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Busy Tone Sometimes Heard Directly for Outgoing Calls Through the E1 Trunk Because Invalid Timeslots Are Polled

Publication Date:  2015-07-24 Views:  160 Downloads:  0
Issue Description
An office is connected to the carrier through the PRA (E1) trunk. Incoming calls can be made properly. When intra-office users make calls to PSTN users, sometimes the busy tone is heard directly.
Handling Process
Based on the site requirements, configure outgoing calls to use only timeslots 1 to 10.

The procedure is as follows:

config add office selectcode no 99 repeatroute no //Configure an irrelevant office route.
config add office no 99 officeselectcode 99 //Configure an irrelevant office route selection code.
config modify cvp type dtu tkcincard 11-31 officeno 99 //Bind circuits 10 to 31 of port 0 to the irrelevant office route.

Based on tests for multiple times, the fault is rectified.

Root Cause
1. When outer-office users make calls to intra-office users, the calls can be connected properly in any scenarios. Therefore, the trunk connection is proper.

2. When intra-office users make calls to outer-office users, sometimes the calls can be connected properly, sometimes the busy tone is directly heard after the number is dialed. It is suspected that some intra-office phones are faulty. Based on the test on all intra-office phones, the fault occurs on all intra-office phones.

3. The cause that all trunk circuits are occupied can be excluded because only one phone is making outgoing call during the test. The circuits are sufficient.

4. Check the E1 hardware cable connection. No problem is found.

5. Capture the call log. Dial 96420005 as 64206920 for 10 times. The first seven calls can be connected. For the eighth call to the tenth call, a message is displayed indicating that the peer party is busy, and the busy tone is heard. The packet capture result is as follows:

[0x000004aa][pri.c 9187][CRNO=  782] PRI_SendMsgToQ921,send q921 msg type is SETUP 
[0x000004aa][pri.c 22845]PRI_PrintMsg 
[0x000004aa][pri.c 22868]ST_Q931_Q921_MESSAGE Head:-- 0x 00 31 00 00 00 00 00 29 19 00 bb 0c 18 
[0x000004aa][pri.c 22875]PRI_PrintMsg,ST_Q931_Q921_MESSAGE PrococolID 08 ; CRLen 02 ; CRV 00d8 ; MsgID 05 
[0x000004aa][pri.c 22878]PRI_PrintMsg,ST_Q931_Q921_MESSAGE Data: 
[0x000004aa][pri.c 22888]a1 04 03 80 90 a3 18 03 a1 83 
[0x000004aa][pri.c 22888]8d 6c 0a 40 80 36 34 32 30 36 
[0x000004aa][pri.c 22888]39 32 30 70 09 c0 39 36 34 32 
[0x000004aa][pri.c 22913]30 30 30 35 
[0x000004aa][pri.c 2163][dwTsn= 2048] PRI_ProcPDMMsg,The PDMType = 106 
[0x000004aa][pri.c 5289]PRI_ProcDLData 
[0x000004aa][pri.c 5318]PRI_ProcDLData,[Tsn=2061] 
[0x000004aa][pri.c 5440]PRI_ProcDLData,[CRNo=782] 
[0x000004aa][pri.c 5512]PRI_ProcDLData,receive q921msg type is RELSECMP 
[0x000004aa][pri.c 22845]PRI_PrintMsg 
[0x000004aa][pri.c 22868]ST_Q931_Q921_MESSAGE Head:-- 0x 40 36 00 00 00 00 00 0b 00 00 02 01 50 
[0x000004aa][pri.c 22875]PRI_PrintMsg,ST_Q931_Q921_MESSAGE PrococolID 08 ; CRLen 02 ; CRV 80d8 ; MsgID 5a 
[0x000004aa][pri.c 22878]PRI_PrintMsg,ST_Q931_Q921_MESSAGE Data: 
[0x000004aa][pri.c 22913]08 02 82 a2 
[0x000004aa][pri.c 7555][CRNo=782][Tsn=2061] PRI_ProcQ921Releasecomp

6. Contact the carrier. It is learned that the customer has purchased only one E1 trunk, which supports only 10 timeslots. By default, timeslots 1 to 10 are available. Since timeslots are polled, an outgoing call fails if a timeslot out of timeslots 1 to 10 is selected.
For faults involving trunk interworking with a carrier, if it is confirmed that the carrier side disconnects calls based on troubleshooting and packet capture, contact the carrier immediately, provide the packet capture result, and locate the fault together with the carrier.