andrewNZ: Thanks Ray. That's a really good explanation.
However I still have concerns.
I'm already on a congested connection, so from what I see (assuming it applies to my location), some people can pay for a better connection, which WILL negativity affect the speeds of others at peak times.
This depends - I am not an expert as we are not chorus customers, but EUBA / BUBA dsl plans that the ISP's offer are only avaliable in certain areas.
So in some areas, an ISP may only be able to order a lower CIR dimensioned service.
The higher CIR's are pretty much avaliable if you are urban, or running off a newer cabinet.
But it is up to your ISP to order the service.
There are a large number of plans that the ISP can order, while still advertising to you a Full Speed / Full Speed PIR
I have shown you a very simplified diagram.
Yes it may be so that others can purchase a faster connection, if they find an ISP that is willing to order the higher priced service and sell it.
Most ISP's wont do this unless they need it to offer a voip or tv service over it though.
If you are in a badly congested area (like running off a conklin) then it probably wont affect you.
Chorus wont be able to offer the higher CIR service because the 12 ports on a conklin would exceed the 2mbit ATM backhaul if all end users ordered the 250kbits CIR
Personally, I see some basement dwelling accountant has stuck his hand up and said "we have found a potential problem, which could bite us in the bum in 5 years time, we better fix it now before we fail on delivery standards"