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Chapter 42 Configuring PFC3BXL or PFC3B Mode MPLS QoS
PFC3BXL or PFC3B Mode MPLS QoS Overview
PFC3BXL or PFC3B Mode MPLS QoS Overview
PFC3BXL or PFC3B mode MPLS QoS enables network administrators to provide differentiated types
of service across an MPLS network. Differentiated service satisfies a range of requirements by supplying
for each transmitted packet the service specified for that packet by its QoS. Service can be specified in
different ways, for example, using the IP precedence bit settings in IP packets.
Specifying the QoS in the IP Precedence Field
When you send IP packets from one site to another, the IP precedence field (the first three bits of the
DSCP field in the header of an IP packet) specifies the QoS. Based on the IP precedence marking, the
packet is given the treatment configured for that quality of service. If the service provider network is an
MPLS network, then the IP precedence bits are copied into the MPLS EXP field at the edge of the
network. However, the service provider might want to set QoS for an MPLS packet to a different value
determined by the service offering.
In that case, the service provider can set the MPLS EXP field. The IP header remains available for the
customer’s use; the QoS of an IP packet is not changed as the packet travels through the MPLS network.
For more information, see the
“MPLS DiffServ Tunneling Modes” section on page 42-32
.
PFC3BXL or PFC3B Mode MPLS QoS
This section describes how PFC3BXL or PFC3B mode MPLS QoS works.
Figure 42-1
shows an MPLS network of a service provider that connects two sites of a customer network.
Figure 42-1
MPLS Network Connecting Two Sites of a Customer’s IP Network
The network is bidirectional, but for the purpose of this document the packets move left to right.
In
Figure 42-1
, the symbols have the following meanings:
•
CE1—Customer equipment 1
•
PE1—Service provider ingress label edge router (LER)
•
P1—Label switch router (LSR) within the core of the network of the service provider
•
P2—LSR within the core of the network of the service provider
CE1
41867
PE1
P1
P2
PE2
CE2
IP
network
MPLS
network
IP
network
MPLS
network
Host A
Host B
Owned by
service provider
