Section: 6.2.3 MAC payload for Random Access Response
Content: The MAC RAR is of fixed size and consists of the following fields: - R: Reserved bit, set to "0". For a BL UE or a UE in CE, this bit is set to "1" to indicate that an UL Grant in Random Access Response is for EDT; - Timing Advance Command: The Timing Advance Command field indicates the index value TA (0, 1, 2… 1282) used to control the amount of timing adjustment that the MAC entity has to apply (see clause 4.2.3 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]), except for NB-IoT UEs using preamble format 2, where the Timing Advance Command field indicates the index value TA (0, 1, 2… 1536). The size of the Timing Advance Command field is 11 bits; - UL Grant: The Uplink Grant field indicates the resources to be used on the uplink (see clause 6.2 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2], or for NB-IoT UEs, see clause 16.3.3 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]). The size of the UL Grant field is 20 bits, except for NB-IoT UEs, where the size of UL grant field is 15 bits, and except for BL UEs and UEs in enhanced coverage level 2 or 3, where the size of the UL grant field is 12 bits. - ER: Extended RAPID bits, indicating the two least significant bits of extended RAPID used when PRACH preamble format 2 is transmitted. - Temporary C-RNTI: The Temporary C-RNTI field indicates the temporary identity that is used by the MAC entity during Random Access. The size of the Temporary C-RNTI field is 16 bits. The MAC RAR is octet aligned.