Definition

POTS

Also known as: Plain Old Telephone Service, plain ordinary telephone service

POTS (Plain Old Telephone Service) is the traditional analog telephone service delivered over a copper pair from a carrier's wire center, providing dial tone, loop current, and in-band signaling.

How it works

The carrier's central office supplies DC loop current and dial tone over a twisted copper pair. Signaling happens in-band — off-hook is a DC loop closure, dialed digits are DTMF tones, and ringing is an AC voltage applied to the line. Because the line itself carries power from the central office, a POTS phone historically kept working during a building power failure.

Why it matters

Decades of equipment was designed around POTS behavior rather than around a data protocol. Fire alarm panels, elevator phones, fax machines, and modems all assume in-band signaling and constant loop current, which is why replacing a POTS line is not simply a matter of moving the service to IP.

Common use cases

Analog voice lines in commercial buildings
Fire and burglar alarm panel signaling
Elevator emergency telephones
Fax machines and dial-up modems

POTS is the baseline against which every replacement option is measured. Understanding what it actually provides — not just voice, but line power and in-band signaling — is what makes it clear why some equipment migrates trivially and some does not.

What replacement has to reproduce

Reading POTS as a specification rather than a service makes migration planning concrete, because each property it provided becomes something a replacement either supplies or does not.

Line power from the central office, which is why analog phones worked during a blackout. Most replacement paths supply nothing equivalent, so backup power moves on-premises and becomes a sizing decision.

Loop current, dial tone and ring voltage within defined ranges — the electrical behavior endpoints were designed against, and the reason a device can work on one replacement and fail on another.

Disconnect supervision, so a device learns the far end hung up and releases the line.

Predictable timing for in-band signaling, which is what fax negotiation and older alarm formats depend on.

A dedicated circuit with its own number, which is why per-line billing was the norm and why port count drives replacement sizing.

Evaluate any replacement against the list, endpoint by endpoint. Voice quality is the property most often demonstrated and rarely the one that fails.

Common misconceptions

“POTS just means any landline phone service.”

A landline delivered over fiber or a VoIP adapter is not POTS. POTS specifically means analog service over copper with in-band signaling and central-office line power.
“POTS lines are free from outages because they are powered by the phone company.”

Central-office line power made POTS resilient historically, but as copper plant ages and carriers stop maintaining it, POTS reliability has been declining rather than improving.

Frequently asked questions

What does POTS stand for?

POTS stands for Plain Old Telephone Service — the analog voice service delivered over a copper telephone pair.

Is POTS being discontinued?

Yes. Carriers are retiring copper networks and the POTS service that runs on them. The FCC's copper retirement rules set the notice process, and AT&T has stated it is working toward nationwide copper retirement.

What replaces a POTS line?

For equipment that must keep its analog interface, a POTS replacement appliance presents RJ-11 FXS ports locally and carries the traffic over managed cellular or IP. For ordinary desk phones, VoIP is usually the simpler path.