MPLS-Enabled Applications: Emerging Developments and New Technologies

9.4. INTERPROVIDER QoS

From the customer's point of view, the QoS expectations are the same, regardless of whether the VPN service is implemented by a single provider or by multiple providers. When VPN traffic crosses several domains, it is necessary for each of the domains to enforce its own policy to ensure the desired QoS.

In the Advanced L3VPN chapter (Chapter 8) we have seen how QoS can be provided for BGP/MPLS VPNs by marking customer traffic with the EXP bits, providing the correct per-hop behavior in the network. The marking is done at the PE and forwarding the traffic in the core is based on the EXP bits. The solution requires mapping DSCP to EXP consistently at the PE-CE boundary. In an interprovider setup, it cannot be expected that the same EXP bits will be used to represent the same per-hop behaviors in both networks. Therefore, it is necessary to remark the EXP bits of the VPN traffic as it crosses the inter-AS link.

The inter-AS link poses other challenges as well. The link is shared between two administrative domains, so it is more difficult to upgrade and can easily become a point of congestion. This problem can be made worse by the fact that often the same link is used to carry Internet traffic between the providers in addition to the VPN traffic. In order to ensure SLAs for the VPN traffic, it is necessary to set up and enforce policies for prioritizing and rate-limiting traffic at the AS boundary. This can be done either at the aggregate level across all VPN ...