FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_timer.h

     /*
      * 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
     * $FreeBSD$
     */
    
    #ifndef _NETINET_TCP_TIMER_H_
    #define _NETINET_TCP_TIMER_H_
    
    /*
     * Definitions of the TCP timers.  These timers are counted
     * down PR_SLOWHZ times a second.
     */
    #define TCPT_NTIMERS    4
    
    #define TCPT_REXMT      0               /* retransmit */
    #define TCPT_PERSIST    1               /* retransmit persistence */
    #define TCPT_KEEP       2               /* keep alive */
    #define TCPT_2MSL       3               /* 2*msl quiet time timer */
    
    /*
     * 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*PR_SLOWHZ)         /* max seg lifetime (hah!) */
    #define TCPTV_SRTTBASE  0                       /* base roundtrip time;
                                                       if 0, no idea yet */
    #define TCPTV_RTOBASE   (  3*PR_SLOWHZ)         /* assumed RTO if no info */
    #define TCPTV_SRTTDFLT  (  3*PR_SLOWHZ)         /* assumed RTT if no info */
    
    #define TCPTV_PERSMIN   (  5*PR_SLOWHZ)         /* retransmit persistence */
    #define TCPTV_PERSMAX   ( 60*PR_SLOWHZ)         /* maximum persist interval */
    
    #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ)         /* initial connect keep alive */
   #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ)      /* dflt time before probing */
   #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ)         /* default probe interval */
   #define TCPTV_KEEPCNT   8                       /* max probes before drop */
   
   #define TCPTV_MIN       (  1*PR_SLOWHZ)         /* minimum allowable value */
   #define TCPTV_REXMTMAX  ( 64*PR_SLOWHZ)         /* 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 */
   
   #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) { \
           (tv) = (value); \
           if ((u_long)(tv) < (u_long)(tvmin)) \
                   (tv) = (tvmin); \
           else if ((u_long)(tv) > (u_long)(tvmax)) \
                   (tv) = (tvmax); \
   }
   
   #ifdef KERNEL
   extern int tcp_keepinit;                /* time to establish connection */
   extern int tcp_keepidle;                /* time before keepalive probes begin */
   extern int tcp_maxidle;                 /* time to drop after starting probes */
   extern int tcp_ttl;                     /* time to live for TCP segs */
   extern int tcp_backoff[];
   #endif
   
   #endif

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