The C-RNTI is allocated by the CRNC and uniquely identifies a UE within one cell. The existence of the UE at a given moment in time is optional. However, if common transport channels (FACH, CPCH, RACH) shall be used as bearer for DCCH- / DTCH-logical channels, the allocation of the C-RNTI is mandatory. This applies in particular in CELL_FACH-state.