An existing network customer does optical port external loopback on the N3SL16 single board of network element A. After doing the loopback, it is found that the multiplexing segment ring where the single board is located is inverted. Check the alarms, the time of multiplexing segment inversion and the time of appearance of LOOP_ALM and MR_RDI alarms are the same, and check that the downstream N3SL16 single board of network element B does not have any alarms in this time period, and the N3SL16 of the upstream external loopback of network element A reports the MS _RDI.

N1SL16 of network element A:

11 MS_RDI MN end 2013-04-14 10:33:19 2013-04-14 10:33:24 0x01 0x00 0x01 0xff 0xff

11 LOOP_ALM MN end 2013-04-14 10:33:19 2013-04-14 10:38:19 0x01 0x00 0x01 0x01 0x00

A network element multiplexing segment alarm:

9 APS_INDI MJ end 2013-04-14 10:33:20 2013-04-14 10:43:23 0x02 0x01 0x00 0x00 0x00 0x00

9 MS_APS_INDI_EX MJ end 2013-04-14 10:33:20 2013-04-14 10:43:23 0x02 0x01 0x08 0x01 0x00

B network element multiplexing segment alarm:

9 APS_INDI MJ end 2013-04-14 10:33:20 2013-04-14 10:43:23 0x02 0x01 0x00 0x00 0x00 0x00

9 MS_APS_INDI_EX MJ end 2013-04-14 10:33:20 2013-04-14 10:43:23 0x02 0x01 0x0b 0x01 0x00

Processing

B network element K-byte event:

1 299 SF_DETECTED 0x0000 2013-04-14 10:33:18 0x04a55485

.......

1 319 SF_CLEARS 0x0000 2013-04-14 10:33:22 0x04e3c202

The following is an example of a Kbyte event on a B network element, where a short SF event was detected in the multiplexing section of the B network element during the external loopback of the optical port, so that the alarm was filtered out and not reported, but the MS_RDI alarm in the upstream indicates that SF did occur in the downstream. based on the consistency of the time of the alarm and the loopback, it is suspected that SF was caused by the external loopback.

Reproduced in the lab, there are indeed SF or SD randomly appearing on the downstream board after the external loopback, and every time the downstream board detects a momentary deterioration in performance at the time of the loopback and immediately returns to normal.

Root Cause

The loopback process can cause performance degradation

The Solution

The cause of the phenomenon was analyzed by chip experts:

The single board to do the process of external loopback is the incoming signal frame processing to return to the sending direction, in this process will be different time nodes of the signal frame structure alignment, and this signal frame alignment process will lead to performance degradation (instantaneous appearance of the BER and pointer adjustments, etc., each time the degradation of the degree is different), complete the loopback action (frame alignment) after the performance will return to normal.

Recommendations and Summary

This phenomenon is determined by the characteristics of the external loopback, is a normal phenomenon, has nothing to do with the single board version, has nothing to do with the single board type, the reason why I did not notice the scene because it is not inevitable, even if it occurs, but also because of alarm filtering will not be reported to the corresponding alarms and did not pay attention to it. This time, if not in the multiplexing segment ring (SF,SD events), may not be found.

The related technical information in this chapter and the troubleshooting process of SDH equipment are collected and organized by Shenzhen Optical Transmission Network Technology Company Limited (www.opticaltrans.com), please retain! Our company specializes in the sale of Huawei SDH optical transmission equipment,SDH transmission equipment.