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DES-7200 Configuration Guide Chapter 3 MPLS QOS
Configuration
3-3
3.1.2.4 <LER>
LER (Label Switching Edge Router) is located at the network edge, and is
responsible for imposing MPLS label upon the traffic entering into MPLS
network and disposing of MPLS label from traffic which is about to leave the
MPLS network. LER is also called Provider Edge (PE) Router.
3.1.2.5 <LSR>
LSR (Label Switching Router) is the core device of MPLS network, allowing
label switching and label distribution. LSR is generally called Provider (P)
Router.
3.1.3 Working principle
This section will describe how MPLS QoS works. We will take the network
topology shown in Fig 3 as the example to describe how to implement MPLS
QoS on the network.
Fig 3 MPLS network topology
Topology description: In this network, CE refers to Customer Equipment. In Fig
3, the leftward part of PE-1 and the rightward part of PE-2 are both IP network.
In this section, we assume that packets are transmitted from left to right. We will
introduce MPLS QoS behaviors on PE-1, P-1, P-2 and PE-2.
3.1.3.1 PE-1
PE-1 is an ingress LER responsible for imposing the MPLS label upon the IP
packets entering into MPLS network. Furthermore, PE-1 also needs to map the
QoS information carried in IP packets into MPLS packets (IP packets carry QoS
information through IP Precedence or DSCP field in IP header, while MPLS
packets carry QoS information through EXP field in MPLS label). On PE-1, we
can configure the EXP value in the MPLS label pushed by forming a mapping
relation between DSCP and EXP, or use IP packets to classify traffic first and
then configure the corresponding EXP value for each class of traffic.