[Sephiroth]

The upstream up to recently operated only between 18 MHz and 45 MHz frequency. That allows about 4 upstream channels at 6.4 MHz bandwidth. The range used by VM has now expanded to 65 MHz which puts 8 channels available at that bandwidth.

This compares with the downstream where each node if you're lucky and each segment in less well structured areas, has 16 downstream channels at a frequence range 10 times higher.

The upstream frequency range is somewhat more sensitive to RF noise than the downstream. So VM can't put the bit density up as high as on the downstream. VM are moving upstream from 16QAM to 64QAM, expanding capacity per packet by 50%. By comparison downstream currently operates at 256QAM (an extra 33% packing density).

You mention fibre. What do you mean by that? BT FTTC (Infinity)? If so, their frequency plan is totally different allowing a faster upstream to be offered.