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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  ( 12*PR_SLOWHZ)		/* max allowable REXMT value */
  102: 
  103: #define	TCP_LINGERTIME	120			/* linger at most 2 minutes */
  104: 
  105: #define TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
  106: 
  107: 
  108: /*
  109:  * Force a time value to be in a certain range.
  110:  */
  111: #define	TCPT_RANGESET(tv, value, tvmin, tvmax) { \
  112: 	(tv) = (value); \
  113: 	if ((tv) < (tvmin)) \
  114: 		(tv) = (tvmin); \
  115: 	else if ((tv) > (tvmax)) \
  116: 		(tv) = (tvmax); \
  117: }
  118: 
  119: extern const int tcp_backoff[];
  120: 
  121: struct tcpcb;
  122: 
  123: void tcp_fasttimo(Slirp *);
  124: void tcp_slowtimo(Slirp *);
  125: void tcp_canceltimers(struct tcpcb *);
  126: 
  127: #endif