Networking is largely about connecting together devices so that information can be shared between them. Since the idea is to send data from one place to another, a very important characteristic of any network is its speed: how fast can data be transmitted and received? This matter of speed turns out to be only one of several issues that determine the overall performance of a network. The issue is complex enough that I decided a section was warranted to introduce the various related topics and help you understand how to look at network performance in a balanced way. When it comes to network performance, there's a lot of hype out there!

In the computing world, performance is, in general, one of the most often discussed but least well-understood characteristics of any system or hardware device. This is true of networking as well. For example, most people know the raw throughput rating of their network hardware, and may even start to draw conclusions about its capabilities based on those numbers. Many, however, don't realize that they will never actually achieve that “rated” amount of performance in the real world.

Most of the other “subtle” issues related to performance are also typically ignored or misunderstood, such as the impact of software drivers on hardware performance, and the fact that certain applications need more than just raw bit speed—they need reliable delivery of data. But even beyond all of this, one of the most important issues related to network performance is understanding what your needs are, to make sure you don't spend too much money for performance you don't need—or worse, create a network that can't meet your requirements.

In this section, I discuss various performance issues and concepts that are related to networking in one way or another. First and foremost, I try to put performance in context, and also contrast it with non-performance issues. Then, I talk about several key performance terms and metrics: speed, bandwidth, throughput and latency. I also talk about some of the units used to measure network performance. I then explain how the real-world performance of a network differs from its theoretical performance, and talk about factors that have an impact on network performance. I conclude by contrasting full-duplex and half-duplex network operation, and talking about quality of service, a concept that is especially important in the use of networks for real-time applications such as streaming multimedia.