Description of the problem

A first-line engineer at a site in the current network opens a service according to the customer's request, and without knowing that the access service is a 16C cascading service, he establishes 16 end-to-end VC4 services on the transmission side of our company (source: NE1 network element No. 18 veneer VC4:1-16; host: NE2 network element No. 3 veneer VC4:1-16), and the mismatch of the service types leads to the disruption of unrelated services on the downstream network element. The AU_CMM and B3_EXC alarms are reported (i.e., service VC4:5 on board 22 of NE2 in the figure below, and the path of this service is shown in the figure below).

The topology diagram of the current network:

Cross-configuration of NE1 with single board 18:

18 1 5 0 26 1 2 0 vc4 active

18 1 6 0 26 1 6 0 vc4 active

18 1 7 0 26 1 7 0 vc4 active

18 1 8 0 26 1 8 0 vc4 active

20 1 4 0 26 1 5 0 vc4 active Cross-configuration of NE2 with board 22:

22 1 2 0 3 1 33 0 vc4 active

22 1 6 0 3 1 34 0 vc4 active

22 1 7 0 3 1 35 0 vc4 active

22 1 8 0 3 1 36 0 vc4 active

22 1 5 0 27 1 5 0 vc4 active

Alarm on board 18 on NE1:

18 AU_CMM MJ start 2013/7/26 12:05 None 0x01 0x00 0x05 0xff 0xff

18 AU_CMM MJ start 2013/7/26 12:05 None 0x01 0x00 0x06 0xff 0xff

18 AU_CMM MJ start 2013/7/26 12:05 None 0x01 0x00 0x07 0xff 0xff

18 AU_CMM MJ start 2013/7/26 12:05 None 0x01 0x00 0x08 0xff 0xff

Alarm on board 22 on NE2:

22 AU_CMM MJ start 2013/7/26 12:05:41 None 0x01 0x00 0x05 0xff 0xff

22 AU_CMM MJ start 2013/7/26 12:05:41 None 0x01 0x00 0x06 0xff 0xff

22 AU_CMM MJ start 2013/7/26 12:05:41 None 0x01 0x00 0x07 0xff 0xff

22 AU_CMM MJ start 2013/7/26 12:05:41 None 0x01 0x00 0x08 0xff 0xff

22 B3_EXC MJ start 2013/7/26 12:05:40 None 0x01 0x00 0x05 0xff 0xff

Processing

For the cascade service, it can be said that the smallest service granule is 4C cascade, corresponding to the requirements of the configuration of the VC4 time slot number must be a multiple of 4, can not be configured arbitrarily, so the NE2 No. 22 single-board port 6,7,8 time slots related to the cascade of 4C services corresponding to the VC4 time slots for 5,6,7,8.

Checking the cross-connections, it can be seen that the services corresponding to slots 6, 7, and 8 of the No. 22 single board 1 optical port of the NE2 network element on the existing network all come from the upstream 16C cascading service, so the detection of the corresponding slots is reported to AU_CMM (indicating that the actual service types received are different from the configured service types); however, the customer questions why the fifth VC4 service does not come from the upstream cascading service, and why it is also reported to AU_CMM, and the customer asks why it is reported to AU_CMM. AU_CMM is reported, and the service reports B3_EXC and interrupts at the same time?

After analyzing the alarm, the reason for service interruption is that B3_EXC has forwarded and inserted the AU-AIS alarm to the downstream, and the reason for generating the AU_CMM and B3_EXC alarms is that: the detection mechanism of the chip for the cascade service of 4C is that, when the pointer value of the 1st+4nth VC4 is detected as a valid pointer, it will detect whether the pointer values of the following 3 VC4 services are all cascade pointers, and if they are all cascade pointers, then it will consider these 4 VC4 services as cascade pointers. then these 4 VC4s are considered to be 4C cascaded services, so that a B3 calculation is performed for all net loads of these 4 VC4s. This leads to the fact that in this case in the current network, the 5th VC4 of board 22 is judged to be a cascade service when it is detected, and because the configured service is a VC4 service as well as the calculation of B3 is done according to the cascade format, the B3 value must be incorrect, and so the AU_CMM and B3_EXC alarms are reported.

Root cause

N/A

Solution

Modify the configuration to modify the 16 individual VC4s into a 16C cascade service.

Recommendations and Summary

This kind of problem has nothing to do with the type of veneer, all the chips in our company detect and judge the cascade service according to the ITUT recommendation, so as long as the 1st+4n VC4 time slots go for non-cascade service, and the next 3 VC4 time slots go for cascade service, the 1st+4n non-cascade service will be detected as a cascade service, and report the AU_CMM and B3_EXC alarms, and if you set the B3_ EXC to insert AIS, the service is also interrupted.

Therefore, it is required that the configured service and the accessed service type must be the same, otherwise similar problems as above will occur.

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