Bandwidth measurement and management guide

Bandwidth is like the soul -- everyone thinks they know what you mean when you discuss it, but they are probably thinking about something entirely different. And that's because, like the soul, bandwidth does not transparently exist in any of the simple ways that we tend to believe.
Why begin this guide with bad metaphysics?

For a start, the word "bandwidth" is not even semantically sound -- it's a vague label improperly attached to a range of meanings (see bandwidth is a misnomer for more insight). Implicitly, it most typically refers to the maximum rate at which data can be transferred, either at a single interface or across an end-to-end path. But even this straightforward idea of "maximum data-transfer rate" can be endlessly qualified. Anything from packet size, to cross traffic, to corruptions can limit the effective transfer rate.

Somehow, though, bandwidth remains the central characterization for most networks. As if size matters. And it does.

For more information, read the "What is bandwidth?" definition from Whatis.com.

Understanding bandwidth

Bandwidth 101 will provide an introduction to bandwidth and reveal why people confuse bandwidth with "bit rate capacity." Learn how to measure bandwidth and why it is important to provide sufficient bandwidth for a signal.

Read bandwidth FAQs:

More on bandwidth management Learn questions you must ask your customers before deciding on bandwidth management services. Find out how to educate customers about traffic management issues and offer bandwidth management solutions and service options.

Most (if not all) QoS mechanisms effectively limit bandwidth (or more properly, data transfer capacity). They do not ever increase it, certainly. They limit how much cross-traffic certain applications see -- at the expense of other applications. And those so-called premium applications will only ever see the network path as it might have appeared without QoS and no other traffic. This is a zero-sum game wherein anything gained for one application is lost elsewhere for others. Only when increasing bandwidth is not an option, technically or economically, should you turn to QoS for help. Even then, it won't be easy or trivially reliable, and it will inevitably cost you elsewhere.

NIC cards, or more specifically the drivers provided for them, won't necessarily perform at Layer 2 specification. In fact, the phrase "your mileage may vary" should be kept firmly in mind -- as well as the fact that there are many ways to improve your mileage and most of them are simple. Find out why NIC could be killing your network performance in this expert tip.

To improve your application performance, you need to identify the "narrowest" performance bottleneck that defines the end-to-end performance and remove it. And then remove the next one. And the one after that, until finally you achieve optimal network performance.

More on bandwidth management and measurement Find a list of free network monitoring tools that will help you keep your network in shape, without spending a dime. Read an excerpt on bandwidth management from CCSP Self-Study: Cisco Secure Virtual Private Networks (CSVPN) to learn how you can configure the Concentrator to deliver the most effective bandwidth settings for your particular network. Read an excerpt from Open Source Network Administration, including information on MRTG,  which produces Web pages that display graphs of bandwidth use on network links on daily, weekly, monthly, and yearly scales.