to abuse them in all sorts of odd ways. Most of those test-specific games don't have any basis in the real world, though. For our purposes, we will stick to the most common scenarios. In the real world, QoS is most often used for a couple of reasons. Either there's some sort of streaming media (like voice or video) that requires low latency and timely delivery, or you've got an oversubscribed link, and the powers that be want to make it work better SO they don't have to buy more bandwidth. Perhaps the new circuit has been ordered, but due to facility problems, it won't be delivered for 120 days. QoS is the answer to help make the existing link a little more useful until the bigger link is delivered. QoS can also be used for some more interesting applications. For example, you could configure your network SO that telnet and SSH have priority over all other traffic. When a virus hits, and you need to telnet to your routers, the telnet and/or SSH traf- fic will always get through (assuming you've rate-limited the CPUs on said routers). Or, if you're eager to please the boss, you could prioritize his traffic above everyone else's (except, of course, your own) SO he'll have a better online experience. While these examples may seem far-fetched, I've been asked to do just these sorts of things for customers. In many cases, the operations department needs better network access than the rest of the company. And once an executive learns about QoS, he may demand that he get "better" treatment on the network. I wouldn't recommend this, but I've seen it happen. Chapter 29: Introduction to QoS In a nutshell, any traffic that can be identified can be prioritized. Deciding whether the traffic should be prioritized (and, if so, in what order) is your job, and it can be an interesting one, to say the least. Types of QoS The term QoS is used to describe any of the myriad functions used to limit how much bandwidth may be used, guarantee how much bandwidth may be used, or pri- oritize certain traffic over other traffic. Technically, 