1*63213Sbostic/* 2*63213Sbostic * Copyright (c) University of British Columbia, 1984 3*63213Sbostic * 4*63213Sbostic * @(#)README.hdlc 7.1 (Berkeley) 06/10/93 5*63213Sbostic * 6*63213Sbostic * X.25 HDLC DATA LINK LEVEL: 7*63213Sbostic * 8*63213Sbostic * 9*63213Sbostic * This module implements the Link Level of the Open Systems Interconnect 10*63213Sbostic * Model. The implementation is based on the ISO High-Level Data Link 11*63213Sbostic * Control (HDLC). These procedures subscribe to the principles of the 12*63213Sbostic * ISO-Class of Procedures for point-to-point. These procedures implement 13*63213Sbostic * two-way asynchronous balanced mode (LAPB) as recommented by the CCITT. 14*63213Sbostic * 15*63213Sbostic * The HDLC protocol layer interface consists of the following procedures: 16*63213Sbostic * Hd_init (pr_init) 17*63213Sbostic * Hd_ouput (pr_output) 18*63213Sbostic * Hd_input (pr_input) 19*63213Sbostic * Hd_timer (pr_slowtimo) 20*63213Sbostic * 21*63213Sbostic * Note: Supervisory commands RR, RNR and REJ are not transmitted by this 22*63213Sbostic * station. 23*63213Sbostic * 24*63213Sbostic * This station never enters a busy (RNR) condition. 25*63213Sbostic * 26*63213Sbostic * The "Generate_rr" variable can be set to FALSE. This means that 27*63213Sbostic * we NEVER send an RR. This works just fine if the network level 28*63213Sbostic * is X.25 packet protocol -- which it is. 29*63213Sbostic * 30*63213Sbostic * Currently, this is only a DTE implementation. 31*63213Sbostic * 32*63213Sbostic * Think about: 33*63213Sbostic * If the remote is busy, no iframes are sent. The remote sends a RR 34*63213Sbostic * to clear this condition. However, this RR may be damaged, causing 35*63213Sbostic * a possible deadlock. A solution is to poll with iframe (P(S)==P(R) 36*63213Sbostic * of RNR) indefinitly. 37*63213Sbostic * 38*63213Sbostic * 39*63213Sbostic * Date: February 1984 40*63213Sbostic * 41*63213Sbostic * Author: Gerald W. Neufeld 42*63213Sbostic * 43*63213Sbostic * Installation: Department of Computer Science 44*63213Sbostic * University of British Columbia 45*63213Sbostic * Vancouver, BC, CANADA. 46*63213Sbostic * 47*63213Sbostic * History: 48*63213Sbostic * 49*63213Sbostic * 50*63213Sbostic */ 51