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      1 /*
      2  * Copyright (c) 1982, 1986, 1993
      3  *	The Regents of the University of California.  All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  * 1. Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  * 2. Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in the
     12  *    documentation and/or other materials provided with the distribution.
     13  * 3. Neither the name of the University nor the names of its contributors
     14  *    may be used to endorse or promote products derived from this software
     15  *    without specific prior written permission.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     27  * SUCH DAMAGE.
     28  *
     29  *	@(#)tcp_timer.h	8.1 (Berkeley) 6/10/93
     30  * tcp_timer.h,v 1.4 1994/08/21 05:27:38 paul Exp
     31  */
     32 
     33 #ifndef _TCP_TIMER_H_
     34 #define _TCP_TIMER_H_
     35 
     36 /*
     37  * Definitions of the TCP timers.  These timers are counted
     38  * down PR_SLOWHZ times a second.
     39  */
     40 #define	TCPT_NTIMERS	4
     41 
     42 #define	TCPT_REXMT	0		/* retransmit */
     43 #define	TCPT_PERSIST	1		/* retransmit persistence */
     44 #define	TCPT_KEEP	2		/* keep alive */
     45 #define	TCPT_2MSL	3		/* 2*msl quiet time timer */
     46 
     47 /*
     48  * The TCPT_REXMT timer is used to force retransmissions.
     49  * The TCP has the TCPT_REXMT timer set whenever segments
     50  * have been sent for which ACKs are expected but not yet
     51  * received.  If an ACK is received which advances tp->snd_una,
     52  * then the retransmit timer is cleared (if there are no more
     53  * outstanding segments) or reset to the base value (if there
     54  * are more ACKs expected).  Whenever the retransmit timer goes off,
     55  * we retransmit one unacknowledged segment, and do a backoff
     56  * on the retransmit timer.
     57  *
     58  * The TCPT_PERSIST timer is used to keep window size information
     59  * flowing even if the window goes shut.  If all previous transmissions
     60  * have been acknowledged (so that there are no retransmissions in progress),
     61  * and the window is too small to bother sending anything, then we start
     62  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
     63  * we go to transmit state.  Otherwise, at intervals send a single byte
     64  * into the peer's window to force him to update our window information.
     65  * We do this at most as often as TCPT_PERSMIN time intervals,
     66  * but no more frequently than the current estimate of round-trip
     67  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
     68  * a window update from the peer.
     69  *
     70  * The TCPT_KEEP timer is used to keep connections alive.  If an
     71  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
     72  * but not yet established, then we drop the connection.  Once the connection
     73  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
     74  * (and keepalives have been enabled on the socket), we begin to probe
     75  * the connection.  We force the peer to send us a segment by sending:
     76  *	<SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
     77  * This segment is (deliberately) outside the window, and should elicit
     78  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
     79  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
     80  * amount of time probing, then we drop the connection.
     81  */
     82 
     83 /*
     84  * Time constants.
     85  */
     86 #define TCPTV_MSL       ( 5*PR_SLOWHZ)          /* max seg lifetime (hah!) */
     87 
     88 #define	TCPTV_SRTTBASE	0			/* base roundtrip time;
     89 						   if 0, no idea yet */
     90 #define	TCPTV_SRTTDFLT	(  3*PR_SLOWHZ)		/* assumed RTT if no info */
     91 
     92 #define	TCPTV_PERSMIN	(  5*PR_SLOWHZ)		/* retransmit persistence */
     93 #define	TCPTV_PERSMAX	( 60*PR_SLOWHZ)		/* maximum persist interval */
     94 
     95 #define	TCPTV_KEEP_INIT	( 75*PR_SLOWHZ)		/* initial connect keep alive */
     96 #define	TCPTV_KEEP_IDLE	(120*60*PR_SLOWHZ)	/* dflt time before probing */
     97 #define	TCPTV_KEEPINTVL	( 75*PR_SLOWHZ)		/* default probe interval */
     98 #define	TCPTV_KEEPCNT	8			/* max probes before drop */
     99 
    100 #define	TCPTV_MIN	(  1*PR_SLOWHZ)		/* minimum allowable value */
    101 /* #define	TCPTV_REXMTMAX	( 64*PR_SLOWHZ)	*/	/* max allowable REXMT value */
    102 #define TCPTV_REXMTMAX  ( 12*PR_SLOWHZ)		/* max allowable REXMT value */
    103 
    104 #define	TCP_LINGERTIME	120			/* linger at most 2 minutes */
    105 
    106 #define TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
    107 
    108 
    109 #ifdef	TCPTIMERS
    110 char *tcptimers[] =
    111     { "REXMT", "PERSIST", "KEEP", "2MSL" };
    112 #endif
    113 
    114 /*
    115  * Force a time value to be in a certain range.
    116  */
    117 #define	TCPT_RANGESET(tv, value, tvmin, tvmax) { \
    118 	(tv) = (value); \
    119 	if ((tv) < (tvmin)) \
    120 		(tv) = (tvmin); \
    121 	else if ((tv) > (tvmax)) \
    122 		(tv) = (tvmax); \
    123 }
    124 
    125 extern const int tcp_backoff[];
    126 
    127 struct tcpcb;
    128 
    129 void tcp_fasttimo _P((void));
    130 void tcp_slowtimo _P((void));
    131 void tcp_canceltimers _P((struct tcpcb *));
    132 
    133 #endif
    134