text: /*
   * Copyright (c) 1995, Mike Mitchell
   * Copyright (c) 1982, 1986, 1988, 1993
   *	The Regents of the University of California.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *	This product includes software developed by the University of
   *	California, Berkeley and its contributors.
   * 4. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   *	@(#)spx_timer.h
   *
   * $FreeBSD: src/sys/netipx/spx_timer.h,v 1.10 1999/08/28 00:49:44 peter Exp $
   * $DragonFly: src/sys/netproto/ipx/spx_timer.h,v 1.2 2003/06/17 04:28:53 dillon Exp $
   */
  
  #ifndef _NETIPX_SPX_TIMER_H_
  #define _NETIPX_SPX_TIMER_H_
  
  /*
   * Definitions of the SPX timers.  These timers are counted
   * down PR_SLOWHZ times a second.
   */
  #define	SPXT_REXMT	0		/* retransmit */
  #define	SPXT_PERSIST	1		/* retransmit persistence */
  #define	SPXT_KEEP	2		/* keep alive */
  #define	SPXT_2MSL	3		/* 2*msl quiet time timer */
  
  /*
   * The SPXT_REXMT timer is used to force retransmissions.
   * The SPX has the SPXT_REXMT timer set whenever segments
   * have been sent for which ACKs are expected but not yet
   * received.  If an ACK is received which advances tp->snd_una,
   * then the retransmit timer is cleared (if there are no more
   * outstanding segments) or reset to the base value (if there
   * are more ACKs expected).  Whenever the retransmit timer goes off,
   * we retransmit one unacknowledged segment, and do a backoff
   * on the retransmit timer.
   *
   * The SPXT_PERSIST timer is used to keep window size information
   * flowing even if the window goes shut.  If all previous transmissions
   * have been acknowledged (so that there are no retransmissions in progress),
   * and the window is too small to bother sending anything, then we start
   * the SPXT_PERSIST timer.  When it expires, if the window is nonzero,
   * we go to transmit state.  Otherwise, at intervals send a single byte
   * into the peer's window to force him to update our window information.
   * We do this at most as often as SPXT_PERSMIN time intervals,
   * but no more frequently than the current estimate of round-trip
   * packet time.  The SPXT_PERSIST timer is cleared whenever we receive
   * a window update from the peer.
   *
   * The SPXT_KEEP timer is used to keep connections alive.  If an
   * connection is idle (no segments received) for SPXTV_KEEP amount of time,
   * but not yet established, then we drop the connection.  If the connection
   * is established, then we force the peer to send us a segment by sending:
   *	<SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
   * This segment is (deliberately) outside the window, and should elicit
   * an ack segment in response from the peer.  If, despite the SPXT_KEEP
   * initiated segments we cannot elicit a response from a peer in SPXT_MAXIDLE
   * amount of time, then we drop the connection.
   */
  
  #define	SPX_TTL		30		/* default time to live for SPX segs */
  /*
   * Time constants.
   */
  #define	SPXTV_MSL	( 15*PR_SLOWHZ)		/* max seg lifetime */
  #define	SPXTV_SRTTBASE	0			/* base roundtrip time;
  						   if 0, no idea yet */
  #define	SPXTV_SRTTDFLT	(  3*PR_SLOWHZ)		/* assumed RTT if no info */
  
  #define	SPXTV_PERSMIN	(  5*PR_SLOWHZ)		/* retransmit persistence */
  #define	SPXTV_PERSMAX	( 60*PR_SLOWHZ)		/* maximum persist interval */
  
  #define	SPXTV_KEEP	( 75*PR_SLOWHZ)		/* keep alive - 75 secs */
  #define	SPXTV_MAXIDLE	(  8*SPXTV_KEEP)	/* maximum allowable idle
  						   time before drop conn */
  
  #define	SPXTV_MIN	(  1*PR_SLOWHZ)		/* minimum allowable value */
  #define	SPXTV_REXMTMAX	( 64*PR_SLOWHZ)		/* max allowable REXMT value */
  
  #define	SPX_LINGERTIME	120			/* linger at most 2 minutes */
  
  #define	SPX_MAXRXTSHIFT	12			/* maximum retransmits */
  
  #ifdef	SPXTIMERS
  char *spxtimers[] =
      { "REXMT", "PERSIST", "KEEP", "2MSL" };
  #endif
  
  /*
   * Force a time value to be in a certain range.
   */
  #define	SPXT_RANGESET(tv, value, tvmin, tvmax) { \
  	(tv) = (value); \
  	if ((tv) < (tvmin)) \
  		(tv) = (tvmin); \
  	else if ((tv) > (tvmax)) \
  		(tv) = (tvmax); \
  }
  
  #endif /* !_NETIPX_SPX_TIMER_H_ */
  