Fast parallel lightpath re-optimization for space-division multiplexing optical networks based on time synchronization

In recent years, driven by the rapid growth of global Internet traffic, optical networks are evolving to provide higher capacities. To enlarge transmission capacity, researchers focused on the dimension of space and proposed the concept of space-division multiplexing (SDM) by introducing multicore fiber and few-mode fiber into optical networks. In SDM networks, one of the main challenges is the crosstalk among SDM (core and mode) channels, which degrades signal quality. This degradation has a serious impact on routing and resource allocation. Previous studies have mostly been confined to the routing algorithms for crosstalk reduction but few focus on the re-optimization mechanisms in SDM networks, defined as re-routing the existing lightpaths to minimize the overall crosstalk without traffic disruption. In this paper, by analyzing the re-routing signaling processes of two straightforward serial re-optimization mechanisms, we find that the signaling interaction between node controllers and serial re-routing execution leads to long re-optimization times, which makes lightpath re-optimization impossible for practical use. In order to achieve fast lightpath re-optimization for crosstalk reduction in SDM networks, we propose a novel software-defined networking (SDN) based parallel lightpath re-optimization mechanism, enabled by high-precision time synchronization. The basic idea of our proposed parallel lightpath re-optimization mechanism is to make all the nodes execute the switching operations co-ordinately with the help of network time synchronization. Besides, we propose two key algorithms to achieve parallel re-optimization: a simulated annealing algorithm to determine the re-routing sequence of the lightpaths and a time arrangement algorithm to determine the exact time points of the switching operations at each node. Finally, we conduct a prototype experiment and large-scale network simulations to evaluate the performance of the proposed mechanism. The results demonstrate that our parallel re-optimization mechanism can reduce the overall crosstalk in a much shorter time by up to three orders of magnitude compared with the conventional serial mechanisms and thus is more practical for real applications.