Compared with 2g, 3g and 4g, what network elements does the ran access network lack?

A controller that manages the base station. For 2G and 3G, RAN includes two network elements: a base station and a controller that manages the base station. By 4G, the network began to flatten, the controller was cancelled, and the base station was directly connected to the core network, indicating that the controller network element for managing the base station was mainly missing. Wireless access network is a part of mobile communication system. It is the realization of wireless access technology. It exists between devices (such as mobile phones, computers or any remotely controlled machines) and the core network (abbreviated as CN), providing communication connection between them.