From: "Emily Smith" <[EMAIL PROTECTED]>
You diagram is unusual in that the a BYE is sent from X to Y, whereas
usually in a blind-transfer scenario, that dialog would be terminated
by a BYE from Y to X. But that makes little difference.
Of course, this diagram simplifies things because the SIP proxy is
actually transmitting all the messages between the parties X, Y, and Z,
they are not going directly from end-point to end-point. Given that, at
the point in the flow where I have added <<******** to the picture, if
the SIP proxy were to send a re-Invite with dialog 1's Call_ID to X (not
from Z or Y but directly from the Proxy engine), that is the question I
am concerned with.
Since the dialog established by F1 and terminated by the unlabeled BYE
from X to Y, the re-INVITE you mention would happen while the dialog
still exists, and so would be followed by 200/ACK, under normal
circumstances.
So, to make my question clearer, perhaps, if the SIP proxy were to send
a re-INVITE with new SDP (port information) to the Transferer X at this
point, in what way should X respond, and should the X device, if indeed
he is onhook, as he would probably be in a SIP blind transfer, rering
the X phone? Or is the answer to this question simply undefined in the
SIP protocol?
Whether the phone is on-hook or not (and it may or may not be
physically on-hook, depending on what the user has done) is
irrelevant; the dialog still exists, so the re-INVITE is valid.
There is never any reason to re-ring a phone when receiving a
re-INVITE.
I think that you are assuming a situation where the user X physically
hangs up UA X before user Z answers the ring on UA Z. But that leads
to a different call flow, where the BYE from X to Y happens before the
200 from Z to Y:
| REFER F3 | |
dialog1 |------------------->| |
| 202 Accepted | |
dialog1 |<-------------------| |
| NOTIFY (100 Trying) F4 |
dialog1 |<-------------------| |
| 200 OK | |
dialog1 |------------------->| |
| | INVITE F5 |
dialog2 | |------------------->|
| | 280 Ringing |
dialog2 | |<-------------------|
| BYE | |
dialog1 |------------------->| |
| 200 OK | |
dialog1 |<-------------------| |
... time passes here ...
| | |<<********
| | 200 OK |
dialog2 | |<-------------------|
| | ACK |
dialog2 | |------------------->|
| NOTIFY (200 OK) F6| |
dialog1 |<-------------------| |
| 200 OK | |
dialog1 |------------------->| |
Once user X has hung up, UA X sends a BYE and the INVITE dialog usage
of the X-Y dialog ends. (The subscription usage continues, and that
is what contains the NOTIFY F6.) But once the INVITE dialog usage
ends, a re-INVITE is no longer valid.
Dale
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