What You Will Learn
After reading this chapter, you should be able to
Binary 1s and 0s don't come out of our mouths when we speak. However, if our voices are to be carried across a Voice over IP (VoIP) network, that's exactly how our voices need to look.
In their natural form, our voices are analog, meaning a continuously varying waveform. VoIP networks, on the other hand, transmit our voices digitally, using binary encoding, meaning a series of 1s and 0s, as shown in Figure 2-1. Obviously some conversion has to occur. We have to have some way of converting our analog voice waves into binary. Not only do we need to convert to binary, but there also has to be a way to convert from binary back to analog. Otherwise, the person at the other end of the call would not be able to understand what we were saying.
Figure 2-1. Analog and Digital Waveforms
In this chapter, you will see how this conversion occurs, but we don't stop there. Once your voice is converted into 1s and 0s and is ready to be sent across the network, you want to make sure that you are not using too much of the network's bandwidth to transmit all of your voice calls. For example, on a wide-area network (WAN), which interconnects geographically separated offices, your company is charged a recurring monthly fee for the bandwidth (that is, the throughput capability) of that WAN link. To make the most efficient use of that link, you might want to take the binary data representing your voice and squeeze it down so that it doesn't take up as much bandwidth. After all, if you can send a voice call using less bandwidth, then you can place more voice calls across that same WAN link without paying any more money to your service provider. What a deal! Different approaches to doing that "squeezing" are covered in this chapter.
Because you might send several voice calls across the WAN at the same time, a critical design decision revolves around how much WAN bandwidth is needed for voice. Even though the required math to calculate this bandwidth can seem daunting, you won't need a math degree to successfully calculate the needed bandwidth. This chapter provides you with links to web-based calculators and shortcut methods for doing these calculations. So, let's get started by exploring how you can take the spoken voice (in analog) and convert it into a series of binary 1s and 0s.