ABSTRACT
One of the main advantages of SDH/SONET over PDH is the “resilience” provided in the SDH networks, besides the direct drop/insert facility and enhanced OAM features. Resilience means that the networks are tolerant to faults, and the customer traffic is not affected by system breakdowns. Although it is never possible to provide a 100% fault tolerant design for any type of network, SDH provides for fault tolerance to a great extent. The electronics of today are by and large very reliable, thanks to the largescale integrated circuits and much improved manufacturing facilities, with much harder specifications as compared to the past. This makes the equipment much less prone to faults as compared to the media (referring to the OFC or buried copper cables), which is extremely prone to damage. The buried or underground OFC is subjected to a very hostile environment because of a large number of activities in the vicinity involving digging by municipal corporations, electricity companies, telephone companies, and private parties. The result is that the cases of damages/cuts to OFC are very frequent, leading to complete disruption of telecommunication traffic.
