The sockets in the previous chapters are unicast : they provide point-to-point communication. Unicast sockets create a connection with two well-defined endpoints; there is one sender and one receiver and, although they may switch roles, at any given time it is easy to tell which is which. However, although point-to-point communications serve many, if not most needs (people have engaged in one-on-one conversations for millennia), many tasks require a different model. For example, a television station broadcasts data from one location to every point within range of its transmitter. The signal reaches every television set, whether or not it’s turned on and whether or not it’s tuned to that particular station. Indeed, the signal even reaches homes with....