For permanent faults, loops can be used at one end, and the other end can be displayed from the switch or segmented and layer-by-layer with the transmission analyzer.
1.1 Transmission Alarms Appear in Pairs
For example, if RJA (remote alarm) occurs on terminal A, then terminal B may be LFA (frame loss of synchronization) or AIS (inbound alarm). Sometimes both types of alarms exist. There is also an LS (lost signal) alarm.
One of the reasons for the failure. There is a problem with the signal sent from the A-side DM, which means that the 2Mb/s signal is sent out in error or interrupted.
Judgment method: Take the A-side DDF loop back to the A-end. If there is an LS or AIS alarm on the A-end, this fault occurs.
Solution: Ask the staff to restart or reload the trunk module to clear the alarm.
The second reason is that there is a problem in the transmission from the low-order group A to the B-side, which causes 2Mb/s signal error or interruption.
Judgment method: If there is a problem from A to B between low-order groups at both ends of A and B, then B end displays an AIS or LFA alarm. If the DM signal is interrupted from the low-order group on the B side, the LS alarm is displayed on the B side.
Solution: According to the obstacles found, or re-do the head of the DDF, or replace the U-Link, or replace the disk to achieve the purpose of restoring the circuit.
1.2 Transmission Alarms Do Not Occur in Pairs
For example, the A-side and R-JA alarms occur on the A side, or the LFA alarm occurs. The peer end does not have any alarm. In this case, the call cannot be performed (taking the S1240 switch as an example).
The reason is that the A-end trunk module (DM) is dead. In this case, the DMs at both ends need to be reactivated. Doing so may restore the circuit and the first case may also occur. If the first case occurs, proceed as described above.
2 intermittent failures
2.1 Individual 2Mb/s Port Alarms
Because intermittent faults are generated instantaneously, switching relay modules DM have different alarm identification times, so single-end alarms may occur. This can be solved by dealing with permanent failures. However, it is better not to use the DDF loopback method to avoid interrupting the circuit and affecting the service.
2.2 Batch 2Mb/s Port Alarms
(1) The alarm module is concentrated on the 34Mb/s port or 8Mb/s port of the multiplexing device. This may be a problem with the high-order group, or there may be a problem with the DDF adapter, or there may be a problem with the chassis. This can be detected by a permanent fault method.
(2) Several DM alarms for a trunk group. This may be a switch problem.
For example, once this problem occurred in our bureau, the search was caused by the heavy workload of the multi-frequency register. At that time, our office used channel-to-channel signaling, and users’ dual-audio phones gradually increased, causing the multi-frequency register to work hard. Later, the use of No. 7 signaling between the bureaus solved the problem.
2.3 A special alarm
It is normal for each 2Mb/s transmission link to be tested individually. That is, there is no alarm on the switching loops at both ends of each DDF, and the U-Link measurement is also normal with a multimeter, but the U-Link is connected to the switch. An alert occurs and cannot be used. At this time, loops are performed on the low-order group-side transmission side of either end of A or B, and are tested at the same location by the transmission analyzer. It is found that ES occurs and the entire link is in a critical state. The processing method is to test the instrument segment by segment until it finds the obstacle point and restores the circuit.
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