Broadband Transport — the Synchronous Digital Hierarchy

Abstract

The ITU has chosen equipment conforming to the synchronous digital hierarchy (SDH) as the transport layer for broadband ISDN (B-ISDN) networks [1]. However, for many operators the majority of their network consists of the older plesiochronous digital hierarchy (PDH) equipment. This chapter describes the development of modern transport networks, the origins and advantages of the synchronous digital hierarchy and the application of the technology to the transportation of data services. The intention is to provide a description of the behaviour and characteristics of modern transport networks so that designers of client networks are able to assess the implications for a specific service. It should be remembered that such transport networks underpin every service offered by modern communications companies. In this sense, data must be viewed in its widest interpretation to include voice, video and other services. Furthermore, this chapter provides a review of transport technology for the core network but does not consider access technologies such as ADSL and PONs.