You don't say what happens *after* they send this 183. That doesn't
terminate the dialog - there still must be some final response. Does the
final response accurately reflect the distinction between busy, invalid,
etc.?
AFAICT this doesn't violate anything, so it is *technically* valid.
But, if the final response isn't clear, this usage is not well conceived
for interoperability. Recipients are explicitly allowed to ignore reason
values they don't understand. So recipients that don't understand Q.850
responses will treat this as just a 183 and won't understand the true
status of the call.
If this approach is used to signal *ringing*, and there is no in-band
alerting, then this is likely to result in the caller experiencing a
long period of silence. Again that is not a good situation.
Basically this seems to be a quality of implementation issue rather than
a formal violation of standards.
Thanks,
Paul
On 5/27/15 9:13 PM, NK wrote:
Dear All,
I have a scenario where our vendor includes Q.850 in proviosnal response
(183 w/sDP) in every call scenerio, doesnt matter whether number is
invalid, busy, unlocatted.
In other words if they want to give us busy they will send 183 w/SDP and in
that they will add "reason header" and will specify that "user-busy". like
as below (there was no annoncement).
*IP/2.0 183 Session Progress*
Via: SIP/2.0/UDP 1.1.1.1:5060;branch=z9hG4bK07Baab30f0ac4907e59
Record-Route: <sip:2.2.2.2:9131;transport=udp;lr>
Call-ID: 285680242_96347916@1.1.1.1
From: <sip:7038805449@1.1.1.1:5060;cpc=ordinary>;tag=gK072fb580
To: <sip:1234568745@2.2.2.2:5060>;tag=sbc040328yrzaa3-CC-1021
CSeq: 17205 INVITE
Allow: INVITE,ACK,OPTIONS,BYE,CANCEL,INFO,PRACK,NOTIFY,MESSAGE,UPDATE
Contact: <sip:2.2.2.2:9131>
P-Early-Media: sendrecv
*Reason: Q.850;cause=17;text="User busy"*
Content-Length: 0
Can you please advise if this is the correct behavior. Is there any draft
or document is there which i can go through it?
Regards,
Nitin Kapoor
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