Essential Guide to Telecommunications, The, Third Edition

Analog and Digital

The public telephone network was originally designed for voice telephone calls. When the telephone was invented in 1876, it was used to transmit speech. Because speech is analog, calls were transmitted in an analog form until the late 1960s. While most of the public telephone and cellular networks are digital, there are still many analog services in use, and portions of the telephone network are analog. The majority of telephones that plug into home telephone jacks are analog instruments. Most broadcast TV signals and telephone lines from homes to the nearest telephone company equipment are analog. These analog phone lines are referred to as plain old telephone service (POTS).

As more people use their computers to communicate ...