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Interconnected Data Communication Equipment Is Down for One Second Even When the ODUk SNCP Protection Switching Time Is Within 50 ms

Publication Date:  2012-07-25 Views:  40 Downloads:  3
Issue Description
The OptiX OSN 6800 is interconnected with NE5000e/NE40e. For details, see the attachment.
If protection switching occurs in both directions of a link consisting of the transmission equipment and the switching interval is about 50�60 ms, the data communication equipment is down.
Alarm Information
OPS_INDI, down
Handling Process
Solution 1
Make sure that the working and protection services of the data communication equipment are transmitted over different fibers.
Improve the service reliability by making proper network design. Connect the links for the working and protection services of the data communication equipment to different transmission links so that the ports for the working and protection services are not down at the same time when a fiber is faulty.
-Solution 2
Increase the down-hold-time for the data communication equipment to decrease the possibility of such a problem. The value 500 is recommended for the down-hold-time.
Root Cause
1. Protection switching of the transmission equipment is determined by unidirectional faults, while the data communication equipment checks the alarms in the transmit and receive directions (that is, the near end and far end). When detecting an anomaly in either direction of the link, the data communication equipment starts a timer. After holdtime (100 ms in the existing network) expires, the data communication equipment checks the link state again. If the alarm that results in the down state of interfaces persists in either direction, the data communication equipment is down. Hence, when the protection switching time in both directions of the transmission equipment plus the switching interval is close to holdtime, there is a possibility that the data communication equipment becomes down (in this case, the two protection switching actions performed by the transmission equipment are actually completed within the required time).
2. Perform a test on a network as shown in the attachment. The test results are as follows:
1) At T0, there is a fiber cut on the main channel from NE40e to NE5000e. The transmission equipment at station A performs protection switching. During the switching, NE5000e detects the LOF alarm and starts the timer. NE40e detects the far-end alarm (the RDI inserted by NE5000e) and starts the timer.
2) Between the time when the protection switching is complete and T1, the entire transmission link is normal.
3) At T1, there is a fiber cut on the main channel from NE5000e to NE40e. The transmission equipment at station B performs protection switching. During the switching, NE40e detects the LOF alarm and NE5000e detects the far-end alarm (the RDI inserted by NE40e). When the holdtime of NE5000e or NE40e expires during the switching, the corresponding data communication equipment becomes down.
3. The protection switching time of the transmission equipment is usually about 20�30 ms. If the interval between T0 and T1 is about 50�60 ms, the problem recurs. The time of the two protection switching actions (about 40�60 ms) plus the switching interval (about 50�60 ms) is about 100 ms. That is, the test value complies with the theoretical value. Protection switching of the transmission equipment is determined by unidirectional faults. During the protection switching, the data communication equipment receives the LOF alarm. The data communication equipment determines the port state (up or down) according to the alarms in the transmit and receive directions (the far end and near end). To prevent jitter on the link (that is, the port state keeps switching between up and down), the down-hold-time can be configured by using command lines for the data communication equipment. After the down-hold-time is configured, the system stops monitoring alarms (to prevent frequent alarm and to suppress the related alarms) from the time when the first alarm is generated to the time when the down-hold-time expires. After the down-hold-time expires, the system checks the alarms. If there are such alarms as OOF, LOF, LOS, and AIS, the port state of the data communication equipment becomes down. If there are no such alarms as OOF, LOF, LOS, and AIS, the port state of the data communication equipment remains unchanged and the system keeps monitoring alarms.
4. According to the preceding analysis, the following conclusion can be drawn:
The port state of the data communication equipment becomes down when the following two conditions are met. This is normal.
* The two fibers in the two direction of the link are broken.
* The interval between two fiber cuts plus the time of the two protection switching actions performed by the transmission equipment is close to the configured down-hold-time for the data communication equipment.
Suggestions
Null

END