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

The Ring Error Monitor observes, collects and analyses hard-error and soft-error reports sent by ring stations on a single ring and assists in fault isolation and correction.

Hard Error Processing Function

Hard errors are detected, isolated and bypassed through the use of a Beacon MAC frame. Hard errors are broken cables, failed equipment, improper signal timing, incorrect voltage levels.

Any ring station that detects a hard error can generate a Beacon MAC frame. The frame is addressed to all other stations on the ring. A Beacon Frame contains the address of the station that discovered the Hard Error, its NAUN and a physical location (the RPS gives this information to the NIC during initialization).

1. Station G hasn't received any frame for a while. Station G starts a Beacon Frame with Station F as its NAUN

2. When Station F receives the Beacon Frame and reads that it is the NAUN of the Fault Domain. It disconnects from the ring and re-attaches to the ring using the Ring Insertion process.

Note: The cable between Station F and Station G is called the Fault Domain. 3. If the fault still remains on the ring, the Beacon Frame originator Station G, disconnects from the ring and re-attaches using the Ring Insertion process.

A fault that can be cured in this manner is called a Temporary Fault. If the fault cannot be cured than it is called a Permanent Fault.

The Ring Error Monitor monitors the Beacon Frame. It reports the location, NAUN, Beacon Originator address and whether it is a Temporary or Permanent Fault to the network management program.

Introduction to Data Communications
Previous	Table of Contents	Next