VoIP primer: How it works - and what the jargon means

IP telephony is nothing short of a revolution. It works in a fundamentally different way to how telephone networks have carried our voice communications over the past 100 years. Traditionally voice is sent as a continuous stream over an open circuit from caller to caller, in what is called 'circuit switching'. The longer the circuit, the higher the tariff. The longer the call, the greater the calling costs. Despite long silences, the call is rated for every second the circuit is open. Even the migration from analogue to digital circuits did little to change this model.

But of course, IP has changed that. Just as a web page can be broken up into 'packets', audio can be sampled with a digital signal processor (DSP), 'packetised' and sent out over an IP-based network as another data stream. The IP network may be a local area network, a company wide area network, a telco's core network or even the public internet. The packets that make up the audio stream may take different routes from node to node over the network in question but and are put back into order at the termination point to make up the audio that we recognise as conversation.