Re: Comment on draft-roach-sipcore-rfc3265bis-00

Paul Kyzivat wrote:
>
>
> Adam Roach wrote:
>
>> Because of the true interoperability nightmare that has resulted from 
>> dialog sharing, my suggestion would be to disable notifier 
>> functionality on those endpoints under such circumstances (perhaps 
>> with an implementation option to fall back to 3265 behavior for the 
>> truly masochistic).
>
> Can you say more about the "true interoperability nightmare that has 
> resulted from dialog sharing"?
>
> I understand that there undoubtedly are interop issues due to some UAs 
> not supporting dialog sharing. There are also interop issues due to 
> the UAs not supporting an event package, or not supporting GRUU, or 
> whatever. Is one more of a nightmare than another?

It's not lack of support that worries me -- it's mismatched views of 
dialog and usage state between two endpoints who both think they've 
implemented dialog sharing. The problem is not that things negotiate 
down to a lesser set of capabilities -- it's that things act broken in a 
way that exposes this mixed-up view of whether a dialog (and its 
associated session/subscription) is active.

> Dialog sharing has been a legal possibility since 3261 was published. 
> So it shouldn't be a surprise to anybody. If somebody didn't implement 
> support, well, what can you say?

As one of the key perpetrators of that particular aspect of 3261, I'm 
comfortable in saying that we added it in a slapdash fashion at the 11th 
hour, without sufficient analysis (and I mean this in a self-deprecating 
way, without intending to cast aspersions on any of 3261's editors). 
Interactions between usages in a dialog were ridiculously 
underspecified. Robert spent a long time trying to rationalize this 
behavior after the fact, with the result being RFC 5057. And RFC 5057 
really helps a lot for the minority of implementors who actually know it 
exists. However, the issue is complicated enough that it takes 26 pages 
to untangle it, and the rules are a tangle of exceptions. Go read 5057 
again, and tell me that people are more likely to get that right than 
they are to get confused.

> It was used primarily because contacts in dialogs often don't have the 
> gruu property, and GRUU hasn't been widely implemented. Has that 
> situation changed? Will 3265bis somehow result in widespread 
> implementation of GRUU by registrars? 

3265bis is less mature than GRUU (in that one is a -00 individual draft, 
and the other is in the RFC editor queue). I think it's reasonable to 
rely on predecessor technologies.


/a
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