AT&T 7300 series, 7500 series, 7100 series, 2500 series Signal Inversion, Restricted ⎜ Unrestricted

MULTIPLEXED COMMUNICATION 1-21

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Signal Inversion

Signal inversion is the replacement of all 1s in a digital transmission stream with 0s; and the replacement of all 0s with 1s. The use of signal inversion is related to the transmission facilities, the DMI mode, and the line coding. Table 1-6gives the conditions under which a signal should be inverted. (The need for signal inversion is given in the last three columns of the table. Note that when no inversion is necessary, the table entry is "normal.") In addition, table 1-7lists, among other things, AT&T data modules and their signal- inversion capabilities. The tables assume the following knowledge of the difference between restricted versus unrestricted channels; between bit-oriented signaling (BOS) and message-oriented signaling (MOS); and among the DMI modes 0 through 3.

∙Restricted channels are channels over which no all-zero bytes can be transmitted. The line equipment transmitters on restricted channels use ZCS line coding.

Unrestricted channels have no restrictions on the number of consecutive zeros of user data that can be transmitted. The line equipment transmitters on restricted channels use B8ZS line coding.

∙Bit-oriented signaling is accomplished by inserting signaling bits in the 24th channel of a DS1 facility. Message-oriented signaling is accomplished by inserting messaging octets in the 24th channel. (See 24th-Channel Signaling later in this chapter.)

Note that for BOS applications (and for any application where MOS is not carried end to end) the bearer

(B) channels should always be considered restricted since BOS cannot declare whether the network path is restricted on a per-call basis.

∙The DMI modes are explained in appendix D. Note that DMI mode-2 transmission is always inverted, regardless of the facility.

			Table 1-6.Signal-Inversion Requirements
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⎜		⎜		⎜		1.544		⎜		⎜
⎜		⎜	Traffic	⎜				⎜	2.048	⎜
⎜ Channel		⎜		⎜	Facilities			⎜		⎜
⎜	Type	⎜	Type	________________________					Facilities	⎜
				⎜		⎜		⎜
⎜		⎜		⎜	Restricted	⎜ Unrestricted		⎜		⎜
⎜		⎜		⎜		⎜		⎜		⎜
⎜	D	⎜	BOS	⎜	Normal	⎜	Normal	⎜	Normal	⎜
⎜		⎜		⎜		⎜		⎜		⎜
⎜	Channel	_	Signaling	⎜		⎜		⎜		⎜
		⎜
⎜		⎜	MOS	⎜	Invert	⎜	Normal	⎜	Normal	⎜
⎜		⎜	Signaling	⎜		⎜		⎜		⎜
_		⎜		⎜		⎜		⎜		⎜
⎜
⎜	Bearer	⎜	Mode 0	⎜	Invert	⎜	Normal	⎜	Normal	⎜
⎜	Channel	⎜	(HDLC)	⎜		⎜		⎜		⎜
⎜		_		⎜		⎜		⎜		⎜
		⎜	Mode 0		Normal		Normal		Normal
⎜		⎜		⎜		⎜		⎜		⎜
⎜		⎜	(non-HDLC)	⎜		⎜		⎜		⎜
⎜		⎜	Mode 1	⎜	Normal	⎜	Normal	⎜	Normal	⎜
		_
⎜		⎜	Mode 2	⎜	Invert	⎜	Invert	⎜	Invert	⎜
⎜		_		⎜		⎜		⎜		⎜
		⎜	Mode 3		Invert		Normal		Normal
⎜		⎜		⎜		⎜		⎜		⎜
⎜		⎜		⎜		⎜		⎜		⎜

Source: Digital Multiplexed Interface Technical Specification, 555-025-204