nt informa- tion for the random-access procedure to start. Random-access procedure After synchronization, the client can track the base station for time and frequency synchroni- zation purposes. It also is aware of allocated preamble format, transmit power, time/ 90 Open Radio Access Network (O-RAN) Systems Architecture and Design PBCH Payload Addit'nal timing related PBCH payload bits ao a1 a2 a3 a4 a5 a6 a7 a ag a10 a11 a12 a13 a14 a15 a16 a17 a18 a19 a20 a21 a22 a23 a24 a25 a26 a27 a28 a29 a30 Subcarrier spacing for SIB1, msg.2/4 for initial access and SI messages. <6GHz : 15/30KHz; >6GHz: 60/120KHz systemFrameNumber subCarrierSpacingCommon = Kssb , frequency offset between subcarrier 0 of SS/PBCH block to subcarrier 0 ssb_SubcarrierOffset of common resource block (offset-ref-low-scs-ref-PRB, Point A)- for SSB. dmrs_TypeA_Position pdcch_ConfigSIB1 cellBarred intraFreqReselection spare SS Block (PSS, SSS, PBCH) FIGURE 2-42 MIB content. MIB, Master Information Block. frequency resources, and other relevant parameters, through the RACH-ConfigCommon parameter that is signaled either through SIB1 or through an RRC reconfiguration messages with dedicated signaling (NSA operation). The client can now send a random-access preamble in the uplink (message 1), which triggers a random-access response (RAR) by the MAC layer of the base station (message 2). The RAR is transmitted in the DLSCH and includes a time advance command to communi- cate the base station estimated timing advance to be applied to compensate for over-the-air latency. It also includes an uplink grant that allocates time/frequency resources to the client and a temporary identifier (TC-RNTI) that (during the random-acces procedure) identifies the client. The first uplink transmission (message 3) from the client to the base station includes this TC-RNTI, a contention resolution identifier and a RRC connection request. The contention resolution identifier is used to resolve any potential contention associated with two clients picking the same preamble. This