What Is Bandwidth?

One of the toughest concepts for anyone to understand is the discussion of bandwidth. To the novice, it becomes even more perplexing when bantered about by telephone company personnel, engineers, and others. However, it is the basis of most of what we do in the telecommunications and telephony world. Think of bandwidth as a water pipe or a garden hose. The greater the size of the pipe, the larger volume of water that will flow through the pipe. The smaller the pipe, the smaller the flow of water. Now, in telecommunications terms, think of bandwidth as a communications pipe. The bigger the pipe, the more information that will flow through it. The smaller the pipe, the less information that will be carried through the pipe. Assume, for example, that we have a lawn and we need to water it regularly to keep it green and moist. If we have an average-sized lawn, the job can be done with the standard ^ garden hose, the type that can be bought in any hardware store. When we turn on the spigot attached to our regular water pipes, a sufficient flow of water comes out of the hose. This is a regulated flow with several control mechanisms in place: The water pipes are perhaps % in diameter, allowing a certain amount of flow through them to begin with.

The garden hose is slightly smaller, so as the flow from the larger pipe to the smaller diameter garden hose occurs, the flow is restricted, but pressure allows the flow to be constant. The spigot also can be used to turn the water on full bore, or constrained to a specific flow that is more to our liking.

Bandwidth can be compared Four kHz of bandwidth Summary of Channel Capacities to carry The Bandpass filter separates to a pipe or a hose. different forms of information. the channels. MHz is a new term here. It represents millions of frequency changes per second. You can imagine the amount of information carried in a TV signal, when sound, motion, and voice are all on the same channel. Think of how a video signal on a TV station would look if the channel was restricted to carrying only 3 kHz of information. By the time some moving picture was created on the set, the viewer would have lost interest. The frequency spectrum of a TV channel shows that a CATV channel is actually allocated 6 MHz of capacity. Yet, the amount actually used approximates 4.5 MHz. The difference is the band limitation on the channel, much the same as the voice channel. In this case, the amount of flow is in the millions of cycles per second (a big pipe is needed here). The band-limited channel uses bandpass filters so that there is a guard band between the TV channels. In other words, as you watch channel 3 on your TV set, the filters are placed on the line to prevent frequencies and information from channels 2 and 4 from overflowing onto channel 3. These guard bands are placed on every channel, thereby restricting the 6-MHz channel to only 4.5 MHz of usable information. The same concept holds true for just about all of the channel capacities used in the telecommunications industry. The available bandwidth is a function of need and cost. You get what you need, but any more will be too expensive.