Subject: RE: SIP 3rd-party call creation?

From: michael dwyer <[email-masked]>
Date: Mon, 20 Dec 1999 16:19:40 -0800

Jon
this is a valid issue and I am sure that people are looking
at it. Particularly from a service node point of view, where the
service node may initiate the session between different participants
but may not take part in the session directly.

Security I feel is definitely an issue here.

Mike

-----Original Message-----
From: Jon.Peterson [mailto:[email-masked]]
Sent: Monday, December 20, 1999 3:47 PM
To: sip
Cc: Jon.Peterson
Subject: SIP 3rd-party call creation?

Has any consideration been given to uninvolved third parties originating
sessions between two SIP endpoints?

If I might provide a clarifying example without endorsing the described
implementation - given two users A and B, each of whom has a SIP phone,
and
an automated entity C (the third party): C somehow decides that a
session
should be initiated between A and B, and thus sends an INVITE to A
which,
due to special properties and/or headers, does not result in a session
between A and C, but rather prompts A to send a new INVITE to B after
some
sort of approval on A's part. Subsequently C might or might not maintain
a
relationship with A throughout the session establishment, and so forth.

I haven't been able to find any existing work that addresses this sort
of
situation; has something been written on this that I've missed? The SIP
Call
Control Services document covers some nearby territory (the Requested-By
and
Also headers could be relevant), but I don't think, from my reading of
the
document, that it endorses third-party call setup unless the third party
is
a participant in the session.

If this hasn't been explored to date, what is the prevailing opinion on
third-party session initiation? Is it something to which SIP can and
should
be applied? Are the accounting and security issues too damaging?

Jon Peterson
Level(3) Communications

---

From: Jean-Hugues ROBERT <[email-masked]>
Date: Thu, 23 Dec 1999 16:50:58 +0100

Hi Jon,

>sessions between two SIP endpoints?

Third party control seems to be out of the scope of SIP currently.
Or I missed it.

I also raised the issue sometimes ago because third party control
is needed to implement CTI (We implement a Hosted VoIP PBX with a JTAPI
CTI interface).

Regarding your specific example, I think that a solution today is for
C to send an INVITE to A, wait until A answers and then immediatly
send a BYE/Also to transfer the call to B.

A limitation of this solution is that C leaves the call and cannot
monitor/control
it any more.

Another alternative, more brutal, is for C to send INVITE to both
ends and to switch all the forthcoming SIP signaling. In that situation
both A and B talk to C (on the control plane), but the RTP media can go
directly from A to B (on the media/user plane).

There must be other solutions, specially if C acts as a proxy server.

Jean-Hugues Robert
Engineering Manager.

At 04:46 PM 12/20/99 -0700, [email-masked] wrote:
>implementation - given two users A and B, each of whom has a SIP phone, and
>an automated entity C (the third party): C somehow decides that a session
>should be initiated between A and B, and thus sends an INVITE to A which,
>between A and C, but rather prompts A to send a new INVITE to B after some
>sort of approval on A's part. Subsequently C might or might not maintain a
>I haven't been able to find any existing work that addresses this sort of
>situation; has something been written on this that I've missed? The SIP Call
>Control Services document covers some nearby territory (the Requested-By and
>Also headers could be relevant), but I don't think, from my reading of the
>document, that it endorses third-party call setup unless the third party is
>third-party session initiation? Is it something to which SIP can and should
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