Bandwidth

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Bandwidth is the amount of data that may be transmitted per second over a network connection. Your typical dialup connection has a maximum rated bandwidth of 56 kilobits per second, meaning you can't ever expect to see anything download faster than 7 kilobytes per second. Broadband internet connections vastly improve upon that figure, so there's really no substitute. If you live out in the middle of nowhere, move closer to a city.

Hosting companies, however, quite often confuse bandwidth with data transfer, and say that "Ultra Super Hosting Plan" has 4 TB of bandwidth per month when they really mean 4 TB of data transfer per month.

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Types of Bandwidth

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Downstream

This is what you, as a user of the internet, notice. Your downstream bandwidth is your maximum download speed. You won't ever see a download go faster than that. There are other limiting factors, including the upstream bandwidth of the server you're downloading the file from.

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Upstream

This can be hard to notice. Any data leaving your computer uses this. Most ISPs give their customers asymmetrical connections, meaning that the downstream bandwidth is much greater than the upstream bandwidth. "Data leaving your computer" includes such things as:

  • Visiting websites (When you tell your browser to load the page, it sends data out to the server the page is on, telling it to send you the page)
  • Sending an instant message
  • Sending emails
  • Uploading images to sites like ImageShack
  • Posting on message boards
  • Talking in voice chat programs
  • Running a webcam
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Rated Bandwidth

Whenever you see an ISP ad claiming super fast speeds and listing specific numbers, those numbers are the rated bandwidth for the connection. You won't always get those speeds, and in practice, especially on faster connections, hardly ever will.

Rated bandwidth also plays an important role on local networks, such as the ones created by wireless routers. Also, wireless networks have an inherent 50% overhead, meaning that whatever the speed is that your router says it will operate at, you will actually see speeds maxing out at around half of that. This is because, unlike wired networks, wireless networks cannot determine whether data actually reached its destination, so the successful receipt of every chunk of data (referred to as a "packet") must be confirmed by sending another packet.

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