Polite protocols [Instrumentation notes]

In engineering, as in life, it pays to be polite. When polite folk engage in conversation, one does not interrupt the other. If two people do happen to start talking at the same time, one of them stops and listens to the other person until that person finishes speaking. Polite people constantly make \´measurements\´ of what is happing around them, and they only talk if they find that no one else is. Many protocols rely on & actually require that - their users be polite. The protocols require that if one instrument would like to transmit, to "talk," while another is transmitting, the instrument that is not yet transmitting must wait for its turn to transmit. We consider two examples of such protocols. First, we consider a piece of the inter-integrated circuit (I2C) protocol, and we describe how the I2C protocol implements a "listen constantly" policy. Then, we discuss and describe a system that allows multiple polite users to share a limited amount of bandwidth - that implements a very simple "virtual cognitive radio."