Cannot Wi-Fi Sync iPad; Appears to see iMac but iMac does not see the iPad

Question

Like many, I have upgraded my iPad (1st Gen) to iOS 5 and for the most part, it's been an easy transistion to learn the new features. However, I've not been able to overcome a Wi-Fi Sync issue.
The iPad does recognize that it can Wi-Fi Sync with my iMac.
When it was connected via cable, I had already selected the "Sync with this [iOS device] over Wi-Fi" Option in iTunes then clicked "Apply."
Under Settings > General > iTunes Sync on my iPad, the "Sync Now" button is grey when I connect to an alternate Wi-Fi network in our house, but when I am on the same Wi-Fi network as my computer, through an Apple Airport Extreme Basestation, the "Sync Now" button becomes actively black as it if recognizes my iMac, but it does not show up under iTunes to sync.
I connected the iPad to an alternate computer which is linked to iPhone running iOS 5 on the alternate Wi-Fi Network I spoke of earlier and through which we succesfully Wi-Fi Synced, but when my iPad was linked to this same computer (connected first by cable to enable "Sync with this [iOS device] over Wi-Fi" Option in iTunes first, it still would not show my iPad. And this time, not even my iPad would see the computer when on the same network, yet I could also see the iPhone mentioned which was upstairs.
I have tried following the steps in this Help Page (http://support.apple.com/kb/TS4062) but without any change. The only thing I haven't followed to the letter is restarting my router. I did tell my Airport Basestation to restart via the Airport Utility.
Has anyone else yet experienced this issue and been able to resolve it? Please share any insight.

Answer 1

When one device can't see another via Bonjour, it suggests a problem with how the network or the devices are handling "multicast" packets. Handling multicasts is tricky on Wi-Fi. Is there any way you can temporarily plug the iMac into the LAN port of the base station via an Ethernet cable, and try the sync that way? If that works, then it's a clear indication of multicast problems on your network.
Apple is usually very good about making sure multicasts work reliably on AirPort base stations and all Macs and iOS client devices. It would be interesting to know which generation of AirPort Extreme you have, what firmware version you're running on it, exactly which wireless security mode you're using (for instance, WPA2 "mixed mode", where both WPA2-style AES-CCMP and original WPA-style TKIP encryption are available, is trickier for multicasts because multicasts have to use a different cipher and key. "WEP TSN" is also tricky for similar reasons). Oh, and what you have your "multicast rate" set to on your base station.