In HDLC (High-Level Data Link Control), the three data transfer modes are:

1.In summary, NRM is suitable for point-to-point communication, ARM provides flexibility for the secondary station to initiate communication, and ABM is ideal for peer-to-peer communication where both stations have equal roles in initiating and responding to frame transmissions.- ARM allows the secondary station to initiate transmission without waiting for a specific request from the primary station, providing more flexibility in communication initiation compared to NRM.Asynchronous Balanced Mode (ABM): ABM is a bidirectional mode where both stations can initiate frame transmission and respond to frames from the other station.Comparison:

- NRM is a unidirectional mode where the primary station initiates communication, and the secondary station responds.This mode is suitable for peer-to-peer communication between two stations.2.3.