Enterprise QoS Solution Reference Network Design Guide

Chapter 5 MPLS VPN QoS Design
Version 3.3
Figure 5-13 MPLS DiffServ Pipe Mode Tunneling Operation
Assume a policer re-marksout-of-contract
traffic’s topmost label to MPLS EXP 0 here.
CE Router
PE Router
IPP3/DSCP AF31 MPLS EXP 4
Packet initially
marked to IPP3/
DSCO AF31.
Direction of Packet Flow
Shaded area represents Provider DiffServ domain.
MPLS EXP 4
IPP3/DSCP AF31
MPLS EXP values
are set independently
from IPP/DSCP values
MPLS VPN
P Routers
MPLS EXP 0
MPLS EXP 4
IPP3/DSCP AF31
Topmost label is
marked down by a
policer.
PE Router
MPLS EXP 0
IPP3/DSCP AF31
Topmost label is
popped and EXP value
is copied to underlying
label.
Provider-Edge QoS Considerations
Unshaded areas represent
Customer DiffServ domain.
PE Edge (to CE) policies
are based on
provider markings.
CE Router
IPP3/DSCP AF31
Original customermarked
IP ToS
values are
preserved.
QoS Groups and Discard Classes can be combined to provide virtual DiffServ PHB classification. For
example, RFC 2597 assured-forwarding PHBs can be mimicked using QoS Group values 1 through 4 (to
represent the AF class) coupled with Discard Class values 1 through 3 (to represent the drop preference).
In general, QoS Group and Discard Class values are arbitrary and have only local significance. However,
an exception is found when WRED is configured to selectively drop based on Discard Class values, in
which case the lower Discard Class values are dropped first (by default). If no Discard Class value is
assigned explicitly, the value defaults to 0.
Figure 5-14 shows the points where policies are required for Pipe Mode MPLS DiffServ tunneling.
Enterprise QoS Solution Reference Network Design Guide
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