VoIP , or VoIP (Voice over IP) is a technique for communicating orally over IP-enabled networks , whether private networks or the Internet. , wired (cable / ADSL / optical) or not (satellite, wifi, GSM) . This technology is most often used to support.
How is the voice transported?
The transport of voice over IP is relatively complicated. The first step is the digitization (coding) of the acoustic signal. Then, the information is divided into frames (blocks of information) that can circulate on a computer network. Many protocols can then be used to route the information to the recipient (s).
How is the voice coded?
In a conversation, the voice produces sounds at different frequencies .
Thanks to these constant frequency changes, we perceive emotions and intonations. This multitude of frequencies would be remarkable by a sinusoidal display if one visualized his signal on an oscilloscope.
The voice causes a sinusoidal signal, which is analog . However, to pass it over a TCP / IP (Digital) network, it will be necessary to convert this signal (analog to digital) in PCM (Pulse Code Modulation) format to 64 kb / s.
Once converted, it is necessary to compress the voice (digitized) through a codec (Compressor / Decompressor) to insert it into an IP packet. This coding must offer the best possible voice quality for the lowest bit rate and compression delay possible. There are several coding techniques that are measured in a completely subjective way.
The method of broadcasting Voice over IP:
The term "VoIP" is generally used to describe " point-to-point " communications . For the broadcast of sound or videos over IP in multipoint mode , it is more about streaming for a simple broadcast, as used by web radio for example. The term multipoint is rather reserved for videoconferences.
Globex Teleccom technique can be done in unicast mode (a transmitter and a receiver), broadcast (a transmitter and all receivers without exception) or multicast (a transmitter and several receivers) on networks .
Voice over IP leads to the replacement of traditional telephones with "IP telephones" whose characteristics are:
- Replacement of telephone jacks (RJ11) with network jacks (RJ45).
- Replacement of analog or digital interfaces of telephones with the network through an IP protocol interface .
- The replacement of the traditional telephone signaling protocol by an IP voice system.
- The replacement of the handset by a new handset having the above characteristics, or by software that can be installed on a computer (with a headset and a microphone).
An IP voice infrastructure may be available for the same availability zones as traditional telephone systems:
- In a closed way ( Intranet ): by the use of a private IP central office .
- In a semi-public way ( Extranet ): by sharing an IP central office with its partners or customers (via a VPN for example = extension of the local network).
- In a public way but limited (Internet): by an opening on the Internet of the central IP.
- In a public and open way (Internet): by an opening on the Internet of the central IP and the affiliation of gateway (s) towards the PSTN network .