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

B-16SYNCHRONIZATION OF DIGITAL FACILITIES

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STRATUM 3				TIMING	TO
REFERENCE #1	CLOCK				TN2131
				OUTPUT,
	INPUT				0
				COMPOSITE
	#1		STRATUM 3
				CLOCK B
			CLOCK A
					SYSTEM 85 AND
	PHASE				GENERIC 2 ONLY
	BUILD
	OUT
STRATUM 3			STRATUM 3	TIMING	TO
			CLOCK B	OUTPUT,	TN2131
REFERENCE #2	CLOCK				1
				COMPOSITE
	INPUT
				CLOCK B
	#2
		-48VDC	POWER
		RETURN	BUS
-48VDC A
-48VDC B	SWITCH		SYSTEM ALARM BUS		TO TN492C
	ALARM
					EXTERNAL
	INTERFACE
RETURN				SYSTEM ALARMS	ALARM

Figure B-8.External Clock

Private network applications that do not have digital connections to stratum-3 or better reference sources will not provide the Reference 1 and Reference 2 inputs or the clock-input #1 and clock-input #2 circuit packs. These types of network applications are not allowed.

For public-network applications, the clock-input circuit pack derives a 1.544-Mbps clock signal from the reference. The clock input #1 and #2 circuit packs generate a 4-kbps stratum-3 clock signal and supply it to the clock and output boards. The composite clock output circuit pack monitors the 4-kbps signals from the references and clocks and, on detecting a failure or other error, automatically changes from the online reference clock to an alternate. Furthermore, an alarm signal alerting you of the problem is generated. Additionally, the composite clock output circuit pack generates a 64-kbps composite clock signal. This signal is a special bipolar (return-to-zero) signal that contains a bipolar violation every eighth bit and is cabled to the switch (for System 85 and Generic 2, the TN2131 circuit pack).