 Telephones consist of a loudspeaker through which you hear the caller and a microphone to pick up your voice when you answer. In the earliest phones, these elements were separated. Now they are joined in one handset. When you pick up the phone, a switch connects you to the network. As you talk, sound waves hit a diaphragm in the microphone that converts them into electrical signals sent along the telephone wire. At the other end, these signals make a diaphragm in the loudspeaker move to create sound again. Instead of wire, mobile phones use radio to send the signals. You can find out more about mobile phones in another section. Originally, each phone call went to a central exchange where an operator manually connected you to the right number. This is now done with an electronic switch. A process called multiplexing allows thousands of conversations to be transmitted at the same time along one cable. Satellites and submarine cables transmit long-distance phone calls and those between continents. Special phones that link directly to satellites are valuable in remote areas or after a natural disaster when the normal infrastructure has been damaged. Nowadays, phone calls are also made online via voice-over internet protocol technologies or internet telephony. ITU's global plan gives each phone its own unique number, while its technical standards ensure, for example, the quality of the sound you hear. In whatever way you make a call, you can connect seamlessly to another telephone in the world thanks to ITU.