A dial plan is a set of rules for determining whether a complete set of numbers has been entered for the IP address of SIP server or not.  

The formal syntax of the dial plan is described by the following notations:  

 

 

• Digit ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"  
  
• Timer ::= "T" | "t"  
  
• Letter ::= Digit | Timer | "#" | "*" | "A" | "a" | "B" | "b" | "C" | "c"| "D" | "d"  
  
• Range ::= "X" | "x" -- matches any digit  
  
• Range ::= "Z" | "z" -- matches any digit, "#", "*"  
  
• | "[" Letters "]" -- matches any of the specified letters  
  
• Letters::= Subrange | Subrange Letters  
  
• Subrange::= Letter -- matches the specified letter  
  
• | Digit "-" Digit -- matches any digit between first and last  
  
• Position::= Letter | Range  
  
• StringElement::= Position -- matches any occurrence of the position  
  
• | Position "." -- matches an arbitrary number of occurrences including 0  
  
• String ::= StringElement | StringElement String  
  
• StringList::= String | String "|" StringList  
  
• DialPlan::= String | "(" StringList ")"
 

A dial plan, according to this syntax, is defined by either a (case insensitive) string or by a list of strings. Regardless of the above syntax, a timer is only applicable if it appears in the last position in a string (for example "12T3" is invalid). Each string is an alternate numbering scheme.  

 

The unit will process the dial plan by comparing the current dial string against the dial plan. If the result is underqualified (partial match for at least one entry) then it will do nothing further. If the result matches or over-qualified (no other digits could possibly produce a match), then send the string to the server and clear the dial string. The Timer T is activated to find a match in strings. The interval between timer T is 4 seconds. For example, a dial plan of (xxxT|xxxxx) will find a match immediately if all 5 digits are entered. When 3 digits are entered it will find a match after a 4 second pause.  

Sample Dial Plans:  

a) Simple Dial Plan: Allows dialing of 7 digit numbers (e.g. 5551234) or an operator with a prefix of "0". The Dial plan is (0T|xxxxxxx).  

b) Non-dialed Line Dial Plan: As soon as a handset is lifted, the unit contacts the gatekeeper (it is used in systems where DTMF detection is done in-call). The Dial plan is denoted by sequence of "x." i.e. find a match against 0 (or more) digits. Note: the dot "." matches 0 or more occurances of x .  

c) Complex Dial Plan: Possible combinations are:  

 

 

• Local operator on 0  
  
• long distance operator on 00  
  
• four digit local extension number starting with 3,4 or 5  
  
• seven digit local numbers are prefixed by an 8  
  
• two digit star services (e.g. 69)  
  
• ten digit long distance prefixed by 91  
  
• international numbers starting with 9011+variable number of digits. An example of this Dial plan is:  
  
  (0T|00T|[3-5]xxx|8xxxxxxx|*xx|91xxxxxxxxxx|9011x.T)