Using an ordinary phone for most people is a common daily occurrence as is listening to your favorite CD containing the digitally recorded music. It is only a small extensionto these technologies in having your voice transmitted in data packets. The transmission of voice in the phone network was done originally using an analog signal but this has been replaced in much ofthe world by digital networks. Although many of our phones are still analog, the network that carries that voice has become digital.
In todays phone networks, the analog voice going into ouranalog phones is digitized as it enters the phone network. This digitization process, shown in Figure 1 below, records a sample of the loudness (voltage) of the signal at fixed intervals of time. Thesedigital voice samples travel through the network one byte at a time.
Figure 1. Digital Sampling of an analog voice signal
At the destination phone line, the byte is put into a device that takesthe voltage number and produces that voltage for the destination phone. Since the output signal is the same as the input signal, we can understand what was originally spoken.
The evolution of thattechnology is to take numbers that represent the voltage and group them together in a data packet similar to the way computers send and receive information to the Internet. Voice over IP is thetechnology of taking units of sampled speech data .
So at its most basic level, the concept of VoIP is straightforward. The complexity of VoIP comes in the many ways to represent the data, setting upthe connection between the initiator of the call and the receiver of the call, and the types of networks that carry the call.
Using data packets to carry voice is not just done using IP packets.Although it won't be discussed, there is also voice over Frame Relay (VoFR) and Voice over ATM (VoATM) technologies. Many of the issues VoIP being discussed also apply to the other packetized voice...