Subject: RE: [Sipping] SIP URL's with telephony numbers

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 12 Nov 2001 12:39:06 -0500

-----Original Message-----
From: Michael O'Doherty [mailto:[email-masked]]
Sent: Monday, November 12, 2001 12:25 PM
To: [email-masked]'
Subject: [Sipping] SIP URL's with telephony numbers

>
>Hi, 
>A question about the use of SIP URL's with the username in the form of a
tel URL: 
>If we want the SIP address to be treated as a SIP address rather than as a
telephone 
>number (e.g. we might want to reach the SIP address associated with a
particular PSTN 
>number) two approaches come to mind that clearly avoid any confusion with a
SIP URL which 
>is intended to be routed to the PSTN:
> (a)    SIP:[email-masked];user=SIP 
> (b)    SIP:[email-masked]; 
>The first option (a) is effectively saying "even though the left part of
the SIP URL looks 
>like a telephone number I want it to be treated as a SIP address".  While
it can be argued 
>that this is the default anyway, it makes it explicit if we can use the
user field like 
>this.
>The second option achieves the same thing but arguably not as cleanly. 
>Any opinions on which is the better approach ? 

This is a non-problem. The user parameter exists already to disambiguate. If
its a phone number, its user=phone. Otherwise, its user=ip.

-Jonathan R.
---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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---

From: "Sean Olson (EUS)" <[email-masked]>
Date: Mon, 12 Nov 2001 11:52:27 -0600

>Hi, 
>A question about the use of SIP URL's with the username in the form of a tel URL: 
>If we want the SIP address to be treated as a SIP address rather than as a telephone number
>(e.g. we might want to reach the SIP address associated with a particular PSTN number)
>two approaches come to mind that clearly avoid any confusion with a SIP URL which is
>intended to be routed to the PSTN:
>

Why not use:
sip:[email-masked];user=ip

It's already part of the BNF and it means basically what
you are asking for. This, of course, is really only a 
hint.

/sean

---

From: "Sean Olson (EUS)" <[email-masked]>
Date: Mon, 12 Nov 2001 13:14:44 -0600

This issue has been raised before. People had varying opinions
on what the user=phone parameter meant. After thinking about
it for a while, it seems to me that the user= parameter can
only ever be a hint. Telling a proxy how it is to route a
given URL is a little too inflexible, especially for telephone
numbers. Even if user=phone meant definitively that a proxy
would interpret the user portion as a E.164 telephone number,
you would have zero guarantees about what that the proxy would do
with that number.

Would ENUM be used? Would local policy dictate how that was routed?
Would the proxy be forced to break out to the PSTN? 

Are you sure you want a SIP URL for the application you have in mind?
Would a tel: URL be more appropriate?

Cheers,
sean

-----Original Message-----

Sean, Jonathan, 
The spec Bis05 says that recipients can interpret the SIP URL as a telephone number even if the 'user=phone' is not present.
What I was looking for was some way for a sender to ensure, for whatever reason, that a particular SIP URL (which may look very like a telephone number) is definitely not interpreted by the recipient as a telephone number. 'IP' rather than 'SIP' is not a problem  - I missed that in the BNF (and didn't see it mentioned any place in the text ?).
If we are saying something like: 
 - with user=phone it must be interpreted as addressing a traditional E.164 telephone number 
 - with user=ip it must be interpreted as addressing a SIP CLIENT 
 - with nothing the recipient may decide 
this would be fine. 
Cheers, 
Mick.

---

From: Richard Shockey <[email-masked]>
Date: Mon, 12 Nov 2001 15:02:09 -0500

>Would ENUM be used? Would local policy dictate how that was routed?

probably but hints can be useful...so long as the tradeoff between privacy 
of user data and need for accurate routing data is understood.

>Would the proxy be forced to break out to the PSTN?

but ENUM ..

well there has been some discussion privately among some folks about how 
SIP should use ENUM and there will be several drafts coming out shortly on 
this but let me make a suggestion here some of the suggestions made here 
may have uses ...

Within RFC 2916 an example is given of a possible NAPTR record for a SIP URL.

   $ORIGIN 4.3.2.1.6.7.9.8.6.4.e164.arpa.
     IN NAPTR  10 10 "u" "sip+E2U"        "!^.*$!sip:[email-masked]!".

There is no particular reason that information that hints at a personal 
name or identity of a SIP user needs to be exposed in the DNS. A SIP user 
agent or proxy could set up a simple alias to obfuscate this mapping, for 
example.

   $ORIGIN 4.3.2.1.6.7.9.8.6.4.e164.arpa.
     IN NAPTR  10 10 "u" 
"sip+E2U"     "!^.*$!sip:[email-masked];user=ip!"

for service providers or enterprises wishing to expose their SIP URL's into 
the DNS this may be more useful

>From: Michael O'Doherty 
>[<mailto:[email-masked]>mailto:[email-masked]]
>
>Sean, Jonathan,
>The spec Bis05 says that recipients can interpret the SIP URL as a 
>telephone number even if the 'user=phone' is not present.
>
>What I was looking for was some way for a sender to ensure, for whatever 
>reason, that a particular SIP URL (which may look very like a telephone 
>number) is definitely not interpreted by the recipient as a telephone 
>number. 'IP' rather than 'SIP' is not a problem  - I missed that in the 
>BNF (and didn't see it mentioned any place in the text ?).
>

sounds reasonable...

