Enterprise QoS Solution Reference Network Design Guide

Provider-Edge QoS Considerations
5-26
Figure 5-14 MPLS DiffServ Pipe Mode Tunneling Policies
CE Router
MPLS EXP values are
explicitly set by
service provider.
(Ingress)
PE Router
Direction of Packet Flow
Enterprise QoS Solution Reference Network Design Guide
MPLS VPN
P Routers
The MPLS EXP value from the final
label is temporarily copied to a QoS
group (and Discard class) on ingress
from the MPLS VPN cloud and then
the label is popped (and discarded).
(Egress)
PE Router
Chapter 5 MPLS VPN QoS Design
CE Router
Egress policies are based on
service provider’s MPLS EXP
markings.
Figure 5-15 illustrates adapting the five-class service provider model to Pipe Mode. The first set of
re-markings shows ingress PE re-marking from DSCP to MPLS EXP values, depending on whether the
traffic is in contract or out-of-contract. The second set of markings shows how these MPLS EXP values
can be mapped to QoS Groups (QG) and Discard Classes (DC) to provide PHB classification and
provisioning on PE-to-CE links (without altering the IP DSCP values of the tunneled packets).
Example 5-11 shows the configuration for bidirectional re-marking on a PE router to support Pipe Mode
operation. Traffic received from CEs is marked explicitly (through MPLS EXP values) to reflect the
service provider’s policies. Then traffic (traversing in the opposite direction) received from the MPLS
VPN core is mapped to QoS Groups and Discard Classes so that PE-to-CE PHB egress policies can be
performed against provider re-markings. In this example, the customer has contracted for 3-Mbps
service over an FE link. Hierarchical policies are used to achieve queuing within (3 Mbps) shaping over
this (100-Mbps) link. Additionally, Discard-class WRED is enabled on the output queues so that
dropping decisions are based on Discard-class values (not IP ToS or DSCP values). Furthermore,
Discard-class dropping thresholds are tuned so that Discard-Class 1 (indicating out-of-contract traffic) is
dropped more aggressively than Discard-Class 0 (mimicking DSCP-based WRED behavior), which is
more consistent with RFC 2597 Assured-Forwarding PHBs.
Version 3.3