 - the Shortened Temporary Mobile Subscriber Identity (S-TMSI), if the mobile is already connected; - a 40 bits random number, otherwise. 4) When the eNB entity receives the RRC ConnectionRequest message, it transmits to the mobile: - the Downlink Control Information (DCI) information in the PDCCH physical channel; - the heading MAC RAR containing the UE CRI (Contention Resolution Identity) control element. This control element reproduces the identity of the RRC ConnectionRequest message to resolve the contention issue. NG-RAN and 5G-NR The mobile extracts DCI information from the TC-RNTI identity. The mobile reads the description of its data in the PDSCH physical channel. The TC-RNTI temporary identity becomes the C-RNTI identity allocated to the mobile. 5) The mobile shows its C-RNTI identifier in the control element of the MAC frame and confirms the connection through the RRC ConnectionSetupComplete message. PRACH (Preamble) PRACH (Preamble) PRACH (Preamble) PDCCH (RA-RNTI) PDSCH / MAC RAR (TA, UL Grant, TC-RNTI) PUSCH / MAC RRC ConnectionRequest PDCCH (TC-RNTI) PDSCH / MAC (CRI) / RRC ConnectionSetup PUSCH / MAC (C-RNTI) / RRC ConnectionSetupComplete Figure 3.1. Random access with contention 3.1.2.2. Random access without contention The random access procedure without contention, i.e. when changing the cell during the session, is described in Figure 3.2. The mobile takes measurements on its cell and neighboring cells and transmits the results to the eNB entity in the RRC MeasurementReport message: 1) During the handover procedure based on the X2 interface, the source eNB entity provides the characteristics of the radio interface to the target eNB entity in a X2-AP HANDOVER REQUEST message. 2) The target eNB entity reserves the resources and responds to the source eNB entity with the X2-AP HANDOVER REQUEST ACK message. This message contains the information element Handover Command, which specifies the preamble the mobile must transmit to the eNB entity for the random access procedure. NG-RAN Network - Procedur