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In order to understand the many concepts represented in the public switched telephone network (PSTN), it is helpful to review the processes that take place in the making of a single call on a traditional wired telephone. To make a call, a telephone subscriber begins by taking the telephone “off-hook”—in the process, signaling the local central office that service is requested. The central office, which has been monitoring the telephone line continuously (a process known as attending), responds with a dial tone. Upon receiving the dial tone, the customer enters the called party’s telephone number. The central office stores the ...(100 of 8665 words)