When calling through to any of the DID number range for a customer, it was found that only a small percentage of calls were successful. The failed calls would either play an ISP announcement or just ring continuously until the timer expired.

This customer had a newly provisioned SIP Trunk to the ITSP and all was working well until this point. No changes had been made by the Internal IT. After tracing successful and failed inbound call attempts it was found the ITSP was sending additional information in the SIP SDP. The information being sent was the QoS SDP Parameters, the local CUBE was not equipped to handle/negotiate these parameters therefore the call negotiation process would fail.

Resolution was to provide the below information to the ITSP to strip the QoS SDP Parameters.

INVITE Captured during trace.

Received:
INVITE sip:2XXXXXXXX@X.X.X.X:5060 SIP/2.0
Via: SIP/2.0/UDP 203.52.1.167:5060;branch=z9hG4bKhs0g8n00eogroamlbun0.1
From: <sip:2XXXXXXXX@X.X.X.X;user=phone>;tag=866784654-1439255743666-
To: “Name”<sip:2XXXXXXXX@domain.com.au;user=phone>
Call-ID: BW111543666110815-468528800@10.83.154.184
CSeq: 220849754 INVITE
Contact: <sip:2XXXXXXXX@203.52.1.167:5060;transport=udp>
Supported: 100rel
Allow: ACK,BYE,CANCEL,INFO,INVITE,OPTIONS,PRACK,REFER,NOTIFY,UPDATE
Accept: application/media_control+xml,application/sdp,multipart/mixed
Max-Forwards: 29
Content-Type: application/sdp
Content-Length: 641

v=0
o=BroadWorks 3668715 1 IN IP4 X.X.X.X
s=-
c=IN IP4 X.X.X.X
t=0 0
a=sendrecv
a=media-release:hngl5rp9pujvivh05pvu6ibgr83pv898756s7s8auvmg62o6u724a2ur96v3nd0v1350ln1-6
a=media-release-con-addr:d6v1k1hv6hvh1002o9j0
m=audio 18064 RTP/AVP 8 0 18 96 97
c=IN IP4 X.X.X.X
b=RR:3000
b=RS:1000
a=curr:qos local none
a=curr:qos remote none
a=des:qos mandatory local sendrecv
a=des:qos optional remote sendrecv
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:96 AMR/8000
a=fmtp:96 mode-set=7;max-red=0
a=rtpmap:97 telephone-event/8000
a=fmtp:97 0-15
a=maxptime:40