Re: [Sip] Is REFER within dialog part of INVITE or subscription usage? (was RE: SIP INFO)

[aayush bhatnagar <abhatnagar192006 at gmail.com>]

REFER if placed within the scope of the existing dialog usage of
INVITE will reuse its dialog usage, and create an implicit
subscription for the refer event package at the recipient. However, if
the recipient chooses to reject the in dialog REFER request, the
communication established by the INVITE should not be affected. Such a
rejection scenario implies that the call transfer failed..however the
existing active call should not be torn down.

REFER if sent outside the scope of any exisiting dialog will behave as
a dialog creating request and will establish a subscription at the
recipient as described above. This subscription is only used to notify
the status of the sip session referral to the originator and is
seperate from any other subscribe usage that may have existed at the
recipient.

As far as accessing the referred resource is concerned...using the
method parameter, it depends upon the business logic of the recipient
of the REFER request. You may send a REFER to a conferencing server
with a method INVITE to invite a user to join a conference. A method
parameter with the value BYE would imply removal from the conference
by the server and so on.

I dont think you can include a SUBSCRIBE in the method parameter of
the REFER request. You have no way of telling the event package usage
of the subscription to the recipient, as the event header cannot be
included in the REFER request. Moreover, you can never be sure whether
the subscription usage is even applicable to the recipient or whether
the recipient even supports it.

aayush

On 3/24/09, Paul Kyzivat <pkyzivat at cisco.com> wrote:
>
>
> Dale Worley wrote:
>> On Mon, 2009-03-23 at 08:18 -0700, Brett Tate wrote:
>>> Everyone: Is REFER within dialog part of INVITE usage, SUBSCRIPTION
>>> usage, or neither?
>>>
>>> I'm asking mainly because of REFER 481 impacts; however the answer
>>> also has potential implications concerning draft-ietf-sip-info-events.
>>> RFC 5057 appears to imply that it is part of the subscription usage;
>>> however I'm not positive if my interpretation and/or RFC 5057 is
>>> correct.
>>>
>>> If REFER isn't considered part of the INVITE usage, how should REFER
>>> 481 be interpreted?  More specifically, should receiver of REFER 481
>>> send BYE?
>>
>> I would argue that the REFER is part of the INVITE usage, because REFER
>> in that context is intimately related to the INVITE usage -- it is
>> intended to transfer the INVITE usage/dialog transferred to a different
>> destination.
>
> Well, I guess there is that implied association. (Part of the "do what
> *I* had in mind" approach that REFER has.) Since this was never spelled
> out, it could also be simply "while this isn't part of an INVITE usage,
> if there happens to be an INVITE usage, please refer that one."
>
> I guess the question is: would it be valid to send a REFER within an
> existing dialog that had no INVITE usage? If it were valid, presumably
> it would have the same meaning as sending one outside a dialog, except
> that the resulting subscription would share the dialog. I expect that is
> a usage it would be difficult to find in the wild.
>
> Ah, but now I want to reconsider. Remember that REFER can take a method
> name. So, rather than referring an INVITE, I could be referring MESSAGE,
> OPTIONS, BYE, or maybe (????) SUBSCRIBE. In some of those cases, the
> association to the INVITE usage is probably meaningless. (Of course its
> meaningful for BYE.)
>
>> And it seems quite safe that if the REFER receives a 481 response, the
>> INVITE usage must not be functional any more, since the far end of that
>> usage has denied that it can act on the REFER.
>
> IIRC, 5057 decided that each dialog usage must get its own 481 before it
> goes away. I don't think there are any cases where a single 481 response
> can make multiple usages go away.
>
> So the important question is whether the REFER is part of the INVITE
> usage and so its 481 takes down the INVITE usage or not. That gets
> especially interesting if  the dialog already had both an INVITE usage
> and a SUBSCRIBE usage. Does it make sense that the refer take down the
> INVITE usage and leave up the SUBSCRIBE usage?
>
>> Now it's possible that the REFER, if it is successful, is the first
>> transaction of the subscription usage.  But I don't think that has any
>> paradoxical consequences, as by hypothesis, the REFER succeeded.
>
> Yeah, its already so weird, why not a little more weird?
>
> Also, I think it has recently been clarified that the 200 of a SUBSCRIBE
> should not be considered to create a dialog - that its the NOTIFY that
> creates the dialog. If so, then I suppose the same should be true of REFER.
>
> Bottom line: I can live with it either way, but think it should be
> documented one way or the other.
>
> 	Thanks,
> 	Paul
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