The broadcast control channel (BCCH) is a point to multipoint, unidirectional (downlink) channel used in the Um Interface

Um Interface

The Um interface is the air interface for the GSM mobile telephone standard. It is the interface between the mobile station and the Base transceiver station . It is called Um because it is the mobile analog to the U interface of ISDN. Um is defined in the GSM 04.xx and 05.xx series of...

 of the GSM cellular standard.
The BCCH carries a repeating pattern of system information messages that describe the identity, configuration and available features of the Base transceiver station

Base Transceiver Station

A base transceiver station or cell site is a piece of equipment that facilitates wireless communication between user equipment and a network. UEs are devices like mobile phones , WLL phones, computers with wireless internet connectivity, WiFi and WiMAX gadgets etc...

 (BTS). These messages also provide a list of Absolute radio-frequency channel numbers (ARFCNs) used by neighboring BTSs. This message pattern is synchronized to the BTS frame clock. The minimum BCCH message set is system information messages 1–4, although other messages are normally present. The messages themselves are described in 3GPP Technical Specification 44.018.

Any GSM ARFCN that includes a BCCH is designated as a beacon channel and is required to transmit continuously at full power.