1+1 Dual-Ended Switching Was Triggered on a DCP Board?

A Huawei WDM network consisted of five rings. An M40v board and a D40 board were used on each NE as the multiplexer and demultiplexer. LDX boards were used to forward 10GE LAN services. Dual-ended intra-board 1+1 protection was configured by using DCP boards. After the PAT, switchovers occurred frequently on the channels between NE 12 and NE2 and on those between NE 13 and NE 2. Related DCP boards reported INTRA_OTU_STA_INDI and INTRA_OTU_PS alarms. The INTRA_OTU_STA_INDI cleared after a while but the INTRA_OTU_PS alarm failed to clear. Services were switched to the protection channel. The switchovers occurred twice. The related information is as follows:

First switchover: When the customer was maintaining the line, the line attenuation between NE 13 and NE 2 transiently increased by 6.5 dB and then restored (queried in the 15-minute performance data). Wavelength 1 between NE 13 and NE2 and Wavelength 2 and Wavelength 3 between NE 12 and NE 2 were switched. Services were transmitted to NE 2 through NE 1.

Second switchover: When the customer was maintaining the line, the line attenuation between NE 13 and NE 2 transiently increased by 1.8 dB and then restored (queried in the 15-minute performance data of the OBU board). Wavelength 1 between NE 13 and NE2 and Wavelength 2 between NE 12 and NE 2 were switched. Services were transmitted to NE 2 through NE 1. Wavelength 3 was normal.

The networking typology is as follows.

networking topology

OSN 8800 T32/P16 version: V100R008C00T

U2000 version: V100R009C00

The conditions for an OLP switchover include R_LOS and POWER_DIFF_OVER. The switchovers in this case were triggered by the POWER_DIFF_OVER alarm caused by optical cable deterioration. On the U200, the default threshold for the difference between optical power on the working and protection channel on the DCP boards is 5 dB. This threshold can be modified by choosing

The default value was used on the network in this case.

First switchover:

On NE 13, Port 1 (TI1/RO1) of the DCP board was used. The optical power at the working port (RI11) and protection port (RI12) was as follows:

RI11: –4.9 dBm

RI12: –5.3 dBm

When the Huawei optical power on the working channel decreased from –4.9 dBm to –11.4 dBm (queried in the 15-minute performance data of the OBU board), the difference between the optical power on the working and protection channels was –5.3 – (–11.4) = 6.1 dB, which exceeded threshold. Therefore, a POWER_DIFF_OVER alarm was generated. This alarm was not reported to the U2000 by default. Huawei queried the historical alarms by choosing More Alarm Operations > History Alarm on NE from the switched NE 13 on the U2000 and found that the DCP board reported a POWER_DIFF_OVER alarm.

Therefore, the switchover was normal. The switchovers on Wavelength 2 and Wavelength 3 between NE 12 and NE 2 were triggered by the same condition.

Second switchover:

On NE 13, Port 1 (TI1/RO1) of the DCP board was used. The optical power at the working port (RI11) and protection port (RI12) was as follows:

RI11: –4.9 dBm

RI12: –5.3 dBm

When the optical power on the working channel decreased from –4.9 dBm to –6.7 dBm (queried in the 15-minute performance data of the OBU board), the difference between the optical power on the working and protection channels was –5.3 – (–6.7) = 1.4 dB, which was less than the threshold. Therefore, no switchover should occur. However, Huawei queried the history alarms by choosing More Alarm Operations > History Alarm on NE from the switched NE 13 on the U2000 and found that the DCP board reported a POWER_DIFF_OVER alarm. The same situation occurred in the switchover of Wavelength 2 between NE 12 and NE 2.

The cause is as follows:

An OBU board collects and reports optical power to the NE software per second. If the optical power during the deterioration is collected, an accurate value is reported to the NE. However, if the duration of the deterioration is short and the board fails to collect the optical power during the deterioration, the reported value is inaccurate and the actual input optical power of the OBU board is lower than the value in the historical performance. Therefore, the difference may exceed the threshold and trigger a POWER_DIFF_OVER alarm, as shown in the following figure.

The optical attenuation increased transiently due to optical cable deterioration.No special handling operations are required because the switchover is triggered by optical cable deterioration. Manually switch services back to the working channel after it is stable.

The optical cables used by the customer are of poor quality and are frequently maintained. Therefore, this problem occurs frequently. The following suggestions are given to the customer:

1. The switching mechanism is used to secure services when an exception occurs on the line. A switchover is completed in 50 ms and services are not affected during the switchover. Therefore, no special operations are required to handle this problem.

2. The alarm threshold parameter on the U2000 of OSN 8800 is Variance Threshold Between Primary and Secondary Input Power. The parameter value ranges from 3 dB to 8 dB and the default value is 5 dB. The value can also be set to 0 dB. The customer can use a high threshold value to work around this problem. However, if the threshold is not met when the optical power on the working channel deteriorates, the switchover cannot be triggered. Therefore, exercise caution when using this method.

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