Rule of thumb when determining which protocol you'll be dealing with that I follow, is that if your upload speed is under 1mbit (ie: 860, 786, etc), your doing ADSL. Anything above 1.5mbit upstream is VDSL2+. It is very hard to support higher then 860 or so on the upstream side with ADSL/2/2+ thanks to line quality, etc.
From my own experiences with Verizon and Qwest, if you have 768/1.5/3 (and sometimes 7) down, you'll see your modem link at G.DMT (ADSL), which means you can use modems from the era of the Cisco 678, early Zoom, etc. From what I can tell, the CO techs will specifically configure the older ADSL protocol with the slower speed, rather then using ADSL2 with the slower speeds. I'm not sure why exactly - maybe their equipment auto picks that protocol without them needing to manually configure it.
7 and above, your going to link at ADSL2/ADSL2+, which will work with any of the more recent ADSL modems like the Cisco 857/877, Actiontec GT7xx series, Q100, etc.--
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