Specifications

2-15
TOKEN RING OVERVIEW
Ring Poll Process
If there is no duplicate address on the ring, the station participates in
neighbor notification by learning its Nearest Active Upstream Neighbor
(NAUN) and identifying itself to its nearest active downstream neighbor.
The AM initiates process by sending out a broadcast AMP frame to its
downstream neighbor. The downstream neighbor sets the address
recognized and frame copied bits, stores the AM address, and generates a
broadcast SMP frame to its downstream neighbor.
The process is iterative and continual. This ensures that the MAC
addresses of stations inserting into the ring are revealed to and recorded
by other stations on the ring.
Request Initialization
The final test performed in the Station Insertion process involves a request
by the new station on the ring for ring parameter values. These values
typically include timer values and the ring number. The new station
requests this information by transmitting a Request Parameters MAC
frame to a Parameter Server on the ring, typically available from a bridge
on the ring. If no server is available, then the station operates in
accordance with its own defaults.
The station is now a legal member of the ring and can start transmission.
However, to verify that the ring is valid, it checks for the presence of an
AM on the ring.
The Active Monitor
The first station to initialize onto the ring is the Active Monitor (AM). As
part of its duties, the AM initializes the ring (Ring Purge) and issues a
token. The AM supplies the master clock for the network, and all other
stations receive their timing from this clock. A ring latency of 24 or 32 bits
(for 4 Mbps or 16 Mbps rings, respectively) is provided by the AM. The
Monitor bit is set and checked by the AM to ensure that tokens and frames
do not recirculate the ring.