Ethernet Bridge for FSO Links

The paper deals with a bridge for atmospheric Free-Space Optical links. The atmospheric turbulence causes fades whose duration is typically in the order of tens of milliseconds, which results in the loss of hundreds or thousands of packets. The loss is misinterpreted by the TCP protocol as network congestion and leads to throttling the sender transmission data rate to a fraction of real channel capacity. The proposed Ethernet-to-FSO bridge uses ARQ procedures on the FSO channel to mitigate the packet loss on the link layer. The bridge is based on Xilinx Virtex-5 FPGA with additional memory for buffers. A special link protocol for the FSO path has been designed. FSO frames can carry complete Ethernet frames without fragmentation.