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Annotation of 43BSDReno/sys/netinet/tcp_timer.h, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1982, 1986 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution is only permitted until one year after the first shipment
        !             6:  * of 4.4BSD by the Regents.  Otherwise, redistribution and use in source and
        !             7:  * binary forms are permitted provided that: (1) source distributions retain
        !             8:  * this entire copyright notice and comment, and (2) distributions including
        !             9:  * binaries display the following acknowledgement:  This product includes
        !            10:  * software developed by the University of California, Berkeley and its
        !            11:  * contributors'' in the documentation or other materials provided with the
        !            12:  * distribution and in all advertising materials mentioning features or use
        !            13:  * of this software.  Neither the name of the University nor the names of
        !            14:  * its contributors may be used to endorse or promote products derived from
        !            15:  * this software without specific prior written permission.
        !            16:  * THIS SOFTWARE IS PROVIDED AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
        !            17:  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
        !            18:  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            19:  *
        !            20:  *     @(#)tcp_timer.h 7.8 (Berkeley) 6/28/90
        !            21:  */
        !            22: 
        !            23: /*
        !            24:  * Definitions of the TCP timers.  These timers are counted
        !            25:  * down PR_SLOWHZ times a second.
        !            26:  */
        !            27: #define        TCPT_NTIMERS    4
        !            28: 
        !            29: #define        TCPT_REXMT      0               /* retransmit */
        !            30: #define        TCPT_PERSIST    1               /* retransmit persistance */
        !            31: #define        TCPT_KEEP       2               /* keep alive */
        !            32: #define        TCPT_2MSL       3               /* 2*msl quiet time timer */
        !            33: 
        !            34: /*
        !            35:  * The TCPT_REXMT timer is used to force retransmissions.
        !            36:  * The TCP has the TCPT_REXMT timer set whenever segments
        !            37:  * have been sent for which ACKs are expected but not yet
        !            38:  * received.  If an ACK is received which advances tp->snd_una,
        !            39:  * then the retransmit timer is cleared (if there are no more
        !            40:  * outstanding segments) or reset to the base value (if there
        !            41:  * are more ACKs expected).  Whenever the retransmit timer goes off,
        !            42:  * we retransmit one unacknowledged segment, and do a backoff
        !            43:  * on the retransmit timer.
        !            44:  *
        !            45:  * The TCPT_PERSIST timer is used to keep window size information
        !            46:  * flowing even if the window goes shut.  If all previous transmissions
        !            47:  * have been acknowledged (so that there are no retransmissions in progress),
        !            48:  * and the window is too small to bother sending anything, then we start
        !            49:  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
        !            50:  * we go to transmit state.  Otherwise, at intervals send a single byte
        !            51:  * into the peer's window to force him to update our window information.
        !            52:  * We do this at most as often as TCPT_PERSMIN time intervals,
        !            53:  * but no more frequently than the current estimate of round-trip
        !            54:  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
        !            55:  * a window update from the peer.
        !            56:  *
        !            57:  * The TCPT_KEEP timer is used to keep connections alive.  If an
        !            58:  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
        !            59:  * but not yet established, then we drop the connection.  Once the connection
        !            60:  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
        !            61:  * (and keepalives have been enabled on the socket), we begin to probe
        !            62:  * the connection.  We force the peer to send us a segment by sending:
        !            63:  *     <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
        !            64:  * This segment is (deliberately) outside the window, and should elicit
        !            65:  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
        !            66:  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
        !            67:  * amount of time probing, then we drop the connection.
        !            68:  */
        !            69: 
        !            70: #define        TCP_TTL         60              /* default time to live for TCP segs */
        !            71: /*
        !            72:  * Time constants.
        !            73:  */
        !            74: #define        TCPTV_MSL       ( 30*PR_SLOWHZ)         /* max seg lifetime (hah!) */
        !            75: #define        TCPTV_SRTTBASE  0                       /* base roundtrip time;
        !            76:                                                   if 0, no idea yet */
        !            77: #define        TCPTV_SRTTDFLT  (  3*PR_SLOWHZ)         /* assumed RTT if no info */
        !            78: 
        !            79: #define        TCPTV_PERSMIN   (  5*PR_SLOWHZ)         /* retransmit persistance */
        !            80: #define        TCPTV_PERSMAX   ( 60*PR_SLOWHZ)         /* maximum persist interval */
        !            81: 
        !            82: #define        TCPTV_KEEP_INIT ( 75*PR_SLOWHZ)         /* initial connect keep alive */
        !            83: #define        TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ)      /* dflt time before probing */
        !            84: #define        TCPTV_KEEPINTVL ( 75*PR_SLOWHZ)         /* default probe interval */
        !            85: #define        TCPTV_KEEPCNT   8                       /* max probes before drop */
        !            86: 
        !            87: #define        TCPTV_MIN       (  1*PR_SLOWHZ)         /* minimum allowable value */
        !            88: #define        TCPTV_REXMTMAX  ( 64*PR_SLOWHZ)         /* max allowable REXMT value */
        !            89: 
        !            90: #define        TCP_LINGERTIME  120                     /* linger at most 2 minutes */
        !            91: 
        !            92: #define        TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
        !            93: 
        !            94: #ifdef TCPTIMERS
        !            95: char *tcptimers[] =
        !            96:     { "REXMT", "PERSIST", "KEEP", "2MSL" };
        !            97: #endif
        !            98: 
        !            99: /*
        !           100:  * Force a time value to be in a certain range.
        !           101:  */
        !           102: #define        TCPT_RANGESET(tv, value, tvmin, tvmax) { \
        !           103:        (tv) = (value); \
        !           104:        if ((tv) < (tvmin)) \
        !           105:                (tv) = (tvmin); \
        !           106:        else if ((tv) > (tvmax)) \
        !           107:                (tv) = (tvmax); \
        !           108: }
        !           109: 
        !           110: #ifdef KERNEL
        !           111: extern int tcp_keepidle;               /* time before keepalive probes begin */
        !           112: extern int tcp_keepintvl;              /* time between keepalive probes */
        !           113: extern int tcp_maxidle;                        /* time to drop after starting probes */
        !           114: extern int tcp_ttl;                    /* time to live for TCP segs */
        !           115: extern int tcp_backoff[];
        !           116: #endif

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