Subject: AW: [Iptel] tel URI and ENUM

From: "Stastny Richard" <[email-masked]>
Date: Wed, 19 Mar 2003 22:44:56 +0100

To start from the end:
 
"What happens if the tel URI with a carrier code in a web page gets a
different carrier?"
 
Correct, but this leads to a second dimension:
What is a tel URI used for?
I see 3 different usage cases:
1. use e.g on Webpage: TH, NP, CP should not be used or are not applicable, TD may be useful
2. use in signalling (e.g. INVITE): TH, TD, NP, CP may be useful
3. use in ENUM: TH and CP are not applicable, TD may be usefull, NP is essential (see below)
 
ENUM or ENUM-like systems may be used to store translation information in a tel URI
e.g. tel:+43123456;rn=8620123456 according to the Yu-extensions.
 
I consider therefore TH, TD and NP as useful, depending on usage, CP is out of scope in ENUM
the question here is how far one should go with this.
 
regards
Richard

	-----Ursprüngliche Nachricht----- 
	Von: Henning Schulzrinne [mailto:[email-masked]] 
	Gesendet: Mi 19.03.2003 20:06 
	An: [email-masked] 
	Cc: 
	Betreff: [Iptel] tel URI and ENUM

	To pick up the discussion that was started in the iptel meeting:
	
	One model of the tel URI is that it is a name identifying an (abstract)
	resource via a telephone number. Other entities are needed to direct a
	request containing the URI (in the SIP case) or to generate an action
	(in the HTML case) causing a connection. This is no different from, say,
	an ISBN URN that invokes a translation service. The subtle difference is
	that a tel URI can both directly reach a specific resource as well as do
	this via translation and that multiple translation steps can be
	involved, but that property is inherent in the phone number (via things
	like 800# translation, number portability and ENUM) and not specific to
	a tel URI.
	
	Like all telephone numbers in protocols, I believe that tel URI numbers
	can be subject to ENUM translation. It shouldn't matter if a tel URI was
	itself the result of an ENUM lookup. Thus, you could have
	
	[SIP UA] tel URI
	[outbound proxy]  ENUM: tel1 -> tel2 (number portability)
	[some other proxy] ENUM: tel2 -> sip URI
	
	I don't see the need for parameters in this case. (In other words,
	parameters might be *useful*, but they shouldn't be *necessary*.)
	
	Thus, 'translation hints' in the tel URI comply with the model. It might
	be interesting to divide the tel URI extensions into categories. There
	seem to be at least four:
	
	(TH) translation history hints ("translation X has been performed");
	
	(TD) translation directive ("translation X should/should not be performed");
	
	(NP) number property: "the number in the tel URI is a 'foo'" (and it
	will be a 'foo' for a long time).
	
	(CP) call property: the call with this tel URI has the following properties
	
	I have to admit that I find (CP) least convincing as a tel URI
	extension. Names and URN-like things like tel URIs should be long-term
	stable.
	
	(NP) is really a URC-like thing, although that concept seems to have
	seen no instantiation in actual usage. The Contact parameters in
	caller-preferences are an example of binding NP-like properties to a SIP
	URI. One could argue that (NP) should be retrieved by reference, to
	avoid sprinkling it all over the place (like web pages and address
	books) where the parameters are hard to change when they do change.
	Thus, including things like carrier codes seems potentially dangerous.
	What happens if the tel URI with a carrier code in a web page gets a
	different carrier?
	
	Henning
	
	_______________________________________________
	Iptel mailing list
	[email-masked]
	https://www.ietf.org/mailman/listinfo/iptel

_______________________________________________
Iptel mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/iptel

---

From: Henning Schulzrinne <[email-masked]>
Date: Wed, 19 Mar 2003 17:26:28 -0500

> 2. use in signalling (e.g. INVITE): TH, TD, NP, CP may be useful

But CP can usually be indicated in a different way, e.g., in Caller-Info 
in SIP. I think that's a better place for CP-style information.

> 3. use in ENUM: TH and CP are not applicable, TD may be usefull, NP is essential (see below)

What are examples of NP in this context?