Section: 5.2.1 EPS bearer identity
Content: An EPS bearer identity uniquely identifies an EPS bearer for one UE accessing via E-UTRAN. The EPS Bearer Identity is allocated by the MME. When using an EPS Radio Bearer, there is a one to one mapping between EPS RB and EPS Bearer, and the mapping between EPS RB Identity and EPS Bearer Identity is made by E-UTRAN. The E-RAB ID value used at S1 and X2 interfaces to identify an E-RAB is the same as the EPS Bearer ID value used to identify the associated EPS Bearer. When using Control Plane CIoT EPS Optimisation for user data transport for the PDN connectivity service, the MME (for uplink) and UE (for downlink) uses the EPS Bearer Identity contained within the NAS PDUs to identify the associated EPS bearer. When there is a mapping between an EPS bearer and a PDP context, the same identity value is used for the EPS bearer ID and the NSAPI/RAB ID. In some SM signalling messages in GERAN/UTRAN, transaction identifier (TI) represents NSAPI. The TI is dynamically allocated by the UE for UE-requested PDP context activation, and by the network for network-requested PDP context activation. A corresponding allocation is also needed for EPS Bearers in order to successfully transfer Bearers to GERAN/UTRAN. The TI is deallocated when a PDP context/EPS Bearer has been deactivated. TI usage is defined in TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7].