QoS is often used on local networks to ensure that high priority traffic receives precedence over other network uses. For example, if your organization runs a voice over IP (VoIP) telephone system, it's likely that you'd want to prioritize that traffic over data communications. Users are much more likely to tolerate a slowdown in their Internet traffic than a disruption in their telephone conversations.
QoS on the Internet is a trickier issue. The short answer is that there isn't really a single, accepted approach to provide QoS between two arbitrary endpoints. However, an organization can certainly negotiate with its service provider to increase the priority of certain types of traffic on a provider's network segments.
You may also be interested in reading the tip, Analyst debunks network QoS myths, brought to you by SearchNetworking.com.
This was first published in February 2007