Pan2 (are you Pan ?)
The Immediate assignment command doesn’t need a Paging Group.
It is sent over the AGCH, not the PCH. If a MS listens to AGCH, it will listen to ALL the AGCH blocks.
Indeed, a MS on the AGCH is not “idle” anymore. It is setting up a call (either originating the call, or merely replying to a paging that was previously sent on the PCH).
DRX Mode applies only when the MS is in Idle Mode, listening to the Paging Requests.