routing area occurs on the PDCH (= pdtch + pacch)
there is no SACCH in GPRS. a MS that sends data in uplink will be allocated “n” PDCH in UL (= pdtch + pacch) and 1 PACCH in DL, most of the time.
There is no closed loop power control in GPRS. The MFS doesn’t recommend any power control to the MS, because it is the MS that decides which TX POWER it should use, without any confirmation from MSC, BSC or BTS.
The GPRS UL PC is VERY specific, and is controlled by ALPHA and GAMMA radio parameters. It is not impacted at all by the GSM power control parameters.
When a TS is shared among 6 users (isn’t the max nb of UL users = 6 on one TS ??) then they will each send, in turn, a burst of data or signalling.