Re: Dual registration without Outbound

On Oct 7, 2008, at 3:37 PM, Paul Kyzivat wrote:

> I think I am missing something here. I presume that the knowledge of  
> the UA is limited to:
> - to proxy addresses
> - an AOR to register
>
> Presumably the address of the registrar is derived from the AOR to  
> register by removing the user part. So the UA, when registering,  
> doesn't specify two different registrars. Whether there are two or  
> not is a function of how the proxy routes the register request. So  
> whether the two registers for the same contact go to one registrar  
> or two is unknown to the UA. In some configurations this would give  
> you redundancy, and in others it would not.
>
> Then, what causes the UA to register two different contacts? Are the  
> wlan contact and the 3g contact registered to *different* AORs? If  
> not I don't see the point. If anything, I would expect that 3g and  
> wlan represent access networks and hence differing proxies, not AORs  
> or registrars.
>

Some IMS networks have mechanisms for discovering the  edge proxy  
based on the air interface. This, a UA might discover one proxy for  
its 3g interface, and another for its WLAN interface. In other words,  
one proxy for each Contact.

So, that's "proxy" discovery.

Registrar discovery is a separate process. With config-framework, the  
UA is configured with a set of proxies with which it may register.  
Under outbound-015, if there are two or more outbound proxies in the  
configured set, the UA must register through at least two of those  
proxies. This assumes a singular contact at the UA.

Juha has, IIRC, proposed that the UA must register with at least two  
of those proxies for each contact. This, I believe, has some merit.  
I'm not sure it's a MUST, but it certainly seems a reasonable SHOULD.

Of course, when the configuration mechanism is different and only one  
proxy is provided per contact, we have a different case.

It seems like we are developing two conflicted use cases here -- one  
for a singular contact with redundant registration paths, and another  
for redundant contacts, each with singular registration path.

Then there may be yet another case, multiple contacts, each with  
redundant registration paths.

--
Dean

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