Okay. Perhaps you could explain for me how Comhem in Sweden are selling 30-50Mb upstream on a EuroDOCSIS network, 65MHz subsplit, or how Comcast in the USA sell 25/5, 50/10 and 100/20 on a US DOCSIS 42MHz subsplit network?
I'll answer my own question. They use more and higher capacity channels - the Superhub can handle 108Mb of upstream capacity in a service group.
At present VM's standard build is 36Mb to a group in the form of 2 upstream channels, however they are working towards increasing that to 54Mb in 2 channels and can also bond the 3rd DOCSIS 2 upstream channel which is present in some areas to deliver 81Mb via 3 channels to a service group.
The restricting factors are that more channels means lower maximum transmit power, so modems have to be 'lined up' on the network differently, less attenuation on the return path, and SNR, higher order modulations require better SNR, 3dB per exponent increase so moving from the regular 16QAM to 64QAM, 18Mb per channel to 27Mb per channel, requires 6dB better SNR.
Another potential issue, though this won't be such a big deal given most of it should have been dealt with during the move from DOCSIS 1.1 to DOCSIS 2 upstreams, is the capacity of the upstream lasers. More and higher order upstreams means more power input to the lasers from the coaxial part of the network, and some older fibre optic nodes with legacy transceivers may struggle and need replacement.
So the keys are ensuring the network is clean enough, through busting ingress and fixing rogue plant, to carry the maximum 4 6.4MHz upstreams at 64QAM, ensuring the network is properly lined up so that modems aren't pushed over maximum transmit power by the increased number of upstreams, and ensuring that the fibre nodes have the transceiver to carry the channels.
The first 2 of those are actually routine network maintenance, if the network isn't kept clean and properly lined up the fault rate goes up as it becomes inadequate for current demands, only the 3rd is exceptional.
It's for the most part about blokes in vans doing the maintenance, not about upgrades, hence labour costs not capital expenditure.
They can do it, it just costs money. Without the business case to increase the urgency it's an 'as and when'.