Cabletron Systems TRMM, Руководство пользователя

Страница: 59 / 70

THE DEVICE STATISTICS SCREEN
6-6
6.1.6 Non-Isolating Errors Fields
Non-isolating errors are “soft” error conditions that could have been
caused by any station on the ring, thus their fault domain cannot be
detected.
Lost Frame Errors
These errors occur when a transmitting station’s TRR (Timer, Return to
Repeat) timer expires before the end of its transmitted frame returns. This
timer ensures that the station returns to the data repeat state (e.g., retrieves
the token, strips it of data, and issues a new token to the ring). The Lost
Frame Errors field tracks these non-returned frames.
Lost frames are usually caused by a station entering or leaving the ring as
the frame is circulating, since this throws the ring temporarily out of clock
synchronization.
Frame Copied Errors
Frame Copied Errors are recorded when a station recognizes a frame
addressed to it, and detects that the frame’s Address Recognized Indicator
(ARI) bits are already set 1. This indicates a possible line surge, or that
another station is duplicating its address.
It is virtually impossible to have a ring with duplicate addresses, since the
ring most often will use the hard-coded addresses on ring adapters, and
duplicate addresses are checked for when a station inserts into the ring.
However, a system administrator can pass a locally assigned address to a
station adapter, so it is possible to unintentionally administer a duplicate
address while a device is on the ring.
Another possible cause is transparent bridges on a ring network. When a
frame first enters the net, it assumes that the first frame it receives is on
another network (even though the intended destination may be on the same
net), since its bridge database has not been updated. It will set the ARI bits
and forward frame data across the bridge. The intended station on the same
side of the net as a bridge’s receive port will perceive that the frame has
already been copied.