MPLS-Enabled Applications: Emerging Developments and New Technologies

4.5. EXTENDING THE DiffServ-TE SOLUTION WITH MULTICLASS LSPs

So far we have seen that LSPs set up according to [RFC4124] carry traffic from a single DiffServ class and are set up along a path that satisfies the bandwidth constraints specified for that class. However, sometimes traffic with different DiffServ behaviors must be mapped to the same LSP and the LSP must satisfy the bandwidth constraints for each one of these classes. We will call these multiclass DiffServ Aware LSPs.

An example scenario for multiclass LSPs arises in the context of ATM trunk emulation using MPLS LSPs. To effectively emulate an ATM trunk, all the traffic classes should follow the same path in the network and should exhibit the same behavior in case of failure. If the EF class fails, so should the BE class. If traffic switches to a protection path, it should use the same path for all classes. In principle, one could argue that this behavior can be achieved by setting up a separate LSP for each class and then adding the necessary control-plane intelligence to keep them synchronized. Apart from being cumbersome to implement, such a solution also has drawbacks with regards to the number of LSPs that must be created and maintained.

This brings us to another application of multiclass DiffServ-TE LSPs: reducing the number of LSPs in a network by setting up reservations for several classes in one LSP rather than one reservation per class. When LSPs are set up with bandwidth reservations from a single class, ...