Step 1 Use the local maintenance terminal (LMT) to obtain logs of the user service abstract module (USAM), call control module (CCM), connect module (CM), resource module (RM), PRINTTIME, and primary rate interface (PRI) modules.
Step 2 Analyze the call connection flow and find that the eSpace U1980 disconnects the call, as shown in Figure 2-1.
Figure 2-1 Call disconnected by the eSpace U1980
Step 3 Check the STATUS message repeatedly sent by the eSpace U1980 and find that the return code is "Mandatory information element is missing", as shown in Figure 2-2. Therefore, the possible cause is that the CALLPROCEEDIN message from the MTG300 has some mandatory information missing.
Figure 2-2 Analyzing the STATUS message
Step 4 Check the CALLPROCEEDING message and find the information "IE Name: Channel identification" missing, as shown in Figure 2-3.
Figure 2-3 Checking the CALLPROCEEDING message
Step 5 Modify the MTG300 configuration by adding the information "IE Name: Channel identification" in the CALLPROCEEDING message.
After the modification, the fault is rectified.