All the answers are in 3GPP documents. I believe you’ll find them in the serie 45.xxx …
The timer expires because it waits for an immediate assignment from the BTS, but actually there is no reply. It can be due to poor radio conditions or SDCCH congestion (and the “immediate assignment reject” message is disabled)
Well, all the above is correct if vanderley’s definition of T3106 is correct 🙂 (i’m sure it is)
I’ve no idea..