Description of the problem

Customer A provides VC-3 level services to user B. This service is mapped from SSN1PL301 into SL64 on a 3500 network element that is connected to a 7500 network element. The 7500 network element then carries user B's service to London over the submarine cable using STM-1 links to other OSN nodes. Customer A reports that the SSN1PL301 board on the 3500 network element has been reporting P_LOS alarms for 30 consecutive seconds on a certain day, during which time user B's service is affected.

The SSN1PL301 board on the 3500 network element reports a P_LOS alarm to the network management, indicating a loss of signal.

Processing

The following may be the cause of the problem: 1. Interface board failure; 2. Loose interface board slot; 3. Loose connection on the DDF; 4. Poor grounding. These problems may occur on our equipment endpoints.

On the user B side of the service provided by customer A, the possible causes are as follows: 1) DS3 board failure of the device; 2) poor grounding of the device; 3) loose interface board slot; 4) the cable from the DDF to the device is too long, and the single board does not support such a long length.

Root cause

Excessive cable length

Solution

We should first check the cable length from our DDF rack to the location of user B's equipment. If the cable length is more than 70 meters, we should ask the customer to reposition the equipment so that the cable length is less than 50 meters; if the cable length is within 50 meters, continue to position the equipment as follows:

If there is an alarm, hard loop back to the corresponding VC-3 on the DDF frame and check whether the alarm disappears;

If the alarm does not disappear, the possible reasons for the power failure of our equipment mentioned above, such as poor grounding, loose interface connections, loose interface slots and loose connections on the DDF rack, will be obvious;

If the alarm disappears, the cause of the problem is not on our equipment endpoints, and other causes need to be located, and User B should be asked to check the status of the DS3 veneer boards, grounding and connections.

Suggestion and Summary

The P_LOS alarm is caused by a cable that is too long (more than 70 meters), and the user device does not support such a long cable length. Therefore, it is recommended to keep the cable length within 50 meters to avoid problems caused by different support situations.

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