Understanding Telephones

Telephones that connect to the PSTN traditionally come in two flavors: analog and digital.
Analog: The type of phone that most people have in their homes today. It connects to
the PSTN via traditional phone lines and sends an analog transmission – a waveform
that varies over time.
Digital: The type of phone that a lot of corporations use. It connects directly to a PBX
and sends formatted digital transmissions: ones and zeros.
Nowadays, specialized IP phones can connect to the PSTN as well, but we’ll discuss those in
a later section and explain how IP phone technology differs from traditional telephones.
However, all telephones have some kind of microphone and speakers. The traditional
phone has a handset that’s held to the ear and mouth during a conversation.
We have not dealt with cellular or mobile telephony technology in this chapter. You can
think of the mobile phone network as an additional extension of the PSTN – most mobile
calls are carried at least partially over the PSTN. The technology and components that the
mobile phone system is built on are beyond the scope of this book.