Subject: Re: [Iptel] comments on rfc2806bis

From: [email-masked]
Date: Tue, 19 Nov 2002 15:59:56 EST

In a message dated 11/19/2002 1:17:27 AM Eastern Standard Time, 
[email-masked] writes:

> > The approach pursued here has the disadvantage that certain services,
> >    such as extensions on a PBX (when direct inward dialing is not used)
> >    or electronic banking, cannot be specified in a URI.
> 
> 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

---

From: Henning Schulzrinne <[email-masked]>
Date: Thu, 21 Nov 2002 18:19:40 -0500

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 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).
> 
> 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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