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Table Of Contents  The TCP/IP Guide
 9  Networking Fundamentals
      9  Network Performance Issues and Concepts

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Balancing Network Performance with Key Non-Performance Characteristics
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Understanding Performance Measurement Units
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Performance Measurements: Speed, Bandwidth, Throughput and Latency
(Page 3 of 3)

Applying Performance Measurement Terms

As with all networking terms, there are no hard and fast rules; many people are rather loose with their use of the terms above. You will even see terms such as “throughput bandwidth”, “bandwidth throughput” and other charming inventions from the department of redundancy department. J More often, you will just see a lot of mish-mashed term usage, and especially, spurious conclusions being drawn about what data streams a network can handle based on its rated speed. Making matters worse is that speed ratings are usually specified in bits per second, but throughput may be given in bits or bytes per second.

In general, “speed”, bandwidth and throughput get a lot of attention, while latency gets little. Yet latency considerations are very important for many real-time applications such as streaming audio and video and interactive gaming. In fact, they are often more important than raw bandwidth.

For example, suppose you move to a rural home and your choices for Internet access are a regular 28.8 kbps modem connection or fancy satellite Internet. The companies selling satellite connectivity call it “broadband” and advertise very high rated speeds—400 kbps or more. They make a big deal about it being “over 10 times as fast as dialup” and they certainly charge a lot for this very high-tech service. This is a slam dunk, right?

Wrong. The satellite connection has high bandwidth, but very poor (high) latency due to the time it takes for the signals to travel to and from the satellite. It is definitely much better than the modem for downloading that nice little 150 MB patch from Microsoft. However, it is much worse than the modem for playing the latest online video game with your buddy over the Internet, because of the latency, or lag, in transmissions. Every move you make in your game will be delayed for over half a second as the signal bounces around between the satellite and the earth, making online gaming nearly impossible. Thus, whether satellite Internet is worth the extra money depends entirely on what you plan to use it for.

Related Information: An important issue closely related to latency is quality of service, a general term that refers (among other things) to the ability of networks to deliver necessary bandwidth and reliable data transfer for applications that need it. See the topic devoted to this subject later in this section.


Key Concept: Where bandwidth and throughput indicate how fast data moves across a network, latency describes the nature of how it is conveyed. It is most often used to describe the delay between the time that data is requested and the time when it arrives. A networking technology with very high throughput and bad (high) latency can be worse for some applications than one with relatively low throughput but good (low) latency.



Previous Topic/Section
Balancing Network Performance with Key Non-Performance Characteristics
Previous Page
Pages in Current Topic/Section
12
3
Next Page
Understanding Performance Measurement Units
Next Topic/Section

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