The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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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  * 4. 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  * $FreeBSD: releng/6.2/sys/netinet/tcp_timer.h 162314 2006-09-15 09:51:05Z glebius $
   31  */
   32 
   33 #ifndef _NETINET_TCP_TIMER_H_
   34 #define _NETINET_TCP_TIMER_H_
   35 
   36 /*
   37  * The TCPT_REXMT timer is used to force retransmissions.
   38  * The TCP has the TCPT_REXMT timer set whenever segments
   39  * have been sent for which ACKs are expected but not yet
   40  * received.  If an ACK is received which advances tp->snd_una,
   41  * then the retransmit timer is cleared (if there are no more
   42  * outstanding segments) or reset to the base value (if there
   43  * are more ACKs expected).  Whenever the retransmit timer goes off,
   44  * we retransmit one unacknowledged segment, and do a backoff
   45  * on the retransmit timer.
   46  *
   47  * The TCPT_PERSIST timer is used to keep window size information
   48  * flowing even if the window goes shut.  If all previous transmissions
   49  * have been acknowledged (so that there are no retransmissions in progress),
   50  * and the window is too small to bother sending anything, then we start
   51  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
   52  * we go to transmit state.  Otherwise, at intervals send a single byte
   53  * into the peer's window to force him to update our window information.
   54  * We do this at most as often as TCPT_PERSMIN time intervals,
   55  * but no more frequently than the current estimate of round-trip
   56  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
   57  * a window update from the peer.
   58  *
   59  * The TCPT_KEEP timer is used to keep connections alive.  If an
   60  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
   61  * but not yet established, then we drop the connection.  Once the connection
   62  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
   63  * (and keepalives have been enabled on the socket), we begin to probe
   64  * the connection.  We force the peer to send us a segment by sending:
   65  *      <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
   66  * This segment is (deliberately) outside the window, and should elicit
   67  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
   68  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
   69  * amount of time probing, then we drop the connection.
   70  */
   71 
   72 /*
   73  * Time constants.
   74  */
   75 #define TCPTV_MSL       ( 30*hz)                /* max seg lifetime (hah!) */
   76 #define TCPTV_SRTTBASE  0                       /* base roundtrip time;
   77                                                    if 0, no idea yet */
   78 #define TCPTV_RTOBASE   (  3*hz)                /* assumed RTO if no info */
   79 #define TCPTV_SRTTDFLT  (  3*hz)                /* assumed RTT if no info */
   80 
   81 #define TCPTV_PERSMIN   (  5*hz)                /* retransmit persistence */
   82 #define TCPTV_PERSMAX   ( 60*hz)                /* maximum persist interval */
   83 
   84 #define TCPTV_KEEP_INIT ( 75*hz)                /* initial connect keepalive */
   85 #define TCPTV_KEEP_IDLE (120*60*hz)             /* dflt time before probing */
   86 #define TCPTV_KEEPINTVL ( 75*hz)                /* default probe interval */
   87 #define TCPTV_KEEPCNT   8                       /* max probes before drop */
   88 
   89 #define TCPTV_INFLIGHT_RTTTHRESH (10*hz/1000)   /* below which inflight
   90                                                    disengages, in msec */
   91 
   92 /*
   93  * Minimum retransmit timer is 3 ticks, for algorithmic stability.
   94  * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
   95  * the expected worst-case processing variances by the kernels
   96  * representing the end points.  Such variances do not always show
   97  * up in the srtt because the timestamp is often calculated at
   98  * the interface rather then at the TCP layer.  This value is
   99  * typically 50ms.  However, it is also possible that delayed
  100  * acks (typically 100ms) could create issues so we set the slop
  101  * to 200ms to try to cover it.  Note that, properly speaking,
  102  * delayed-acks should not create a major issue for interactive
  103  * environments which 'P'ush the last segment, at least as
  104  * long as implementations do the required 'at least one ack
  105  * for every two packets' for the non-interactive streaming case.
  106  * (maybe the RTO calculation should use 2*RTT instead of RTT
  107  * to handle the ack-every-other-packet case).
  108  *
  109  * The prior minimum of 1*hz (1 second) badly breaks throughput on any
  110  * networks faster then a modem that has minor (e.g. 1%) packet loss.
  111  */
  112 #define TCPTV_MIN       ( 3 )                   /* minimum allowable value */
  113 #define TCPTV_CPU_VAR   ( hz/5 )                /* cpu variance allowed (200ms) */
  114 #define TCPTV_REXMTMAX  ( 64*hz)                /* max allowable REXMT value */
  115 
  116 #define TCPTV_TWTRUNC   8                       /* RTO factor to truncate TW */
  117 
  118 #define TCP_LINGERTIME  120                     /* linger at most 2 minutes */
  119 
  120 #define TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
  121 
  122 #define TCPTV_DELACK    (hz / PR_FASTHZ / 2)    /* 100ms timeout */
  123 
  124 #ifdef  TCPTIMERS
  125 static const char *tcptimers[] =
  126     { "REXMT", "PERSIST", "KEEP", "2MSL" };
  127 #endif
  128 
  129 /*
  130  * Force a time value to be in a certain range.
  131  */
  132 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
  133         (tv) = (value) + tcp_rexmit_slop; \
  134         if ((u_long)(tv) < (u_long)(tvmin)) \
  135                 (tv) = (tvmin); \
  136         else if ((u_long)(tv) > (u_long)(tvmax)) \
  137                 (tv) = (tvmax); \
  138 } while(0)
  139 
  140 #ifdef _KERNEL
  141 extern int tcp_keepinit;                /* time to establish connection */
  142 extern int tcp_keepidle;                /* time before keepalive probes begin */
  143 extern int tcp_keepintvl;               /* time between keepalive probes */
  144 extern int tcp_maxidle;                 /* time to drop after starting probes */
  145 extern int tcp_delacktime;              /* time before sending a delayed ACK */
  146 extern int tcp_maxpersistidle;
  147 extern int tcp_rexmit_min;
  148 extern int tcp_rexmit_slop;
  149 extern int tcp_msl;
  150 extern int tcp_ttl;                     /* time to live for TCP segs */
  151 extern int tcp_backoff[];
  152 
  153 struct tcptw;
  154 
  155 void    tcp_timer_init(void);
  156 void    tcp_timer_2msl(void *xtp);
  157 struct tcptw *
  158         tcp_timer_2msl_tw(int _reuse);          /* XXX temporary */
  159 void    tcp_timer_2msl_reset(struct tcptw *_tw, int rearm);
  160 void    tcp_timer_2msl_stop(struct tcptw *_tw);
  161 void    tcp_timer_keep(void *xtp);
  162 void    tcp_timer_persist(void *xtp);
  163 void    tcp_timer_rexmt(void *xtp);
  164 void    tcp_timer_delack(void *xtp);
  165 
  166 #endif /* _KERNEL */
  167 
  168 #endif /* !_NETINET_TCP_TIMER_H_ */

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