scope:

This document describes the protection switching protocols and algorithms for optical interfaces referred to as SONET. The SONET optical interface standard is specified in American National Standard for Telecommunications - Digital hierarchy - Synchronous Optical Network (SONET) - Basic description including multiplex structures, rates, and formats, T1.105-1995. In its initial version, this standard addresses protection switching for linear 1 + 1 and 1:n topologies, and bidirectional line-switched ring network topologies. Nested protection is for further study.

SONET automatic protection switching schemes utilize two bytes, K1 and K2, to implement a bit-oriented protocol for time critical switching operation. Other operations channels, including the Section and Line Data Communications Channels, may also provide non-time critical (e.g., graterthan 50 ms) protection switching functions.

Independent protection of overhead channels, such as the DCC, are beyond the scope of this standard. Any special considerations pertaining to the use of wave-division multiplexing or directional couplers for transmitting multiple signals over the same fiber are beyond the current scope of this standard.