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Collaboration, Voice & AV · Foundational

Plain Old Telephone Service (POTS)

Basic analog voice service delivered over a copper loop with loop-start signaling, dial tone and ringing voltage.

Definition

POTS is the traditional analog telephone service provided over a two-wire twisted-pair local loop from the carrier central office. The CO supplies -48 VDC talk battery, dial tone and an AC ringing signal, and the line carries a voice band of roughly 300 to 3400 Hz. Many carriers are retiring copper POTS lines, which affects alarm panels, elevators and fax machines that depend on them.

Example

A fax machine in a branch office is still plugged into a POTS line from the local carrier.

Exam tip

When a question mentions analog phones, fax or overhead paging, think FXS ports or ATAs to connect POTS-style devices to the IP network.

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