delay, to the delay in moving bits along the entire path, or, more specifically, to the variable arrival of packets. There are two main types of delay: jitter and entry-to-exit-point delay. Say that your end-to-end delay might meet the desired minimum of 150 milli- seconds, but between switches 1 and 2, the delay is 20 milliseconds and between switches 2 and 3, it's 130 milliseconds. That variation will hamper some applications, SO it needs to be controlled SO that the network can support demanding applications. Packet loss occurs as congestion occurs at the packet switches or routers, and it can considerably degrade real-time applications. For example, if a few packets of a voice call are lost, you'll hear pops and clicks, but if the loss climbs into the 30% to 40% range, the voice might sound like "ye ah ng ng ah mm mm ah." This is the experience that some people today find at times when using the public Internet for telephony, where at peak periods of day, packet loss can be as great as 40%. But it is important to note that this varies greatly around the world; in some countries and locations, the loss is close to zero on the average, whereas other regions or providers may suffer double-digit packet loss during peak hours. Given these drawbacks and the way packet-switched networks evolved, these networks originally gave no QoS guarantees-they offered only best-effort QoS. But they guaranteed high reliability because you would be able to route packets through alternate nodes or pathways if they encountered link-resistant failures along the way; thus, you were guaranteed that information would be transported, but not within metrics such as latency and packet loss. Currently, protocols are being developed that will enable real-time applications such as voice, video, audio, and interactive multimedia to perform properly on packet-switched networks. The pricing mechanism that evolved with packet-switched networks was a bit different from that used for circuit-switched networks. It was not based on time and distance