Flow Protocols

At the transport level, data is exchanged through either a half-duplex (HDX) protocol or a full-duplex (FDX) protocol.

When a half-duplex protocol is used, data flows in only one direction at a time, with one LU sending only and the other receiving only. In a half-duplex flip-flop protocol, both LUs recognize which LU has the right to send and which to receive. At specified times the partner LUs agree to change the direction so that the receiver can send and the sender can receive.

When a full-duplex protocol is used, data can flow in either direction at any time. Both LUs can send and receive without constraint.