Section: 4.7.6 Bearer Control Mode in EPC
Content: The Bearer Control Mode (BCM) for E-UTRAN access is always UE/NW. Hence, explicit signalling between the UE and the network to determine BCM for E-UTRAN access does not occur. GERAN/UTRAN/E-UTRAN capable UEs negotiate the BCM of a PDN Connection applicable for GERAN/UTRAN access during E-UTRAN Initial Attach and during UE Requested PDN Connectivity procedure. Such UEs provide the Network Request Support UE (NRSU) parameter to the PDN GW in PCO. The PDN GW derives the BCM applicable to GERAN/UTRAN access based on the NRSU and operator policy. The selected BCM, valid for GERAN/UTRAN, is provided back to the UE in PCO IE in the E-UTRAN Attach Accept or PDN Connectivity Accept message. The selected BCM is also stored in the PDN GW and the UE, and applied by UE upon moving to GERAN or UTRAN access unless explicitly informed by PDN GW of a change in BCM (see TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7]) via PCO IE. NOTE 1: In Rel-8 it was not mandatory for GERAN/UTRAN/E-UTRAN capable UEs to provide NRSU to the PDN GW during E-UTRAN Initial Attach and UE Requested PDN Connectivity procedure. When a GERAN/UTRAN/E-UTRAN capable UE moves from UTRAN or GERAN access to E-UTRAN access, it stores the BCM used in UTRAN or GERAN access to be used again when the UE moves back to UTRAN or GERAN access unless explicitly informed by PDN GW of a change in BCM (see TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7]) via the PCO IE. If PCC is deployed, the PDN GW requests PCRF to perform BCM selection for the RAT the UE is accessing at IP-CAN session establishment and IP-CAN session modification. The PCRF, determines the applicable BCM, based on a number of factors (see TS 23.203[ Policy and charging control architecture ]  [6]), and informs the PDN GW. If the BCM has changed, the PDN GW informs the UE of the new BCM via the PCO IE.