mobile synchronization for the uplink direction; - Allocation of a resource (UL Grant) for the uplink direction SO that the mobile can transmit the following RRC messages: - Request for connection establishment, - ReestablishmentRequest for connection re-establishment, - ReconfigurationComplete when a handover occurs; - Temporary Cell Radio Network Temporary Identifier (TC-RNTI) allocated to the mobile. Unitary Unitary Unitary Unitary header header header message header message Octet 1 Octet 1 RAPID message Figure 8.20. MAC RAR structure of frame 8.4.3. Control element 8.4.3.1. BSR control element The Buffer Status Report (BSR) control element is transmitted by the mobile to provide the memory status in order to obtain the resource for transmission in the Physical Uplink Shared Channel (PUSCH). The BSR control element can be transmitted periodically, when new and priority data are stored in the memory, or when the size of the MAC frame filling field is greater than that of the control element. The short and truncated report provides the status of a single memory and contains two fields: - the Logical Channel Group (LCG) ID field identifies the group of logical channels assigned to that memory; 5G-NR Radio Interface - Data Link Layer - the Buffer Size field contains an index corresponding to the size of data available in the memory. The long report provides the status of all the memories and contains the four Buffer Size fields corresponding to the four logical channel groups. 8.4.3.2. C-RNTI control element The Cell Radio Network Temporary Identifier (C-RNTI) control element contains the identifier assigned to the mobile during random access. The C-RNTI control element is transmitted by the eNB entity simultaneously with the RRC ConnectionSetup message. 8.4.3.3. DRX control element The Discontinuous Reception (DRX) control element enables discontinuous reception to increase the battery life. If the mobile is idle, in the RRC-IDLE state, discontinuous reception allows it to avoid analyzing all of the Physical Down