A class of self-healing ring architectures for SONET network applications

SONET technology has made high-speed self-healing ring (SHR) architectures practical and economical for use in intra-LATA telecommunication networks. This paper reviews a class of SONET SHR architectures and their control schemes. The SHR architectures can be divided into two basic classes: bi-directional SHRs (B-SHRs) and uni-directional SHRs (U-SHRs). Bidirectional SHRs using four fibers and have evolved from today’s point-to-point protection automatic switching systems ( A P S s ) , while uni-directional SHRs use two fibers and may evolve from today’s APS or a new SONET path-level protection switching system system made possible by SONET pointers. The cost and capacity tradeoffs between B-SHRs and U-SHRs depend strongly upon the application, the network size and the demand pattern. BSHRs with four fibers can be operated under today’s operations environment without a significant change. However, U-SHRs using a path protection switching method may ease intervendor compatibility problems and can be implemented on a timely basis without changing the well-defined SONET AF’S protocol. The selection of appropriate SONET SHR architectures will depend upon the operating telephone companies’ economic analysis, emphasis on multi-vendor environment, SHR implementation time frame, and standards progress on making change to support a bi-directional ring architecture.