What Is Bandwidth

photo of John Michael Pierobon By: John Michael Pierobon

What is bandwidth? I get asked that question a lot.

The rate at which data flows is the short answer.

It is a measurement of throughput. Many confuse it with speed. The speed of data is, in theory, equal to the speed of light. Let me use two analogies to further explain the difference between speed and throughput.

Your car can certainly go faster than the legal speed limit. However, when you get on I-95 on a Friday afternoon you rarely get to go as fast as the speed limit. Bandwidth in this instance is not measured in miles per hour (MPH), but should be measured in cars per minute or cars per hour. For this reason the bandwidth of Calle Ocho is much less than I-95, not because of the speed limit, but because Calle Ocho has fewer lanes than I-95.

Suppose you had to fill a bucket full of water and you had two water hoses. The bigger hose will fill the bucket faster, because it has a larger diameter, and therefore more water can flow out of it. Hence the bigger hose has a bigger bandwidth. The speed of the water coming out of the hose is a function of the water pressure and gravity, not how big the hose is. We measure the speed of water in feet per second or meters per second, but we measure bandwidth in gallons per second or cubic feet per minute.

So we measure Internet traffic, not in miles per second, but in bits per second. Bits are like drops, and kilobits are like gallons. Because the Internet is fast, we use terms like kilobits (Kb) and megabits (Mb), or kilobits per second (Kbps) and megabits per second (Mbps).

When we download an image on the Internet we are not interested in how fast one bit of information is downloaded, but we are interested in how long it takes to download all the bits that make up the picture. If the size of the image is 33.6 Kb and the modem connect speed is 33.6 Kbps, then, in theory, the image will download in one second.

In reality, it might take longer to download. Data has to flow through many "pipes" along the Internet to reach you. The rate of data transfer is constrained by the narrowest pipe, or by the most congested pipe. The most congested pipe could be your ISP or the web server that you are downloading the image from. In most, but not all cases, the narrowest pipe is your modem.

Upgrading your modem from 14.4 Kbps, 28.8 Kbps or 33.6 Kbps to 56 Kbps may solve most of your bandwidth issues. These new V.90 compliant modems transmit at 56 Kbps and have recently come down in price.

John Michael Pierobon is an Internet consultant based in Fort Lauderdale.
John Michael may be reached by sending electronic mail to pierobon@pierobon.org

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