I have been using MTNL broadband 512 Kbps unlimited plan since Feb 2011. Till Aug 2011 everything was fine and i was getting download speed 60+ kbps. Then first my line got some problem that was rectified and then my modem (provided by MTNL delhi) went defective. I got that changed four times but the problem persists till date. the problem is frequent disconnections sometime lasting up to hrs. When i open 192.168.1.1 and login two modems always shown me as guest, i have to login by my landline no and by CA no and save & reboot the modem. Now that is not the scene with my present modem but when i open 192.168.1.1 sometimes it gives me a msg DT 815 and i can not log in sometimes the msg DT 815 is not there and i can login. I tried one of my friends modem it worked fine.
My SNR margin on both modems is 32 - 35db (down stream)
Line attenuation is 24 - 28 db (down stream)

Then i started pinging the 192.168.1.1,
With my present modem
When i am connected the time is >=1ms and TTL is 64
when the msg DT 815 come time varies between 28sec to 38 sec and TTL also varies sometimes 224, 254.
Sometimes the time is in 100-400 ms

With my friends modem
Time is always >=1ms and TTL is always 254 and i am always connected.

The MTNL rep visited two times last week with some old modems but all modems worked as my present modem is working. (did not work)

I am not a very technical person but i am trying to provide as much detail as i can, may some one please tell me what exactly is problem with my connection. Could it be line problem or is it modem problem. My modem did not work on my friends line. I assume modem to be defective, but MTNL rep initially tired to blame that windows OP is corrupt. But it works on other connection. Today he blamed line and asked me to contact lineman which i will do tomorrow. I want know if i buy a modem will it solve the problem?