USF Uplink State Flag
The Uplink State Flag is used on PDCH (Packet Data Channel) to allow multiplexing of radio blocks from a number of GPRS mobiles. USF is used in dynamic and extended dynamic medium access modes. The USF comprises 3bits at the beginning of each Radio Block that is sent on the downlink. It enables the coding of eight different USF states which are used to multiplex the uplink traffic.
