Ring Poll Process: NAUN - AMP - SMP

Token-ring adapters are able to isolate (locate) certain ring errors. This can only be done because each adapter knows its next addressable upstream neighbor (NAUN); the NAUN's MAC address is referred to as SUA or UNA. Token-ring error messages always contain the NAUN address in order to enable ring recovery.

Learning the NAUN addresses depends on the ring poll process or NAUN process initiated by the active monitor.

The active monitor (AM) sends active monitor present (AMP) notification MAC frames in intervals of 7 seconds (AC bits set to zero). The following station detects that it is the first station behind the active monitor because the AC bits are still set to zero; it learns its NAUN address and sets AC=11. All other stations will ignore this AMP frame because of AC bits set to all binary one. After the AMP frame has passed, all other stations subsequently send standby monitor present (SMP) notification MAC frames.

AMP and SMP frames are sent to the functional address 0x'C0-00-FF-FF-FF-FF' (multicast = 'this ring' broadcast); they are ignored by token-ring bridges.

Active Monitor Present - AMP

The active monitor present notification MAC frame is sent with AC bits set to zero (AC=00).

The active monitor's downstream neighbor recognizes by means of AC=00 (a) that it is the next downstream neighbor and (b) that it is the first station that receives the AMP frame because the AC bits are still set to zero. The downstream station learns its NAUN address (the active monitor's MAC address) that is notified in the AMP frame. Then the downstream station sets the AC bits to one (AC=11). All other ring station will now ignore the current AMP frame. The downstream station resets its Timer: Receive Notification that is used to control if the AMP frames arrive in time. If this timer exceeds a claim token process is started.

Now the downstream station captures the next token in order to transmit a standby monitor present (SMP) notification MAC frame. The next downstream station will process this SMP frame the same way as describes above, then it will send a SMP frame itself (and so on). All ring stations learn their NAUN address by this way.

If the active monitor receives a SMP frame with AC=00 the ring poll process is completed sucessfully.

If the ring poll process isn't completed successfully the AM sends an error message the the CRS. Then the AM purges the ring (if the NAUN process wasn't interrupted by hardware errors).

Token-ring analyzers monitor the NAUN process frames. As a result, analyzers can display ring topology and each adapter's status.