The radio access network (RAN) is the part of a telecom network that sends radio signals to your phone and receives the signals your phone sends. It includes the towers, the radio units and antennas mounted on them, and the software that controls them. RAN is the part of the network that an operator spends the most on, because a country as large as India needs lakhs of tower sites.
Imagine a one-day cricket match at a stadium in Kolkata. Sixty thousand fans try to post videos at the same moment. Every phone in the stadium needs a share of a limited amount of radio spectrum, the range of frequencies the operator has bought from the government.
Outside the stadium, the radio units and antennas on nearby towers send and receive the signal. Each radio unit focuses separate beams on separate groups of phones, so many phones can use the same frequency at once. In the crowded streets around the ground, small cells on poles add extra capacity close to the people. Inside the stands and the concrete corridors, a distributed antenna system (DAS) places small antennas throughout the building. It carries the signals of every operator.
Every millisecond, the RAN software decides which phone may send or receive in which slot. It then passes the data to the packet core. With Open RAN, this software and the radio hardware can come from different companies.
The same parts can also serve one company only. A port or a factory can run private 5G, its own small network, where only its machines and staff may connect.