What is a Plain Old Telephone Service (POTS)?

Plain old telephone service, originally Post Office Telephone Service/System (POTS) is the voice-grade telephone service that remains as the basic form of residential and small business service connections to the telephone network in many parts of the world.

The name is a reflection of the telephone service still available after the advent of more advanced forms of telephony such as ISDN, mobile phones and VoIP. POTS has been available almost since the introduction of the public telephone system in the late 19th century, in a form mostly unchanged to the normal user despite the introduction of Touch-Tone dialing, electronic telephone exchanges and fiber-optic communication into the public switched telephone network (PSTN).

POTS includes bi-directional, or full duplex, voiceband path with limited frequency range of 300 to 3400 Hz. More clearly, it is a signal to carry the sound of the human voice both ways at once. Other feature include call-progress tones, such as dial tone and ringing signal; subscriber dialing; operator services, such as directory assistance, long distance calling, and conference calling assistance; and a standards-compliant analog telephone interface including BORSCHT functions.