tcp_timer.h

<B>Digital的Unix操作系统VAX 4.2源码</B>

/* @(#)tcp_timer.h	4.1	(ULTRIX)	7/2/90	 */

/************************************************************************
 *									*
 *			Copyright (c) 1985 by				*
 *		Digital Equipment Corporation, Maynard, MA		*
 *			All rights reserved.				*
 *									*
 *   This software is furnished under a license and may be used and	*
 *   copied  only  in accordance with the terms of such license and	*
 *   with the  inclusion  of  the  above  copyright  notice.   This	*
 *   software  or  any  other copies thereof may not be provided or	*
 *   otherwise made available to any other person.  No title to and	*
 *   ownership of the software is hereby transferred.			*
 *									*
 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
 *   Laboratories.  Use, duplication, or disclosure is  subject  to	*
 *   restrictions  under  license  agreements  with  University  of	*
 *   California and with AT&T.						*
 *									*
 *   The information in this software is subject to change  without	*
 *   notice  and should not be construed as a commitment by Digital	*
 *   Equipment Corporation.						*
 *									*
 *   Digital assumes no responsibility for the use  or  reliability	*
 *   of its software on equipment which is not supplied by Digital.	*
 *									*
 ************************************************************************/

/************************************************************************
 *			Modification History				*
 *									*
 *	
 *	15-Jan-88	lp
 *		Merge of final 43BSD changes.
 *
 *	Larry Cohen  -	09/16/85					*
 * 		Add 43bsd alpha tape changes for subnet routing		*
 *									*
 ************************************************************************/

/*
 * Copyright (c) 1982, 1986 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 *
 *	tcp_timer.h	7.3 (Berkeley) 6/30/87
 */

/*
 * Definitions of the TCP timers.  These timers are counted
 * down PR_SLOWHZ times a second.
 */
#define	TCPT_NTIMERS	4

#define	TCPT_REXMT	0		/* retransmit */
#define	TCPT_PERSIST	1		/* retransmit persistance */
#define	TCPT_KEEP	2		/* keep alive */
#define	TCPT_2MSL	3		/* 2*msl quiet time timer */

/*
 * The TCPT_REXMT timer is used to force retransmissions.
 * The TCP has the TCPT_REXMT timer set whenever segments
 * have been sent for which ACKs are expected but not yet
 * received.  If an ACK is received which advances tp->snd_una,
 * then the retransmit timer is cleared (if there are no more
 * outstanding segments) or reset to the base value (if there
 * are more ACKs expected).  Whenever the retransmit timer goes off,
 * we retransmit one unacknowledged segment, and do a backoff
 * on the retransmit timer.
 *
 * The TCPT_PERSIST timer is used to keep window size information
 * flowing even if the window goes shut.  If all previous transmissions
 * have been acknowledged (so that there are no retransmissions in progress),
 * and the window is too small to bother sending anything, then we start
 * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
 * we go to transmit state.  Otherwise, at intervals send a single byte
 * into the peer's window to force him to update our window information.
 * We do this at most as often as TCPT_PERSMIN time intervals,
 * but no more frequently than the current estimate of round-trip
 * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
 * a window update from the peer.
 *
 * The TCPT_KEEP timer is used to keep connections alive.  If an
 * connection is idle (no segments received) for TCPTV_KEEP amount of time,
 * but not yet established, then we drop the connection.  If the connection
 * is established, then we force the peer to send us a segment by sending:
 *	<SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
 * This segment is (deliberately) outside the window, and should elicit
 * an ack segment in response from the peer.  If, despite the TCPT_KEEP
 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
 * amount of time, then we drop the connection.
 */

#define	TCP_TTL		60		/* default time to live for TCP segs */
int	tcp_ttl;			/* time to live for TCP segs */
/*
 * Time constants.
 */
#define	TCPTV_MSL	( 15*PR_SLOWHZ)		/* max seg lifetime */
#define	TCPTV_SRTTBASE	0			/* base roundtrip time;
						   if 0, no idea yet */
#define	TCPTV_SRTTDFLT	(  3*PR_SLOWHZ)		/* assumed RTT if no info */

#define	TCPTV_PERSMIN	(  5*PR_SLOWHZ)		/* retransmit persistance */
#define TCPTV_PERSMAX   ( 60*PR_SLOWHZ)         /* maximum persist interval */

#define	TCPTV_KEEP	( 75*PR_SLOWHZ)		/* keep alive - 75 secs */
#define	TCPTV_MAXIDLE	(  8*TCPTV_KEEP)	/* maximum allowable idle
						   time before drop conn */

#define	TCPTV_MIN	(  1*PR_SLOWHZ)		/* minimum allowable value */
#define	TCPTV_REXMTMAX	( 64*PR_SLOWHZ)		/* max allowable REXMT value */

#define	TCP_LINGERTIME	120			/* linger at most 2 minutes */

#define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */

#ifdef	TCPTIMERS
char *tcptimers[] =
    { "REXMT", "PERSIST", "KEEP", "2MSL" };
#endif

/*
 * Force a time value to be in a certain range.
 */
#define	TCPT_RANGESET(tv, value, tvmin, tvmax) { \
	(tv) = (value); \
	if ((tv) < (tvmin)) \
		(tv) = (tvmin); \
	else if ((tv) > (tvmax)) \
		(tv) = (tvmax); \
}

#ifdef KERNEL
extern int tcp_backoff[];
#endif