There's a solid definition, including things that affect the experienced data rate at: http://whatis.com/dsl.htm

I've emailed this, per your request but figured others might be interested, too.

In my case I passed loop qualification for 1.2Mbit/s downspeed and 384Kbit/s upspeed (ADSL). That doesn't mean I see those rates. In reality I get reliable, tested speeds of about 784Kbit/s bi-directionlly for a measly US$60.00/mo. including a /28 netmask of static IPs.

I'm not complaining, but affordable VDSL would be nice -- can you say 52Mbit/s bidirectional??? I thought you could! =]

-- Bleys

"If you would judge, understand." -- Seneca