Quality of Service is a subject of crucial importance to your success with VoIP. Not surprisingly, QoS technologies aren't often well- understood by traditional telephony people. But those with a data background have never had to use them, either. So this chapter will introduce you to QoS concepts and protocols, the problems they solve, and the complexities they introduce. Don't let that scare you, though. There are QoS approaches for networks that have a few dozen endpoints, and there are approaches for giant, high-capcacity networks, too.