This chapter covers the following topics:
Integrated Services Digital Network (ISDN) introduction—The introduction is geared towards explaining the development and progress of ISDN as a digital network structure.
ISDN network—This section introduces you to the physical attributes of the ISDN network and how ISDN circuits are typically deployed. Both Basic Rate Interfaces (BRIs) and Primary Rate Interfaces (PRIs) are detailed and the associated ISDN reference points.
ISDN specifications—This section describes the different ISDN specifications and how they operate in the ISDN network. This section is intended to give you an in-depth view on how ISDN works.
BRI—This section details how BRI circuits operate and how they are deployed in North America, Europe, and Japan. It covers both line-coding schemes and deployments.
PRI—This section describes the operation of primary rate circuits and how they are deployed around the world.
ISDN Introduction
In the days of old, the service providers infrastructure was deployed as a series of analog services. Analog services are acceptable in short distances, but they simply can't provide the quality of service (QoS) and bandwidth over the long haul. Remember that when analog circuits become too attenuated, the signal is merely amplified. This amplification also increases the noise content.
The analog infrastructure was never designed to provide voice, video, and data integration for customers. In today's market, these features have become more and more prevalent, and because of that something had to be designed that could handle these functions.
Modern telecommunication technologies are based on digital principles for reasons of flexibility, efficiency, and feature capability. Although many digital services are available today, ISDN offers some unique features that will solidify its place in telecommunication for years to come.
Originally, ISDN was developed as two separate types of service, N-ISDN (narrowband) and B-ISDN (broadband). The N-ISDN offerings are what this chapter focuses on, and they include BRI and PRI services. BRI and PRI are deployed over what are considered to be narrowband circuits, ranging from 16 kbps of a 64-kbps digital signal 0 (DS0), to a 2.048-Mbps circuit. B-ISDN is directly related to Asynchronous Transfer Mode (ATM) and is discussed in Chapter 10, "ATM and B-ISDN."
ISDN made the first real attempt at bringing services such as voice/video applications to end subscriber premises. If you take a closer look at the abbreviation ISDN, you can begin to understand the basis of the technology. ISDN is meant to integrate services such as voice, video, and data over a digital network. ISDN, because it is digital, offers customers more bandwidth than standard analog service, nominally running at 128 kbps for BRI service (144 kbps if D channel usage is allowed) and 1.544 Mbps for T1 PRI or 2.048 Mbps for E1 PRI.