Analysis of Elastic Traffic Effects on WDM Dynamic Grooming Algorithms

Traffic grooming in IP over WDM networks introduces a coupling between the optical layer and the IP layer. Grooming algorithms are normally studied with a very simple traffic model that completely ignores this interaction. This paper compares the performance of two simple grooming algorithms with a traditional, Poisson based traffic model and a more complex one that takes into account the IP traffic elasticity and the inherent interaction between the IP routing and the optical layer. Simulation results, supported by heuristic considerations and a very simple analytical model highlighting the interaction effects, show that ignoring the two layer interaction is not correct and may lead to wrong conclusions. Besides, it is shown that grooming algorithms that ignore the interaction between the IP and the optical routing, can lead to great resource waste, because the IP routing over the virtual, lightpath based topology, has no knowledge of the actual resource use, while the optical layer, when required to open a new lightpath ignores the overall traffic pattern, taking a decision that is based on a local optimum that may negatively affect later decisions.