16.1 Introduction

An increasing number of bearer and transport technologies are used in the access network to deliver to customers an expanding and diverse range of products and services; synchronous digital hierarchy (SDH) is one of them. SDH was originally deployed in core networks, to take advantage of the improved reliability and network management for delivery of premium services. The technology has subsequently been used to provide efficient and reliable transport connectivity between broadband switch elements. Today, it represents a mature and stable technology used by many operators around the world. The resultant economies of scale, coupled with obsolescence of older technologies, are driving its increased use in the access domain.

This chapter describes how SDH technology is used to support the delivery of a broad portfolio of products and services. Experience from the BT network is used to describe and discuss the technology's generic functionality, deployment and potential.

SDH equipment has been present in customer sites since a decision was made to introduce the new technology into the network; however, until now it has been standard core network equipment rather than something specifically designed for the purpose. The first part of the chapter, Section 16.2, describes how SDH is deployed in the network and provides an overview of core networks and developments to date. The type of components found at customer sites is then described along with the ways in which these components can be connected back into the core network. Some examples of the...