MESCAL’s intra-domain traffic engineering approach is based on layer 3 mechanisms (rather than MPLS-TE, for example). Its purpose is to compute a set of OSPF link weights to balance network load while honouring the QoS constraints of the traffic; and to provide answers to “what if” scenarios posed by Inter-domain Traffic Engineering in order to coordinate and optimise inter-domain and intra-domain traffic engineering decisions.

The IPTE approach is built on classical OSPF routing, but additionally introduces DSCP based routing to form multiple OSPF routing planes in the network. Each DSCP plane has individual link weights and can thus route traffic independently of the other planes. Each plane may be used to route traffic of an equivalent QoS-class to meet the performance constraints of that class. Another benefit of this approach is that multiple routing planes – even for a single QoS-class – allow for better load balancing across an AS.
The IPTE algorithm runs off-line at Resource Provisioning Cycle epochs. Given a traffic demand matrix and the network topology, the algorithm computes a set of link weights using a search heuristic. The optimisation is cost function based, so that individual QoS class constraints as well as other optimisation goals can be taken into account by factoring them into the algorithms cost function. This allows for parallel existence of hop-count-constrained, bandwidth-constrained and best effort traffic classes.

Because the solution relies on IP routing, the IPTE approach is more lightweight than MPLS-TE in terms of state-information required to be maintained in the network and the associated management configuration overhead for establishing LSPs. Since QoS information remains at the management layer in the off-line algorithms, no QoS awareness is required at layer 3. Recent MT-OSPF Internet Drafts provide the required DSCP based routing support, so potentially no major changes at the router level are required for the approach to be implemented.

The IP-based Intra-domain traffic engineering simulations show that DSCP aware routing can successfully be used for providing individual routing to different traffic classes. Bandwidth- as well as hop-count-optimised routing classes can be configured to run in parallel on the same physical network, using the link weight optimisation techniques proposed in deliverable D1.2. In addition the simulations show that the load is balanced more evenly across the network than with standard shortest path routing on inverse capacity link weights. Simulations have demonstrated that the approach is scalable to large ASs consisting of 100s of routers.

Further reading:

MESCAL deliverable D1.3, "Final specification of protocols and algorithms for inter-domain SLS management and traffic engineering for QoS-based IP service delivery", Chapter 10, section 10.6. [link]

MESCAL deliverable D3.2, "Final experimental results: validation and performance assessment of algorithms and protocols for inter-domain QoS through service-driven traffic engineering", Chapter 3, section 3.3. [link]