Telephony URL and Phone-Context

SIP URIs include Telephony URLs [RFC 3966] and [RFC 5341].

A Telephony URL looks like:

tel: +358-555-1234567

fax: +358-555-1234567

a telephone terminal a fax machine

Digit separators of "-" or "." are ignored.

A Phone-Context sets the conditions under which the number can be used, e.g.

tel: 1-800-555-1234;phone-content:+1 972

a phone number that can only be valid within North America (+1) and within the 972 exchange
the absence of the "+" in the telephone number indicates that this is a local number, rather than a global number -- but the interpretation of these local numbers is problematic (i.e.,there is no assured geographic area nor can one depend on 7 digit numbers being local to a Class 5 exchange {the traditional case in North America}) ⇒ a proposal to deprecate the use of unqualified local digit strings see [Mahy 2004].

Slide Notes

H. Schulzrinne, The tel URI for Telephone Numbers, Internet Request for Comments, ISSN 2070-1721, RFC 3966, RFC Editor, December 2004, Updated by RFC 5341, http://www.rfc-editor.org/rfc/rfc3966.txt

C. Jennings and V. Gurbani, The Internet Assigned Number Authority (IANA) tel Uniform Resource Identifier (URI) Parameter Registry, Internet Request for Comments, ISSN 2070-1721, RFC 5341, RFC Editor, September 2008, http://www.rfc-editor.org/rfc/rfc5341.txt

R. Mahy, “Proposed Clarification of Encoding of Telephone Numbers in SIP URIs”, IETF Internet-Draft, Oct. 2003, Expired: March 31, 2004

Transcript

[slide215] Now, if we're used to normal telephone numbers, these E.164 numbers, we see that we have a telephone number there, we see they are separated by dashes or periods. They prefix the country codes by a plus. In North America and Canada and the Caribbean, we have the problem that plus one, which is North America, treats numbers differently depending upon which exchange you're in. And so if you dial, for instance, 1-800-555-1234, you have to say where you are to know how to interpret that number. Why? This is a free phone number and if it doesn't know what exchange you're in, it doesn't know where to send that call. So here in Sweden, for instance, there's a number, 020-2020 if I remember right, which is a taxi company. They have a nationwide company. But if I'm in Stockholm, do I want the taxi in Gothenburg? Probably not. So I somehow have to look at where the user is and decide how to translate that number to connect it to them for the local service. This lets us put the phone context in by saying it's in North America and it's in area 972. There's also this problem about in North America, plus until recently wasn't used in phone numbers at all. And you only had to dial 7 digits. When I was growing up in a small town, you actually only had to dial four digits. I had graduated from college before you had to dial more than four digits. It was a big problem, right, because you don't know where those four digits are with respect to the universe. Right? It's locally meaningful, but if someone just saw the four digits and they were there at their cell phone, they would have no idea how to make that phone call.