The firmware and power supply update done by Airtel technician did not help. The lines continues to drop during certain times of the day.
Had another Airtel technician(s) come over today to check the physical line out. The SNR levels (as measured via statsadsl.html on the modem’s HTTP interface) was <10db and the Total ES was >2. Ideally, the SNR should be >30db while the Total ES should be 0. I hope it stays fixed now.