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Annotation of kernel/bsd/netinet/tcp_timer.h, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
        !             3:  *
        !             4:  * @APPLE_LICENSE_HEADER_START@
        !             5:  * 
        !             6:  * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
        !             7:  * Reserved.  This file contains Original Code and/or Modifications of
        !             8:  * Original Code as defined in and that are subject to the Apple Public
        !             9:  * Source License Version 1.1 (the "License").  You may not use this file
        !            10:  * except in compliance with the License.  Please obtain a copy of the
        !            11:  * License at http://www.apple.com/publicsource and read it before using
        !            12:  * this file.
        !            13:  * 
        !            14:  * The Original Code and all software distributed under the License are
        !            15:  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
        !            16:  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
        !            17:  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
        !            18:  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
        !            19:  * License for the specific language governing rights and limitations
        !            20:  * under the License.
        !            21:  * 
        !            22:  * @APPLE_LICENSE_HEADER_END@
        !            23:  */
        !            24: 
        !            25: /* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
        !            26: /*
        !            27:  * Copyright (c) 1982, 1986, 1993
        !            28:  *     The Regents of the University of California.  All rights reserved.
        !            29:  *
        !            30:  * Redistribution and use in source and binary forms, with or without
        !            31:  * modification, are permitted provided that the following conditions
        !            32:  * are met:
        !            33:  * 1. Redistributions of source code must retain the above copyright
        !            34:  *    notice, this list of conditions and the following disclaimer.
        !            35:  * 2. Redistributions in binary form must reproduce the above copyright
        !            36:  *    notice, this list of conditions and the following disclaimer in the
        !            37:  *    documentation and/or other materials provided with the distribution.
        !            38:  * 3. All advertising materials mentioning features or use of this software
        !            39:  *    must display the following acknowledgement:
        !            40:  *     This product includes software developed by the University of
        !            41:  *     California, Berkeley and its contributors.
        !            42:  * 4. Neither the name of the University nor the names of its contributors
        !            43:  *    may be used to endorse or promote products derived from this software
        !            44:  *    without specific prior written permission.
        !            45:  *
        !            46:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            47:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            48:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            49:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            50:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            51:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            52:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            53:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            54:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            55:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            56:  * SUCH DAMAGE.
        !            57:  *
        !            58:  *     @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
        !            59:  */
        !            60: 
        !            61: /*
        !            62:  * Definitions of the TCP timers.  These timers are counted
        !            63:  * down PR_SLOWHZ times a second.
        !            64:  */
        !            65: #define        TCPT_NTIMERS    4
        !            66: 
        !            67: #define        TCPT_REXMT      0               /* retransmit */
        !            68: #define        TCPT_PERSIST    1               /* retransmit persistance */
        !            69: #define        TCPT_KEEP       2               /* keep alive */
        !            70: #define        TCPT_2MSL       3               /* 2*msl quiet time timer */
        !            71: 
        !            72: /*
        !            73:  * The TCPT_REXMT timer is used to force retransmissions.
        !            74:  * The TCP has the TCPT_REXMT timer set whenever segments
        !            75:  * have been sent for which ACKs are expected but not yet
        !            76:  * received.  If an ACK is received which advances tp->snd_una,
        !            77:  * then the retransmit timer is cleared (if there are no more
        !            78:  * outstanding segments) or reset to the base value (if there
        !            79:  * are more ACKs expected).  Whenever the retransmit timer goes off,
        !            80:  * we retransmit one unacknowledged segment, and do a backoff
        !            81:  * on the retransmit timer.
        !            82:  *
        !            83:  * The TCPT_PERSIST timer is used to keep window size information
        !            84:  * flowing even if the window goes shut.  If all previous transmissions
        !            85:  * have been acknowledged (so that there are no retransmissions in progress),
        !            86:  * and the window is too small to bother sending anything, then we start
        !            87:  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
        !            88:  * we go to transmit state.  Otherwise, at intervals send a single byte
        !            89:  * into the peer's window to force him to update our window information.
        !            90:  * We do this at most as often as TCPT_PERSMIN time intervals,
        !            91:  * but no more frequently than the current estimate of round-trip
        !            92:  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
        !            93:  * a window update from the peer.
        !            94:  *
        !            95:  * The TCPT_KEEP timer is used to keep connections alive.  If an
        !            96:  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
        !            97:  * but not yet established, then we drop the connection.  Once the connection
        !            98:  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
        !            99:  * (and keepalives have been enabled on the socket), we begin to probe
        !           100:  * the connection.  We force the peer to send us a segment by sending:
        !           101:  *     <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
        !           102:  * This segment is (deliberately) outside the window, and should elicit
        !           103:  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
        !           104:  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
        !           105:  * amount of time probing, then we drop the connection.
        !           106:  */
        !           107: 
        !           108: /*
        !           109:  * Time constants.
        !           110:  */
        !           111: #define        TCPTV_MSL       ( 30*PR_SLOWHZ)         /* max seg lifetime (hah!) */
        !           112: #define        TCPTV_SRTTBASE  0                       /* base roundtrip time;
        !           113:                                                   if 0, no idea yet */
        !           114: #define        TCPTV_SRTTDFLT  (  3*PR_SLOWHZ)         /* assumed RTT if no info */
        !           115: 
        !           116: #define        TCPTV_PERSMIN   (  5*PR_SLOWHZ)         /* retransmit persistance */
        !           117: #define        TCPTV_PERSMAX   ( 60*PR_SLOWHZ)         /* maximum persist interval */
        !           118: 
        !           119: #define        TCPTV_KEEP_INIT ( 75*PR_SLOWHZ)         /* initial connect keep alive */
        !           120: #define        TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ)      /* dflt time before probing */
        !           121: #define        TCPTV_KEEPINTVL ( 75*PR_SLOWHZ)         /* default probe interval */
        !           122: #define        TCPTV_KEEPCNT   8                       /* max probes before drop */
        !           123: 
        !           124: #define        TCPTV_MIN       (  1*PR_SLOWHZ)         /* minimum allowable value */
        !           125: #define        TCPTV_REXMTMAX  ( 64*PR_SLOWHZ)         /* max allowable REXMT value */
        !           126: 
        !           127: #define        TCP_LINGERTIME  120                     /* linger at most 2 minutes */
        !           128: 
        !           129: #define        TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
        !           130: 
        !           131: #ifdef TCPTIMERS
        !           132: char *tcptimers[] =
        !           133:     { "REXMT", "PERSIST", "KEEP", "2MSL" };
        !           134: #endif
        !           135: 
        !           136: /*
        !           137:  * Force a time value to be in a certain range.
        !           138:  */
        !           139: #define        TCPT_RANGESET(tv, value, tvmin, tvmax) { \
        !           140:        (tv) = (value); \
        !           141:        if ((tv) < (tvmin)) \
        !           142:                (tv) = (tvmin); \
        !           143:        else if ((tv) > (tvmax)) \
        !           144:                (tv) = (tvmax); \
        !           145: }
        !           146: 
        !           147: #ifdef _KERNEL
        !           148: extern int tcp_keepidle;               /* time before keepalive probes begin */
        !           149: extern int tcp_keepintvl;              /* time between keepalive probes */
        !           150: extern int tcp_maxidle;                        /* time to drop after starting probes */
        !           151: extern int tcp_ttl;                    /* time to live for TCP segs */
        !           152: extern int tcp_backoff[];
        !           153: #endif

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