AT&T 7100 series, 7500 series, 2500 series, 7200 series, 7400 series, 7300 series manual Primary

SYNCHRONIZATION OF DIGITAL FACILITIES B-9

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System 85 or Generic 2 with a duplicated architecture and cross-coupled cables.

PRIMARY
		MODULE	SWITCHING
DS1	SCS 0	CLOCK
			NETWORK
INTERFACE		OR TMS
			0
		CLOCK 0
	SECONDARY
			PORT
			CARRIERS
	PRIMARY
SECONDARY
DS1		MODULE	SWITCHING
	SCS 1	CLOCK
			NETWORK
INTERFACE		OR TMS
			1
		CLOCK 1

Figure B-5.Duplicated Synchronization Architecture and Cross Coupling

The TN767 is a DS1 circuit pack for a universal module; the ANN11 is a DS1 circuit pack for a traditional module. The standard cable that comes with the TN767 is the H600307. It can be ordered in eight different lengths, up to 650 feet, by ordering one of eight different group numbers (groups 1 - 8). See System 85 R2V4 to DEFINITY Communications System Generic 1.1 via ISDN PRI Access (555-037-233), DEFINITY Communications System Generic 1.1 to 4ESS via ISDN PRI Access (555-037-234), and DEFINITY Communications System Generic 2.1 to 4ESS via ISDN PRI Access (555-037-237), for specific cabling and administrative information. The synchronization software consists of a series of tasks that monitor several system status parameters and thus maintain the best synchronization source online. (The online source is the synchronization reference currently in control. This reference can be either the primary or secondary reference, or an on-board local oscillator.) Several levels of control are maintained. One level is controlled by a 1-second software task that uses the system status to keep the best incoming DS1 reference clock online. The other is controlled both by hardware and the 1-second software task to maintain a healthy SCS on line. If a SCS can receive a suitable reference clock from a DS1, then the best combination is chosen.

The principal error conditions used to determine if a switch to a different DS1 clock reference is needed are, in order of importance:

∙Loss of signal (LOS) at the SCS circuit for more than 200 ms. A switch is made to the high-accuracy clock (HAC) on the SCS by the SCS. A further analysis is then made to determine if the LOS is network related or switch related. A switch to a healthy reference is done if appropriate.

∙Blue alarm means that the switch cannot be used as a reference.

∙Out-of-lock (OOL) condition means that the HAC is unable to lock onto the incoming clock from the current DS1 reference. A switch to a healthy reference is done if one is available. Otherwise, a switch to the HAC is performed.