IP-telephony previously called as VoIP or Voice over Internet Protocol) – a special protocol designed to transmit voice over the Internet or other networks with a similar organization.

Basically, the term IP-telephony often refers to the specific execution of the protocol or service providers, and not the protocol itself. Nowadays, many of the Internet Service Providers (ISP’s) offer a standard set of IP telephony services along with the Internet Access, Hosting, etc…

The very first experiment with the network voice protocol was done in ARPANET in Year 1973. However, before the arrival of high speed communication channels, the IP telephony was not able to establish its presence widely. In order to make an IP phone call, it is required to have a computer system connected with the network, a microphone with headphones and a special software that could transfer the data over the network, as well as the possibility of a direct connection for IP-based network. The subscriber receiving the call also needs to have the same set of hardware and software, if expecting a call from outside.

Over time, there were some IP-phones available, almost no distinct in visual aspect from ordinary mobile phones and usually connected via USB to the computer system. The rule of functioning is not much diverse from the microphone and headphones, however as a rule, the USB-phones have some extra helpful features. For example, it has a built-in sound card that enables you to use even on computer systems without a sound card, and also offers chance to listen to music during the discussions.

In case, a local network is connected to the telephone, then a user can use a VoIP phone to call a mobile or landline. Along with the development of IP-telephony, the appropriate gateways connected to the Internet appeared and to the PBX which brought together a virtual telephony network with the traditional appearance. Now you are able to dial direct telephone numbers using the IP phones.

To make calls with the VoIP network, usually the traditional telephone numbers are used. Skype is one of the popular VoIP service providers in the industry. The VoIP service has various advantages over direct call from one PC to another.