- Normal Response Mode (NRM)
- A Secondary station running in an Unbalanced communications environment may may only communicate when signalled to do so by a Primary.
- Asynchronous Balanced Mode (ABM)
- hen in a Balanced communications environment, either Combined station may initiate communications. (LAPB Mode on combined stations only.)
- Asynchronous Response Mode (ARM)
- When in an Unbalanced environment, the Secondary may transmit at will, however the Primary is still responsible for error detection, line and flow control.