Introduction

MPLS QoS behavior permits tunneling of DiffServ, where encapsulated IP packet's QoS fields are not modified within the MPLS core. Customers can have their own QoS schemas that are independent of carrier's QoS schema. There are three DiffServ tunneling models.

DiffServ Tunneling Models

• There are three tunneling models:
  • Uniform Model - Service provider's network may modify the IP DSCP marking of tunneled packets if congestion occurs or some other policy event.
    • Idea is the the network is uniform and any changes should be applied upward and downward of the label and IP packet.
    • This is used when both IP and MPLS QoS is controlled by the same entity.
    • Ingress to PE - Copy the IP DSCP to the MPLS EXP labels imposed.
    • Egress to CE - Copies the MPLS EXP to the IP DSCP when queueing to CE. If policing or other actions are applied to the MPLS EXP values.
  • Pipe Model - Service provider's network won't modify the IP DSCP marking, even under congestion.
    • IP QoS values are tunneled.
    • Scheme used to keep SP and customer QoS separate.
    • Will never change the IP DSCP.
    • Ingress to PE - Manually set the MPLS EXP to core QoS policy values.
    • Egress to CE - For queueing uses the MPLS EXP values. Keeps the IP DSCP to CE.
  • Short Pipe Model -Service provider's network won't modify the IP DSCP marking, even under congestion.
    • IP QoS values are tunneled.
    • The only difference between Pipe and Short-pipe is the mpls2ip queuing (Egress to CE).
    • Ingress to PE - Manually set the MPLS EXP to core QoS policy values.
    • Egress to CE - For queueing uses the IP DSCP values. Keeps the IP DSCP to CE.
    • In Pipe the last interface uses the POPed EXP vs in Short Pipe mode which uses the IP DSCP value.

Additional Resources

MPLS VPN QoS Design - Enterprise QoS Solution Reference Network Design Guide
BRKRST-2501 WAN & Branch QoS Design - Cisco Live
Configuring MPLS QoS on the PFC - Cisco 7600 Series Cisco IOS Software Configuration Guide, 12.2SR
DiffServ Tunneling Modes for MPLS Networks - Design Technotes

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