Re: [Iptel] comments on rfc2806bis

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

Again, the view of tel as an identifier might help here. I agree that 
for E.164, this should be done like a subaddress, which it seems closely 
related to. There are two usages for tel URIs:

- as a unique identifier; in that case, comparison would take it into 
account.

- as a way to place a call; depending on the type of equipment dialing 
the number, it would be ignored or dialed. After all, ISDN subaddresses 
are also pretty meaningless to non-ISDN devices.

Related question: I suspect that having both subaddress and extension 
wouldn't make any sense, but is this a hard fact?

> > I plead stupidity here. I don't see why you can't do PBX extensions with
> > a tel URI. Isnt this just a local number with an appropriate 
> > phone-context?
> I think of a PBX extension as being sort of the same functionality in 
> some cases as the ISDN subaddress. Since the way to carry ISDN 
> subaddress is included, it seems reasonable to be able to include PBX 
> extensions (which are not part of the E.164 address).
>
> There are maybe two cases:
>
> 1. carrying just a PBX extension (say within the PBX itself) - I believe 
> this can be carried as "local".
>
> 2. carrying a PBX extension in addition to the full E.164 number of the 
> PBX. This is what was referred to above as "cannot be specified".
>
> Of course, trying to do case 2 seems to lead to a practical problem, 
> since the protocol issues at an interworking point (to traditional PSTN 
> signaling schemes in the US) really don't support the use of this PBX 
> extension in the forwarded signaling, so one could ask, "Why bother 
> including it in the tel:uri?".
>
> In some other countries, the situation is a little different (relates to 
> use of overlap). Because of the old equipment, it was possible to tack 
> the "PBX extension" onto the number used to get to the PBX, and directly 
> dial it, meaning that the total number of digits could exceed the 
> previous 12-digit max. With the current 15-digit max, I don't know if 
> any case in the world could exceed this. I hope not. If not, the PBX 
> extension is included as part of the E.164 number.
>
> Mike Pierce
> Artel

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