Dial plan

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A dial plan establishes the expected sequence of digits dialed on subscriber premise 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, or 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
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