Whats the solution to this problem ?
: Actually of the main reason of this problem is due to Telephone line errors, i.e. firstly check your telephone line for cracks and joints, try to avoid the joints in the telephone line straight from the Pole.
If there is any problem in Telephone line , contact your nearest BSNL telephone exchange and get the problem solved by putting new cable (This trick and also increase your Internet speed too).

If the wiring the nice and without joints, just do one trick .
Put off the dial of your telephone,(also try to hit the button below the dial two three times to get the link , if its gone) means your telephone will stay engaged. but due to this your line will get higher priority than others so link problem will get solved and your can enjoy the constant , high speed broadband . or try resetting your router.
Note that : This trick will keep your telephone engaged , so better use it when you are need of Broadband but not the telephone.

I personally own Dareglobal DB108 Router, and its working fine with this trick.
Even if the problem persists do contact me