Bandwidth constraints models for DS-TE MPLS networks

The implementation of DiffServ mechanisms in a MPLS network is designed by the DS-TE architecture, where Class-types and TE-classes are identified.

A Class-Type (CT) is used for link bandwidth allocation determination, constraint-based routing and admission control. One traffic trunk belongs to the same CT throughout the links it crosses. A CT comprises a given number of traffic trunks on a link that governed by the same set of bandwidth constraints.

A TE-Class is comprised by a Class-Type and a preemption priority defined for that class-type. Therefore an LSP transporting a given traffic trunk would use the associated preemption priority as a set-up priority, a holding priority or both.

One of the fundamental requirements that support the implementation of DiffServ aware MPLS in network is the possibility to enforce different bandwidth constraints for each class of traffic.

The three possible bandwidth constraints models for DS-TE are Maximum Allocation Model (MAM), Maximum Allocation with Reservation (MAR) and the Russian Dolls Model.

In the MAM model each traffic class has a given bandwidth constraint and a maximum bandwidth reservation value is associated to the link capacity. The sum of all bandwidths constraints can exceed the maximum reserved bandwidth, and therefore the higher priority traffic can preempt the lower priority traffic to get its allocated bandwidth [1].

The MAR model is similar to the MAM model in the sense that a maximum bandwidth allocation is determined to each Class-type, but in this model, each class-type may only exceed its bandwidth allocation under conditions of no congestion if the network is overloaded the that traffic class-type bandwidth allocation is fixed to its current allocation [1].

In the Russian Dolls Model the maximum bandwidth usage allowed in a link is achieved by the accumulation of successive class-type according to their priority class. A lower priority traffic may use a higher priority class' bandwidth reservation up to the sum of their bandwidth constraint values, while a higher priority traffic can preempt a lower priority traffic to use its full allocated bandwidth [1].

[1] Din, N.; Hakimie, H. & Fisal, N. (2008), 'Bandwidth sharing scheme in DiffServ-aware MPLS networks''Telecommunications and Malaysia International Conference on Communications, 2007. ICT-MICC 2007. IEEE International Conference on', IEEE, 782--787.