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Code Error in Interconnection of 2M Timeslots Between OptiX OSN 7500 and AL 7500 Router Through the 622M Port

Publication Date:  2012-07-25 Views:  43 Downloads:  0
Issue Description
In office W, the OptiX OSN 7500 is interconnected with the 7750 router from AL by connecting the 622M port to the 2M BER tester. The transmission network performs convergence of the BTS 2 Mbit/s circuits to the 622M port on the AL 7750 router. AL 7750 router forwards the 2 Mbit/s service to the switching side. After the service is commissioned, the 2 Mbit/s service of each transmission device at the BTS reports background error blocks, and error codes occur at the switching side. No error codes are reported from the 622M port on the OptiX OSN 7500, the 622M port on the 7750 router, or the transmission network lines.
Alarm Information
B3-SD
Handling Process

1.       Test the 2 Mbit/s channel to the BTS transmission device through the 622M port on the OptiX OSN 7500. No anomaly is found. The faults of the transmission network are ruled out. The cause is the interconnection fault or the fault of the 7750 router.

2.       Analyze the clock configuration of AL 7750 router.

3.    Set the system clock of the 7750 router to the external BITS clock. Error codes disappear.

Root Cause

1.       Test the 2 Mbit/s channel to the BTS transmission device through the 622M port on the OptiX OSN 7500. No anomaly is found. The faults of the transmission network are ruled out. The cause is the interconnection fault or the fault of the 7750 router.

2.       It is found by analyzing the clock configuration of the AL router that AL 7750 router has two clocks: a system clock and a line clock. The system clock of the 7750 router is a self-oscillation clock. The 622M port clock is the clock of the transmission line. It is found through analysis that the working clock of the 7750 router is different.

       The system clock of the 7750 router is used for encapsulation of the 2 Mbit/s service. The root cause for error codes is 
        inconsistency between the system clock and the line clock.
Suggestions
When 2 Mbit/s error codes occur during interconnection between OptiX OSN 7500 and AL 7750 router, AL needs to check whether the router clock configuration is correct.

END