Alan Johnston wrote:
>
> Adding Call Pickup and Park is on my to do list for the SIP
> Service Examples I-D (draft-ietf-sip-service-examples-00.txt),
> but I haven't had any suggestions for how to do this.
>
> 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?
I think this would work. The Proxy could perhaps just fork
again upon receipt of F6, letting both B and C ring and doing
the CANCEL on which ever leg doesn't answer 200.
However, I don't really like promoting the use of REGISTER
for this as a good idea. It overloads REGISTER and is using
SIP as a call control protocol. The whole area of a SIP call
control framework seems to need more work so I wouldn't want
this perceived to be _the_ way. Anyway if users have intelligent
and intuitive access to forwarding services through CPL call
pick up is redundant.
Cheers,
Neil.
--
Ubiquity Software Corporation, UK http://www.ubiquity.net
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