ABSTRACT

Recently, a variety of voice-oriented services, where voice is essentially coded into streams of IP packets, have been offered. The technologies used to deploy these services over communication networks are often referred to as voice over IP (or VoIP). A typical VoIP system is depicted in Figure 14.1 and works as follows: At the sender side, the voice sound is first sampled using a microphone. Then, the sampled

traffic is translated into a digital representation by an analog-to-digital converter (ADC) to obtain a bit stream. The stream is packed into IP packets and sent over an IP network. At the receiver side the samples are first removed from the IP packets. Then, they are put in a playback buffer. This buffer is needed to compensate for the variation of the jitter generated between packets over the network. Finally, a digital-to-analog converter (DAC) converts the bit stream back into an analogue signal. To provide a two-way communication, VoIP replicates the system depicted in Figure 14.1 reversely between the receiver and the sender.