Abstract Among the exchanging link protocols, HDLC is becoming more and more popular. But the standards which define it contain options and parameters to be selected according to the actual environment. A model of the information exchange phase of a balanced HDLC link is presented. The choice of two parameters (the maximum window width and a timer constant) is discussed with the help of simulation results. Information frames are of random length and two types of Supervisory frames are used (RR and REJ). The link has been simulated in saturated and nonsaturated situations with different transmission error rates. P/F checkpointing is not used, line propagation times are neglected. The illustrated performances include the link efficiency and various delays associated with the transmission of Information frames.