 country code "46" for Sweden, area code "(0)8" (leaves out zero) for Stockholm, and sub- scriber number "xxxxx." The international prefix is actually all that the lower-level exchanges in Finland need to know. When exchanges in the A call is routed to Helsinki area The number is analyzed by To other regions and (0)9 to subscriber 13115. each exchange on the way to the international and routed further. (0)9 13115 exchange Regional Regional center routes calls to center subscriber numbers 2xxxx and 3xxxx 00 46 8 XXXXX 44098 440xx 1xxxx to the left-hand and 4xxxx to the right-hand sides of the branch. 44032 Primary Primary center center 21305 31365 44xxx 21xxx Subscriber 13115 441xx A subscriber makes a call to Stockholm, 00 for 44173 international call, 46 for Toll center 130xx Sweden, 8 for Stockholm, or local exchange and XXXXX for a certain 131xx 44114 subscriber. Figure 2.13 Telephone call routing. Introduction to Telecommunications Network Engineering switching hierarchy detect it, they route this call up toward the international exchange. The international exchange then analyzes the country code and selects an outgoing route to Sweden. Another example in Figure 2.13 illustrates routing of a long-distance call from a subscriber in another region. A subscriber in another region dialed "09 13115" for a long-distance call to Helsinki. The first digit "0" tells the exchanges that this is a long-distance call and is to be routed to the regional exchange. The regional center is connected to other regional centers and then routes this call, with the help of other regional centers, to Helsinki according to the next digit, "9." The regional center of Helsinki analyzes the next two numbers, "13," and selects the route down to the primary center where these subscribers are located. (Operator has defined in his numbering plan that the subscriber numbers 2xxxx and 1xxxxare placed on the left-hand branch from the regional center.) The primary center then checks the follow- ing numbers, "131," and notices that this is not "