SDH network evolution in Japan

NTT has entered the second phase of its deployment of synchronous digital hierarchy (SDH)-based transmission systems, with a primary focus on creating a more reliable network with lower costs and improving network operation systems for these SDH-based network elements. This article describes the evolution of NTT´s network from a plesiochronous digital hierarchy (PDH)-based network to an SDH-based network. First, we see the evolution from a network element point-of-view. Then, we focus on the network operation system, which has been unified to achieve flow-through operation