Richard Shockey, Senior Manager, Strategic Technology Initiatives
NeuStar Inc.
45980 Center Oak Plaza   Bldg 8     Sterling, VA  20166
1120 Vermont Ave NW Suite 400 Washington DC 20005
Voice 571.434.5651 Cell : 314.503.0640,  Fax: 815.333.1237
<mailto: [email-masked]> or
<mailto: [email-masked]>
<http://www.neustar.com>
<http://www.enum.org>
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

---

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 12 Nov 2001 18:25:08 -0500

-----Original Message-----
From: Michael O'Doherty [mailto:[email-masked]]
Sent: Monday, November 12, 2001 1:36 PM
To: 'Jonathan Rosenberg'; [email-masked]'
Subject: RE: [Sipping] SIP URL's with telephony numbers

>The spec Bis05 says that recipients can interpret the SIP URL as a
telephone number even 
>if the 'user=phone' is not present.
>
reason, that a 
>particular SIP URL (which may look very like a telephone number) is
definitely not 
>interpreted by the recipient as a telephone number. 'IP' rather than 'SIP'
is not a 
>problem  - I missed that in the BNF (and didn't see it mentioned any place
in the text ?).
> - with nothing the recipient may decide 

No, that is not the intent. user=phone is a hint that this refers to a PSTN
number. Of course, the domain owning that number can ignore that, but the
hint is clear. With user=ip, it pretty much means its at the discretion of
the owner of the namespace to whom you are addressing the request. Nothing
else makes sense; only the owner of a namespace can decide how to properly
process a name within its scope. 

-Jonathan R.

---
  
-----Original Message----- 
From: Michael O'Doherty [mailto:[email-masked]] 
Sent: Monday, November 12, 2001 12:25 PM 
To: [email-masked]' 
Subject: [Sipping] SIP URL's with telephony numbers 
telephone 
particular PSTN 

SIP URL which 
the SIP URL looks 
it can be argued 
user field like

---

From: "Michael O'Doherty" <[email-masked]>
Date: Thu, 22 Nov 2001 13:46:04 -0000

Ben,

I think we are just going over the same stuff here again but for what its
worth ...

One example where it might be useful to distinguish between a SIP address
that looks like a telephone number and one which is actually a telephone
number is where the request goes VIA an outbound (or other) proxy which
'bends' the rules and try to ensure that all SIP to PSTN calls break out to
the PSTN via its gateway. Obviously if the call is not actually intended to
hit the PSTN it would be good to avoid this (and yes I know we don't want to
keep adding stuff to allow for entities which don't follow the rules
properly ...).

Another example might be where we want to associate both a SIP device and a
PSTN phone with the same username in the same domain and use the 'user'
field to distinguish between the two.

Using the user filed as Sean describes as a hint is fine so I think we can
likely close discussion on this (although it may be worth adding some text
to the spec to explain clearly that it is a hint rather than a rule).

Cheers,

Mick.

-----Original Message-----
From: Ben Campbell [mailto:[email-masked]]
Sent: 21 November 2001 21:45
To: O'Doherty, Michael [MDN05:MD01:EXCH]
Cc: 'Jonathan Rosenberg'; [email-masked]'
Subject: Re: [Sipping] SIP URL's with telephony numbers

Sorry for the late entry to the discussion. Comments inline.

> BNF (and didn't see it mentioned any place in the text ?).

And in the case of a sip: url, why should the caller have the ability to 
do that? Shouldn't the interpretation of the user part of the URL be 
entirely up to the domain specificied in the domain part? Why should the 
caller have any control over the interpretation of that name-space?

>  - with nothing the recipient may decide

I think that for a SIP URL, it should always be up to the designated 
domain to decide.

---

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 27 Nov 2001 16:52:56 -0500

-----Original Message-----
From: Michael O'Doherty [mailto:[email-masked]]
Sent: Thursday, November 22, 2001 8:46 AM
To: 'Ben Campbell'
Cc: 'Jonathan Rosenberg'; [email-masked]'
Subject: RE: [Sipping] SIP URL's with telephony numbers

worth ... 
>One example where it might be useful to distinguish between a SIP address
that looks like 
>a telephone number and one which is actually a telephone number is where
the request goes 
>VIA an outbound (or other) proxy which 'bends' the rules and try to ensure
that all SIP to 
>PSTN calls break out to the PSTN via its gateway. Obviously if the call is
not actually 
>intended to hit the PSTN it would be good to avoid this (and yes I know we
don't want to 
properly ...).

This is a really, really bad thing. As Ben has said, only the owner of the
domain in the URI can interpret the user part. Interpreting the user part
outside of that domain is just going to be trouble. If the caller really
wanted to call a pstn number, the r-uri to the outbound proxy would be a tel
URL, not a sip url. In that case, there is no domain of ownership. Now, this
still might not be a pstn number (i.e., enum might show its a sip url), but
at least it is a valid number to dial on the pstn.

>Another example might be where we want to associate both a SIP device and a
PSTN phone 
>with the same username in the same domain and use the 'user' field to
distinguish between 
>the two.

If you want the caller to decide about terminal preferences, use the caller
preferences specification. 

>Using the user filed as Sean describes as a hint is fine so I think we can
likely close 
>discussion on this (although it may be worth adding some text to the spec
to explain 
>clearly that it is a hint rather than a rule).

THe spec is right as defined; it says that the BNF follows the definition of
telephone-subscriber. How thats interpreted depends on the domain owning the
name.

-Jonathan R.

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