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Annotation of 43BSDTahoe/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 and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  *
        !            17:  *     @(#)tcp_timer.h 7.6 (Berkeley) 6/29/88
        !            18:  */
        !            19: 
        !            20: /*
        !            21:  * Definitions of the TCP timers.  These timers are counted
        !            22:  * down PR_SLOWHZ times a second.
        !            23:  */
        !            24: #define        TCPT_NTIMERS    4
        !            25: 
        !            26: #define        TCPT_REXMT      0               /* retransmit */
        !            27: #define        TCPT_PERSIST    1               /* retransmit persistance */
        !            28: #define        TCPT_KEEP       2               /* keep alive */
        !            29: #define        TCPT_2MSL       3               /* 2*msl quiet time timer */
        !            30: 
        !            31: /*
        !            32:  * The TCPT_REXMT timer is used to force retransmissions.
        !            33:  * The TCP has the TCPT_REXMT timer set whenever segments
        !            34:  * have been sent for which ACKs are expected but not yet
        !            35:  * received.  If an ACK is received which advances tp->snd_una,
        !            36:  * then the retransmit timer is cleared (if there are no more
        !            37:  * outstanding segments) or reset to the base value (if there
        !            38:  * are more ACKs expected).  Whenever the retransmit timer goes off,
        !            39:  * we retransmit one unacknowledged segment, and do a backoff
        !            40:  * on the retransmit timer.
        !            41:  *
        !            42:  * The TCPT_PERSIST timer is used to keep window size information
        !            43:  * flowing even if the window goes shut.  If all previous transmissions
        !            44:  * have been acknowledged (so that there are no retransmissions in progress),
        !            45:  * and the window is too small to bother sending anything, then we start
        !            46:  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
        !            47:  * we go to transmit state.  Otherwise, at intervals send a single byte
        !            48:  * into the peer's window to force him to update our window information.
        !            49:  * We do this at most as often as TCPT_PERSMIN time intervals,
        !            50:  * but no more frequently than the current estimate of round-trip
        !            51:  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
        !            52:  * a window update from the peer.
        !            53:  *
        !            54:  * The TCPT_KEEP timer is used to keep connections alive.  If an
        !            55:  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
        !            56:  * but not yet established, then we drop the connection.  Once the connection
        !            57:  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
        !            58:  * (and keepalives have been enabled on the socket), we begin to probe
        !            59:  * the connection.  We force the peer to send us a segment by sending:
        !            60:  *     <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
        !            61:  * This segment is (deliberately) outside the window, and should elicit
        !            62:  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
        !            63:  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
        !            64:  * amount of time probing, then we drop the connection.
        !            65:  */
        !            66: 
        !            67: #define        TCP_TTL         30              /* default time to live for TCP segs */
        !            68: /*
        !            69:  * Time constants.
        !            70:  */
        !            71: #define        TCPTV_MSL       ( 30*PR_SLOWHZ)         /* max seg lifetime (hah!) */
        !            72: #define        TCPTV_SRTTBASE  0                       /* base roundtrip time;
        !            73:                                                   if 0, no idea yet */
        !            74: #define        TCPTV_SRTTDFLT  (  3*PR_SLOWHZ)         /* assumed RTT if no info */
        !            75: 
        !            76: #define        TCPTV_PERSMIN   (  5*PR_SLOWHZ)         /* retransmit persistance */
        !            77: #define        TCPTV_PERSMAX   ( 60*PR_SLOWHZ)         /* maximum persist interval */
        !            78: 
        !            79: #define        TCPTV_KEEP_INIT ( 75*PR_SLOWHZ)         /* initial connect keep alive */
        !            80: #define        TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ)      /* dflt time before probing */
        !            81: #define        TCPTV_KEEPINTVL ( 75*PR_SLOWHZ)         /* default probe interval */
        !            82: #define        TCPTV_KEEPCNT   8                       /* max probes before drop */
        !            83: 
        !            84: #define        TCPTV_MIN       (  1*PR_SLOWHZ)         /* minimum allowable value */
        !            85: #define        TCPTV_REXMTMAX  ( 64*PR_SLOWHZ)         /* max allowable REXMT value */
        !            86: 
        !            87: #define        TCP_LINGERTIME  120                     /* linger at most 2 minutes */
        !            88: 
        !            89: #define        TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
        !            90: 
        !            91: #ifdef TCPTIMERS
        !            92: char *tcptimers[] =
        !            93:     { "REXMT", "PERSIST", "KEEP", "2MSL" };
        !            94: #endif
        !            95: 
        !            96: /*
        !            97:  * Force a time value to be in a certain range.
        !            98:  */
        !            99: #define        TCPT_RANGESET(tv, value, tvmin, tvmax) { \
        !           100:        (tv) = (value); \
        !           101:        if ((tv) < (tvmin)) \
        !           102:                (tv) = (tvmin); \
        !           103:        else if ((tv) > (tvmax)) \
        !           104:                (tv) = (tvmax); \
        !           105: }
        !           106: 
        !           107: #ifdef KERNEL
        !           108: extern int tcp_keepidle;               /* time before keepalive probes begin */
        !           109: extern int tcp_keepintvl;              /* time between keepalive probes */
        !           110: extern int tcp_maxidle;                        /* time to drop after starting probes */
        !           111: extern int tcp_ttl;                    /* time to live for TCP segs */
        !           112: extern int tcp_backoff[];
        !           113: #endif

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