Plain old telephone service (POTS) is based on the Bell telephone system. It is an analog telephone service implemented over copper twisted pair wires. This system connects homes and businesses to neighborhood central offices. A central office is ultimately connected to other offices and a long distance facility. POTS is generally restricted to about 52 Kbps (52,000 bits per second). The main difference between POTS and non-POTS such as ISDN and FDDI are speed and bandwidth. Other characteristics of POTS includes bi-directional (full duplex) communications, voiceband of 300 to 3400 Hz (frequency range of human voice), signaling using call-progress tones, such as dial tone and ringing signal, subscriber dialing, and various operator services, such as directory assistance, long distance calling, and conference calling assistance.