AT&T DS1/DMi/ISDN-PRI manual Megacom, 4INTRODUCTION

1-4INTRODUCTION

The BRI terminates at a subscriber’s residence or office. There, it connects either to an ISDN compatible terminal or to a conventional terminal via a terminal adapter. The BRI channel structure consists of a 2B + 1D format. Each B or bearer channel provides a 64K-bps information channel. Each D-channel provides a 16K-bps signaling channel.

NOTE: Specific descriptions for BRI layers 1, 2, and 3 are not included here. Another document that fully describes ISDN-BRI architecture, specific administration requirements, and service provisioning is being developed. (Refer to ISDN-BRI Reference Manual (555-025-102) for more information.)

When connecting customer-premises switches to the public network, consider the features and services supported on each end of the connection. At the time of this publication, the AT&T public network supported the following services:

●Switched digital service

●M E G A C O M ®

●MEGACOM 800

●Call-by-call (CBC) Service Selection

●Automatic number identification (ANI)

System 85 R2V4 supports ISDN-PRI but not ISDN-BRI. However, System 85 R2V4 uses the line- side digital communications protocol (DCP) to provide end-to-end digital connectivity. The DCP channel structure consists of 2I + 1S channel format. Each I-channel provides a 64K-bps information (voice/data) channel, while the S-channel provides an 8K-bps signaling channel. The DCP is similar to ISDN-BRI, both in structure and in function. The DCP was AT&T’s early attempt to offer (what at that time was) the evolving BRI standard. Figure 1-1,System 85 R2V4 ISDN Configuration, shows various trunk-side and line-side connections to a System 85 R2V4.