Service protection for synchronous networks

There are a range of techniques which can be employed to make a fault-tolerant network. Some are best used in isolated portions of a larger network whilst others can be employed effectively on a network-wide basis. The aim of a fault-tolerant network is a high level of circuit availability as perceived by the customer, but this of course can only be achieved at some cost to the operator. In simplest terms this extra cost is due to the increased hardware needed to provide standby circuits through the network. However, two other important cost factors must be allowed for, namely the cost of the control mechanisms (for example software) used to ensure that failed circuits are restored and the cost of extra maintenance staff. A comparison is included of the available protection techniques listed in order of increasing complexity