sport mechanisms. eCPRI Services Other Synchronization Connection OAM eCPRI SyncE IPSEC Ethernet MAC MACSEC Ethernet Ethernet PHY FIGURE 2-38 IQ sample protocol stack. Initial access Initial access is a complex topic in both 4G/LTE and 5G/NR systems, which touches on CU (CP), DU (MAC layer, PRACH), and RU (PRACH) components. We provide a high-level 88 Open Radio Access Network (O-RAN) Systems Architecture and Design To M/S-Plane and control U-Plane From 2G/ Tx IQ plane 3G/4G/5G C-Plane Compress Buffer Modem C-Plane eCPRI U-Plane Manager framer C-Plane C-Plane Manager Ethernet U-Plane To 2G/3G/ Rx IQ 4G/5G U-Plane De-compress Buffer Modem FIGURE 2-39 eCPRI protocol termination. eCPRI, Enhanced Common Public Radio Interface. overview of the process to explain the relevant components, focusing on 5G/NR deployment -but note that 4G/LTE uses a comparable procedure. Synchronization Before starting any communication between client and base station, the client needs to syn- chronize to the RAN both in time and frequency domain. Keep in mind that, unlike Wi-Fi, 3GPP networks are synchronous in nature and that this requires the client to acquire a notion of timing alignment before it can receive (or transmit!) anything. The first step in the synchronization procedure is reception of the Synchronization Signal Block (SS Block or SSB, refer to Fig. 2-40). The SSB is a handful of subcarriers that transmit primary and secondary synchronization channels as well as the Physical Broadcast Channel. The SSB is transmitted in a regular pattern defined by a burst set (one or more SSBs), a burst period and burst duration that are defined in 3GPP 38.213. For FR2/mmWave operation, SSB transmit pattern includes a beamforming aspects where each SS burst has a unique associ- ated (base station transmit side) beam associated with it, where the client can assume beam reciprocity to identify the direction it should transmit to during initial access later on. The SSB location in time (OFDM symbols 0, 1, 2, 3) and frequency (starting from subca