In the simplest of terms, data broadcasting, sometimes called datacasting, is the distribution of data from a single location to multiple locations at the same time. Most data is distributed today using point to point communications methods. In point to point communications, if you want to send a one megabyte file to 500 locations, you must send it 500 times, once to each destination. The typical modem connection from one PC to another is a common example of point to point communications.
An analogy to help explain data broadcasting would be to think of how people communicate at a party or a large gathering. If you have several friends with whom you would like to speak, you might have a conversation with each of them, one at a time, before the party is over. You would each have something to say and thus have a two-way conversation. This is an example of point to point communications. If you are the host of the event and you have something to say to a large number of guests, they would listen as you broadcast your message to everyone at the same time.
This analogy illustrates certain principles about data broadcasting. As a recipient (the receiver) of a broadcast message, you can only listen to what the person talking (the transmitter) has to say. You do not have the opportunity to say something back during the middle of the broadcast if you missed a word or did not hear a part of the message. Data broadcasting is much the same way. The receiving computers can only listen to the incoming broadcast message. They are not able to respond to the sender while the broadcast message is being sent. In a pure broadcast only system, the receivers have no way to communicate with the host. It is often desirable for the host to be able to confirm that the remote sites actually received the data that was sent. These are communications methods employed in addition to the broadcast system, and are not typically considered to be part of it. Options for implementing return paths will be discussed later.
You are already familiar with the concepts of broadcasting. Each time you listen to your radio or watch TV, you are experiencing the results of a broadcast. The radio or TV are simply receivers which can listen to the incoming messages. They do not have a way to communicate with the station that sent the message. The station that broadcasts the programs does not have a way to determine if these programs are being received, or if the TV or radio receiver is even turned on. In data broadcasting, instead of just sending sound and images, any type of information can be broadcast. This includes data files, software programs, digital video or digital audio.
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