Free-space optical communication assisted emergency communication scheme against multiple fiber link failures in low-edge-connected optical networks.

The optical network may become disconnected under fiber link failures if its edge connectivity is not greater than the number of link failures, this will make the transmissions of many services to be interrupted. In the optical network with lengths of fiber links from several kilometers to more than 10 km, free-space optical (FSO) links can provide considerable capacity for the transmissions of large-bandwidth services. Using FSO links to establish the emergency communication path for uninterrupted transmission can be seen as a viable scheme. In this paper, we propose the FSO communication assisted emergency communication (FSOC-EC) scheme against multiple fiber link failures in the low-edge-connected optical network. Using FSO links and fiber links to establish emergency communication paths can achieve a quick recovery for communication. The layout of FSO transceivers can be seen as a classic NP-hard problem. To reduce capital expenditure (CAPEX), we propose an integer linear programming (ILP) model and a heuristic algorithm for the layout of FSO transceivers. And to improve the protection success rate (PSR) of services, we propose an ILP model and a heuristic algorithm to pre-allocate the wavelengths on FSO links. We consider the adverse influence of rainfall on FSO links and propose the corresponding schemes to alleviate this on FSOC-EC. Simulation results show that adding available FSO links in different locations can alleviate the adverse influence of rainfall and increase the network connected rate (NCR) under multiple fiber link failures, and FSOC-EC can greatly improve PSR.