Re: [sipcore] RFC5626 and REGISTER with multiple contacts

["Kevin P. Fleming" <[e-mail]>]

On 05/09/2012 06:49 AM, Ivo Sedlacek wrote:
> RFC5626 states that only one delivery (unless flow fails) is attempted to contacts with the same AOR and instance-id - see exceprt above.

That's correct, because as Inaki posted previously, the RFC is covering 
the case where a UA registers multiple contacts using different 
transports/addresses/etc. that reach the *same* UA. In that case, the 
proxy only needs to send the request using one of those Contact URIs, 
because they are all the same UA.

It's clear at this point that what you are trying to do was not 
contemplated by the combined authors of RFCs 3261, 3841 and 5626. That 
doesn't mean it can't be done, but there isn't a mechanism that exists 
today which is fully compliant with all of these RFCs and doesn't also 
result in requests being forked to your applications.

With that said, though, you've stated previously that your applications 
have mutually exclusive capability sets; if that's the case, and you 
registered Contact URIs for each of them, then a proxy following RFC3841 
rules would only select the *one* that is compatible with the caller's 
preferences. The others would be dropped from the candidate set before 
the request was forwarded, and no forking would occur, even if the 
registered URIs all had distinct sip.instance values.

If that's not true, then it appears that the underlying problem is that 
RFC3840 capability specifications aren't expressive enough to describe 
your UA's capabilities. You need both conjunctive and disjunctive logic, 
and grouping.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
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