In order to understand how and why 802.11 (WiFi) devices behave as they do, it is invaluable to perform a wireless packet capture ("sniffer".) This can be especially important when working with Cisco TAC to resolve a technical problem. The following articles will help you to choose and use a wireless sniffer.
Additionally, there are several commercially available wireless sniffer products:
OmniPeek from WildPackets
AirMagnet WiFi Analyzer from Fluke
CommView for WiFi from TamoSoft
AirPcap from Riverbed (formerly CACE)
When providing Cisco TAC with wireless packet captures, please supply them in a format that is readable by current Wireshark, and that includes 802.11 meta data (RSSI, channel, data rate) - such as OmniPeek (Airopeek) or Netmon 2.0 format.