Griem, J; (2007) Traffic engineering for multiservice IP networks. Doctoral thesis , UCL (University College London).

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Abstract

The central cause of strain on today's IP network infrastructure steins from the industries striving to extend the network to carry voice and other advanced services that it was not designed for. This thesis develops the reasons why more sophisticated mechanisms are required for ensuring that the best-effort infrastructure becomes both predictable and controllable, if the current IP infrastructure is to replace circuit switched networks. The main theme of the thesis are the IP traffic engineering (IPTE) traffic engineering algorithms that were developed by the author. The goal of the proposed approach is to compute a set of Open Shortest Path First (OSPF) link weights to balance network load, while honouring bandwidth, hop count and propagation delay constraints of the traffic. The proposed solution is built on classical OSPF routing and additionally uses the multi topology concepts that were recently proposed as an extension to OSPF. Using Multi Topology OSPF (mt-OSPF), multiple routing planes can be implemented. Each Multi Topology (MT) routing plane is assigned its own link metrics and thus traffic can be routed independently. 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 constraints can be taken into account per routing plane. Using this approach, constraint information remains in the "offline" IPTE algorithms and thus no extra constraint awareness is required at layer 3. Since recent Cisco implementations of mt-OSPF and Multi Topology IS-IS (M-ISIS) provide the required multi topology routing support, no major changes at the router level are required for the approach to be realised. Extensive simulations presented in this thesis show that IPTE has the potential to provide the differentiated routing and load balancing that it was designed for. In addition the simulations show that load is balanced more evenly across the network than with standard shortest path routing on inverse capacity link weights. A network management system is discussed that acts as the binding element for all enabling components. A simplified architecture for such a management system is presented and it is discussed how several traffic engineering mechanisms could coexist with IPTE on one network infrastructure. The use of the authors IPTE approach in the context of this management system is discussed in depth: Dangers associated with potential network disruption caused by frequent link weight modifications are analysed from both intra- and inter-domain point of view. A strategy for solving the problem of disruptions caused by link weight changes is presented by using several network planes to migrate traffic, rather than causing disruptions to a "live" plane through link weight modification and resulting OSPF routing table updates. The strategy is simulated, showing that any detrimental effects of the transition are avoidable. However, the work is ongoing and the results presented are indicative. Overall the thesis presents an approach for traffic engineering using traditional routing techniques, to (1) preserve the original intrinsic advantages of the IP design and (2) help ready IP networking for the much more restricting requirements of the future mutiservice network. It presents algorithms, simulations and frameworks showing how the work fits into the current IP networking world.

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