The role of SDH and ATM in broadband access networks

With the introduction of equipment using the synchronous digital hierarchy (SDH), network operators are providing an infrastructure for the support of many different services. It is shown how this basic infrastructure will be developed to support asynchronous transfer model (ATM) based services, and thereby evolve to broadband ISDN (integrated services digital networks). SDH synchronous multiplexing at base rates of 155 Mbit/s and higher will provide the backbone transport for all services from telephony to broadband. The method of carrying services will initially be based on synchronous transfer mode (STM) and the lower levels of the synchronous multiplexing hierarchy. This method of transport is sufficient for services as they exist today and for the next few years. The use of SDH will allow a greater flexibility in the selection of service rates by its property of allowing bandwidth to be concatenated. Even greater flexibility will be provided by the use of ATM. As well as providing additional bandwidth flexibility, it allows efficient carriage of variable bandwidth service