Simple questions (RID, fragmentation, handover)

[yamada kenta]

Hi all,

I am new to HostAP. 
I have three questions as follows.

1. 
What's RID ? I think it Resource IDentifier. 
And if RID is Resource IDentifier what's this?
 
2. 
When Packet size is larger than 802.11x frame size , packet is
fragmented. Is this fragmentation processed by firmware or HostAP driver ?

3. 
How to select APs when handover happend ? 
and Is this event processed by firmware or HostAP driver ?

Can anybody please answer these questions ?
Thanks in advance,

Yamada Kenta