Chapter 17. VoIP

Voice over IP (VoIP) is simply a means of carrying voice (telephone calls) over Internet Protocol (the Internet). Instead of using pairs of wires to carry the signal electrically, the sound is sampled and converted to a sequence of bytes. This is normally what is done in the telephone exchange before the data is sent over the telephone network. The key difference with VoIP is that the bytes are placed in packets, typically 20ms long, and these are sent via Internet Protocol. Unlike the telephone network, IP can cause packets to be delayed, lost or even copied. It is the job of the receiving end to cope with this and produce the audio again for the recipient to hear.

The end result is that telephone calls can be made over the Internet. This can cause confusion as this is often seen simply as free calls. Apart from costs for Internet traffic, this is indeed true where calls do not involve the traditional telephone network and you control both ends, but typically you will need to subscribe to a carrier who can route calls to and from the traditional telephone network.

The FB2500's role in this it to handle the IP packets used for VoIP. It does not get involved in converting sound to, or from, packets of data, but in passing those packets of data between VoIP devices and carriers. The protocol involves complex sequences of messages for control and authentication which the FB2500 handles.