again for errors. If the active monitor fails to
receive the ring-purge frame or continues to receive "errored" ring-purge
frames until the ring-purge timer expires, the active monitor then evokes the
token-claiming process which results in the re-election of the active monitor.
Type 2 soft errors result in some type of error relating to the validity of the