Undersea fiber optic lines are crucial to making the internet hum, but upgrading their capacity is no mean feat when you may have to replace thousands of miles of cables. Facebook and Nokia don't think that's necessary, though. They've successfully tested a technique that can boost the capacity of a fiber line by up to 2.5 times its stated capacity. Their approach revolves around Nokia's probabilistic constellation shaping, which relies on 'shaped' modulation formats (i.e. a lot of clever math) to push the capacity to near the physical peak of a given connection. In tests on a 3,400-mile line between New York and Ireland, the two companies managed to wring out 200Gbps on commercial-grade wavelengths, and an even speedier 250Gbps on an experimental link.