Mind the paths you choose: Speeding up segment routing-based traffic engineering with path preprocessing

Many state-of-the-art Segment Routing (SR) Traffic Engineering (TE) algorithms rely on Linear Program (LP)-based optimization. However, the poor scalability of the latter and the resulting high computation times impose severe restrictions on the practical usability of such approaches for many use cases. A promising way to address these issues is to preemptively limit the number of SR paths considered during optimization by employing certain preprocessing strategies. In the first part of this paper, we conduct an extensive literature review of such preprocessing approaches together with a large-scale comparative performance study on a plethora of real-world topologies, including recent data from a Tier-1 Internet Service Provider (ISP). In the second part, we then use the insights gained from the former study to develop a novel combined preprocessing approach which also guarantees to not interfere with the satisfiability of practically important latency bound constraints. Our approach is able to reduce the number of SR paths to consider during optimization by as much as 97%–99%, while still allowing to achieve close to optimal solutions. This facilitates an around 10$\times$ speedup for different LP-based SR TE algorithms, which is more than twice as good as what is achievable with any of the previously existing methods. Finally, we also study the applicability of the path preprocessing paradigm to the use case of tactical TE, showing that it facilitates an around 37% speedup in this context as well. All in all, this constitutes a major improvement over the current state-of-the-art and further facilitates the reliable use of LP-based TE optimization for large segment-routed networks.