Airport Extreme drops connection when MacBook sleeps

If I let my MacBook go into sleep mode, and then wake it up, my wifi connection to my Airport Extreme is gone. Even if I click on the airport icon in the toolbar the MacBook does not see the network. I have to restart the MacBook in order to get the wifi connection back. I have the latest update in the Airport and in the MacBook. Anyone have any ideas how to fix this issue?

What kind of router do you have? Did you upgrade the firmware? What wireless encryption are you using?

I used to have that problem on my macbook pro 13" but once I upgraded the firmware and then changed the wireless encryption to WPA (you might even try to change it to WPA2 if your router supports that) and then BAM no more problems and everything has been smooth and relatively faster. Hope this helps.

Already using WPA2 encryption. Router is an ADSL unit called Billion. I can't see how the router could be the problem though as it is in line after the Macbook and the Airport Extreme. They are the ones not shaking hands when the Macbook wakes up.