iPhone/iPad unable to see iMac/Apple TV until router reboot (affects AirPlay, Remote app, Wi-Fi sync)

Every few days my iPhone (4) and/or iPad (3rd generation) lose their ability to "see" my iMac and/or Apple TV on the network. This means: * The Remote app shows zero sources available for Home Sharing (normally will show both the iMac and the Apple TV) * AirPlay cannot be used to send audio or video to the Apple TV * Wi-Fi sync will not work (states that it will resume when iMac is available) Power cycling my router (a Linksys E2000) fixes the problem temporarily, but it always comes back. Thanks for your help.