A dial plan establishes the permitted sequences of digits dialed on subscriber or station lines with subscriber premises equipment, such as [[telephone|0896-7587-7776]0tp 129152] and private branch exchange (PBX) systems. Dialing plans in the public switch telephone network (PSTN) have traditionally been more commonly referred to as dialing procedures. The dialing plan of a private telephone system or a customer premise equipment, such as an analog telephone adapter (ATA) or an IP phone, is sometimes also called dial plan. The digit sequences (numbers) permissible in a dialing plan may be as short as a single digit, e.g. for reaching an operator, or as long as a complete international telephone number, including trunk prefixes and international prefixes.
Public switched telephone network (USA)
- 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.
Private telephone systems
PBX equipment, carrier switching systems, or end-user telephones may specify a variable-length dial plan or a fixed-length dial plan. In private branch exchanges in the U.S. a dialing plan may specify the addresses for the following destinations:
- Internal extension numbers of two, three, or four digits.
Analog telephone adapters, IP phones, and many other VoIP media gateways have configuration options that establish the digit sequences that can be dialed with the equipment. The dial plan of these devices is established by a digit map. The following syntax may be used for such dial plan, as adapted from RFC 2705, the specification for the Media Gateway Control Protocol.
To specify a
Enter the following
|Digit||Identifies a specific digit (do not use #)|
|Range||Identifies any digit dialed that is included in the range|
|Range||Specifies a range as a comma separated list|
|Wild card||x matches any single digit that is dialed|
|Wild card||. matches an arbitrary number of digits|
|Timer||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:
For calls to