Re: [Simple] Device priority

[Paul Kyzivat <pkyzivat at cisco.com>]

Adding to what Jonathan said:

Goeman Stefan wrote:
> Hello All,
>
> I have a small question.
> Suppose I have two devices, a laptop and a mobile phone with the same 
> communication means ( they use same communication addresses). However, 
> if both devices are active (and registered), I would like to receive IM 
> on my laptop, and not on my phone.

You say they use the same communication address. Since they are separate 
devices, they must have separate contact addresses. So it must be the 
Address of Record that is the same, which presumably is also the 
presentity address.

There is some other detail you didn't provide:

- Is the laptop limited to IM, or does it also do voice?
  (I presume the mobile phone does both.)

- Do they use the same contact address for IM and voice?
  (sip for both.) Or do they use separate addresses
  for voice and IM? (e.g. sip: for voice, im: for IM.)

> Is there a way to express to express the priority of the laptop over the 
> mobile phone for receiving IMs? I do not (immediately) find this in the 
> relevant RFC and IDs.
>
> The way I understand the format of the presence document (RFC3863) is 
> that it groups a number of communication addresses (contact means + 
> contact address), and these communication addresses are decoupled from 
> the devices or user agents (which is not a bad idea I think).
>
>  
> Can someone enlighten my here?
> Thanks in advance!

If the the laptop only does IM, then its contact can be assigned a 
higher priority than that the mobile phone contact(s). As Jonathan 
mentioned, capabilities can be used to describe that this one does IM 
and not voice.

If they both do IM & voice, and they each use a single sip contact it 
gets a bit more tricky. With just two tuples you can't describe that one 
is better for IM, but not better for voice. To achieve this effect, you 
would have to publish two tuples for the laptop - one with the contact 
at a high priority, with capabilities of IM and not voice. Another 
tuple, with the same contact address but a lower priority, could show 
capabilties for both IM and voice. The mobile phone could be described 
by either one or two tuples, with capabilties and priorities assigned to 
achieve the kind of prioritization you want.

If IM and voice are handled using different contact addresses then you 
are forced to have separate tuples anyway, and to describe the 
capabilities separately. And of course you can set the priorities as you 
wish.

In some cases a useful presence document can be derived from 
registration information (particularly if you use callee capabilties in 
the registration). But in registration you aren't permitted to have two 
entries with the same contact address. So you can't derive a presence 
document that has two tuples with the same contact from registration. 
Either you must separately publish the presence doc, or else you must 
hack the registration - using multiple addresses for the same device in 
order to register it twice. But this isn't a good idea because it can 
result in the same device getting tried twice for the same call.

	Paul



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