I myself use 4 mbps PTCL dsl at home and its great (with lower ping 50 ms or lower), i have absolutely no issues with it. We have optic fibre in our area too, so it supports high speeds easily.
If the phone lines are weak in the area, then people must use 1 mbps or two 2 mbps PTCL DSL at max. Higher speed DSL (4 mbps and above) cause problems in Internet.
I used to have 4 mbps connection with weak lines and it never worked good. Downgraded to 2 mbps and it got some better. Downgraded further to 1mbps and it got perfect. That's the solution to use PTCL DSL on weak phone lines.
Every modem shows those perimeters and conditions of phone line. Screenshots attached of my phone lines perimeters (with optic fibre, so results are very good).
