IBM 8260 manual Ring Errors, Token-Claiming Process

ring purge process may be triggered after detecting the loss of a token, frame, or errors caused by adapter-insertion or adapter-removal operations.

To purge the ring, the active monitor initiates a Ring Purge MAC frame broadcast and starts the Ring-purge timer. If the Ring Purge MAC frame has not returned to the active monitor when the timer expires, the token-claimingprocess is initiated.

8.1.2.2 Token-Claiming Process

This process is used to elect a new active monitor. Any station who suspects the active monitor is absent can activate this process.

During the process, a Claim Token MAC frame is broadcast at a defined interval and the ring station who manages to capture three of its own Claim Token MAC frames will be appointed the active monitor.

8.1.3 Ring Errors

In the event of errors or faults, the token-passing protocol has built-in features to automatically reconfigure the ring to identify and bypass the fault and resume operation. This is an advantage over the CSMA/CD protocol.

Each ring station is capable of detecting and reporting any occurrences of errors or faults. Errors can be classified into the following categories:

∙Hard error

Hard errors are permanent faults that stop all normal traffic on the ring. They are usually first detected at the receive side of the next active downstream station from the fault. That ring station will immediately transmit a Beacon MAC frame to alert every station. It continues to transmit Beacon MAC frames at a specified time interval until its input signal is restored or until it removes itself from the ring.

∙Soft error

Soft errors are defined as intermittent faults that temporarily disrupt normal ring operation. Each station maintains a set of counters to keep track of soft error occurrences. The values of the soft error counters are sent in the form of a Soft Error Report MAC frame to the Ring Error Monitor station (for example, Bridge or LAN Manager station) at two-second intervals.

∙Isolating error

Isolating errors are identified because the fault domain is known. A fault domain is the physical section of the segment bounded by two adapter MAC addresses. A beacon is an example of an isolating error.

∙Non-isolating error

Non-isolating errors exist where the fault domain cannot be identified. The origin of these errors cannot be located. A Frame-copied error is an example of a non-isolating error.

Chapter 8. 8260 Token-Ring Support 131