MPLS-Enabled Applications: Emerging Developments and New Technologies

11.7. ADMISSION CONTROL OF LAYER 2 CONNECTIONS INTO NETWORK

Sometimes service providers offer Layer 2 transport services based on pseudowires as a replacement for services that have guaranteed bandwidth, such as ATM CBR services or leased lines. Therefore, it may be advantageous to the service provider to also offer bandwidth guarantees for such pseudowire services. Guaranteed bandwidth implies that the traffic does not suffer contention when it crosses the service provider's network. This can be achieved in the following ways:

• Traffic is carried in RSVP-signaled LSPs. Each LSP has a bandwidth reservation, and admission control ensures that an LSP is only set up along a path that has the required bandwidth resources (bandwidth availability on a link or within a particular queue on the link). In order to maintain the bandwidth guarantee, overbooking is not used.

• If other traffic is allowed to use the same resources and is not subjected to admission control, that traffic must be marked to have lower priority than the traffic subjected to admission control (e.g. through EXP marking).

• Policing occurs at the ingress PE, to ensure that the traffic rate entering the LSP does not exceed the bandwidth reservation.

In some cases, there might be several LSPs between a given pair of PEs, in order to spread the load across the network, and a large number of pseudowires using those LSPs, those pseudowires belonging to various end-customers. For such cases, some implementations offer an automated ...