Dial plan

A dial plan establishes the expected sequence of digits dialed on subscriber premises equipment, such as telephones, in private branch exchange (PBX) systems, or in other telephone switches to effect access to specific telephone networks for telephone calls, and to effect or activate specific telephone system features.

In private branch exchanges in the U.S. a dial plan may specify the dialing for the following destinations:

• Internal extension numbers of two, three, or four digits.
• Local numbers of seven or ten digits, which may be preceded by a 9, if required to access an outside line.
• Long distance numbers of eleven digits, consisting of a 1, a three-digit area code, and a seven-digit number; preceded by a 9 if required.
• International numbers of any length starting with 011 and preceded by a 9 if required.

Similarly, telephony service operators may provide dialing sequences for special services, such as directory assistance and emergency services.

PBX equipment, carrier switching systems, or end-user telephones may specify a variable-length dial plan or a fixed-length dial plan.

Syntax

The following syntax used to identify a dial plan in a digit map is adapted from [RFC 2705].

Dial Plan Syntax

To specify a	Enter the following	Result
Digit	0 1 2 3 4 5 6 7 8 9 *	Identifies a specific digit (do not use #)
Range	[digit-digit]	Identifies any digit dialed that is included in the range
Range	[digit-digit, digit]	Specifies a range as a comma separated list
Wild card	x	x matches any single digit that is dialed
Wild card	.	. matches an arbitrary number of digits
Timer	T	Indicates that an additional time out period of 4 seconds should take place before automatic dialing starts

Some dial plan examples using the above syntax look as follows:

Dial Plan Syntax Examples

For calls to	Users dial	Dial plan
Internal Extension	a two digit number	xx
Local Number	9 (if required for an outside line) and then a seven digit number	9xxxxxxxT
Emergency	911	911
Local Operators	9 (if required for an outside line) then 0	90T
Long Distance	9 (if required), 1, area code and local number	91xxxxxxxxxx
International	9 (if required), 011, any number of additional digits	9011x.T

See also

• Numbering plan