Subject: RE: [SIP] E.164 request-uri domain's.

From: Jonathan Rosenberg <[email-masked]>
Date: Sun, 3 Jun 2001 01:43:02 -0400

-----Original Message-----
From: Fairlie-Cuninghame, Robert [mailto:[email-masked]]
Sent: Saturday, June 02, 2001 11:26 AM
To: [email-masked]'
Subject: [SIP] E.164 request-uri domain's.

>Hi, 
>
>We have had this discussion quite a few times but I thought I would throw
in a new idea. 
>
>When building a request-uri containing an E.164 number which does not
"belong" or is 
>associated with a particular domain name then the most desirable action is
to place a tel: 
>URL in the outbound request-uri. However, if a tel URL cannot be generated
or received for 
>whatever reason, then a SIP url must be used instead and a domain name must
selected for 
>the url.
>
>The easiest option is to simply place the outbound proxy/destination's
address or hostname 
>in the host portion. Eg "sip:+12135551234@<proxy hostname>;user=phone". I
remember that 
>some people had some academic objections to this approach because the
request-uri referred 
>to an "intermediate destination" rather than the final destination. 

That doesn't make sense to me. As long as a call traverses proxies, the
request URI will always refer to intermediate destinations. 

I personally believe 
>that it is easy to ignore the domain name for the telephone subscriber case
at a proxy 
>(that is you 
>simply treat a "user=phone" request-uri as a simple telephone number (ala
tel URL) if the 
>domain name is that of the proxy's). With the new loop detection rules I
don't believe 
>this creates any problems. This removes the objection  due to the
"intermediate 
>destination" concept. 

The interpretation of the LHS of the @ is entirely up to the administrator
of the domain. A very common usage of that namespace is that any usernames
that are purely numbers, and start with +, are E.164 formatted numbers, and
should be handled in whatever way is appropraite for international phone
numbers. So, the domain is not really ignored, nor should it be. It points
to a server handling the domain which knows how to interpret the user
portion of the URI in this way. 

Also, I believe this is a fairly common usage in real implementations.

>Alternatively, for E.164 numbers what do people think about allowing
"sip:+12135551234
>@e164;user=phone"? e164 is the domain stem used by ENUM for doing DNS
lookups of E.164 
>numbers. In this case the host name of the sip URL correctly indicates that
domain of the 
>user portion.

Now, this I object to. I should be able to take a SIP URL, and always be
able to route it somewhere for further processing. Thats why the domain name
is mandatory. By using e164 as the domain, you would require every host to
know the semantics of that and have proper handling for it. Yuck.

-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: "Fairlie-Cuninghame, Robert" <[email-masked]>
Date: Mon, 4 Jun 2001 08:42:58 -0700

Thanks for the reply.

Comments below.

-----Original Message-----
From:	Jonathan Rosenberg [mailto:[email-masked]]
Sent:	Sunday, June 03, 2001 6:43 AM
To:	'Fairlie-Cuninghame, Robert'; [email-masked]'
Subject:	RE: [SIP] E.164 request-uri domain's.

-----Original Message-----
From: Fairlie-Cuninghame, Robert [mailto:[email-masked]]
Sent: Saturday, June 02, 2001 11:26 AM
To: [email-masked]'
Subject: [SIP] E.164 request-uri domain's.

in a new idea. 
"belong" or is 
or received for 
selected for 
address or hostname 
remember that 
request-uri referred 

I personally believe 
at a proxy 
tel URL) if the 
don't believe 
"intermediate 

[RFC] Sorry, "ignore" was a bad choice of words.

[RFC] Yes I also believe you are correct - this is what many people are
doing currently. The purpose of my original email is try to correlate what
should and what is being done. 

Also treating sip:+12135551234@proxyaddress (or UA address) and
tel:+12135551234 synonymously is introducing some assumptions into the
system - not necessarily bad but they do need to be considered (especially
in multi-service-provider networks). Of course it's all a matter of local
policy not protocol specification.

"sip:+12135551234
lookups of E.164 
domain of the 

[RFC] I agree. I only suggested it because of my perceived objections to
this "intermediate destination" concept, which I also agree is an entirely
valid concept! However, I think I slightly misinterpreted one of Henning's
earlier statements about outbound proxies. 

Henning's answer to the question "When refering to [the Request-URI being
the] current destination, does it mean the next hop destination or the
current logical destination ?" is:

		"Current SIP destination. The outbound proxy is by
definition not a SIP
		destination (with its own SIP URL). Thus, putting its
address in the
		request URI makes no sense. I would prefer not to introduce
yet another
		term ("logical destination"), as this increases complexity.
The
		definition of the outbound proxy is that it differs from the
Request-URI
		address, so I'm not sure how much confusion there can be.
(If you stick
		the address of the proxy in the request-URI, it's no longer
an outbound
		proxy.)"
		
This is effectively the crux of what I am talking about. However, when I
reread it, I think that the last bracketed sentence is allowing one to use
the default outbound proxy address as the SIP URL domain name when
requesting a proxy to route an "un-domained" telephone subscriber. However,
in this case the default outbound proxy is no longer acting as an "outbound
proxy" using Henning's definition of the term. 

To me, Henning's definition seems to be slightly at odds with the outbound
proxy definition in
http://search.ietf.org/internet-drafts/draft-ietf-sip-srv-02.txt
<http://search.ietf.org/internet-drafts/draft-ietf-sip-srv-02.txt>  :

"Outbound proxy: A proxy that is located near the originator of requests. It
receives all outgoing requests from a particular UAC, including those
requests whose Request-URLs identify a host other than the outbound proxy.
The outbound proxy sends these requests, after any local processing, to the
address indicated in the Request-URI. (All other proxy servers are simply
referred as proxies, not inbound proxies.)"

Perhaps we need to describe this more clearly in a BCP somewhere, ie the
interactions between the domain name, a telephone-subscriber and outbound
proxies. That is, the difference between tel:+12135551234,
sip:+12135551234@proxyaddress;user=phone (or UA address) and
sip:+12135551234@calldomain;user=phone. 

Cheers,

Robert.