Hello Pride,
Here Sankha. See when a speed of a net connection gets down, many reasons work behind it. The most common is your telephone line. Here the wire they are providing may get carbonized and at that time you will get a noise in your phone. The internet and the speed will disturb at that time. Then problem may also occur at their local BSNL exchange from where your connection came. And moreover, the connection may also get slowed down due to your machine cookies. So there are some ways every net user should follow to keep their machines light and their lines not get jammed, one of which is deleting these cookies periodically.

If you have any more questions or any problem, contact me freely. I'll help you as much as I can.