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

	ADMINISTRATION OPTIONS AND REQUIREMENTS — GENERIC 2	7-57
Field 7	This field is functionally equivalent to the Per-Channel Signaling and common
	channel signaling options used with System 85 R2V4. However, the terms have
	been changed to facility associated signaling (FAS) and NFAS.
	This field is used to specify the method used to constructed signaling bits for each
	DS0 B-channel. The option (23B + 1D) is also referred to as FAS. This is the
	default option (field encode 0). It is required for all DS1/DMI links. It is also
	required for all ISDN-PRI links that transmit B-channel signaling information with
	that particular DS1 link.
	The option (24B) is also referred to as NFAS. It is required for those ISDN-PRI
	links that have their B-channel signaling information transmitted over a different
	ISDN-PRI link. Field encode 1 enables this option.
	For each ISDN-PRI facility using NFAS (field 7 translated with a 1), that facility
	must be translated as part of a D-channel group in procedure 116, word 1. Each
	D-channel group number must be associated with a particular ISDN-PRI facility that
	transmits the signaling for all links within the group. The (23B + 1D) ISDN-PRI
	equipment location that provides this capability is called the primary D-channel.
	Reliability may be increased by administering an alternate (23B + 1D) ISDN-PRI
	equipment location as the backup D-channel (as administered with procedure 262,
	word 2).
Field 8	Offers the choice of 24th-channel or RBS. The choice of signaling method used is
	dependent on the application. The DS1/DMI-BOS applications may be translated
	for either option. However, non-NFAS ISDN-PRI applications always require	that

24th-channel signaling be selected. With NFAS, it is possible that no D-channel exists for this DS1 link.

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.