RAN software and Open RAN are two sides of the software that controls a mobile tower's radios. RAN software decides, every millisecond, which phone may send or receive, and it processes the radio signals into data. RAN stands for radio access network. Open RAN is a way of building this network in which the software and the radio hardware can come from different companies, because both follow a public standard.
The software has two main layers. The first layer, called the distributed unit, works close to the radio. It does the fast signal processing and the scheduling, which means sharing out the radio time and frequencies among the phones. The second layer, called the central unit, handles slower tasks. It sets up each phone's connection, manages handovers from one tower to the next, and passes the data to the packet core. The radio unit on the tower only converts between radio waves and digital samples.
Traditionally, an operator bought all of this as one sealed package from one equipment maker. The radio unit, the software and the computer it ran on came together, and they connected to each other in ways that only that maker knew. To add a new feature, the operator waited for that maker.
Open RAN changes this. The O-RAN Alliance, a group of operators and suppliers, publishes standard interfaces between the radio and the software. The software runs on ordinary servers, like any other program. So an operator can buy radios from one company and the software from another. This is the tower's version of hardware-software disaggregation.
Say an operator is adding 4G and 5G coverage to 300 villages in a district of Rajasthan. Under the old model, it would buy every site as one package. Under Open RAN, it buys radio units from one maker and the RAN software from a second company. The software for 30 nearby sites runs on a few servers in one building in the district town. When the software company releases a new scheduling feature, the operator installs it on those servers, as it would update any application.
Open RAN also brings a new piece, the RAN intelligent controller. It runs small add-on programs, often written by third parties. One program might switch off part of a radio at 3 a.m., when there is little traffic, to save electricity.
Open RAN has costs too. When parts come from several companies, someone must test that they work together, and someone must answer when they do not. The software sends fault reports to telecom service assurance systems, which help the operator's teams find the cause.