Time-Division is Better Than Frequency-Division for Periodic Internet Broadcasting

The broadcast disk provides an effective way to transmit information from a server to many clients. Information is broadcast cyclically and clients pick the information they need out of the broadcast. An example of such a system is a wireless web service where web servers broadcast to browsing clients. We consider two ways to send items over a broadcast channel and compare them using the metric of expected waiting time. The first is frequency-division, where each item is broadcast on its own subchannel of lower bandwidth. We find the optimal allocation of bandwidth to the subchannels using this method. Then we look at time-division, where items are sent sequentially on a single full-bandwidth channel. For items of equal length, we show that for any frequency-division broadcast schedule, we can find a better time-division schedule. Thus time-division is better than frequency-division.