Introduction to Data Communications
Previous	45m. Token Ring Monitors and Servers (cont'd)	Next

At any time during the neighbour notification cycle, certain events could happen that could affect the Neighbour Notification process. The Active Monitor checks for these conditions and takes appropriate action:

1. The Active Monitor's Neighbour Notification Timer runs out. The ring is taking too long to complete the Neighbour Notification process. The Active Monitor restarts the Neighbour Notification process and reports a Neighbour Notification Incomplete MAC frame to the Ring Error Monitor (REM - just another node on the ring that has the job of monitoring ring errors).

2. The Active Monitor Present Frame takes too long to circle the Ring. The AM initiates token claiming so it can retransmit an Active Monitor Present frame.

3. If a Standby Monitor Present Frame is received after Neighbour Notification is complete, the Neighbour Notification is ignored and restarted. Another station has just connected to the ring and by inserting into the ring, has changed the NAUN order.

4. If another Active Monitor Present Frame is received with a source address different from its own. This means that there is another Active Monitor on the Ring. The receiving Active Monitor shuts down and becomes a Standby Monitor.

5. A hard error (cable fault, student playing with RI and RO ports) causes the ring to go down. After the hard error is fixed, the Neighbour Notification process is restarted.

Introduction to Data Communications
Previous	Table of Contents	Next