Enterasys Networks MicroMMAC-T Lost Frames, Congestion Errors, Token Errors, Frequency Errors

Token Ring Statistics

Lost Frames

Displays the number of lost frame errors detected on the ring. These occur when a station is transmitting and its TRR (Timer, Return to Repeat) timer expires. This timer ensures that the station returns to the data repeat state.

Lost frames are usually caused by a station entering or leaving the ring as the frame is circulating – since this often throws the ring temporarily out of synchronization. Lost frames will cause the active monitor to initiate the ring purge process and issue a new token.

Congestion Errors

Displays the total number of error conditions when a ring station recognizes a frame addressed to it, but has no available buffer space; that is, the station is receiving frames faster than its adapter can copy information from the buffers. This indicates that the station is congested.

F.C. Errors

Displays the count of frame copied (FC) errors detected on the ring. These are recorded when the management station recognizes a frame addressed to it and detects that the Frame Status field’s Address bits are set to 1, indicating a possible line surge or duplicate 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 the ring. This error is more commonly caused by transparent bridging on a token ring network.

Token Errors

Displays the number of token errors detected on the ring. These occur when the management station, as the active monitor, recognizes an error condition that needs a token transmitted. This occurs when the TVX (Timer, Valid Transmission) timer expires. This timer records the time in which a valid transmission can occur.

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 the 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.

3-8 Network Level Statistics