CHAPTER 8 Asynchronous Communication If you have any experience with radio communication, whether it be with a walkie-talkie or a proper CB radio, you know how different it is from talking on a cell phone. For one, it's a half-duplex system, meaning you cannot talk while somebody else is talking. You have to patiently listen, wait for your turn and then speak up, trying to be as concise as possible to give others the possibility of joining the conversation too. A simple verbal handshake system is used to prevent conflicts and misunderstanding. This is exactly how it works in aviation. There is a precise protocol, a set of rules that dictates who should talk at any given point in time, what they should say and how. There are specific roles, such as the air traffic controllers, the pilots, the flight stations and the towers; and they all share the media in a coordinated and efficient way. This works well as an introduction to the many asynchronous serial protocols. Some are full-duplex, other are just half-duplex, some are multipoint, others are point-to-point, but they all require coordination and adherence to basic rules (standards) that make communication