Three QoS Models in MPLS

  1. Three Models
    1. Pipe Model
      1. Ingress PE defines its MPLS EXP bits (SP Defined)
      2. at egress PE, forwarding is based on EXP
      3. Same QoS for each customer in Egress PE, that is reduces QoS configuration at PE
      4. A change on the outer EXP is not copied to DSCP
      5. When to use: when MPLS core and the cutomer networks have difference QoS policy, and when SP want to use EXP marking to PE to CE link. Typcial for L3VPNv3 Managed CPE customers. PE Config is more complex compare to short pipe since the MPLS EXP info needs to be stored on a temporary field on PE after it was removed on the inbound interface from core. The PE then refers to the tempoery field to set its outbound queueing
    2. Short Pipe Model
      1. Ingress PE defines its MPLS EXP bits (SP Defined)
      2. at egress PE, forwarding is based on DSCP
      3. Different QoS for each customer in Egress PE, mode complex QoS configuration at PE
      4. A change on the outer EXP is not copied to DSCP
      5. When to use: when the MPLS core and the customer networks have difference QoS Policy, and when SP wants to honor customer DSCP marking on egree PE to CE link. Typical for L3VPNv3 unmanaged CPE customers
    3. Uniform Model
      1. EXP bits on all LSP (Top) and Tunnel (Bottom) labels are copied from customer IP Precedence Bits across MPLS network
      2. That means customers define the MPLS EXP bits
      3. A change on the outer EXP is not copied to DSCP
      4. A change of EXP in MPLS will be copied to all labels and DSCP
      5. when to use: when the MPLS network and the Customer network share the same QoS policy, typical for large enterprise that run their own MPLS core
  2. In all three models, customer can set their IP Precedence Bit at ingress, the bits will be preserved at egress.
  3. Pipe and short pipe models only different at the egress PE forwarding.
Tunneling Mode IP –> Label Label –> Label Label –> IP
Uniform Copy IP Prec/DiffServ into MPLS EXP (may be changed by the SP also) MPLS EXP may be changed by SP MPLS EXP copied to IP Prec/DiffServ
Pipe MPLS EXP set by the SP QoS policy Original IP Prec/Diffserv preserved (egress queuing based on MPLS EXP)
Short-Pipe Original IP Prec/Diffserv preserved (egress queuing based in IP Prec/DiffServ)

External Links:

  1. Cisco Config Example
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4 comments

  1. J.A

    Hi Ken,
    Thanks for your blog as I use it for my studies!
    I think your comment “In all three models, customer can set their IP Precedence Bit at ingress, the bits will be preserved at egress.” is not 100% correct.If we take the uniform model as the SP can override customers DSCP/IPP values.
    Cheers,
    J.A

    • Ken Yeo

      J.A, thank you for the correction, you are right, on the uniform model, provider can monify the MPLS EXP bits and will be propagated to the customer’s IP precedence values at egress.

    • Ken Yeo

      The diagram is correct. The description is misleading. In PIPE mode, the PHB on a PE is decided by the service provider’s EXP bit, not by the customer payload DHCP bit. The customer DHCP is untouched in PIPE mode.

      Pipe mode is useful if the ISP is the one that decides what the PHB selection is on the link immediately exiting the MPLS network. Typically, this is in a managed CPE scenario, in which the ISP does not want to extend MPLS all the way out to the CPE but wants PHB selection control over the link to the CPE.

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