ASUS RT N10U B1 Router is a 3G/4G Router which works well with many 3G Dongles including that of Airtel.
You could download the Router manual and see. The ASUS site also gives a list of compatible Dongles.
Now I have been trying to get an answer to two questions.
1. Can we use a 4G Sim card on a 3G dongle?
2. If that can be done may be we could get a compatible 3G Dongle, slip your 4G Sim card into that and use it with ASUS router.
Theoretically it is possible.
But then you have to experiment with a old 3G Dongle and the Asus Router.