RE: [Sipping] comments on draft-roach-sipping-callcomp-bfcp-00

["Michael Hammer \(mhammer\)" <[e-mail]>]

I still have not seen a convincing explanation that any abuse exists.  This feature is about meta information; precisely the type of information that the events framework was intended. 

When the 486 Busy is received, that call is done.  It is then about what is the state of the queue, and who should initiate the next call involving the called party.

My problem with the way this is headed, is that it is designing a SIP feature using PSTN thinking.  You could get the same user experience, but is modeling this with a mechanism designed for conference calls the way to go?

Mike


> -----Original Message-----
> From: GARCIN Sebastien RD-CORE-ISS 
> [mailto:[e-mail]] 
> Sent: Friday, November 03, 2006 5:17 AM
> To: Adam Roach; Jonathan Rosenberg (jdrosen)
> Cc: IETF Sipping List
> Subject: RE: [Sipping] comments on 
> draft-roach-sipping-callcomp-bfcp-00
> 
> hi 
> 
> >>The objections that I have repeatedly raised with the "abuse" of 
> >>SUBSCRIBE to activate a service aren't purely academic
> 
> I am still missing the "non-academic" arguments that would 
> convince me not to the procedures in draft-ploetz.
> 
> Thanks for clarifying that part.
> 
> sébastien
> 
> -----Message d'origine-----
> De : Adam Roach [mailto:[e-mail]] Envoyé : jeudi 2 
> novembre 2006 16:43 À : Jonathan Rosenberg Cc : IETF Sipping 
> List Objet : Re: [Sipping] comments on 
> draft-roach-sipping-callcomp-bfcp-00
> 
> Jonathan Rosenberg wrote:
> > Its not clear to me that this mechanism works well in the face of 
> > forking. Seems like you could end up with disparate queues 
> for each of 
> > my phones.
> 
> That's pretty much what I intended, yes. As far as I can 
> tell, the net result -- that is, the behavior of the system 
> -- would end up being identical (or, at least, substantially 
> the same) with queues maintained on each of your devices 
> versus a single, centralized queue -- unless there's more 
> than one of you, in which case neither solution will behave 
> particularly gracefully (although I believe the forking setup 
> has better recovery properties under such circumstances).
> 
> When I get a spare moment, I'll work through a few scenarios 
> to demonstrate how the externally observed system behavior is 
> the same between distributed management of several queues and 
> centralized management of one queue.
> 
> > Similar issues arise when the originating user has multiple 
> devices. 
> > So if I call you from phone 1, and later you are available, 
> does the 
> > ringback happen only at phone 1 or all of my phones? Seems like the 
> > latter is much more desirable. That too implies that a UA-based 
> > solution on the originating side has some problems.
> 
> That depends. Are you asserting this as a new requirement? No 
> one has raised this capability as a requirement so far, and 
> the previously offered solution certainly didn't have this property.
> 
> To be clear: I agree that this is probably an improvement on 
> the service; however, the more requirements we pile on, the 
> harder a solution becomes -- and we've become experts at 
> putting so many requirements on a problem that the solution 
> space dwindles down to nothing.
> 
> > There is clearly a relationship between all of this and presence; I 
> > think you need to call that out.
> 
> Martin beat me to it, but I'll reiterate his comment: the 
> relationship here isn't related as much to presence as it is 
> to dialog state. And that is called out in the discussion 
> about centralized queue management.
> 
> > On whether BFCP is the right thing or not for this problem, I'm not 
> > sure. In one sense, you could characterize this as really a problem 
> > with RFC3265 in general; that for certain event packages, 
> notification 
> > of an event to all watchers can cause them to take actions 
> that result 
> > in a further change to that same state. This is a race condition.
> 
> Not in general -- this race condition arises in the 
> draft-poetzl document because it's doing something with 
> SUBSCRIBE that SUBSCRIBE was never meant to do: changing the 
> state of the thing that is watched.
> 
> Let's go back to first principles: SUBSCRIBE is a request to 
> retrieve the state of a resource, and receive that state 
> whenever it changes. 
> It's a way for an observer to *LOOK* at a state.
> 
> Now, as I'm always having to tell my kids: you look with your 
> eyes, not with your hands. If the act of subscribing to a 
> state changes that very state, then you're no longer looking 
> -- you're touching. SUBSCRIBE doesn't touch the state it's 
> monitoring. (Now, we have defined some
> *meta* state regarding the very state of that subscription, 
> but you need to subscribe to that separately, and the act of 
> subscribing to that meta-state doesn't change the meta-state).
> 
> If you violate the basic principles on which a protocol was 
> developed, then, yes, you end up with protocol 
> characteristics that are highly undesirable. The race 
> condition you describe is one. The objections that I have 
> repeatedly raised with the "abuse" of SUBSCRIBE to activate a 
> service aren't purely academic: if you use a protocol in a 
> way that is well outside its original design, then clearly 
> identifiable bad things happen.
> 
> > I share John's concerns as to whether this really 
> interoperates with 
> > the PSTN. Perhaps if you had some call flows demonstrating it, this 
> > would help.
> 
> Martin has put together some pretty nice call flows showing 
> how this interoperates with the PSTN. Perhaps he could be 
> convinced to share them with the wider group?
> 
> /a
> 
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