telephony (IPT) is the transport of telephone calls over the Internet. IPT could
use traditional telephony devices, multimedia PCs or dedicated terminals to take
part in the calls. The calls could entirely or partially be transmitted over the
Phone, fax and video calls (IP telephony) can now be placed over the Internet (or any IP network) using market available client software or hardware. In most instances, users will only need to make a one-time purchase of client software or hardware to begin placing unlimited long distance calls for the cost of an Internet connection. The quality of the calls will not match that of calls placed over the traditional phone network. However with additional hardware and software purchases, higher quality communications can be achieved.
Briefly, an Internet telephony application compresses and digitizes your analog voice signals and sends them as individual packets across an IP network (a digital network) to the recipient Internet telephony application. The recipient application then decompresses the voice transmissions as a result you have Internet voice communications.
Generally, you will need at least a 75 MHz system, with a sound card, microphone, speakers, a connection to the Internet and the software or hardware application that will enable you to place and receive calls over the Internet. Most of the Internet telephony applications will only allow you to communicate with other users of the same application, so both you and your call's recipient must be using the same Internet telephone application.