Re: [Simple] Presence data model: devices

[Henning Schulzrinne <hgs at cs.columbia.edu>]

> "can you call me back on my land-line phone? I can't hear you very well on
> this
> cell phone".

None of this requires a device abstraction. The caller can only choose 
the mobility modality if

(1) there are two separate service entries (one stationary, one mobile)

or

(2) there is one service entry and the caller uses caller preferences 
that the callee chooses to honor.

Neither requires nor benefits from a device tuple. (Devices tuples 
cannot be contacted directly.)

In many cases, we'll have a single watcher-visible modality that 
encompasses multiple devices. For example, on trips to Europe, I carry 
both my GSM phone (works in both places) and my CDMA phone (works in 
only one, but is cheaper). I want the caller to reach my mobile service, 
but don't necessarily want to have to expose the devices as that's none 
of the caller's business. Thus, I need the ability to declare a mobile 
*service* (which is then routed according to my service preferences to 
one of my phones, e.g., depending on how much an incoming call is going 
to cost me.) [The proposed model allows this, as far as I can tell, so 
no disagreement here.]

> Modes of communication vary. They can include audio/visual (send audio and
> receive
> video after appropriate translations, send audio and receive audio, send
> video and
> receive audio, send video and receive video), sensory, and tactile
> communication modes.
> It is possible but rare that one device can support all these modes;
> however it most likely
> that the various modes will be supported on different devices optimized for
> each mode.
> So, I am not sure if we can  dimish the importance of device addressability.

I don't think anybody is arguing that we outlaw one-device service 
tuples if the user wants to publish these.

Only services are addressable in the proposed model. Thus, the presence 
of device tuples does not help or hinder their addressability.

Henning

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