My cable modem pulls 120Mbps down, pushes 10Mbps. 24/7. DOCSIS 3.1 promises up to 10Gbps down, 1Gbps up (again, because it biases the bandwidth to down). It's a signal on a medium.

And when we talk about fiber optics, 9 times out of 10 it isn't really fiber optics. The vast majority of BT "fiber optic" installs are a copper twisted pair, with exactly the issue I mentioned. But their junction box, just like cable internet applications, has fiber optics going to it, for what's that worth. For a real pure fiber optic connection, which is rare, the service usually is symmetric because that compromise didn't need to be made.