Subject: [sipcore] Comments on draft-kaplan-dispatch-sip-205-response-00

From: [email-masked] (Dale R. Worley)
Date: Thu, 29 Aug 2013 11:20:52 -0400 (EDT)

It's not clear to me why we need a separate response code for this
function.  It seems to me that the same functionality could be
obtained with a 200 response with an additional header that means "I
may not be the droid you're looking for."

The concept of "not the originally intended target" doesn't seem to be
defined anywhere.  For the 205 code to be useful, the UAC and UAS need
to have the same understanding of that phrase; that is, it must be
standardized.  That may be difficult in light of the possibility for
multiple redirections between UAC and UAS.

We should also note that using the Reason header in responses to carry
SIP response codes isn't defined generally; the suggested use of
Reason is an extension relative to previous practice.  That meshes
with the fact that the suggested examples of Reason in the draft
explicitly define what those examples mean ...  which means that we
need to provide an explicit definition of the meaning of Reason with a
SIP response code in a response.

Dale

---

From: Paul Kyzivat <[email-masked]>
Date: Thu, 29 Aug 2013 12:21:33 -0400

> may not be the droid you're looking for."

Sure. That would also work. But a different response seems to serve the 
purpose without cluttering things up with a new header.

> multiple redirections between UAC and UAS.

This is indeed the think that needs to be sorted out - can we come up 
with a clear and useful definition of this.

The case that prompted this proposal is pretty clear - the routing 
process has been truncated due to max-forwards reaching zero. Normally 
that would be an error. But in this case we want it to be a success, but 
its a special kind of success.

If we define a code for that specific case, should it be generalized to 
any other cases? The one that comes to mind is redirection, to a device 
that doesn't speak for the AOR. But that itself is a fuzzy concept.

- At one extreme, a proxy acting for the *caller* my intercept a call 
that has been ringing too long and send it to an IVR that asks what you 
want to do. IMO that would qualify as not being the intended target.

- At the other extreme, a proxy acting for the *callee* (target AOR) 
might intercept a call that has been ringing too long and send it do an 
IVR to do VM. Depending on your point of view, you might consider that 
to be an unintended target, or not. (If the call includes caller 
preferences saying that it doesn't want to talk to an automaton, and it 
is still routed to an automaton, then it might be clearer.)

The simple answer would be to say that this code is *only* for the 
max-forwards case.

> SIP response code in a response.

Yes.

	Thanks,
	Paul