Set Asynchronous Balanced Mode (SABM) is a command of the LAP-B protocol that is transmitted in the Unnumbered Frame
(U-Frame). SABM is used to establish a connection at the link layer, namely for the connection between the network node and the end device as well as in the opposite direction. SABM ensures the start of the equal spontaneous operation at which one of the two stations initiates the connection setup. In doing so, the counters for the data blocks of both stations are set to zero. The data blocks themselves are transmitted as information frames, I-frames
. SABM operates in modulo 8 mode and ensures that an active station is present on the physical layer. The extended operating mode with modulo 128, which is used to activate the HDLC extended mode, carries the abbreviation SABME.