Symptom:
The  Cisco CUBE / IOS Gateway uses  an incorrect and obsolete  payload  19  for  Comfort Noise  :

m=audio 19464 RTP/AVP 0 19


The mandate Payload type for Comfort noise  is  13  .Pls refer to section 5.1 of  RFC  3389  "usage of SDP" :
"
When using CN with the RTP/AVP profile [10] and a codec whose RTP
   timestamp clock rate is 8000 Hz, such as G.711 (PCMU, static payload
   type 0), the static payload type 13 for CN can be used:

         m=audio 49230 RTP/AVP 0 13  "

http://tools.ietf.org/html/rfc3389

Conditions:
The  Cisco CUBE / IOS Gateway uses  an incorrect and obsolete  payload  19  for  CN   :

m=audio 19464 RTP/AVP 0 19


The mandate Payload type for Comfort noise  is  13  .Pls refer to section 5.1 of  RFC  3389  "usage of SDP" :
"
When using CN with the RTP/AVP profile [10] and a codec whose RTP
   timestamp clock rate is 8000 Hz, such as G.711 (PCMU, static payload
   type 0), the static payload type 13 for CN can be used:

         m=audio 49230 RTP/AVP 0 13  "

http://tools.ietf.org/html/rfc3389