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ISDN Interfaces
Timing and Synchronization
Strata CTX I&M 06/04 7-35
ISDN Interfaces
Loop-back Test
1. Remove the PRI modular cord from the RPTU RJ45 jack and remove the RPTU from its card
slot.
2. Place the JP1 and JP2 jumpers to the LB-On position. Install the RPTU with the Strata CTX
power Off and the PRI modular disconnected from the RPTU RJ45 jack.
3. Turn the Strata CTX power On and connect the PRI modular cord to RPTU RJ45.
4. After the PRI line and RPTU are synchronized, have the CO generate the loop-back test sign
(all “1s” or “0s”).
CAUTION! Do not have the CO do a QRS loop-back test, because the test signal may
cause the Strata CTX to drop all calls and/or stop operating.
5. If the loop-back test fails, perform tests to isolate the problem with an ISDN test set, such as the
Sunbird, ISDN, or Trend DUET. In this case, the network PRI line is disconnected and the test
set is connected to the CSU network input jack. For testing details, refer to the ISDN test set
operating procedures.
Timing and Synchronization
The Digital Network is connected by timing clocks that synchronize the network and have various
degrees of precision (stratum levels). There are four stratum levels – 1 is the highest and 4 is the
lowest. They are associated with the following sources:
• Stratum – 1: Public Telephone Network clock
• Stratum – 2: #4 ESS Toll Switches
• Stratum – 3: #5 ESS Central Offices
• Stratum – 4: Digital PBXs
In the Strata CTX, one PRI, BRI, or T1 PCB can be programmed to extract the Stratum clock
signal. It uses the signal as the Strata CTX system Primary clock reference. The clock provider
should be a reliable source, such as a Telco or common carrier (AT&T). All other PRI, BRI, or T1
lines connected to the Strata CTX will be synchronized to the same clock provider. If the PRI,
BRI, or T1 are not synchronized to the same clock provider, the Strata CTX could experience
“slip” problems.
The timing or synchronization program determines how the Strata CTX digital voice or data
transmission path is synchronized with the far-end digital path. For proper PRI, BRI, and T1
operation, the equipment at each end of the line must be synchronized.