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List:       sip-implementors
Subject:    Re: [Sip-implementors] Use of REGISTER with Contact different than the UA's contact
From:       Paul Kyzivat <pkyzivat () cisco ! com>
Date:       2008-12-15 13:51:25
Message-ID: 494660DD.3050309 () cisco ! com
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Iñaki Baz Castillo wrote:
> El Viernes, 12 de Diciembre de 2008, Paul Kyzivat escribió:
>> There are a few uses that I know of:
>>
>> 1) to forcibly *unregister* a device. For instance, you have a device
>>     registered from work, and then you go home without turning it off.
>>     From another suitable device at home you can unregister the device
>>     at work. Of course you may have to keep doing it each time it
>>     refreshes its registration. And you can get into a real battle if
>>     it subscribes to the reg event package and so discovers when it has
>>     been unregistered, and immediately reregisters.
> 
> Well, I hope this case is more a "workaround" XD

One guy's "workaround" is another guy's feature. But in general I agree.

>> 2) You can use a registration to accomplish forwarding. For instance,
>>     Bob's UA could register Alice's AOR as a Contact on his own AOR,
>>     either in addition to his own phone, or instead.
> 
> Ok, this would work because SIP allows it, but sincerelly, is it really used?
> Sometimes I've created manually entries in my registrar location table to 
> forwards calls to one AoR to other AoR (as you say) but I can't expect a UA 
> sending such a REGISTER, in fact it should be "denied" in some way.

I am not aware of any UA that actually does this as a matter of course.
Lets see if somebody else here does.

regarding denying it - there has been some discussion of that. Some 
people agree with you that you should only be permitted to register 
addresses that you have ownership/control over. That seems good in 
theory, but its not clear it is practical to enforce. The consent 
framework speaks to this.

IMO there is not a huge difference between my UA sending a 3xx to a URI 
each time it is called, and it registering that URI with its registrar. 
If we don't ban one, then why ban the other.

	Thanks,
	Paul

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