eration Networks Table 10.3 ATM Classes of Service Parameter VBR-NRT VBR-RT Cell loss ratio Cell transfer delay Cell delay variation Peak cell rate Sustained cell rate Minimum cell rate Maximum burst size Allowed cell rate that all share the same QoS requirement: All CBR streaming video traffic may go over virtual path 1, all bursty TCP/IP data traffic may go over virtual path 2, and all MPEG-2 compressed video traffic may go over virtual path 3. In this way, we can organize all the virtual channels that have the same demands from the network into a common virtual path, thereby simplifying the administration of QoS and easing the network management process for the carrier. Within the cell structure, the key identifier in the header is which path and which channel is to be taken between any two ATM cells. The channel assignments change, depending on what channels were reserved at the time the session was negotiated. Remember that because it is connection oriented, ATM gives service providers the traffic-engineering tools they need to manage both QoS and utilization. In pro- visioning a network, the service provider can assign each virtual circuit a specific amount of bandwidth and set the QoS parameters. The provider can then dictate what path each virtual circuit takes. However, it does require that the service pro- vider manage the ATM switches and whatever else is running over that ATM net- work (e.g., IP routers). IP QoS There are two IP schemes for QoS: IntServ and DiffServ. The following sections describe each of these schemes; IP QoS mechanisms are also discussed in Chapter 8. The Next-Generation Network Infrastructure IntServ IntServ was the IETF's scheme to introduce QoS support over IP net- works. It provides extensions to the best-effort service model to allow control end-to-end packet delays. In essence, IntServ is a bandwidth reservation technique that builds virtual circuits across the Internet SO that applications running in the hosts can request bandwidth. IntServ was introduced first as a setup pr