It's asynchronous
I believe it's a two way thing. At the moment it's a bit like upload speeds. You get more speed down than up on current DSL technology.
Likewise ISP's need to be a bit more transparent about how they handle traffic instead of burying vague terms and conditions way down in the smallprint which nobody reads because it's never supplied to them in the postal agreement nor is a link given to them in an email when you sign up online.
Basically ISP's need to stop hiding and lying about what you can do with your connection you are paying for. I understand that connections need to be traffic managed. Otherwise those few people hogging it 24/7 will impact everyone else. The reason prices are kept competive in the broadband industry is because they can squeeze so many customers into a limited pipe. There's no point buying bucketloads of fatpipes if it never gets utlized either. It's costlier to the ISP and the customer.
I have no issue with traffic management as long as it is made VERY clear in the T&C's. But the problem is ISP's advertise unlimited when in fact it clearly is not.
Same goes for BT who say they have just lifted the 300GB limit on their full fat milk Infinity package. As long as they were to send an email out to every customer letting them know this I would be happy with it. But I don't know if they have and it's only through news outlets like this one that we know of it.
Basically ISP's need to converse more with their customers and being honest about just what they mean by 'unlimited'.