SRNC, CRNC & DRNCCRNC: Controlling RNCSRNC: Serving RNCDRNC: Drift RNCSRNC and DRNC are concepts that are tied to a UE-UTRAN connection on the Uu interface. In other words, an SRNC serves a particular UE and manages the connections towards that UE. Likewise, DRNC fulfills a similar role to the SRNC except that it is involved only in the case of a soft handover.Thus the UE initially starts a connection with an RNC that becomes its SRNC. If the UE moves towards a cell edge, SRNC may decide to put the UE in soft handover state. If the new RLs added to UEs Active Set are under the control of a different RNC, that RNC becomes the DRNC.The terms CRNC, SRNC and DRNC are only logical definitions based on functionality. Physically, an RNC may be a CRNC+SRNC or CRNC+DRNC.CRNC is responsible for the controlling the resources of a Node-B. It manages common transport resources, code allocation, load and congestion control. If new radio links (RLs) are to be established CRNC does the job.SRNC manages the connection to the UE and maintains the UE context within UTRAN. (For this purpose, S-RNTI allocated to the UE identifies the UE uniquely within the SRNC. This identity is managed by the SRNC and will be reallocated during SRNC Relocation.) Thus, outer loop power control, handover and RANAP signalling are managed from the SRNC. DRNC manages resources under its control but relies on SRNC for most decisions and commands.