TABLE OF CONTENTS Every communications process is based on agreements about certain conventions, or agreements about how messages are to be sent, and what they mean. A communications protocol must address questions like:
Medium: what is the medium by which messages are to be exchanged? People use the media of speech, writing, and pantomime to communicate directly with each other. Machine-to-machine communication can be based on electrical signals carried by a cable, light in a silica fiber, ultrasound, or radio waves.
Message format: speech can be formatted in English, Swedish, Japanese, Hindi, or any of the wonderful panoply of languages that have arisen over the millennia since humans invented the ability to harangue their spouses. Each language has a vocabulary of phonemes and words and a grammar describing how these elements are to be combined.
Medium access: in some cases, a particular medium a wire is dedicated to a particular communications process, and there is no possibility of contention, but many media are shared. The audible medium is shared when a group of people congregate to talk; some means must be arranged to allocate the medium so that individuals can be understood. In informal situations, a person usually waits until no one else is speaking and then attempts to talk; if they collide with another person with similar intent, both go silent and wait for a random time to try again. This scheme, dressed up as carrier-sense multiple access with collision...
