"connection time-out occurred" when my mac goes to sleep.

When My macbook goes to sleep I get a "connection time-out occurred" when I try to connect to the internet. and I have to restart my mac and restart the router. The is always a BT hotspot page displayed on the screen.

I have a 2011 macbook pro. This happens on my son's as well. he has the same model. he recently got a new retina display macbook and there hasn't been any problems. this doesn't happen on our phones either.

-Thanks for any help