Description of the problem

An industry network using OSN3500 and OSN2000 equipment composed of 622M two-fiber bidirectional multiplexing segment ring, the number of nodes on the ring is 15: A-B-C .... M-N-O, the line is less than 300km, engineering acceptance of MSP inversion time, the customer insists on measuring the inversion time of the long path routing, that is, configured from A to O across 13 stations of the VC12 level of service, the results of the test multiplexing segment inversion time of 70-80ms, the customer believes that more than 50ms, do not agree with the acceptance.

Alarm Information

No alarm information is involved

Processing

According to the above analysis results, in the acceptance meeting held by the customer, test unit and agent, we explained to the customer as follows:

1, ITUT G.841 and the national standard of the reversal part of the standard to the customer to tell clearly, MSP reversal time refers to the reversal completion time, does not include the service recovery time, the meter shows the interruption time including the alarm detection time, the reversal completion time and the service recovery time, and the recovery time of each site of the VC12 service is about 2ms, so that the 15 sites need 30ms, the meter shows the test results will certainly exceed 50ms. The test result displayed by the meter will definitely exceed 50ms.

2. When the service is actually used, the shared ring of the multiplexing segment must not be configured with long-path services such as A-B - ..... -O such a long path service, because this is an unreasonable use of resources.

3, the test can use the VC4 level of service, so that even if it is a long path routing, because the AU pointer synchronization time is shorter, each station is calculated according to 300us, 15 stations a total of 4.5ms, instrumentation measurements show that the interruption time is usually not more than 50ms.

The customer agreed to change the test methodology to test VC4 level services and the test results were less than 50ms.

Root Cause

Definition of MSP inversion time in ITUT G.841 Recommendation:

Inversion Time - On rings with no additional services, with all nodes in idle state (no detected failures, no activated automatic or external commands, only idle Kbytes received) and with a fiber length of less than 1200km, the inversion (ring and zone) completion time shall be less than 50ms for failures on a single zone.

Note that G.841 specifies that the inversion (ring and zone) completion time should be less than 50ms, whereas the outage time monitored by the instrument during our inversion test includes: alarm detection time, inversion completion time, and service recovery time.

Check the national standard of the Ministry of Posts and Telecommunications again:

The synchronization time of low-order TUs is 500~1500us, so the service recovery time of low-order TUs is longer, and the longest time for each site may reach 2ms.

Refer to the national standard: <> Appendix A

According to the above analysis, the 2M circuit tested in this ring passes through 15 stations, and the inversion time + low-order service recovery time takes about 30ms, so that the test result displayed by the meter will definitely exceed 50ms.

Recommendation and Summary

Compared with carrier customers, industry customers have relatively insufficient knowledge of products and principles, and may be the first time to use our products. When encountering difficulties in acceptance testing, firstly, figure out the causes of the problems internally, and then collect persuasive evidence, and at the same time, plan how to enter into the problem with the customer and start the communication, so as to do the analysis of the problem of the layers of progressive guidance, to persuade people with reason.

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