Understanding the network.pdf - Back to Home

• Beacon (BCN)—Two classifications for Token Ring erroblrs exist: soft errors
and hard errors. Soft errors affect the transmission of data, but do not
represent a condition that alters the configuration or disables the ring.
Depending on the severity of the soft error, different ring recovery
procedures are initiated so that the ring can return to a normal state as
quickly as possible. A Token Ring hard error represents failure that halts the
ability for the ring to transmit data. When hard errors occur, the ring
attempts to reconfigure itself by removing the faulty elements from the ring.
This process, known as beaconing, is initiated by having the station that has
detected the hard error transmit beacon frames. When a station enters a
beaconing state, the beacon frames notify the other stations of the ring error
and the status of the recovery process.
• Claim Token (CTK)—When a standby monitor has reason to believe the
active monitor has failed or has been removed from the ring, it generates a
Claim Token in order to initiate the token claiming process.
• Ring Purge (PRG)—When the active monitor needs to reset the ring due to an
error, it transmits a ring purge frame. The "ring purge" resets the ring back
to the ring's normal operational state.
• Active Monitor Present (AMP)—The AMP frame is transmitted by the active
monitor to all the standby monitors as part of the active monitor's neighbor
notification monitoring process. If a standby monitor fails to get an AMP once
every 15 seconds, the standby monitor generates an error and a claim token,
initiated the token claiming process.
• Standby Monitor Present (SMP)—The SMP is sent as part of the neighbor
notification process when the station joins the ring. It is used to notify its
nearest active downstream neighbor (NADN) of its MAC address.
• Duplicate Address Test (DAT)—The DAT is used by a ring station to verify
that no other station on the ring has the same address. In addition to the ring
insertion process, DAT frames are also transmitted when a ring station is
involved in a hard error condition.
Of the 25 IBM MAC frame types, the majority of them are used to notify the
configuration report server of changes (and, in some cases, failures) in the ring's
operation. Here are descriptions of the IBM MAC frames that pertain to error
reporting in conjunction with IBM's LAN Manager product or equivalent product that
can function as an REM and the Ring Parameter server:
• Report Soft Error (RSE)—When a station detects a soft error, its first action
is to collect data on the nature of the error. The error collection process is a
timed event. When the soft error timer has expired, it generates a report and
sends it to the REM (provided one exists).
• Report Neighbor Notification Incomplete (RNNI)—The neighbor notification
process is a timed event. If the notifying station fails to receive a response
from its NAUN in the allotted time, an RNNI is generated and sent to the
REM.