What is VoIP?

1An introduction to VoIP

VoIP is a set of technologies that enable voice calls to be carried over the Internet (or other networks designed for data), rather than the traditional telephone landline system — the Public Switched Telephone Network, or PSTN.

The term VoIP was coined by the VoIP Forum which was set up in May 1996 as an industry group concerned with promoting and developing product interoperability and a high quality of service for Internet telephony products. Initially, one of the main drivers in developing VoIP was the potential to cut the cost of telephone calls. Traditional voice calls, running over the PSTN, are made using circuit switching, where a dedicated circuit or channel is set up between two points before the users talk to one another — just like old-fashioned operators, plugging in the wires to connect two callers. The advantage of this is that once the circuit is set up, the call quality is very good, because it is running over a dedicated line. But this type of switching is expensive because the network needs a great deal of (mostly under-used) capacity.

The development of VoIP represents a major change in telecommunications. VoIP uses IP protocols, originally designed for the Internet, to break voice calls up into digital ‘packets’. In order for a call to take place the separate packets travel over an IP network and are reassembled at the far end. The breakthrough was in being able to transmit voice calls, which are much more sensitive to any time delays or problems on the network, in the same way as data.

Whereas calls over the PSTN are metered, so the user pays for the amount of time taken by their call, Internet usage is not metered. The user pays a set fee for their Internet service and their VoIP service and can then use the Internet to get free phone calls to other users on the same VoIP service, or pay a small fee to call users on other VoIP services or on the PSTN.

Packetized voice also enables much more efficient use of the network because bandwidth is only used when something is actually being transmitted. Also, the network can handle connections from many applications and many users at the same time, unlike the dedicated circuit-switch approach. This greater efficiency is one of the main reasons that all major carriers, such as BT with its 21CN (21^st Century Network) project, are changing their own networks so that they are IP-enabled.