Subject: tel:# versus sip:#@host;user=phone

From: "Donovan, Steven R." <[email-masked]>
Date: Wed, 05 Jan 2000 17:46:38 +0000

Discussions in the "URL Generalization for Portability (was TRIP)" thread
have me a little confused.

It was my understanding that the reason for the user=phone construct in the
sip url was because the tel url definition was still in draft stage.  As
such, I had always thought that a sip url with user=phone represented the
same address as a tel url with the same number.

As such, in my mind (warped as it might be) the following two INVITE
messages are used to call the same PSTN phone number:

INVITE sip:[email-masked];user=phone SIP/2.0
...

INVITE tel:+19725551212 SIP/2.0
...

In both of these cases, the caller wants to reach someone at the number
19725551212.

Note that this does not necessarily mean in either case that the call will
routed to a PSTN phone that has 19725551212 printed on the front of it or
that is connected to a switch via a line interface that is identified by
that number.  There are many points between the caller and callee of the
call where the caller address can be changed.  It is equally valid for both
of the above cases to change +19725551212 to [email-masked]
and have the call fowarded to a SIP based directory assistance platform as
illustrated in the following:

Callee to Proxy Server
INVITE tel:+19725551212 SIP/2.0
From: joe@home
To: tel:+19725551212
...

Proxy Server to Directory Assistance Platform

INVITE [email-masked] SIP/2.0
From: joe@home
To: tel:+19725551212
...

The resent discussions imply that the tel url and sip user=phone addresses
would be treated differently.

This does not seem wise to me.

Steve

---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 05 Jan 2000 14:45:45 -0500

> same address as a tel url with the same number.

No; the user=phone simply stated that the user portion is built using
the
BNF of telephone-subscriber. Beyond that, its still a SIP URL.

> would be treated differently.

Not differently in the sense you describe. In either case, it would
still be true that the call might be routed to some other URL which is
not associated with the telephone number at all
(sip:[email-masked], for example).

The debate is really around numbers that are not uniform, in the sense
that they aren't usable everywhere. For an international e164 number,
using the tel URL for:

tel:+17327417244

or

sip:[email-masked]

is likely to have the same effect. But, with a number which is private,
the tel URL doesn't (I've been arguing) provide sufficient information
to figure out how to resolve the number, while the SIP URL form does.

-Jonathan R.

-- 
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