Helsinki An example: 00 or + 567835 International Country code Trunk- (area-) prefix Subscriber number National number (max. 10 digits) International number (max. 12 digits) 15 digits, max Figure 2.8 The structure of the telephone number hierarchy. Introduction to Telecommunications Network Engineering Germany, 44 for the United Kingdom, 52 for Mexico, 358 for Finland, and 1809 for Jamaica. 2.5.3 Trunk Code, Trunk Prefix, or Area Code The trunk code defines the area inside the country where the call is to be routed. The first digit is a long-distance call identification and other numbers identify the area. The first digit is not needed in the case of an international call because that type of call is always routed via the long-distance level of the destination network. In the case of cellular service, the trunk code is used to identify the home network of the subscriber instead of the location. With the help of this network code, a call is routed to the home network, which then determines the location of the subscriber and routes the call to the destination. The trunk code and the subscriber number together create a unique identification for a subscriber at the national level. This is called a national number and its maximum length is 10 digits. Trunk codes start with a 0 in Europe, but the 0 is not used in calls com- ing from abroad. In countries where multiple operators provide long-distance telephone service, the subscriber may select an operator by dialing an operator prefix in front of the trunk code. In Finland, two examples of the long- distance operator numbers are 109 for Finnet and 1041 for Song Networks. 2.5.4 Subscriber Number The subscriber number in a fixed telephone network is a unique identifica- tion of the subscriber inside a geographical area. To connect to a certain sub- scriber, the same number is dialed anywhere in the area. Because of the numbering hierarchy, the subscriber part of the telephone number of one subscriber may be the same as that of another subscriber in another area. If provi