Re: meaning of tel URI in presence data model, was: Re: [Simple] Presence Data Model: Identifying services

[Paul Kyzivat <[e-mail]>]

Jonathan Rosenberg wrote:
> 
>> Why? There is no particular reason why tel: should mean voice. We 
>> don't restrict sip: that way, and http: doesn't say much about what 
>> you can do either. (I can use http to exchange html, vxml, xcap, etc.)
>>
>> AFAIK, tel: is an addressing format and namespace. The following is 
>> from  draft-ietf-iptel-rfc2806bis-09:
>>
>>    The "tel" URI telephone number is not restricted in the type of
>>    termination point it refers to.  The termination point can be in the
>>    public telephone network, a private telephone network or the
>>    Internet. The termination point can be fixed or wireless and address
>>    a fixed wired, mobile or nomadic terminal.  The terminal addressed
>>    can support any electronic communication service (ECS) including
>>    voice, data and fax.
> 
> 
> Sigh... here is another case where the tel URI's confusion about what it 
> really is, is getting us into trouble.
> 
> If you think about the tel URI as a urn scheme, whereby resolution to an 
> actual set of communication resources is done using a resolution service 
> (ala DDDS), then it becomes fairly obvious (to me at least) that you 
> would simply never even put that URN into the <contact> of a presence 
> document, since it doesnt represent a communications service at all. If 
> anything, it's closer to a presentity identifier. Rather, you would put 
> the individual service URIs that result from the DDDS lookups.
> 
> However, the tel URI is somewhat schizophrenic. Its not a URN, even 
> though it can use (but doesnt require) URN-like resolution services such 
> as enum. It's like a URN in that it can refer to an abstract name and be 
> resolved to a wealth of different URIs of many different schemes and 
> services. Its unlike a URN in that it is also used to refer to telephone 
> resources, and the implication of the tel URI is that "I can dial this 
> from a PSTN phone or enterprise phone and reach something". In that 
> aspect, its more like a protocol URI.
> 
> What does this mean for presence? To be honest, in the discussion in the 
> data model draft, I have assumed the protocol URI meaning. That is, it 
> refers to a PSTN (or private network) circuit endpoint, period. That, of 
> course, is a BIG assumption, and something we should discuss. I would 
> propose that we keep this assumption and merely state it. In such a 
> case, it would not make sense for the recipient of a presence document 
> to look up  such a tel URI in enum. Rather, it knows its a telephony 
> resource right away and can "dial it".

This feels wrong to me.

I think it is better viewed as "this CAN be reached via the PSTN, and 
MAY also be reachable other ways". At the very least, if I choose to use 
this published address, and there are ENUM entries for it, I should be 
free to use them (potentially making an e2e sip call).

 From a practical perspective, I think this means that if all I have is 
a PSTN phone, then I can consider this contact as one to try. If I have 
a sip device that supports tel uris and ENUM and has a pstn gateway, 
then I can also consider trying this contact. The tuple with this 
contact could show support for all sorts of media if it wants, and if my 
device supports those media then it might try them as well.

	Paul


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