89 MPLS QOS CONFIGURATIONMPLS QoS Overviewn To understand the contents in this chapter, you should have some backgroundknowledge related to MPLS. Refer to “MPLS Basics Configuration” on page 1311for the description of MPLS basic concepts and related configurations.The QoS solution for MPLS mainly completes the following functions:■ Classify the service traffic on CE or PE according to specific needs. For example,classify into three types: voice, video and data.■ When PE adds a Label to the packet, it will map the IP precedence flag carriedby the IP packet to the EXP domain of the flag, and thus the class informationcarried by IP is carried by the flag now.■ Among the PEs, the differentiated dispatching (such as PQ, WFQ, and CBQ) isperformed, that is, transmit the service traffic with flag on a LSP in the mode ofdifferentiated QoS.n The EXP field in an MPLS label is processed in the following ways■ The TOS field in an IP packet is directly changed into the EXP field in an MPLSlabel when an MPLS label is encapsulated into an IP packet.■ Any forwarding device can re-assign a value to the EXP field of a top label.■ The EXP field remains unchanged when label switch is performed.■ In a push operation, the EXP field of a newly pushed outer label inherits theEXP field of an inner label.■ After a pop operation, if the packet is still an MPLS packet, the popped EXPfield is duplicated to an inner label (meaning the EXP field remains unchangedif the packet is still an MPLS packet); if the packet is an IP packet after the popoperation, the EXP field will not be duplicated to the TOS field of the IP packet.Configuring MPLS QoS To configure MPLS QoS, you should first perform the related configuration ofMPLS and specify to display the route forwarding mode. For detailedconfigurations of MPLS, refer to “MPLS Basics Configuration” on page 1311. Thischapter only describes MPLS QoS configuration.MPLS QoS configuration includes:■ MPLS PQ. Refer to “Configuring MPLS PQ” on page 1690 for configurationdetails.
