ATM switch and crossconnect architectures

Asynchronous transfer mode (ATM) is a key technique for deployment in the telecommunications network, due to its flexibility, efficient use of bandwidth and future-proof nature. This tutorial introduces the architectural aspects of electronic ATM switches and crossconnects, providing a framework for understanding optical ATM architectures. An ATM switch is dominated in both cost and size by the interfaces that surround the switch fabric itself; they perform functions such as O/E conversion, E/O conversion, timing recovery, line card control, header processing, cell formatting, concentration, expansion, SDH framing, SDH multiplexing, and SDH demultiplexing. Thus the switch fabric forms a small, but highly critical, part of the whole switch. Switch fabrics are generally made up from many switch elements; the switch elements are usually small enough to be implemented on one board, although there are no strict rules about this. For example, the knockout switch may be considered either as a switch element or a switch fabric. It describes how switch fabrics can be built up from switch elements. It concentrates on the two switch functions of switching and buffering (or contention resolution). Chips for ATM switching are typically fabricated in CMOS or BiCMOS, the latter allowing bipolar technology to be used for interfaces and clocks, thus avoiding degradation due to line loading.