Hello Vijay,
in GPRS we have TBF, USF and TFI
– TBF can be from net. to MS or vice versa ( temporary block flow )
– USF (uplink status flag)
– TFI (temporary flow indetifier)
USF is used (on a PDCH basis)
to allow multiplexing of uplink Radio blocks, from a number of MSs, in the same PDCH.
In DL, from the TFI the MS detects its own data transmitted, while from the USF the MS knwos when it can transmit on the next uplink block
so by this, MSs can be multiplexed and the network knows which block belongs to which MS.
Good Luck