says:
It could be all the old DOCSIS 1.0/1.1 modems still in use which are cluttering up the network; I recall reading they generate more noise than the later versions.
We are due to be upgraded by VM to 50Mbit/s in October. I called "Customer Services" in March asking whether I could have a new modem as I am still running my fourteen year old Motorola Surfboard SB4100 (DOCSIS 1.0) and wouldn't they prefer such old kit off their network?
They still wanted me to pay £20 for the privilege so I still have it, although it won't ever reach 50Mbit/s when the higher speed kicks in.
Biting the hand that feeds IT
