Enterasys Networks MicroMMAC-T manual Burst Errors, Abort Sequences, Internal Errors

Token Ring Statistics

The first station detecting the data corruption sets the E bit to 1 in the ending delimiter of the frame and logs the error. This prevents other stations from logging the error and isolates the portion of the line which is causing the data corruption.

Burst Errors

Displays the total number of burst errors detected on the ring. These errors occur when a station does not clock an incoming data signal correctly.

Token ring protocol uses Differential Manchester Encoding for its signalling format. Using this code, each bit time is halved, with a correct signal having a transition at the center of the bit time (i.e., switching between 0 and 1, or vice versa, in the middle of the bit time). Burst errors occur when a station receives five half-bits of Manchester encoded data without a change in phase from 0 to 1 (thus indicating no change in data value).

These usually occur when there was a brief disruption on the cable, or a brief electrical surge or electronic noise on the network.

A.C. Errors

The count of AC Errors detected on the ring. These indicate that the reporting station’s Nearest Active Upstream Neighbor (NAUN) is faulty, because it is unable to report its address during neighbor notification.

If a station receives more than one Active Monitor Present (AMP) or Standby Monitor Present (SMP) frame with the Address Recognized Indicator (ARI) and Frame Copied Indicator (FCI) bits set to 0 without receiving an intervening AMP frame with these bits set to 1, it recognizes that its NAUN failed to set the ARI/FCI bits.

The detecting station indicates the error to the active monitor, then ends the ring poll process by not transmitting an SMP frame.

Abort Sequences

The count of abort delimiters transmitted on the ring. These are recorded when a station detects a corrupted token while transmitting, then sends an abort delimiter to halt frame transmission before the expected end-frame sequence.This error will cause the active monitor to restore the ring through the ring purge process. This error is somewhat uncommon, and often indicates a failing adapter. A common cause of abort sequences is overheating by the adapter in an overloaded system. Note that the adapter may also issue an Internal Error simultaneously, which will cause the adapter to remove itself from the ring.

Internal Errors

Displays the total number of internal errors detected on the ring. These are recorded when a station recognizes a recoverable internal error in its own adapter. You can use this to detect a station in marginal operating condition, possibly with an inoperable chipset, timers, or counters. A large number of internal errors can indicate that one or more stations on the monitored ring are in marginal operating condition.

Network Level Statistics 3-7