AT&T Technical Reference 50010 (December 1997)

TR 50010, December 1997

AT&T ISDN Basic Rate Interface Reference Guide

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Scope

This Technical Reference (TR) is provided to support AT&T’s digital services over Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI). More precisely, the TR addresses these BRI-based services over diverse central office (CO) switches. The intent of the document is to be a reference guide to BRI terminal developers who will provide customer premises equipment (CPE) in support of AT&T digital services. It is not the intent of this document to provide new nor updated information over and above that provided in each of the referenced specifications. The information herein directs BRI terminal developers to the specification of each central office switch under consideration. The TR currently focuses on CO switches manufactured by Lucent Technologies (formerly AT&T), Northern Telecom, and Siemens Stromberg-Carlson. Respectively, these switches are the 5ESS®, DMS-100®, and EWSD®.

In each instance the referenced specification defines the requirements for the Physical Layer (Layer 1), the Data Link Layer (Layer 2) , and the Network Layer (Layer 3). All specifications adhere to the ITU-TS (formerly CCITT) definition of a Basic Rate Interface. As such, the interface is defined as a bi-directional 144 Kbps digital subscriber loop segmented such that there are two 64-Kbps B-channels and one 16-Kbps D-channel. The B-channels transport user voice and/or data while the D-channel transports signaling and packet data.

The specifications have their basis in the CCITT ISDN Recommendations, Series I , Q, and X, the Bellcore TRs and SRs, and the ANSI T1 Standards. Each specification represents the switch manufacturer’s interpretation and subsequent implementation of the standards. As the interpretations are not unique, and as manufacturers wish to provide service differentiators, there are some variations in the realization of the interface and the type of services provided.

Organization

Section 1 provides an introduction and discusses the scope of the document as indicated above.

Section 2 discusses the implementation of the three ISDN BRI layers on the CO switches and the standards on which they are based. Across the switches, a common set of Standards is referenced for the implementation of each layer. For the Physical Layer (Layer 1), the Standards are ANSI T1.601-1991 for the U reference point and ANSI T1.605-1991 and ITU-TS Recommendation I.430 for the S/T reference point. At the Data Link Layer (Layer 2), the implementations are consistent with ITU-TS Recommendations Q.920 (I.440) and Q.921 (I.441) and with ANSI T1.602-1988. The Bellcore TRs and SRs are the primary drivers of the specifications at the Network Layer (Layer 3).
By committing to support National ISDN, the switch vendors have agreed to develop interfaces that are consistent with National ISDN-1 (NI-1), NI-2, and NI-3
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Section 3 identifies and provides references to each of the ISDN BRI specifications for the CO switches. The information for ordering the specifications is excerpted below:

For further information Contact:

AT&T Developmental Relations Group
Room 5356C3
295 N. Maple Avenue
Basking Ridge, NJ 07920

ISDN Vendor testing program is currently suspended

For more information about AT&T documents, see: Catalog Of Communications Technical Publications Publications Catalog (10000).

1. Recall that NI-1 defines the protocol at the user-network interface (UNI) with little attention to feature operation on the different vendor switches. In NI-2, the feature operations are standardized across the switches. NI-3 then defines a minimum set of features to be offered at the UNI by all the switch vendors.

2. Limited support is provided for earlier generics of the 5ESS switch. The specifications for 5E5, 5E6, and 5E7 are 235-900-311, 235-900-321, and 235-900-331 respectively. These are custom (proprietary) interfaces and the specifications can be obtained from the CIC.

3. As in the case of the 5ESS, some support is available for earlier generics of the DMS-100. NIS S208-4 and NIS S208-5 are the proprietary specifications for BCS 32. The documents can be obtained by contacting Nortel at the above telephone number.

4. All generally available generic Releases of the EWSD software have been in support of National ISDN. As appropriate, Release 13.0 provides full backward compatibility.