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Chapter 8. MPLS Quality of Service

Chapter 8. MPLS Quality of Service

This chapter covers the following topics:

  • Quality of Service— Service providers that offer IP services over an MPLS backbone must support IP quality of Service (QoS) over their MPLS infrastructure. This means supporting IP QoS over MPLS VPNs or MPLS traffic-engineered paths. MPLS can help service providers offer IP QoS services more efficiently over a wider range of platforms, such as ATM LSRs.

  • Integrated Services— Integrated Services (IntServ) refers to an overall QoS architecture developed by the Internet Engineering Task Force (IETF). IntServ specifies a number of service classes designed to meet the needs of different application types. IntServ also specifies various signaling protocols.

  • IP Precedence— This section discusses IP Precedence, which classifes packets at the edge of the network into one of eight different classes. This is accomplished by setting three precedence bits in the ToS (type of service) field of the IP header. IP precedence closely resembles differentiated service code point (DSCP) and serves as a prestandard DSCP implementation.

  • Differentiated Services— The DiffServ model divides traffic into a small number of classes and allocates resources on a per-class basis. This model is similar to the IP precedence model. A 6-bit differentiated service code point (DSCP) marks the packet's class in the IP header.

  • Modular QoS CLI— The Modular QoS command-line interface (MQC) is a provisioning mechanism in IOS software that allows for separation of packet classification configured using class maps, from policies configured using policy maps applied on the defined classes, and from the application of those policies on interfaces and subinterfaces configured using service policies.

  • MPLS Implementation of DiffServ— This section examines the MPLS implementation of DiffServ. MPLS LSRs do not examine the contents of the IP header and the value of its DSCP field, as required by DiffServ. This means that the appropriate PHB must be determined from the label value.

  • MPLS VPN Support of QoS— This section discusses the two models used to describe QoS in the VPN context—the pipe model and the hose model. Various MPLS QoS classes of service should be available on a per-VPN basis, and applications should receive various classes of service within the VPN.

  • MPLS QoS Implementation— This section discusses MPLS QoS enhancements that allow service providers to classify packets according to their type, input interface, and other factors by marking each packet within the MPLS experimental field without changing the IP precedence/DSCP field.

  • Configuring QoS for MPLS VPNs— The Modular QoS CLI is used to configure QoS on ingress PE routers. It allows users to specify a traffic class independently of QoS policies. The Modular QoS CLI configures traffic classes to classify IP packets according to various criteria using class maps. It utilizes service policies implemented using policy maps and associates input interfaces with the service policies.

  • MPLS QoS Case Study— This section discusses a case study that considers an MPLS VPN configured with Modular QoS CLI.


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