Plain old telephone service (POTS) is the traditional analog phone line: a pair of copper wires running from the phone company’s central office to a building, carrying voice as an analog signal and connecting to the public telephone network. The line itself was powered from the central office, so a basic phone kept working when the building lost power. People often call it a “copper landline”, though that label is imprecise: copper describes the wire, and not every landline is POTS. POTS lines still serve many businesses for fire alarm panels, elevator emergency phones, gate and door entry, fax machines, card terminals and modems, even where staff phones moved to VoIP long ago.
At a glance
- A POTS line is an analog voice circuit over copper from the local phone company to the premises.
- Traditionally the carrier powered the line, which is why it worked during building power outages.
- Many carriers are retiring copper or no longer selling new analog lines, and prices for remaining lines have risen in many areas.
- Life-safety and building devices are often the last things still on POTS, and they need approved replacements.
- Lines from cable or VoIP providers can look the same at the jack but are not POTS.
What problem it solves
POTS gave buildings a simple, standardized way to reach the phone network. A compliant phone, fax machine, modem or alarm dialer could generally plug into the jack and work, with no configuration, network equipment or local power. That simplicity is why so many building systems were designed around a phone line, and why codes and monitoring contracts long assumed one.
For buyers today, POTS is less a solution than a legacy dependency. The question is usually which devices still rely on copper lines, what those lines cost, how long the carrier will keep providing them, and what should replace them.
How it works
The loop. A copper pair, often called the local loop, runs from the carrier’s central office (or a remote terminal) to the building’s demarcation point. The central office supplies dial tone, ringing voltage and the power to run the line.
Signaling. Phones signal the network with tones (DTMF) or, on much older equipment, pulses. Devices such as fax machines and alarm panels send their data as audio tones over the same analog path.
Connection to the network. At the central office, the line connects to a switch that is part of the public switched telephone network (PSTN). Calls to other numbers travel across the network, which is now largely digital and increasingly IP-based behind the scenes.
Who provides it. POTS is usually provided by the incumbent local phone company, in the US often a regional Bell operating company (RBOC) or other incumbent. Competitive local exchange carriers (CLECs) have resold or provided analog lines in some markets, though availability has narrowed over time.
Related services. The same copper can carry DSL internet alongside voice. Larger phone systems historically used digital trunks such as PRI rather than many individual POTS lines.
Emergency calls. On a POTS line, the 911 location comes from the address the carrier has on file for the line. Moving to another service means making sure location data for E911 stays correct.
When it matters for buyers
- When a carrier sends a price increase or discontinuance notice for analog lines. In the US, notice and approval requirements vary by service and state.
- When auditing telecom bills, since forgotten POTS lines at closed sites or for removed equipment are a common source of waste.
- When a copper line fails and repair takes days, especially on a fire alarm or elevator line.
- During building renovations, alarm upgrades or inspections, which are natural points to change the communication path.
- When acquiring sites, because analog lines are often undocumented.
Questions to ask vendors
- Which of our lines are true copper POTS, and which have already been moved to another platform?
- What are the planned price changes or retirement dates for analog service at each of our locations?
- What device is behind each line, and does it have life-safety or code requirements?
- What replacement options do you offer for alarms, elevator phones and fax, and are they approved for those uses in our jurisdictions?
- How much battery backup does a replacement provide, and does that meet the codes that apply to our equipment?
- How will 911 calls from replaced lines send the correct address?
- Can we keep our existing numbers, and who handles porting?
How it differs from POTS replacement
POTS is the analog copper line itself. POTS replacement is the work and the services that move devices off those lines onto cellular, broadband or IP connections while still presenting them with a working phone jack. An analog telephone adapter (ATA) is one simple way to do that; purpose-built POTS replacement services add battery backup, multiple network paths and testing for alarm and fax signals.
For help planning the move off copper lines, see our POTS replacement solution page.