Depends on the WISP.
Some of them do it properly, and they have a proper leased line.
The cheap (read crap) ones use multiple ADSL lines, and generally provide a poor service.
Ye that would be the proper way for sure put the price of diginet is seriously high is it even profitable? Unless they have a high contention ratio and or slow speeds surely a wisp in sa cant go down the diginet road unless they have 200+ clients. Imagine what a 30mbps diginet pipe costs.
Let me fix that lie for you:
You can run 20 people on an single 4mbs line and offer them an up to 256k uncapped account and they will still have a great service sometimes.
There ya go.
We backhaul using 802.11n over a otherwise where we can get it we connect using MetroConnect Fibre. We also run people over diginet via our Office DC, however we focus our licensed WISP on Voice products and inter-branch connections for clients rather than internet access.
The WISP should have a statement of quality of service that usually guarantees a minimum rate which takes account of their conduct. As mentioned GT is the neck of the bottle, not the wireless network.