Cell roaming is not addressed in Wi-Fi or 802.11. If you use products from differing vendors, you may or may not lose data or lose your session when you roam from one AP to another. The problem occurs when in the process of sending data you associate to another cell. If your equioment is all Aironet, the data from the "old" AP is sent to the "new" AP via the ethernet, and then sent to the destination host from the "new" AP. This gives you "seamless" roaming.