Optical Network Design and Implementation

SONET Protection Architectures

This section discusses various SONET protection architectures and mechanisms. This includes APS, linear, and ring protection architectures. SONET rings use path-switching or line-switching, self-healing techniques. The Telcordia GR-253-CORE specification requires SONET protection architectures to restore within 50 ms. For example, SONET defines a maximum switch time of 50 ms for a BLSR ring with no extra traffic and less than 1200 km of fiber. The specification actually states 60 ms, with 10 ms for discovery of the problem and 50 ms to perform the switch, but this is commonly referred to as just 50 ms. However, most SONET networks are much smaller and simpler than this example and even faster. Y-cable switchover ...