1/* 2 * Copyright (c) University of British Columbia, 1984 3 * 4 * @(#)README.hdlc 8.1 (Berkeley) 06/10/93 5 * 6 * X.25 HDLC DATA LINK LEVEL: 7 * 8 * 9 * This module implements the Link Level of the Open Systems Interconnect 10 * Model. The implementation is based on the ISO High-Level Data Link 11 * Control (HDLC). These procedures subscribe to the principles of the 12 * ISO-Class of Procedures for point-to-point. These procedures implement 13 * two-way asynchronous balanced mode (LAPB) as recommented by the CCITT. 14 * 15 * The HDLC protocol layer interface consists of the following procedures: 16 * Hd_init (pr_init) 17 * Hd_ouput (pr_output) 18 * Hd_input (pr_input) 19 * Hd_timer (pr_slowtimo) 20 * 21 * Note: Supervisory commands RR, RNR and REJ are not transmitted by this 22 * station. 23 * 24 * This station never enters a busy (RNR) condition. 25 * 26 * The "Generate_rr" variable can be set to FALSE. This means that 27 * we NEVER send an RR. This works just fine if the network level 28 * is X.25 packet protocol -- which it is. 29 * 30 * Currently, this is only a DTE implementation. 31 * 32 * Think about: 33 * If the remote is busy, no iframes are sent. The remote sends a RR 34 * to clear this condition. However, this RR may be damaged, causing 35 * a possible deadlock. A solution is to poll with iframe (P(S)==P(R) 36 * of RNR) indefinitly. 37 * 38 * 39 * Date: February 1984 40 * 41 * Author: Gerald W. Neufeld 42 * 43 * Installation: Department of Computer Science 44 * University of British Columbia 45 * Vancouver, BC, CANADA. 46 * 47 * History: 48 * 49 * 50 */ 51