I think the part that is not clearly specified is when the referee may
terminate the subscription. It must send at least one NOTIFY, but I
think it principle it could set the subscription state to terminated in
the very first NOTIFY if it wanted, even though the referred request is
still incomplete.
Conversely, AFAIK there is no requirement that the subscription be
terminated when the referred operation completes. If the REFER was for
an INVITE, normally the subscription is terminated on the final
response, but it could in principle keep sending notifications while the
call is active.
For the original question, take a look at RFC 4488, defining the
norefersub option. If the referror doesn't want the subscription then
this is an option. But it isn't an option for the referee on its own.
Paul
Scott Lawrence wrote:
> On Thu, 2008-02-21 at 16:33 -0800, Dushyant Godse wrote:
>> Hello
>> I was referencing the RFC 3515 regarding messaging for transfers based
>> on SIP REFER.
>> Is the UA processing the REFER required to send NOTIFY subscription
>> event messages to the sender agent notifying the progress of the
>> transfer like 100 trying, 180 ringing, 200 OK. Is this a MUST?
>>
>> I am pasting below a snippet of the RFC which says it must. I would like
>> to confirm this within the forum
>> If a REFER request is accepted (that is, a 2xx class response is
>> returned), the recipient MUST create a subscription and send
>> notifications of the status of the refer as described in Section
>> 2.4.4.
>
> What is the ambiguity? MUST means what it says.
>
>
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