text: /*
   * Copyright (c) 1982, 1986, 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.
   *
   *	@(#)tcp_timer.h	8.1 (Berkeley) 6/10/93
   * $FreeBSD: src/sys/netinet/tcp_timer.h,v 1.18 1999/12/29 04:41:03 peter Exp $
   */
  
  #ifndef _NETINET_TCP_TIMER_H_
  #define _NETINET_TCP_TIMER_H_
  
  /*
   * The TCPT_REXMT timer is used to force retransmissions.
   * The TCP has the TCPT_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 TCPT_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 TCPT_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 TCPT_PERSMIN time intervals,
   * but no more frequently than the current estimate of round-trip
   * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
   * a window update from the peer.
   *
   * The TCPT_KEEP timer is used to keep connections alive.  If an
   * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
   * but not yet established, then we drop the connection.  Once the connection
   * is established, if the connection is idle for TCPTV_KEEP_IDLE time
   * (and keepalives have been enabled on the socket), we begin to probe
   * the connection.  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 TCPT_KEEP
   * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
   * amount of time probing, then we drop the connection.
   */
  
  /*
   * Time constants.
   */
  #define	TCPTV_MSL	( 30*hz)		/* max seg lifetime (hah!) */
  #define	TCPTV_SRTTBASE	0			/* base roundtrip time;
  						   if 0, no idea yet */
  #define	TCPTV_RTOBASE	(  3*hz)		/* assumed RTO if no info */
  #define	TCPTV_SRTTDFLT	(  3*hz)		/* assumed RTT if no info */
  
  #define	TCPTV_PERSMIN	(  5*hz)		/* retransmit persistence */
  #define	TCPTV_PERSMAX	( 60*hz)		/* maximum persist interval */
  
  #define	TCPTV_KEEP_INIT	( 75*hz)		/* initial connect keepalive */
  #define	TCPTV_KEEP_IDLE	(120*60*hz)		/* dflt time before probing */
  #define	TCPTV_KEEPINTVL	( 75*hz)		/* default probe interval */
  #define	TCPTV_KEEPCNT	8			/* max probes before drop */
  
  #define	TCPTV_MIN	(  1*hz)		/* minimum allowable value */
  #define	TCPTV_REXMTMAX	( 64*hz)		/* max allowable REXMT value */
  
  #define TCPTV_TWTRUNC	8			/* RTO factor to truncate TW */
  
  #define	TCP_LINGERTIME	120			/* linger at most 2 minutes */
  
  #define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */
  
  #define	TCPTV_DELACK	(hz / PR_FASTHZ / 2)	/* 100ms timeout */
  
  #ifdef	TCPTIMERS
  static char *tcptimers[] =
      { "REXMT", "PERSIST", "KEEP", "2MSL" };
  #endif
  
  /*
   * Force a time value to be in a certain range.
   */
  #define	TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
  	(tv) = (value); \
  	if ((u_long)(tv) < (u_long)(tvmin)) \
  		(tv) = (tvmin); \
  	else if ((u_long)(tv) > (u_long)(tvmax)) \
  		(tv) = (tvmax); \
  } while(0)
  
  #ifdef _KERNEL
  extern int tcp_keepinit;		/* time to establish connection */
  extern int tcp_keepidle;		/* time before keepalive probes begin */
  extern int tcp_keepintvl;		/* time between keepalive probes */
  extern int tcp_maxidle;			/* time to drop after starting probes */
  extern int tcp_delacktime;		/* time before sending a delayed ACK */
  extern int tcp_maxpersistidle;
  extern int tcp_msl;
  extern int tcp_ttl;			/* time to live for TCP segs */
  extern int tcp_backoff[];
  
  void	tcp_timer_2msl __P((void *xtp));
  void	tcp_timer_keep __P((void *xtp));
  void	tcp_timer_persist __P((void *xtp));
  void	tcp_timer_rexmt __P((void *xtp));
  void	tcp_timer_delack __P((void *xtp));
  
  #endif /* _KERNEL */
  
  #endif /* !_NETINET_TCP_TIMER_H_ */
  