Balancing CapEx reduction and network stability with stable routing-virtual topology capacity adjustment (SR-VTCA)

This paper investigates the merits of the SR-VTCA (Stable Routing-Virtual Topology Capacity Adjustment) approach as a mechanism to find a beneficial trade-off between network stability and reduction in capital expenditures (CapEx). These are two main objectives for the entities that own the optical infrastructure, such as Network Operators (NOs), and those also acting as Internet Service Providers (ISPs). The SR-VTCA scheme is a novel approach to adapt transparent optical networks to time-varying traffic by adjusting the number of lightpaths between node pairs, while keeping the IP routing unchanged. Lightpath bundling (LB) and anycast (AS) switching are combined in SR-VTCA operation to advertise lightpath additions/removals to the IP layer as mere adjustments (increments or decrements) in the capacity, allowing to keep the IP routing stable, and thus, simplifying control plane operations. On the contrary, a fully-reconfigurable (FR) network design, where IP routing can be also modified, would increase the burden in the control plane, but at a higher CapEx reduction, since the optical infrastructure is used more efficiently. In this work, we investigate the CapEx overprovision introduced by SR-VTCA with respect to a FR scheme. In order to do this, SR-VTCA planning problem is first modeled as a MILP formulation. A heuristic procedure based on traffic domination is then proposed to solve large instances of the problem. Exhaustive experiments are conducted comparing the SR-VTCA solutions obtained by the aforementioned MILP and heuristic proposal with solutions found by other optimization methods presented in the literature to solve the FR planning problem. Finally, the results show that SR-VTCA can achieve similar results to the FR case in terms of CapEx reduction, while a huge number of IP reroutings are saved by maintaining IP stability. Thus, SR-VTCA provides an advantageous balance between CapEx overprovisioning and the control plane overhead associated with IP rerouting. Keywords— Optical communications, multi-hour traffic, virtual topology design, capacity adjustment, stable routing, traffic domination.