34 Chapter 1 An Introduction to Policy-Enabled NetworksPacket flow using QoSUsing DiffServ and QoS, a specific performance level for packets can bedesignated. This system allows for network traffic prioritization. However, itrequires some thought to configure the prioritization. A number of policiescan be specified and each policy can match one or many flows, supportingcomplex classification scenarios.This section contains a very simplified introduction to the many ways toprioritize packets using QoS. In simple terms, the methods of prioritizingpackets depend on the DSCP and the 802.1 priority level and dropprecedence.The QoS class basically directs which group of packets receives thebest network throughput, which group of packets receives the next bestthroughput, and so on. The level of service for each packet is determinedby the configurable DSCP.The available levels of QoS classes are currently named Network, Premium,Platinum, Gold, Silver, Bronze, and Standard. The level of service for eachpacket is determined by the configurable DSCP.Classifier elements, classifiers, and classifier blocks basically sort thepackets by various configurable parameters. These parameters includeVLAN IDs, IP source and subnet address, IP protocol, and many others.The classifiers/classifier blocks are associated with policies, and policiesare organized into a hierarchy. The policy with the highest precedence isevaluated first. The classifier elements, classifiers, and classifier blocksare associated with interface groups, in that packets from a specific portwill have the same classification parameters as all others in the particularinterface group (role combination).Meters, operating at ingress, keep the sorted packets within certainparameters. A committed rate of traffic can be configured, allowing a certainsize for a temporary burst, as In-Profile traffic. All other traffic is configuredas Out-of-Profile traffic. If you choose not to meter the flow, you do notconfigure meters.Actions determine how the traffic is treated.The overall total of all the interacting QoS factors on a group of packetsis a policy. Policies can be configured that monitor the characteristicsof the traffic and perform a controlling action on the traffic when certainuser-defined characteristics are matched."QoS Policy Schematic" (page 35) provides a schematic overview of QoSpolicies.Nortel Ethernet Routing Switch 4500 SeriesConfiguration — Quality of ServiceNN47205-504 (322816-B) 03.01 Standard5.1 23 November 2007Copyright © 2007, Nortel Networks.
