VoIP, or Voice over IP, stands for voice over internet protocol. It is a communication protocol (set of rules and methods) for transmission of phone calls over the internet and other networks that follow the same rules. Voice over IP is therefore mainly a telephony technology that handles voice calls, fax transmissions and similar activities. In today’s world, voice over IP is thought to offer advantages in cost and feature set over traditional analog telephony.

Voice over IP phones are the internet-based products that individuals use to make and receive voice over IP calls – the equivalent of an analog telephone in the copper-wire world of the Public Switched Telephone network (PSTN). Voice over IP phones typically cannot make calls on the PSTN, but analog phones can often be fitted with an adapter (ATA) that allows them to function like Voice over IP phones.

Voice over IP phone calls are broken up into small pieces called packets. These packets are then packaged and encoded in a way that allows them to be sent over the internet to the correct destination, where they are unpackaged and put back together into a recognizable voice stream. Sometimes there are voice over IP phones at both ends of the conversation, but at other times, only one end has a voice over IP phone and in some cases, neither phone is a voice over IP phone. When a voice over IP transmission has a standard analog phone at one or both ends, gateways, usually provided by the voice over IP provider, translate between IP and PSTN.