How VoIP is used, its background and history

Most people are aware of VoIP through the Skype consumer telephone service which has gained large-scale public recognition recently, particularly since its purchase by Ebay. However, VoIP has not suddenly appeared in the last few years as an opportunity afforded by the World Wide Web. Skype is only one particular implementation of VoIP and its related technologies and it is important to understand that VoIP has an important technological history, intertwined with the telecommunications industry in general, in order to appreciate the complexities of VoIP technologies and applications.

The idea of voice over IP has been discussed since the 1970s but it was the mid-1990s before commercial products became available with the introduction, in 1995, by Israeli company Vocaltec, of the first commercial system (Varshney et al., 2002). These early VoIP systems were designed to connect one PC to another and required each PC to have a sound card, speakers, microphone, modem and VoIP software. The software encoded and compressed the voice signal, converting it into IP packets that could be transmitted over the Internet. With this approach, both users used headsets, plugged into their PCs. The calls could only be made between PCs and could not connect to the PSTN network.

In parallel, from the 1970s onwards, traditional telecommunications carrier companies were developing new systems that introduced IP-enabling software for traditional telephony equipment. Human speech is an analogue wave signal and historically, voice telephone calls had been made over networks using analogue circuits which provided a temporary end-to-end connection, through the network, for each call (Sherburne and Fitzgerald, 2004). This is known as circuit switched, and builds on the original phone network of local telephone exchanges, in which wires between households were literally connected together for the duration of the call by a telephone operator. The companies that provided these services were often public agencies, usually part of a country’s post office service, and such networks became known as Post Office Telephone Systems (POTS), sometimes also referred to (post privatization) as Plain Old Telephone Systems. The Public Switched Telephone Network was the name given to the overall network created by telephone companies.

Between the 1950s and the 1990s these analogue systems were replaced by digital networks and telephone exchanges which made use of high-speed leased lines (known as T1 lines) and modern digital computer technology in the telephone exchanges, and digital signaling protocols such as ISDN between exchanges. However, these newer systems still relied on the circuit switch concept for end-to-end connection so for the consumer, things remained analogue since, by and large, the connection between the local exchange and the household remained a simple copper wire.

In the 1990s, with the Internet and Web boom, telephone equipment manufacturers and telecoms companies also began to make increasing use of the idea of transmitting digital information between exchanges through IP-based packets. This was in part driven by the lower costs associated with transmitting voice calls in this manner, as bandwidth use is more efficient. From the mid-1990s onwards, telephone equipment manufacturers added IP capabilities to their existing PBX telephony switches and, more recently, software has been developed to enable users to plug a VoIP adaptor into their traditional telephone. In this way, VoIP calls can start and end on the PSTN, but are then routed, via a software gateway, over the Internet.

This history means that VoIP is operating in a heterogeneous environment that extends way beyond the Internet. Voice calls need to have the potential to be carried over a variety of different networks including local networks, PBXs, PSTN and the Internet. Advances in VoIP technology mean PC telephony software is available from many software developers. Gateway servers with voice-processing cards are also available, to act as an interface between the Internet and the PSTN, enabling users to make calls either from their PCs, or from an IP phone, into the traditional telephone networks. Calls can also be made using IP handsets, which look similar to traditional phones, but which are plugged into an IP-based network rather than into the traditional telephony network, and have more features and capabilities than traditional telephones. The result is that there are now a number of ways in which VoIP can be implemented:

· PC to PC. Both the caller and recipient use headsets plugged into their PC.

· PC to PSTN. Only the caller uses a headset. The recipient receives the call in the

traditional way.

· PSTN to PSTN. The caller uses an IP adaptor on their traditional telephone and

The call is received on a traditional phone. But the call travels over an IP network.

· IP phone to PSTN. The caller uses an IP phone, and the call transfers from the

IP network to the telephone network via a gateway.

· IP phone to IP phone. The call travels over an end-to-end IP network.

It should be noted that there is confusion amongst communications professionals and industry commentators as to the use of terms like “VoIP”, “Internet Telephony” and “IP Telephony'. In this report we shall use the term VoIP to refer to the set of technologies that allow voice to be transported over an IP infrastructure (in effect, an IP-enabled PSTN) and the term IP telephony (IPT) to refer to VoIP technologies that also incorporate and build on the more advanced functionality provided by the old PBX systems.