uity. Similarly, the international prefix must not form the initial part of any area code. There is also Far East and Middle East a need to reserve codes for accessing various services. For example, Spare code in the UK the code '999' is used for emergency services, '100' is used to obtain operator assistance, '192' for directory enquiries, and given a single-digit code. Each country within a zone has the zone SO on. Thus, the digits '0', '1' and '9' are not available as initial number as the first digit of its country code. However, the European digits for local numbers. This reduces the capacity of the numbering numbering zone has been allocated two codes because of the large schemes of all local areas. The numbering capacity of local areas is number of country codes required within this zone. The codes for also reduced by the need to provide direct dialling in (DDI) to the world numbering zones are listed in Table 29.2. PABXs. This requires each extension to have a number within the Within each zone, every country has been allotted a single 2- or scheme for the area. Thus, a PABX uses a large block of numbers 3-digit code number. For example, within zone 3 (Europe) Holland instead of a single number. The advent of the integrated services has the code '31' and Albania has '355'. The 3-digit codes have been digital network (ISDN) also has an impact. It may be necessary for allocated to smaller countries, having fewer digits in their national Routing 29/15 numbering plans, to minimise the total number of digits in sub- (which are non-geographic). An international exchange will analyse scribers' international numbers. Exceptions occur where an inte- six digits to determine a route. These can therefore include digits grated numbering plan covers an entire zone; countries in these within the NDC in addition to the country code, in order to route a zones require only a single-digit code. Thus, '1' is the country code call to the appropriate network in the destination country. for all countries in the North-American n