AT&T DS1/DMi/ISDN-PRI manual Important Concepts, Common-Channel Signaling, 22INTRODUCTION

1-22INTRODUCTION

The method used to provide ACCUNET® switched digital service (used by D4-channel banks) also maintains the 1s-density requirement. This method uses only seven of the eight bits for each DS0 channel's 8-bit word to carry user data. The remaining bit (8) is “wired” to a 1. (MPDM/M1* is compatible with ACCUNET switched digital service).

IMPORTANT CONCEPTS

Important concepts discussed in this section include:

●Common-channel signaling

●Alternate voice/data (AVD) trunks

●Bearer capability (BC)

●ISDN call processing

●CBC Service Selection

●Networking restrictions and ISDN-PRI limitations

Common-Channel Signaling

Originally, common-channel signaling (CCS) meant that any of the 24 channels could be used to transmit signaling for the other 23. To offer CCS, both RBS and 24th-channel signaling would have to be disabled to make all 24 channels available to transmit signaling.

Current AT&T applications use only the 24th-channel as the signaling channel and, therefore, the term CCS has been used more and more as a synonym for 24th-channel signaling. Misuse of the term CCS and its original definition have contributed to some misunderstanding. When comparing System 75 and System 85 DS1/DMI administration procedures, you will find that:

a. The current definition of CCS is used when administering System 75 and Generic 1, although it is 24th-channel signaling that is actually being administered.

b. The original definition of CCS cannot be administered for System 85 or Generic 2, however, 24th-channel signaling can be administered. For Generic 2, the equivalent terms, 23B + D or 24th-channel signaling, are used rather than CCS.

Alternate Voice/Data (AVD) Trunks

AVD is an attribute of trunks used with System 85 R2V4 and earlier releases, and System 75 R1V3 and earlier releases, and all Generic 1 switches. For Generic 2, bearer capability, which identifies the capabilities previously identified with AVD plus many more, is used instead.

AVD relates a trunk group’s translations to the type of signaling required to support the trunk group. From the software perspective (and when applicable), a trunk group is administered for either AVD or voice. Trunk groups administered for AVD may be used for both voice and digital data applications and require a DS1 that is administered for 24th-channel signaling.