I’ve been trying to work out which of these two types of ADSL work best on my line as my line is quite noisy so there are lots of errors, even though the line is not particularly long.
Since moving to ADSL2+ last March I have noticed that the Ping Graph (which the ISP uses to monitor the health of the line) has been showing lots of green spikes which are generally NOT a good sign if this occurs when the line is inactive (ie overnight).
Compare these two graphs, firstly the one using ADSL2+:
with this one, where ADSL1 (g.dmt) is used:
The part of the graph I’m interested in is during the early hours of the morning where there is no activity. At this point there should be no variation in the ping time (the ISP pings my router once per second in order to create this graph) and i’d expect the ping to be about 12ms and vary by plus or minus 1ms. However when using ADSL2+ I get regular “ping spikes” where it’s up to about 30ms, but there are no “ping spikes” when using ADSL1.
Another thing I have noticed is that errors reported by my router are much lower when using ADSL1.
BT (who are the wholesale supplier to my ISP) monitor these errors and their systems will set a high noise margin when they detect errors. This meant that when I was “upgraded” to ADSL2 it had the effect of reducing my sync speed from 8128 to 6656 so the BRAS got reduced from 7.15mb/s to just 5.5mb/s.
I have since set my router to force ADSL1 so my sync speed has been restored to 8128, and it has another benefit in that the uplink is not throttled to 448kb/s any more and it’s now 1024kb/s. Prior to ADSL2 the uplink used to be capped at 448 or 896 depending on whether you have standard or premium service option, but luckily these silly caps have now been abandoned.