AT&T DS1/DMi/ISDN-PRI manual 109

ADMINISTRATION OPTIONS AND REQUIREMENTS — SYSTEM 75 7-109

Signaling The default option is common-channel. This option is the same as 24th-channel or

ModeAVD for System 85. The alternate choice is robbed-bit. The choice of signaling mode used is dependent on the application.

Common-channel signaling multiplexes all signaling information for channels 1-23 into the 24th-channel. This makes available the full 64K-bps bandwidth (of channels 1-23) for voice and/or digital data transmission. This capability is sometimes referred to as Alternate Voice Data (AVD).

The term AVD is a software attribute for a trunk. AVD allows pure 64K-bps digital data to be transmitted over those DS1 trunks that use 24th-channel signaling. Although AVD trunks are designed for digital data transmission they may also be used for voice and voice-grade data transmission. However, a pooled modem is required to transmit voice-grade data over AVD trunks.

CAUTION: Due to a change in the evolving DS1/DMI protocol specification, two methods for providing 24th-channel signaling exist. The two methods are not compatible with each other. The earlier method is known as the AT&T proprietary format (conventional T1 test equipment cannot analyze it). This latter version is known as the DMI-BOS format (T1 test equipment can analyze this format).

Either the AT&T proprietary format or the DMI-BOS format, depending on the circuit pack configuration, may be used with another System 75 or System 85. The DMI-BOS format is required to provide 24th-channel signaling capability with other vendors’ digital switches. Common-channel signaling (both methods) are not compatible with channel banks and multiplexers.

CAUTION: The TN722 circuit pack provides the AT&T proprietary format; the circuit pack does not provide DMI-BOS. The TN722B circuit pack may be administered to provide either the proprietary format or DMI-BOS format.

DMI-BOSAssigns the DS1’s format. Field encodes and their descriptions are:

n AT&T proprietary. This option assumes that common-channel signaling is selected; otherwise, RBS is used.

y DMI. This option is equivalent to a 1 in field 14 of procedure 260.