[pmontra]

Very difficult to do that with ADSL. The bandwidth varies for every customer, according to the length and the status of their copper cable. They should advertise the minimum bandwidth of some reference cable but how does it help us?

With fiber, yes, that's possible. They're not advertising it in commercials but the website of my ISP has a page with those data. It matches what I experience with fiber.

[nordify]

For ADSL you define classes. Then for each class (i.e. line speed that you sync at) you offer speed guarantees.

[c3833174]

Stability of the sync should also be taken into account, to ensure the connection doesn't drop continuously at peak hours.