Tuesday, April 22, 2014

CUCM outside caller still hears ringing after call is answered through H323 gateway

Call flow was SIP trunk -> CUBE -> H323 -> CUCM -> SCCP phone.

Symptom was inbound callers would call a PSTN number, the SCCP phone would ring and present caller ID, the SCCP phone user would pick up, and the outside caller would continue to hear ringing.  Reviewing debugs, I found via debug voice ccapi inot that the disconnect cause code was 47.

Apr 22 18:48:13.441: //2545/76D263EE875D/CCAPI/cc_api_call_disconnected: Cause Value=47, Interface=0x22ABFFE0, Call Id=2545

This typically is a result of codec mismatches or negotiations.  I threw in some easy peasy transcoding like so, with no luck.

dspfarm profile 1 transcode universal
 codec g729br8
 codec g729r8
 codec g711ulaw
 codec g711alaw
 codec g729ar8
 codec g729abr8
 maximum sessions 24
 associate application CUBE

My issue was because I was using the H323 trunk from the CUBE to CUCM, I needed to accommodate for what would be early offer on the SIP trunk.  Although I had transcoders available, the media exchange in the SDP (Session Description Protocol) where the codecs are negotiated was happening in the initial invite.  With that, the call through the H323 trunk was setting up without the carrier, CUBE and CUCM deciding on the appropriate CODEC.  Hence the disconnect cause 47.

On the CUCM and H323 gateway side, you can emulate the SIP early offer negotiation settings, via Enable Inbound FastStart and / or Wait for Far End H.245 Terminal Capability Set.

1 comment:

  1. Anonymous2:21 PM

    Thank you for your post, was struggling with this for a few hours in my lab, glad it was a simple fix!