163213Sbostic/* 263213Sbostic * Copyright (c) University of British Columbia, 1984 363213Sbostic * 4*63215Sbostic * @(#)README.hdlc 8.1 (Berkeley) 06/10/93 563213Sbostic * 663213Sbostic * X.25 HDLC DATA LINK LEVEL: 763213Sbostic * 863213Sbostic * 963213Sbostic * This module implements the Link Level of the Open Systems Interconnect 1063213Sbostic * Model. The implementation is based on the ISO High-Level Data Link 1163213Sbostic * Control (HDLC). These procedures subscribe to the principles of the 1263213Sbostic * ISO-Class of Procedures for point-to-point. These procedures implement 1363213Sbostic * two-way asynchronous balanced mode (LAPB) as recommented by the CCITT. 1463213Sbostic * 1563213Sbostic * The HDLC protocol layer interface consists of the following procedures: 1663213Sbostic * Hd_init (pr_init) 1763213Sbostic * Hd_ouput (pr_output) 1863213Sbostic * Hd_input (pr_input) 1963213Sbostic * Hd_timer (pr_slowtimo) 2063213Sbostic * 2163213Sbostic * Note: Supervisory commands RR, RNR and REJ are not transmitted by this 2263213Sbostic * station. 2363213Sbostic * 2463213Sbostic * This station never enters a busy (RNR) condition. 2563213Sbostic * 2663213Sbostic * The "Generate_rr" variable can be set to FALSE. This means that 2763213Sbostic * we NEVER send an RR. This works just fine if the network level 2863213Sbostic * is X.25 packet protocol -- which it is. 2963213Sbostic * 3063213Sbostic * Currently, this is only a DTE implementation. 3163213Sbostic * 3263213Sbostic * Think about: 3363213Sbostic * If the remote is busy, no iframes are sent. The remote sends a RR 3463213Sbostic * to clear this condition. However, this RR may be damaged, causing 3563213Sbostic * a possible deadlock. A solution is to poll with iframe (P(S)==P(R) 3663213Sbostic * of RNR) indefinitly. 3763213Sbostic * 3863213Sbostic * 3963213Sbostic * Date: February 1984 4063213Sbostic * 4163213Sbostic * Author: Gerald W. Neufeld 4263213Sbostic * 4363213Sbostic * Installation: Department of Computer Science 4463213Sbostic * University of British Columbia 4563213Sbostic * Vancouver, BC, CANADA. 4663213Sbostic * 4763213Sbostic * History: 4863213Sbostic * 4963213Sbostic * 5063213Sbostic */ 51