Bridging
With a SONET link, there are three levels of error conditionsÑanomalies, defects, and failures.
¥Anomalies are small discrepancies between a desired and actual characteristic of an item, which when occurring singly will not interrupt the ability of the SONET network elements to perform their required functions.
¥Defects indicate that anomalies have reached a level where the ability of the SONET network elements to perform their required functions has been interrupted. Defects are used in performance monitoring and in determining the faultÕs cause, and have impact on consequent actions on the network.
¥Failures indicate that a network element has been unable to perform its required functions beyond a maximum time allocated to a given error condition.
These errors can occur in any of the four optical layers of a SONET network, which are (in order from lowest to highest layer in the hierarchy) the physical Medium, Section, Line, and Path layers.
¥The Medium layer is the Photonic layer that physically converts electrical signals to optical signals.
¥The Section layer deals with the transport of frames across the optical medium, including framing and scrambling data for transmission, the error monitoring and maintenance between
¥The Line layer is responsible for reliably transporting the
¥The Path layer transports services between
It maps signals into a format required by the line layer, and reads, interprets, and modiÞes path overhead for performance monitoring and automatic protection switching.
Error reporting occurs at the Section, Line, and Path layers, and is carried within the corresponding SONET overhead. In terms of the SONET protocol stack, the three layers with overhead are mapped to the SONET link as shown in the following diagram.
SONET Port Configuration |
