The evolution of service protection in the BT network

The evolution of telecommunications transmission technology from analog and metallic cables to digital and optical fiber, coupled with new service demands, has caused network protection strategies to change their focus. The way in which BT (British Telecom) has addressed this problem is examined and future SONET and PON options are considered. The discussion is supported by computed path availability characteristics for a range of equipment, plant, and topology options. It is noted that network protection is not a static problem. With each new transmission technology the key sensitivity points have migrated from the line system and cable to the multiplexer and terminal equipment. Passive optical networks look set to offer the ultimate path diversity protection. In the BT network it is the local/access networks that offer the most difficult environment, with true path diversity being hard to achieve due to the inherent tree and branch topology of the ducts. In contrast, long and medium-haul networks are more fully meshed and well adapted to triangulation and diversity