By default, all packets of data travelling across a local-area network (LAN) are created equal. If all of the traffic on a network is text- or file-transfer-based, the system is workable - and no one notices when a 40MB file is delayed by 50 milliseconds as more bandwidth is made available to all users and applications.

If one type of application on a network is dramatically different from the others and requires far more bandwidth, however, problems can occur. The most common examples involve Voice-over Internet Protocol (VoIP) phone service and streaming video.

Data packet delays can introduce out-of-sync sound and jittery, pixelated images, or worse. Left uncorrected, such a system may deliver smooth video on some occasions, and awful video on others. One way to stack the odds in your favour is through Quality of Service (QoS) capabilities.

QoS is networking à la George Orwell's "Animal Farm": Some data packets are more equal than others. The preferred packets will be at the top of the queue when passing through a network port, while lesser packets cool their heels. The result is smoother audio and video presentation, even when the network is humming with file transfers and general business traffic.

How to know if you need QoS

Whether you need QoS depends on the mix of applications that run on your network. Whether you can achieve it depends on your network infrastructure's capabilities. Let's look at each of these factors.

For the vast majority of network users, QoS boils down to making sure that voice and video applications perform well. If your company's only voice calls occur over Skype and involve personal communications, and if its only video use consists of YouTube downloads viewed during employee breaks, then QoS isn't worth the bother.

On the other hand, if you use VoIP as your standard office phone system, or if you want to make extensive use of video conferencing to replace business travel, proper attention to QoS can significantly upgrade employee productivity and your company's perceived quality in the marketplace. But how do you establish QoS on your network?

Getting started With QoS

QoS has a specific set of meanings in networking, and it's distinct from various things you can do to improve the overall performance of the network. (At the end of this article we'll look at ways to boost network performance.)

In most instances, small businesses will see QoS established in the network's router, and perhaps elsewhere. If you dive deeply into the internal structures of network traffic, you'll find two basic flavours of QoS: Integrated Services (IntServ) and Differentiated Services (DiffServ). IntServe permits relatively fine-grain control of traffic streams and tends to be used within small networks or between closely related networks. The DiffServe protocol works on a less precise basis and most often is used between service providers and Internet backbone companies.