Canonical Phone Numbers in Software

Encoder QR-Code in Software Canonical Phone Numbers

Canonical phone number format was developed in order to overcome the limitations of dial strings It allows for the specification of location-independent, absolute references to a particular device in a telephone network Canonical numbers are meant for use by people (on stationery, business cards, personal calendars, etc), by computers (in scheduling programs, personal information managers, databases, etc), and by telephone systems As a result, the format uses punctuation that is easy for a person to write and for a computer or telephone system to interpret Phone numbers expressed in canonical representation can be absolute because they allow the inclusion of all the information necessary to identify a particular device, regardless of the context For example, a particular device could be called from within the same telephone system, from a different telephone system, or from anywhere in the public network using the same canonical number In each case, the information necessary to establish a call from the location in question is intelligently extracted from the canonical phone number A device reference in canonical phone numbers may include: A country code, area code, and subscriber number; A sub-address and/or extension number; and A name Various portions of the canonical format are optional Incomplete canonical numbers are interpreted based on other context information For example, if a given canonical number included only a name, a telephone system with access to a directory could simply look up the name and establish a call to the corresponding person Other portions not provided are appropriately interpreted as either not being applicable to the device, or as being the same for the location of the caller See the sidebar "Canonical Phone Number Format" for the complete set of symbols used in a canonical phone number and their meanings

Canonical phone number format consists of a sequence of up to 64 characters using the following syntax: O<[DPR1, DPR2, , DPRn] +CC (AC) SN *SA xEXT>NM The bold items are symbols that are replaced by the appropriate data The other symbols are delimiters used to punctuate the string The different portions of the canonical number are as follows:

'O' The leading 'O' indicates that this number is in canonical format In practice, the 'O' is only used when communicating canonical numbers electronically People do not require this character, so it will not appear in what they see and use '<' '>' The angle brackets indicate that a name (NM) is included in the canonical number If no name is present, the angle brackets are not present If a name is present, they enclose the rest of the canonical number '[' ']' The square brackets indicate that a list of one or more dial plan rule strings (DPRs) is included in the canonical number A dial plan rule specifies how the other portions of the canonical number are to be interpreted Most often the canonical number refers to a device in the public telephone network, so no dial plan rule is required If the device is in a private network, however, the dial plan rule identifies the private network involved If multiple dial plan rules are required, they are separated by commas '+' The '+' character indicates the presence of a country code (CC) '(' ')' The parentheses enclose the area code (AC) portion of the canonical phone number The presence of a dial plan rule for a private network might indicate that this portion is to be interpreted as a subnetwork SN This represents the actual subscriber number portion of the canonical phone number It is required for use with the public network '*' The '*' character indicates the presence of a sub-address (SA) 'x' The 'x' character indicates the presence of an extension number (EXT) NM This represents the name associated with the device being referenced

Canonical Phone Number Format (Continued)

All portions of a canonical phone number are optional However, a canonical number is required to include at least a subscriber number, extension number, or name If the area code is not included and there are no dial plan rules indicating this is a private network reference, the area code will be interpreted either as not applicable, or as being the same as that of the device interpreting the number (depending on the country code) If the country code is not included and there are no dial plan rules indicating this is a private network reference, the country code will be interpreted as being the same as that of the device interpreting the number The following are two examples of complete device references in canonical phone number format for extension 789 behind the directory number 555-1234 in New York City Example: "O+1(212)555-1234 789" Example: "O<+1(212)555-1234 789>John Smith" The following are other examples of device references in canonical phone number format: Example: "O[MYNET](4) 40220" In this example, a dial plan rule ("MYNET") indicates that the device referenced is in the private network MYNET The area code ("4") is then interpreted as a particular subnetwork in MYNET and "40220" is a particular extension on that subnet Example: "O+33(1)12345678*06" In this example, the canonical phone number refers to a particular bridged device with a subaddress of "06" at the subscriber number "12345678" in Paris (country code "33" and area code "1") Example: "0555-1234" In this example the canonical phone number is only partially specified It is a valid device identifier in canonical format, but it requires the interpreter to assume the missing information In this case, if the interpreter were in New York City, the country code would be assumed as "1" and the area code would be assumed as "212"

Canonical Phone Number Format (Continued)

Example: "O 40220" This is another example of a partially specified device in canonical number format In this case the device in question is extension "40220" in the telephone system being used Example: "O<>John Smith" Canonical numbers support call by name, that is, specifying the destination as a name that is then resolved by a computer or by the telephone system

At the moment, canonical representation is used primarily by computers, which translate them into appropriate dial strings for telephone systems This will change as telephone systems become more intelligent