User Manual

79-7
Considering the difficulty of deploying TE over the whole network, the Diff-serv model is usually the method of
implementing QoS in real networking resolutions.
The basic mechanism of Diff-Serv is mapping a service to a certain service class at the network edge,
according to the required service quality. The service is uniquely identified via the DS segment (originated
from ToS field) of IP packet. According to the segment, the routers in the backbone network will apply
pre-configured service policy to different services, ensuring the service quality.
The service quality class mechanism and the label mechanism of Diff-Serv are similar to the label distribution
mechanism of MPLS. In fact, the MPLS-based Diff-Serv is implemented via the combination of the DS
distribution and MPLS label distribution.
79.1.5 MPLS PHP
In the MPLS network, the core LSR will forward packets according to their labels. The Egress router (Egress
LER) will remove the label before implementing IP forwarding.
In fact, in simple MPLS applications, where the Egress routers only implement IP forwarding, labels will
become useless. In such cases, popping the labels out via the Penultimate Hop Popping feature at the
penultimate router will stop the Egress router from processing the labels.