exchange to digits identify complete subscribers' numbers for distant subscribers (in- stead of only area codes) and to access a complete national database Director area to determine the routing for every such call (Webster, 1989). Non-director 29.7.2 International numbering The introduction of international subscriber dialling made it necess- ary for every subscriber's station in the world to have a unique number. In the CCITT world numbering plan each subscriber's digits. The total number of dialled digits, excluding the trunk prefix, number consists of a country code followed by the subscriber's thus varies between seven and nine. This complies with the CCITT national number (CCITT, 1989a). recommendation that national numbers (excluding prefix digits) For numbering purposes, the world is divided into zones, each shall not exceed 11 digits minus the country code (for the UK, the country code is 44 and 11-2=9). The long-term objective is to have a national number of fixed length with 6-digit or 7-digit local Table 29.2 World numbering zones numbers (McLeod, 1990). A national numbering scheme must make a generous allowance for growth in the number of subscribers for up to 50 years ahead. However, growth is not uniform and the numbering schemes in North America (including Hawaii and Caribbean some areas become exhausted before the others. For example, the islands, except Cuba) London area, which previously had a single numbering code (01) Africa has had to be split into two (Banerjee,1989), 071 for inner London 3 & 4 and 081 for outer London. Similar changes have been made in a Europe number of American cities. In France, the entire country has been South America and Cuba divided into two numbering zones: L'Isle de France covering the South Pacific (Australasia) region around Paris and La Province covering the rest of France. The capacity of national numbering schemes is reduced by the need to avoid use of the trunk prefix as the initial digit of any North Pacific (Eastern Asia) local-exchange code to avoid ambig