Digital network synchronization

With respect to network timing, the introduction of SONET equipment into the public network offers both problems and opportunities. Wide-scale deployment of SONET equipment and the use of SONET line timing for reference distribution will eventually provide improved timing performance in terms of both wander and jitter. One of the main motivations for developing the SONET architecture was to establish standards for interconnecting optical transmission equipment from different suppliers. In the process of establishing the SONET standard other (e.g. synchronization) technical issues were addressed. The article compares the existing (asynchronous) network architecture with the new (synchronous) architecture in terms of their respective performance in transporting the clock rates of tributary digital signals. Of primary interest is the timing quality of a first level digital signal such as the North American DS1 signal or the ITU-T (formerly CCITT) El signal. Although the new architecture offers eventual promise in solving numerous timing and interfacing problems for such tributary signals, the new equipment must necessarily co-exist and inter-operate with the existing facilities. Thus, another major topic of the article concerns the performance of interim networks with mixtures of asynchronous and synchronous multiplexing