AT&T DS1/DMi/ISDN-PRI manual Voice/data AVD, V3-V4

	ADMINISTRATION OPTIONS AND REQUIREMENTS — SYSTEM 85		7-9
Field 8	V1-V4
	Offers the choice of 24th-channel or robbed-bit signaling (RBS). The choice of
	signaling method used is dependent on the application. The DS1/DMI-BOS
	applications may be translated for either option. However, ISDN-PRI applications
	always require that 24th-channel signaling be selected.
	With RBS, information is transmitted in the least-significant bit (LSB) position of
	each channel every six frames. This effectively limits the channel’s use to voice and
	voiceband analog data applications. Digital data ports connected to Digital
	Communications Protocol (DCP) data modules must use the modem pooling
	capability to transmit data over DS1/T1 RBS facilities. Analog data ports must be
	configured with analog modems.
	24th-channel signaling multiplexes all signaling information for channels 1 through
	23 into the 24th channel. This makes available the full 64K-bps bandwidth (of
	channels 1 through 23) for voice and/or digital data transmission called alternate
	voice/data (AVD).
	AVD allows pure 64K-bps digital data to be transmitted over those digital trunk
	facilities that use 24th-channel signaling. Although AVD trunks are designed for
	digital data transmission, they may also be used for voice transmission. However,
	because of a modem-pooling limitation, AVD trunks cannot easily be used for
	analog voice-grade data transmission.
	24th-channel signaling is required for those trunk groups that are translated AVD
	(from procedure 101, field 17).
	Either the AT&T proprietary format or the DMI-BOS format may be used with
	another System 85 or System 75. The DMI-BOS format is required to provide
	24th-channel signaling capability with other vendors’ digital switches. 24th-channel
	signaling (both methods) is not compatible with D4-channel banks. The AT&T
	proprietary format is provided by the ANN11C version-8 (or later) circuit pack. All
	previous versions will eventually be replaced via a class-A change. The DMI-BOS
	format is provided by the ANN11D or ANN11E circuit pack. When 24th-channel
	signaling is optioned, the ANN11D or ANN11E circuit pack automatically
	interrogates the far-end and provides the required format. For System 75, the
	proprietary format is administered by translating a	n in the DMI-BOSfield. To
	select the DMI-BOS format, simply administer a y	for the DMI-BOSfield.
	V3-V4
	A mode 1 data call requires a Line+Trunk-mode circuit pack with RBS option.