a mistake of my ViciDial configuration or carrier's?

FACTS:
I'm getting few messages at Asterisk CLI of "service unavailable" from my SIP carrier but my carrier claims that I have something wrong in my configuration since they got a cancel message from me.
Please take a look at the following example:
it took 3 seconds from the moment vicidial executed AGI to the reception of circuit-busy message.
The call was automatically labeled as NA.
=> CLI messages:
=>Carrier's perspective:
it took 18 seconds from the moment they started ringing to when cancel message was received.
They say:
"we got here normal call clear, not any error"
"our switch sent ringing signal to that number and see the CANCEL from your switch after 180 ringing message to you"
Their support:
By the way, I'm not getting any error like those if I dial through a different sip termination carrier.
Questions
- is carrier guilty or not?
- is it part of handshake process that ViciDial / Asterisk sends a cancel signal back after getting a circuit-busy signal from SIP Carrier?
I'd appreciate your comments.
I'm getting few messages at Asterisk CLI of "service unavailable" from my SIP carrier but my carrier claims that I have something wrong in my configuration since they got a cancel message from me.
Please take a look at the following example:
it took 3 seconds from the moment vicidial executed AGI to the reception of circuit-busy message.
The call was automatically labeled as NA.
=> CLI messages:
[Oct 12 14:39:25] VERBOSE[6149] logger.c: [Oct 12 14:39:25] -- Executing [852018717212442@default:1] AGI("Local/852018717212442@default-dc57,2", "agi://127.0.0.1:4577/call_log") in new stack
[Oct 12 14:39:25] VERBOSE[6149] logger.c: [Oct 12 14:39:25] -- AGI Script agi://127.0.0.1:4577/call_log completed, returning 0
[Oct 12 14:39:25] VERBOSE[6149] logger.c: [Oct 12 14:39:25] -- Executing [852018717212442@default:2] Dial("Local/852018717212442@default-dc57,2", "SIP/sip_iVoice/528717212442||tTor") in new stack
[Oct 12 14:39:25] VERBOSE[6149] logger.c: [Oct 12 14:39:25] -- Called sip_iVoice/528717212442
[Oct 12 14:39:27] VERBOSE[6149] logger.c: [Oct 12 14:39:27] -- SIP/sip_iVoice-08211238 is ringing
[Oct 12 14:39:27] VERBOSE[6149] logger.c: [Oct 12 14:39:27] -- SIP/sip_iVoice-08211238 is making progress passing it to Local/852018717212442@default-dc57,2
[Oct 12 14:39:28] VERBOSE[4742] logger.c: [Oct 12 14:39:28] -- Got SIP response 503 "Service Unavailable" back from 208.89.104.241
[Oct 12 14:39:28] VERBOSE[6144] logger.c: [Oct 12 14:39:28] -- SIP/sip_iVoice-08205df8 is circuit-busy
=>Carrier's perspective:
it took 18 seconds from the moment they started ringing to when cancel message was received.
They say:
"we got here normal call clear, not any error"
"our switch sent ringing signal to that number and see the CANCEL from your switch after 180 ringing message to you"
Their support:
-------------------------- 12 Oct 15:39:27.019/GLOBAL/ser[64011]: SENDING message to 189.238.21.76:5060: SIP/2.0 180 Ringing Via: SIP/2.0/UDP 189.238.21.76:5060;branch=z9hG4bK71af5b62;rport=5060 Record-Route: <sip:208.89.104.241;ftag=as5b7a854b;lr> From: V1012143924000474568 <sip:0000000000@189.238.21.76>;tag=as5b7a854b To: <sip:528717212442@208.89.104.241>;tag=49f9625c6cd516eeaabc6ca1cd78fef6 Call-ID: 1f5b80f201c6df3c3e2d41b460f2c003@189.238.21.76 CSeq: 103 INVITE Server: Sippy Content-Length: 195 Content-Type: application/sdp
--------------------------- 12 Oct 15:39:45.233/GLOBAL/ser[64011]: RECEIVED message from 189.238.21.76:5060: CANCEL sip:528717212442@208.89.104.241 SIP/2.0 Via: SIP/2.0/UDP 189.238.21.76:5060;branch=z9hG4bK71af5b62;rport From: "V1012143924000474568" <sip:0000000000@189.238.21.76>;tag=as5b7a854b To: <sip:528717212442@208.89.104.241> Call-ID: 1f5b80f201c6df3c3e2d41b460f2c003@189.238.21.76 CSeq: 103 CANCEL User-Agent: DigestPBX Max-Forwards: 70 Remote-Party-ID: "V1012143924000474568" <sip:0000000000@189.238.21.76>;privacy=off;screen=no Content-Length: 0 ---------------------------------------------------
By the way, I'm not getting any error like those if I dial through a different sip termination carrier.
Questions
- is carrier guilty or not?
- is it part of handshake process that ViciDial / Asterisk sends a cancel signal back after getting a circuit-busy signal from SIP Carrier?
I'd appreciate your comments.