Most of the subscribers on the network are telephones. The telephone contains a transmitter and receiver for converting back and forth between analog voice (sound waves) and analog (voice-frequency) electrical signals.

• 网络中的大多数用户是电话机。电话机包括一个送话器和一个受话器，用来在模拟语音(声波)和模拟(声频)电信号之间进行变换。