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Silence with SPANless call recorder

I'm trying to build a SPANless call recorder. It's registered as a SIP trunk and hooked up as a call recorder. I have a phone setup for automatic recording and when it's on a call I get 2 INVITEs and then 2 RTP streams. It does work but only sometimes.


Most of the time I get silence in both RTP streams. By silence I mean all audio samples are equal to 127. However, if I restart the phones I will get the correct audio streams (I can convert them to WAV and listen to them). It also tends to work if I apply config to the phones from admin which is probably causing them to re-register themselves.


There is a routing number for the call recorder and if I dial that directly I always get the stream (only 1 stream since it's just a phone call in this case).


I'm using IPBlue softphones - both of which are running on the same box. Because of the pandemic I haven't had a chance to try any hard phones yet. I noticed that when the call is being recorded the phone will push 2 RTP streams to the CM - one for each participant (non recorded calls just stream directly to the far end and don't involve CM). I used Wireshark and it's sending the correct audio, even when the call recorder gets silence. There must be something going on between CM -> Call Recorder Trunk.


I also get an error tone played back on the phones if I accept both INVITEs. But the audio streams still work - when they work. If I only accept 1 INVITE the phone does not play the error tone. Not sure if this is related.

Cisco Employee

"I'm using IPBlue softphones - both of which are running on the same box" makes it shaky to try and guess possible reasons.  I would certainly try this using Jabber or Cisco IP Communicator (from separate PCs) before diving in too deep into troubleshooting...

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