Standardized Telephone Number formats work even on old phones!

There are many different address books and directories online, and there are almost just as many different ways they store telephone numbers. I guess most people don’t realize that there are actually standards for representing phone numbers. A little bit of standardization would go a long way towards interoperability.

The standard for phone number formatting is set by the International Telecommunication Union in [E.123] and [E.164] (see the references below). The standards documents are available for a fee from the ITU. A summary is available in the Google (UseNet) discussion group, titled Need ITU-T E.123 summary.

In short, a North American telephone number should look like:

+C-AAA-PPP-NNNN;ext=xxxx

• “+” shows where the dialing prefix goes. This is one of either the International Direct Dialing (IDD) prefix (for Canada this is “011″ for overseas dialing) or the National Direct Dialing (NDD) prefix (“1″ for calls within North America, omitted for toll-free calls),
• “C” is the Country Code (North America’s CC is “1″, and it is omitted for dialing within North America),
• “AAA” is the area code (always required for dialing in Kitchener, Toronto, and other jurisdictions),
• “PPP” is the Exchange (or Private Branch Exchange “PBX”; look in the phone book to see which exchanges are supported),
• “NNNN” is the local portion of the number,
• “;ext=” optionally identifies the next portion as an extension and “xxxx” are the digits for that extension. This syntax is usable in URIs and e-mail.

Note that the sequence “AAA-PPP-NNNN” is called a “local number” and “+C-AAA-PPP-NNNN” is called a “global number”. The “-” (hyphen) is a visual separator, as are “.” (period) , “(” (left bracket) and “)” (right bracket), which dialing applications should ignore.

I’m mostly interested in making phone number formats in e-mail addressbooks compliant with e-mail standards. The document that covers this is the IETF’s RFC3191, Minimal GSTN address format in Internet Mail . The requirement is that GSTN (Global Switched Telephone Network) numbers use the global-number syntax (“+C-AAA-PPP-NNNN”).

Global-number GSTN numbers can be used for other purposes as well, such as Web page URIs. See RFC3966, The tel URI for Telephone Numbers. This document re-iterates that:

5.1.4.

Global Numbers Globally unique numbers are identified by the leading “+” character. Global numbers MUST be composed with the country (CC) and national (NSN) numbers as specified in E.123 [E.123] and E.164 [E.164]. Globally unique numbers are unambiguous everywhere in the world and SHOULD be used.

5.1.5.

Local Numbers Local numbers are unique only within a certain geographical area or a certain part of the telephone network, e.g., a private branch exchange (PBX), a state or province, a particular local exchange carrier, or a particular country. URIs with local phone numbers should only appear in environments where all local entities can successfully set up the call by passing the number to the dialling software. Digits needed for accessing an outside line, for example, are not included in local numbers. Local numbers SHOULD NOT be used unless there is no way to represent the number as a global number.

Local numbers SHOULD NOT be used for several reasons. Local numbers require that the originator and recipient are configured appropriately so that they can insert and recognize the correct context descriptors. Since there is no algorithm to pick the same descriptor independently, labelling numbers with their context increases the chances of misconfiguration so that valid identifiers are rejected by mistake. The algorithm to select descriptors was chosen so that accidental collisions would be rare, but they cannot be ruled out.</p

If you work at a company that does work with organizations and staff members outside of the context of your area code (ie. internationally) be sure to standardize your directory on global-number syntax.

–Bob.

References:

• [E.123] ITU-T Recommendation E.123: Telephone Network and ISDN
  Operation, Numbering, Routing and Mobile Service: Notation
  for National and International Telephone Numbers. 1993.
  http://www.itu.int/rec/recommendation.asp?type=items&lang=e&parent=T-REC-E.123-200102-I

   

• A summary of [E.123] is available:
  http://groups-beta.google.com/group/comp.std.internat/msg/24fc32228689a620?dmode=source

   

• [E.164] ITU-T Recommendation E.164/I.331 (05/97): The International
  Public Telecommunication Numbering Plan. 1997.
  http://www.itu.int/rec/recommendation.asp?type=items&lang=e&parent=T-REC-E.164-200502-I

   

• A summary of [E.164] is available:
  http://en.wikipedia.org/wiki/E.164

   

• International Telecommunications Union -
  Telecommunications Standardization Sector (ITU-T)
  Phillips Business Information Inc.
  1201 Seven Locks Road, Suite 300
  Potomac, MD 20854

  or call: +1-800-666-4266

   

• See also: INTERNATIONAL DIALING CODES
  http://countrycode.org/

   

• RFC3191: Minimal GSTN address format in Internet Mail
  http://www.rfc-editor.org/rfc/rfc3191.txt

   

• RFC3192: Minimal FAX address format in Internet Mail
  http://www.rfc-editor.org/rfc/rfc3192.txt

   

• RFC2846: GSTN Address Element Extensions in E-mail Services
  http://www.rfc-editor.org/rfc/rfc2846.txt

   

• RFC3601: Text String Notation for Dial Sequences and Global Switched Telephone Network (GSTN) / E.164 Addresses
  http://www.rfc-editor.org/rfc/rfc3601.txt

Image: Telephone Dial by Leo Reynolds, used under Creative Commons v2.0 BY-NC-SA.

There appears to be some contention whether valid HTML makes a difference to search engines or not. Some say it doesn’t; or that it depends on the search engine; others have evidence it matters a lot.

Even if you’re not coding by hand, I urge you to have a look at HTML Dog, a set of tutorials on creating valid HTML. When things don’t work as expected you can turn here for examples in XHTML.

http://htmldog.com/

If you’re going to be using an editor for your Web pages, pick an editor that creates proper HTML code. Abandon FrontPage. I suggest using KompoZer, which is based on the same rendering engine as Firefox (Gecko).

http://www.kompozer.net/

You should also be checking your pages in Opera, which is a browser that is even better for standards-compliance than FireFox. The Chief Technology Officer for Opera is the same guy that wrote the Cascading Style Sheets specification, so it has a good pedigree.

http://opera.com

If you’re using Firefox then be sure to check your pages with the HTML Validator addon:

http://users.skynet.be/mgueury/mozilla/

And when you think your site is done, check each page with the full-strength validator:

http://validator.w3.org/

http://jigsaw.w3.org/css-validator/

<heavy sigh… />

–Bob.