IP Telephony, How Does It Work?

First a brief return to traditional telephony. The positions of traditional phones are connected directly to the public for private branch exchanges or PBXs through in business. It provides for the exchange line during the unit’s power. The transmitted signal is an analog signal.

The public switches are interconnected by specialized networks for voice transmission. The telephone number corresponds physically to a telephone line on the switch designated. To make a call, it is necessary to establish a connection, a circuit between the calling line and the line drawn through these exchanges. Fifty years ago, these switches were made with extraordinarily large complex electromechanical systems. It had huge rooms to install them. In the early 1970s, these systems have gradually been replaced by computers. The size and price of the systems decreased significantly, but the telecoms engineers have questioned the system architecture which has remained the same. Most technical advances have been made between the PBX, the interface of the subscriber line remained the same.

IP telephony is a set of telephone functions using the IP to transmit voice and manage phone functions. voice, digitized and compressed, is transmitted as packets routed in the same manner as data packets. So there is more switching circuits is the standard feature of Internet routing is used.

Netmeeting was one of the first applications to transmit voice over IP. He had a PC connected to the Internet to digitize voice and send it. The result was not famous. The sound settings were delicate and the latency (time forwarding packets) added to the time compression of voice, did not allow a natural conversation. With the advent of ADSL and computers 20 times faster, the situation has changed. Skype, released in September 2003, was the first VoIP software to make usable. The system is owned and unfortunately his phone features are limited. It does so between 2 PCs equipped with Skype. In early 2004, Skype has introduced the function and conference since July 2004, Skype offers a paid service to call or be called by landlines.

To aspire to replace fixed telephony, it takes a whole lot more advanced features. NetMeeting uses the H.323 standard developed by ITU-T, who copied the principles of traditional telephony.
A new protocol, much better suited to the Internet was developed by the IETF SIP. It is this protocol that will enable the development of telephony features. It also helps develop “SIP phones” that allow you to connect directly to the Internet by way of PC.