C-12 2 0 0 0 - A 2 - G B 2 2 - 0 0The problem with this accumulation approach, however, is that it is hard forthe gateway to predict how many numbers it needs to accumulate beforetransmission. For example, using the phone on our desk, we can dial thefollowing numbers:------------------------------------------------------| 0 | Local operator || 00 | Long distance operator || xxxx | Local extension number || 8xxxxxxx | Local number || #xxxxxxx | Shortcut to local number at|| | other corporate sites || *xx | Star services || 91xxxxxxxxxx | Long distance number || 9011 + up to 15 digits| International number |------------------------------------------------------The solution to this problem is to have the Call Agent load the gateway with adigit map that may correspond to the dial plan. This digit map is expressedusing a syntax derived from the Unix system command, egrep. For example,the dial plan described above results in the following digit map:(0T|00T|[1-7]xxx|8xxxxxxx|#xxxxxxx|*xx|91xxxxxxxxxx|9011x.T)The formal syntax of the digit map is described by the DigitMap rule in theformal syntax description of the protocol − support for basic digit map lettersis REQUIRED while support for extension digit map letters is OPTIONAL. Agateway receiving a digit map with an extension digit map letter notsupported SHOULD return error code 537 (unknown digit map extension).A digit map, according to this syntax, is defined either by a (case insensitive)"string" or by a list of strings. Each string in the list is an alternativenumbering scheme, specified either as a set of digits or timers, or as anexpression over which the gateway will attempt to find a shortest possiblematch. The following constructs can be used in each numbering scheme:* Digit: A digit from "0" to "9".* Timer: The symbol "T" matching a timer expiry.* DTMF: A digit, a timer, or one of the symbols "A","B", "C", "D", "#", or "*". Extensions may be defined.* Wildcard: The symbol "x" which matches any digit ("0"to "9").* Range: One or more DTMF symbols enclosed betweensquare brackets ("[" and "]").* Subrange: Two digits separated by hyphen ("-") whichmatches any digit between and including the two. Thesubrange construct can only be used inside a rangeconstruct, i.e., between "[" and "]".* Position: A period (".") which matches an arbitrarynumber, including zero, of occurrences of the precedingconstruct.A gateway that detects events to be matched against a digit map MUSTdo the following:
