iMac reachability over sleep I've got an issue with my iMac...

Let me explain the configuration:


The router is connected to the internet, the WiFi is turned off.
Time Capsule is connected to the router with an ethernet cable, it's in Bridge Mode, the WiFi is set to 802.11 n only, the 5GHz is set to channel 36 and the 2.4GHz is set to channel 8.
Airport Express is connected to the network created from Time Capsule, it extends the network in 2.4GHz (this AirPort Express doesn't support dual bands).
Apple TV is connected to the network in 5GHz.
iPad 2 is connected to the network in 2.4GHz.
iMac is connected to the network in 5GHz.
iPhone 4S is connected to the network in 2.4GHz.
MacBook Pro is connected to the network in 2.4GHz.
The printer is connected to the network in 2.4GHz.


The trouble is:


When the iMac is in sleep mode, after a few hours it dissapear from the network. So I cannot access it while on the go with my iPhone through 3G network, neither from my Macbook Pro on the same network.


Well, I hope everything is clear to understand...

Thanks in advance
I found someone else with this specific problem.  My understanding is that Apple's Airport Base Stations simply "forget" the previously attached computer.  

Two things to check:


Create a static IP address in network configuration on the iMac
in Airport Utility make sure you've created a MAC address based DHCP reservation for this iMac.  Apparently, the AEX AEB &amp; TC will still "forget" but it might be longer now, like 6-8 hours.  


The work around: using either and application or System Preferences > Energy Save schedule the iMac to "wake up" and turn back off every 6 hours or so if not being used.  This should re-up the IP.  Alternatively, DD-WRT router software supports WOL out of the box.  Wireless WOL is not part of the spec, however, I believe wireless WOL is an Apple deal.