G.dmt or ADSL2+ ?

Hello guys,On my 220BX modem, I had ADSL2+ enabled earlier, the ping I was getting to speedtest New Delhi server was 55-60 ms,Today I went to the router settings, unchecked everything except G.Dmt, and now my pings are WAY better, New delhi is 15-25 ms now, Singapore/ HK are also 40-50 ms lower , What I wanna ask is, what is the difference between G.dmt mode and adsl2+ mode?

To some (like myself) G.Dmt gives more stable connection, but ADSL2+ is supposed to be more advanced mode.