claration of Conformity Service Data Unit Slave eNB Single Frequency Network Secondary Information Block Subscribed Identity Module Single Instruction Multiple Data Service Level Agreement Session Management Function Sequence Number Signal to Noise Ratio Semi Persistent Scheduling Signaling Radio Bearer Sounding Reference Signal Synchronization Signal Block Streaming Signaling Extensions Secondary Synchronization Signal Supplementary Uplink Software Telecom Boundary Clock Telecom Grand Master T-TSC Telecom Time Slave Clock International Atomic Time Transport Block Three Color Marker Transmission Control Protocol Temperature Controlled Oscillator Acronyms Telecom Infrastructure Project Time Division Duplex Time Division Multiplexing Tunnel Endpoint Identifier Transparent Mode Top of Rack Transmit Power Control Transmit Receive Point Time Sensitive Networking Transmit Time Interval Unmanned Arial Vehicle Uplink Control Information User Equipment Uplink ULSCH Uplink Shared Channel Unacknowledged Mode Unlicensed Mobile Access Universal Mobile Telecommunication System User Plane User Plane Function URLLC Ultra Reliable Low Latency Communication Coordinated Universal Time Vehicle to Infrastructure Vehicle to Pedestrian Vehicle to Anything Voltage Controlled Oscillator WCDMA Wideband Code Division Multiple Access Working Group Wireless Fidelity WiMAX Wireless Interoperability for Microwave Access Weighted Random Early Discard Open radio access network overview This chapter provides an introduction to the Open Radio Access Networks (O-RAN) (with a dash!) Alliance and its goals and main deliveries. We then discuss related standards bodies as well as 5G spectral aspects and a short history of 3GPP standards and their implementation in terms of sys- tems architecture. Note that although O-RAN standards cover both Long-Term Evolution (LTE) and 5G/NR networks, we are using 5G terminology throughout for simplicity and ease of reading. The Open Radio Access Networks Alliance Founding members of the O-RAN Alliance are AT&T, Chin