asynchronous balanced mode (HDLC) (ABM)

The Asynchronous Balanced Mode (ABM) is a basic operating mode of the HDLC protocol. In ABM mode, all stations have equal rights. Local Area Networks is an operating mode used in the upper sublayer, Logical Link Control( LLC), of the link layer. Devices connected to a local area network( LAN) can use ABM operation to send connection commands and initiate responses independently of each other.

In bit-oriented control methods, Asynchronous Balanced Mode refers to a mode of operation in which each station is independently responsible for its temporary transmissions and spontaneously controls them as a master station. The receiving station is the slave station and executes the commands of the master station. Since both stations can act as master or slave station, one also speaks of hybrid stations, which can send and receive unsolicited DCE blocks. This mode of operation is enabled by a control block; it refers to transmission equipment. Recovery procedures initiated by a hybrid station may be valid for one or both transmission facilities. ABM operation is implemented in LAP B and in High Level Data Link Control (HDLC).

In contrast to ABM operation is Normal Response Mode( NRM) with one-way communication without symmetric command structures.