User guide

MPLS Module Installation and User Guide 3-7
Overview of MPLS
Figure 3-2: LSR types
The functions of the LSR types are described in Table 3-2.
Supporting Quality of Service Features
Quality of Service (QoS) LSP support is an important attribute of MPLS. MPLS supports
the Differentiated Services (DiffServ) model of QoS. The DiffServ QoS model is
supported by mapping different traffic classes to different LSPs, or by using the EXP
bits in the MPLS shim header to identify traffic classes with particular forwarding
requirements.
Table 3-2: LSR Functions
LSR Function
Ingress LER Inserts one or more labels into packets transmitted onto an
LSP.
Intermediate LSR Forwards packets via label swapping.
Egress LER Removes the last label(s) before forwarding packets received
from an LSP.
MPLS_12
MPLS cloud
Egress LER
for LSP B
Egress LER for LSP A
LSR
LSR for
LSP
A
LSP B
LSP A
Ingress
LER
Source IP
network
Destination
IP network
for LSP B
Destination
IP network
for LSP A