What about using the mechanism described in bis, but hiding it from
the caller behind a proxy? The REGISTER message from C would expire
immediately and be directed at B via the proxy. The proxy could then
cross-reference the pending INVITE to B, consult policy to see if C is
authorized to pickup B's calls, then cancel the pending INVITE and direct
the call to C.
Caller A
Proxy B Called
C Picks Up Call
|
|
|
|
| INVITE
F1 |
|
|
|--------------->|
INVITE F2 |
|
|(100 Trying) F3 |------------->|
|
|<---------------|180 Ringing
F4|
|
| 180 Ringing F5 |<-------------|
|
|<---------------|
|
|
|
|
| REGISTER F6 |
|
|<---------------------------------|
|
|
| 200 OK F7 |
|
|--------------------------------->|
|
|
|
|
|
| CANCEL F8 |
|
|
|------------->|
|
|
| 200 OK F9 |
|
|
|<-------------|
|
|
| 487 F10 |
|
|
|<-------------|
|
|
| ACK F11 |
|
|
|------------->|
|
|
|
| INVITE F12 |
|
|--------------------------------->|
|
|
| 180 Ringing F13 |
| 180 Ringing F14|<---------------------------------|
|<---------------|
| 200 OK F15 |
|
|<---------------------------------|
| 200 OK F16
|
|
|
|<---------------|
|
|
|
ACK F17 |
|
|
|--------------->|
| ACK F18 |
|
|--------------------------------->|
|
Both way RTP Established
|
|<=================================================>|
Comments?
Thanks,
Alan Johnston
WorldCom
Neil Deason wrote:
Richard Verhoeven wrote:
>
> > Redirecting a ringing call to the contact
> > of an unregister message seems like
> > unobvious behavior to me.
>
> OK. According to the SIP draft, section 4.2.6,
> it is reasonable behavior for a SIP user agent
> to redirect an invitation in progress upon
> a changed registration. So, it is already
> possible to use a normal register request for
> call pickup.
>
> In the same section, it mentions that the
> registrar may use an expire time shorter than
> the one in the request. So, on a SIP user
> agent, the registration can expire immediately
> after the ringing call is redirected. In
> fact, it could be the default behavior.
>
> > We got into
> > trouble for overloading the user of the
> > "contact" header, lets not do it again
> > with REGISTER.
>
> It is part of the SIP draft, so the overloading
> of REGISTER is already there.You are both right - it is there and it is perhaps not
the best thing. In the light of other comments on this
thread, that there are better ways to achieve the end
result, perhaps this text could be removed. It seems to
me to have been a bit of an after thought anyway.Cheers,
Neil
--
Ubiquity Software Corporation, UK http://www.ubiquity.net
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