link access protocol Bm (LAP-Bm)

The LAP- Bm protocol is used for bit- synchronous data transmission on the link layer.

LAP-Bm(Link Access Procedure Bm) is the adapted version of the LAP-B protocol for secure user data transmissionin GSM systems. The "B" stands for Balanced and indicates that the communicating stations, namely base station and mobile station, have equal rights; the "m" stands for mobile.

Since both communication partners in a mobile radio system can be master and slave station, the respective master station organizes the transmission and requests the receiving station, the slave station, to accept and confirm the data. In the case of opposite transmission, the stations' areas of responsibility are reversed.