Cabletron Systems TRMMIM manual Token Errors, Frequency Errors

Statistics

Lost frames are usually caused by a station entering or leaving the ring as the frame is circulating. Lost frames will cause the active monitor to initiate the ring purge process and issue a new token.

Congest

A congestion error occurs when a station recognizes a frame addressed to it, but is unable to copy the frame because it has no available buffer space.

Although this indicates a station which is performing poorly, it will not adversely affect other stations on the network; therefore, no ring recovery procedures are initiated.

Frame Copy

An FC error is counted each time a station recognizes a frame addressed to itself and detects that the Frame Status field’s ARI bits are already set to 1, indicating that there has possibly been a line surge, or that another station is duplicating its address.

Note that it is virtually impossible to have a ring with duplicate addresses, since most of the time the ring uses the hard-coded address on the adapter, and duplicate addresses are checked for when a station inserts itself into the ring. However, a system administrator can pass a locally assigned address to the adapter, so it is possible to unintentionally administer a duplicate address while a device is on a ring. This error is more commonly caused by transparent bridging on a Token Ring network.

Token Errors

A token error is counted when the active monitor either does not see a token circulating on the ring before its TVX (Timer, Valid Transmission) timer expires (e.g., a lost Frame error has occurred), or sees a recirculating frame or token. Each time a token error is noted, the active monitor purges the ring and issues a new token.

As in lost frames, the major cause for token errors is the disruption of the ring as stations enter or leave the ring. Note that token errors are only reported by an active monitor. If you see a token error reported by another station, it was serving as active monitor at some previous time.

Frequency Errors

A frequency error occurs when the ring clock frequency and a station’s internal crystal clock frequency differ by an excessive amount. This type of error happens more often on 16 Mbps rings than on 4 Mbps rings; it can also be a symptom of too many stations on the ring.

Detection of a frequency error initiates the monitor contention process, since this typically indicates that the active monitor is not present or is malfunctioning.

Ring and Station Variables 5-11