14.1 Introduction

Customer requirements are becoming more exacting as quality expectations rise and the demand for new services escalates. With the increasing range of services, bandwidth requirements are also increasing. Although 64 kbit/s circuits are adequate for telephony, the emergence of multi-media services is spawning massive increases in bandwidth requirements. The convergence of the computing, IP, broadcast/media and telecommunications industries is consistent with this demand. The term 'broadband' is used to describe high-bandwidth capabilities. Although the term is not strictly defined, it is generally applied to bandwidths of greater than 2 Mbit/s. The term 'Narrowband' is used to describe lower-bandwidth capabilities, typically 2 Mbit/s or less.

Networks are responding to these rapidly changing requirements by establishing secure and flexible high-bandwidth transport capabilities. These capabilities can be used as a solid platform upon which the increasing range of services can be carried. New switching systems are based on evolving standards for asynchronous transfer mode (ATM) technologies.1 ATM will provide the backbone for high-bandwidth communications.

This Chapter describes the ITU-T signalling platform for broadband networks. Section 14.2 summarises the signalling relations that are available. Section 14.3 describes the architecture for access and inter-nodal signalling. The rest of the chapter focuses on the lower layers of the architecture that provide a platform for broadband signalling, namely the ATM layer and ATM Adaptation layer (AAL). The higher layers (B-ISUP and DSS2) are described in Chapters 15 and 16, respectively.

Other standards for broadband signalling are also being proposed. The ITU-T standards are used here...