Re: [Simple] Presence data model: devices

[Paul Kyzivat <pkyzivat at cisco.com>]

Jonathan Rosenberg wrote:
> There are other benefits.
>
> If my presence server receives information that says that the service 
> runs on multiple devices, and it separately learns that one device 
> fails, it can know that the service is still available.
>
>  From a watcher perspective, I think it helps in selecting. Lets say I 
> have a messaging service which I see runs on a mobile device and a fixed 
> device, and a voice service on a fixed device. If I know you are 
> traveling, I might be inclined to use the messaging service, since there 
> is the possibility you can be reached.
>
> You've missed the third, key case, though:
>
>
> - A particular device maps to multiple services
>
> Now, this one is really interesting for both watchers and presence 
> servers as consumers.
>
> For watchers, it allows you infer important correlation that can help 
> you make a choice. Some examples:
>
> * Jon told me to contact him on his cell. I see that his cell has sms 
> and voice, but his voice service reports its busy. So I'll send him an 
> sms to that phone
>
> * Jon is PTTing with me. The quality stinks. He says, "go circuit". I'd 
> like to call him back on the circuit voice on the same device his PTT 
> service is on (since I know he's got that).

All of the above work just as well if service tuples contain device 
id(s) for purposes of correlation, without any separate device state.

> * Bob and I are talking. I see from his presence doc that he has a 
> videophone app on the same PC running his voice softphone app. I want to 
> also use video to talk to him. His softphone doesnt do video, so a 
> reinvite won't help. His pres doc indicates two video devices - one is 
> on his PC as well, another is a hard videophone somewhere else. Since I 
> know he's at the PC with the softphone, I contact the videophone on the 
> PC too.

As an example it works, but it seems far fetched. Since a video phone 
should be able to do voice-only calls, why would you want to run both a 
voice-only softphone and a soft-video-phone on the same PC at the same 
time? (Among other problems, they will have to compete for the audio 
resources of the PC, so they can't both be in a call at the same time.)

	Paul


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