/* Copyright (c) University of British Columbia, 1984 */

/*
 *                                                                          
 *  X.25 HDLC DATA LINK LEVEL:                                           
 *
 *                                                                            
 *  This module implements the Link  Level of the Open Systems Interconnect
 *  Model.  The implementation  is based  on the ISO  High-Level  Data Link 
 *  Control (HDLC).  These procedures  subscribe to the  principles  of the 
 *  ISO-Class of Procedures for  point-to-point. These procedures implement
 *  two-way  asynchronous balanced mode (LAPB) as recommented by the CCITT.
 *
 *  The HDLC protocol layer interface consists of the following procedures:
 *    Hd_init       (pr_init) 
 *    Hd_ouput      (pr_output)
 *    Hd_input      (pr_input)
 *    Hd_timer      (pr_slowtimo)                       
 *             
 *  Note: Supervisory commands RR, RNR and REJ are  not transmitted by this
 *        station.
 *     
 *        This station never enters a busy (RNR) condition.
 *		
 *	  The "Generate_rr" variable can  be set to FALSE.  This means that
 *	  we NEVER  send an RR.  This works just fine if  the network level
 *	  is X.25 packet protocol -- which it is.
 *
 *        Currently, this is only a DTE implementation.
 *
 *  Think about:
 *        If the remote is busy, no iframes are sent. The remote sends a RR
 *	  to clear this condition. However, this RR may be damaged, causing
 *	  a possible deadlock. A solution is to poll with iframe (P(S)==P(R)
 *	  of RNR) indefinitly.
 *
 *
 *  Date:             February 1984
 *
 *  Author:           Gerald W. Neufeld
 *                     
 *  Installation:     Department of Computer Science
 *                    University of British Columbia
 *                    Vancouver, BC, CANADA.
 *
 *  History:
 *  
 *                                                                      
 */