The Beaconing Process

The Beaconing Process

Generally, the first station that is powered-up on a Token Ring network automatically becomes what is called the active monitor station. The responsibility of the active monitor station is to announce itself to the next active downstream station as the active monitor station and request that station to announce itself to its next active downstream station. The active monitor station sends this beacon announcement every seven seconds.

After each station announces itself to its next active downstream neighbor, the announcing station becomes the nearest active upstream neighbor (NAUN) to the downstream station. Each station on a Token Ring network has an upstream neighbor as well as a downstream neighbor.

After each station becomes aware of its NAUN, the beaconing process continues every seven seconds. If, for some reason, a station doesn’t receive one of its expected seven-second beaconed announcements from its upstream neighbor, it attempts to notify the network of the lack of contact from the upstream neighbor. It sends a message out onto the network ring, which includes the following:

The sending station’s network address
The receiving NAUN’s network address
The beacon type

From this information, the ring can determine which station might be having a problem and then attempt to fix the problem without disrupting the entire network. This process is known as autoreconfiguration. If autoreconfiguration proves unsuccessful, manual correction becomes necessary. Figure 4.17 shows a Token Ring network utilizing the beaconing process.