ched networks, other parameters need to be controlled in order to guarantee QoS, including latency end to end (i.e., from entry to exit point), jitter (i.e., the variation in delay between any two points), loss (i.e., dropped packets), sequencing (i.e., the order of delivery of the packets), and errors (i.e., the result of various impairments that affect transmission). When the Internet was first conceived of and IP protocols were initially cre- ated, QoS was not seen as a critical feature. In fact, the Internet was built on the principle of best effort. When the traffic flows consisted of simple, bursty data, the economies of best effort were an advantage. But today, with the introduction of more and more real-time traffic, such as VoIP or video, and interactive applica- tions, QoS is a requirement that cannot be ignored. In fact, services cannot be offered until QoS can be guaranteed, and best effort is simply not good enough. As a result, much attention is being focused on developing QoS mechanisms and proto- cols that enable packet-switched networks to properly accommodate the demanding needs of the emerging era of multimedia applications and services. QoS Mechanisms There is a growing requirement to meet or exceed expectations of end users and applications communicating over a packet-switched network. To fulfill this require- ment, we can take several approaches: We can overprovision networks SO that bandwidth exceeds the demand and there are enough routers to always ensure available capacity, we can use traffic engineering to steer away from congestion, and we can use fancy queuing so that where there is contention for bandwidth, demand exceeds supply. This final approach requires QoS mechanisms. Figure 8.22 shows the four main QoS mechanisms: classification (used for packet identification), conditioning (used for traffic shaping), queue management (used to manage the queue depth), and queue scheduling (used for packet scheduling). Classification identifies packets for subsequent forwarding treatment. Class