Re: [sipcore] RFC5626 and REGISTER with multiple contacts

[Iñaki Baz Castillo <[e-mail]>]

2012/5/7 Ivo Sedlacek <[e-mail]>:
> When reading RFC3261, I was not able to find any text stating that a SIP UA can have only a single contact. Quite the opposite, RFC3261 states that UA can register several Contacts and update its own contact addresses:
> --------------------------------------------------
> 10.2.1 Adding Bindings
> ...
>   The REGISTER request sent to a registrar includes the contact
>   address(es) to which SIP requests for the address-of-record should be
>   forwarded.
> ...
> Typically, a UA
>   only updates its own contact addresses.
> ...
> --------------------------------------------------


Right, it could occur that the same UA register a UDP and a TCP binding.



> I have not found any statement that when outbound is used, each contact of a UA must be the same. Can you please point me to such text in RFC5626?
>
> Moreover, when outbound is used, each contact is different due to reg-id even if UA is monolithic. Given Kevin's statement above, each such contact would have to have different sip.instance which defeats the purpose of the outbound.
>
> Moreover, Inaki stated that contacts can differ even for the same sip.instance:

>> First it's registered fom my home WiFi network but then I leave my home and my mobile connects via 3G to Internet. So the SIP app sends a new REGISTER indicating the same sip.instance but a different Contact SIP URI (i.e. different IP).

Yes, but all those Contact SIP URIs point to the same UA so to the
same instance, that's the purpose of Outbound.



> To Inaki:
>> Said that, IMHO it's useless that you set different SIP URI usernames in each Contact header since Contact matching in the registrar just considers the sip.instace and reg-id Contact parameters.
>> With this in mind, a REGISTER with multiple Contact headers providing the same sip.instance is useless and/or invalid.
>
> Disagree. Several contacts enable expressing user agent capabilities which cannot be expressed in single contact. See the example in the other mail.

But user agent capabilities mean *UA* capabilities, and a UA is
represented by a single and unique sip.instance.

-- 
Iñaki Baz Castillo
<[e-mail]>