Plain Old Telephone Service (POTS) refers to the standard telephone service that most homes use. POTS has been available for more than 100 years from analogue telephones prior to the introduction of electronic telephone exchanges into the public switched telephone network (PSTN).
In contrast, telephone services based on high-speed, digital communications lines, such as ISDN, DSL and FDDI, are not POTS. The main distinctions between POTS and non-POTS services are speed and bandwidth. POTS is generally restricted to about 52 Kbps (52,000 bits per second). However, some new digital line communications such as Asymmetric Digital Subscriber Line (ADSL) and Integrated Services Digital Network (ISDN) connections provide some part of their channels for "plain old telephone service" while providing most of their bandwidth for digital data transmission.
Specifically, POTS services include:
- bi-directional, or duplex, voice path with limited frequency range of 300-3400Hz
- dial tone and ringing signals
- subscriber dialing
- operator services, such as directory assistance and long distance and conference calling assistance
With the Intelligent Network (IN) introduced, more services are offered on PSTN including POTS lines such as:
- voice mail
- caller ID
- call waiting
- reminder calls
- (three-way) conference calling
- Enhanced 911
The new services were made possible by the introduction of the support network for the ISDN as well as raised consumer expectations from services offered on mobile telephones.