I think there is something called Autodisconnect in Windows. But it should show you a dialog box. My sister has photon and has no such issues.
BTW Tata is crap except for Tata Sky. I had got their cordless phone and net and suffered a lot. Even my ISP since last year had switched to Airtel for leasing bandwitdh. Even I did not know this but there is a remarkable increase in speed and decrease in downtime.