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., > 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.