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      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  */
     14 
     15 /*
     16  * Definitions of the TCP timers.  These timers are counted
     17  * down PR_SLOWHZ times a second.
     18  */
     19 
     20 #ifndef	_NETINET_TCP_TIMER_H
     21 #define	_NETINET_TCP_TIMER_H
     22 
     23 #pragma ident	"@(#)tcp_timer.h	1.4	05/06/12 SMI"
     24 /* tcp_timer.h 1.13 89/06/16 SMI; from UCB 7.6 6/29/88 */
     25 
     26 #ifdef	__cplusplus
     27 extern "C" {
     28 #endif
     29 
     30 #define	TCPT_NTIMERS	4
     31 
     32 #define	TCPT_REXMT	0		/* retransmit */
     33 #define	TCPT_PERSIST	1		/* retransmit persistance */
     34 #define	TCPT_KEEP	2		/* keep alive */
     35 #define	TCPT_2MSL	3		/* 2*msl quiet time timer */
     36 
     37 /*
     38  * The TCPT_REXMT timer is used to force retransmissions.
     39  * The TCP has the TCPT_REXMT timer set whenever segments
     40  * have been sent for which ACKs are expected but not yet
     41  * received.  If an ACK is received which advances tp->snd_una,
     42  * then the retransmit timer is cleared (if there are no more
     43  * outstanding segments) or reset to the base value (if there
     44  * are more ACKs expected).  Whenever the retransmit timer goes off,
     45  * we retransmit one unacknowledged segment, and do a backoff
     46  * on the retransmit timer.
     47  *
     48  * The TCPT_PERSIST timer is used to keep window size information
     49  * flowing even if the window goes shut.  If all previous transmissions
     50  * have been acknowledged (so that there are no retransmissions in progress),
     51  * and the window is too small to bother sending anything, then we start
     52  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
     53  * we go to transmit state.  Otherwise, at intervals send a single byte
     54  * into the peer's window to force him to update our window information.
     55  * We do this at most as often as TCPT_PERSMIN time intervals,
     56  * but no more frequently than the current estimate of round-trip
     57  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
     58  * a window update from the peer.
     59  *
     60  * The TCPT_KEEP timer is used to keep connections alive.  If a
     61  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
     62  * but not yet established, then we drop the connection.  Once the connection
     63  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
     64  * (and keepalives have been enabled on the socket), we begin to probe
     65  * the connection.  We force the peer to send us a segment by sending:
     66  *	<SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
     67  * This segment is (deliberately) outside the window, and should elicit
     68  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
     69  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
     70  * amount of time probing, then we drop the connection.
     71  */
     72 
     73 #define	TCP_TTL		60		/* default time to live for TCP segs */
     74 /*
     75  * Time constants.
     76  */
     77 #define	TCPTV_MSL	(30*PR_SLOWHZ)		/* max seg lifetime (hah!) */
     78 #define	TCPTV_SRTTBASE	0			/* base roundtrip time; */
     79 						/* if 0, no idea yet */
     80 #define	TCPTV_SRTTDFLT	(3*PR_SLOWHZ)		/* assumed RTT if no info */
     81 
     82 #define	TCPTV_PERSMIN	(5*PR_SLOWHZ)		/* retransmit persistance */
     83 #define	TCPTV_PERSMAX	(60*PR_SLOWHZ)		/* maximum persist interval */
     84 
     85 #define	TCPTV_KEEP_INIT	(75*PR_SLOWHZ)		/* initial connect keep alive */
     86 #define	TCPTV_KEEP_IDLE	(120*60*PR_SLOWHZ)	/* dflt time before probing */
     87 #define	TCPTV_KEEPINTVL	(75*PR_SLOWHZ)		/* default probe interval */
     88 #define	TCPTV_KEEPCNT	8			/* max probes before drop */
     89 
     90 #define	TCPTV_MIN	(1*PR_SLOWHZ)		/* minimum allowable value */
     91 #define	TCPTV_REXMTMAX	(64*PR_SLOWHZ)		/* max allowable REXMT value */
     92 
     93 #define	TCP_LINGERTIME	120			/* linger at most 2 minutes */
     94 
     95 #define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */
     96 
     97 #ifdef	TCPTIMERS
     98 char *tcptimers[] =
     99 	{ "REXMT", "PERSIST", "KEEP", "2MSL" };
    100 #endif
    101 
    102 /*
    103  * Force a time value to be in a certain range.
    104  */
    105 #define	TCPT_RANGESET(tv, value, tvmin, tvmax) { \
    106 	(tv) = (value); \
    107 	if ((tv) < (tvmin)) \
    108 		(tv) = (tvmin); \
    109 	else if ((tv) > (tvmax)) \
    110 		(tv) = (tvmax); \
    111 }
    112 
    113 #ifdef	__cplusplus
    114 }
    115 #endif
    116 
    117 #endif	/* _NETINET_TCP_TIMER_H */
    118