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DMG2000 One way audio

Symptom / Introduction:   

There are a few reports from the field that SIP users/applications do not hear audio from TDM party, or do not detect DTMF tones. Even though TDM capture shows DTMF or speach is present. The Wireshark trace between DMG and SIP end point has shown that audio are sent and received at SIP end point.

This may occur intermittently.  

Reason for the issue / Background:  (delete as appropriate)

Further investigation on these cases shows that for some reason DMG sends RTCP with packet type Good Bye. See below link for identifying the packet type GoodBye 203 (=0xCB).

http://www.networksorcery.com/enp/protocol/rtcp.htm.

Once SIP end point receives RTCP GoodBye, it stops forwarding received RTP to its users. In fact, DMG2000 continues to send RTP using the same the terminated SSRC. I believe this is the cause that SIP end point stops forwarding.

All the issues reported from the field are either with Microsoft Lync server or Microslft Speech server.

Attached is the screenshot of the wireshark trace. One easy way to identify is look for decoded RTCP packet type message. See highlighted "Session Stopped".

Fix / Solution / Procedure / Details: 

Since DMG engineering is under transition, engineering has not working on this issue yet.

Workaround: 

There are a few workarounds and it is based on case by case.

1. Enable DMG2000 PRACK under Config>VoIP>Media, require Reliable Provisional Responses. This requires Early Media support enabled.

2. If this occurs on outbound call, change outbound call connecte timeout from 10000ms to 60000ms seconds. This is found because of DMG sends RTCP GoodBye about 10 seconds after call is made. This also explains why it occurs intermittently. Root cause needs to be addressed.

3. If this occurs on incoming calls, adjust the time when incoming calls are answered. This is observed from customer Talx who uses MS speech server. Once introduced a few seconds of delay (by sending out Ringing), their DTMF detection works just fine. Root cause still needs to be identified.

Update (9/24/2012):

A confirmed workaround from the field. Set "Outbound Call Connect Timeout" from 10000ms to 0ms.

Update (8/7/2013):

For outbound call using with Lync Server, TSS is able to repro all the call flow cases reported by customers.

Engineering has provided a fix below:

 \\buffls001\Scimitar\SW\DefectReportLogs\6.0.SU9.0.005_102587.1

or \\pysnas01\infofactory\VA_Team_Repository\DMG\Issues\IPY102587\6.0.SU9.0.005_102587.1

 This will be included AFTER SU9.

Product List:

All reports are for DMG2000. I believe it might occur to DMG1000.