/* 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:
* Note: Supervisory commands RR, RNR and REJ are not transmitted by this
* 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.
* 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)
* Author: Gerald W. Neufeld
* Installation: Department of Computer Science
* University of British Columbia