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RNTI stands for Radio Network Temporary Identifier that is allocated by the UMTS UTRAN, LTE E‐UTRAN, and 5G NG‐RAN to UEs. An RNTI uniquely identifies a UE and is used during the communication between UTRAN or E‐UTRAN or NG‐RAN and a UE over their air interface: Uu. The RNTIs used in the LTE system is described below:

 LTE E‐UTRAN: Allocation of RNTIs, TS 36.300 [92]

LTE E‐UTRAN also allocates several RNTI types to address a particular UE over its air interface. However, unlike the UMTS system, it is also possible to address multiple UEs in the LTE system. This is because the LTE E‐UTRAN uses the physical downlink shared channel (PDSCH) to transmit control as well as user data to a UE. Thus, a mechanism is required by an LTE UE to differentiate the type of information received from the E‐UTRAN. To achieve this, different types of RNTIs are used by E‐UTRAN as described below. For more information on LTE RNTI values and usages, refer to TS 36.321 [93]:

 System Information (SI)‐RNTI – It is used to broadcast system information from the E‐UTRAN to the UEs/cell through the Broadcast Control Channel (BCCH). SI‐RNTI is part of the cyclic redundancy check (CRC) added to the contents of the downlink control information (DCI) format 1A.

 Paging (P)‐RNTI – It is used by the UEs for the reception of paging from the E‐UTRAN through the Paging Control Channel (PCCH).

 Cell(C)‐RNTI – C‐RNTI uniquely identifies a UE having RRC signaling connection, and scheduling, with E‐UTRAN in a particular cell. C‐RNTI is used by the E‐UTRAN to provide an uplink transmission grant and downlink assignment.

 Temporary C‐RNTI – It is generated by the MAC layer of an eNodeB and sends it in the Random Access Response (RAR) to the UE as a response to the Random Access Preamble transmitted by the UE. Temporary C‐RNTI is later changed to the C‐RNTI once the UE contention is resolved at the eNodeB end.

 SPS‐CRNTI – Semi‐Persistent Scheduling RNTI is used in case the SPS activation/reactivation/retransmission is performed.

 TPC‐RNTI – It is used to send Transmit Power Control command to a UE.

 Random Access (RA)‐RNTI – RA‐RNTI unambiguously identifies which time‐frequency resource was utilized by the UE to transmit the Random Access Preamble. The eNodeB uses the RA‐RNTI in the RAR from the E‐UTRAN to UE. The eNodeB scrambles Physical Downlink Control Channel’s (PDCCH's) CRC with RA‐RNTI for transmission of PDSCH that carries RAR(s).

 M‐RNTI – It is used to notify a UE about an MCCH information change.