Roaming in ESS network

[代尔欣 <daierxin gmail com>]

Hi all,
     Have an question about roaming in ess network, NetworkManager support this capability or not? From the NM codes, after established the wifi connection, the NM semms in idle state and just listening some signals. So seems NM itself can't do this. Then which  module handle the roaming action? driver? wpa_supplicant? Hardware? My understanding is driver, if it is, those drivers in linux distrubition support or not? or need open some compile options? 

Thanks!