Do not assume that you will get the speeds the operators advertise in their advertisements.
Fixed Internet service providers (ISPs) have to mention the minimum, maximum and generally available speeds in their contracts and on their websites as well.
A BIPT Decision defines how these values have to be interpreted concretely, taking into account the set-up of networks in Belgium:
The actual speeds shall be between the minimum and maximum speeds and preferably as close as possible to the generally available speed.