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/*
 * 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	2.2 - 89/09/25
 */

#ifndef _h_TCP_TIMER
#define _h_TCP_TIMER
#ident "@(#)tcp_timer.h	2.2 - 89/09/25"

/*
 * 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		30		/* time to live for TCP segs */
/*
 * Time constants.
 */
#ifdef OLDHBTCP
#define	TCPTV_MSL	( 15*PR_SLOWHZ)		/* max seg lifetime */
#else
#define	TCPTV_MSL	( 30*PR_SLOWHZ)		/* max seg lifetime */
#endif /*OLDHBTCP*/
#define	TCPTV_SRTTBASE	0			/* base roundtrip time;
						   if 0, no idea yet */
#define	TCPTV_SRTTDFLT	(  3*PR_SLOWHZ)		/* assumed RTT if no info */

#ifdef OLDHBTCP
#define	TCPTV_KEEP	( 45*PR_SLOWHZ)		/* keep alive - 45 secs */
#define	TCPTV_PERSMIN	(  5*PR_SLOWHZ)		/* retransmit persistance */
#else
#define	TCPTV_PERSMIN	(  5*PR_SLOWHZ)		/* retransmit persistance */
#define	TCPTV_PERSMAX	( 60*PR_SLOWHZ)		/* maximum persist interval*/

#define	TCPTV_KEEP_INIT	( 75*PR_SLOWHZ)		/* initial connect keep alive*/
#define	TCPTV_KEEP_IDLE ( 120*PR_SLOWHZ)	/* dflt time before probing*/
#define	TCPTV_KEEPINTVL ( 75*PR_SLOWHZ)		/* default probe interval*/
#define	TCPTV_KEEPCNT   8			/* max probes before drop*/
#endif /*OLDHBTCP*/

#ifdef OLDHBTCP
#define	TCPTV_MAXIDLE	(  8*TCPTV_KEEP)	/* maximum allowable idle*/
#endif /*OLDHBTCP*/

#define	TCPTV_MIN	(  1*PR_SLOWHZ)		/* minimum allowable value */
#ifdef OLDHBTCP
#define	TCPTV_MAX	( 30*PR_SLOWHZ)		/* maximum allowable value */
#else
#define TCPTV_REXMTMAX	(64*PR_SLOWHZ)		/*max aloowable REXMT value*/
#endif /*OLDHBTCP*/

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

#define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */

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

#ifdef OLDHBTCP
/*
 * Retransmission smoothing constants.
 * Smoothed round trip time is updated by
 *    tp->t_srtt = (tcp_alpha * tp->t_srtt) + ((1 - tcp_alpha) * tp->t_rtt)
 * each time a new value of tp->t_rtt is available.  The initial
 * retransmit timeout is then based on
 *    tp->t_timer[TCPT_REXMT] = tcp_beta * tp->t_srtt;
 * limited, however to be at least TCPTV_MIN and at most TCPTV_MAX.
 */
long	tcp_alpha, tcp_beta;

/*
 * deal with scaled integer arithmetic since we want fractional values in
 * calculating the smoothed round-trip time value for retransmission.
 */

#define SCALEFACTOR 256
#define SCALE(n)	(SCALEFACTOR*(n))
#define SMUL(n,m)	(((n)*(m))/SCALEFACTOR)
#define SDIV(n,m)	(SCALE(n)/(m))
#define UNSCALE(n)	((n)/SCALEFACTOR)

/*
 * Initial values of tcp_alpha and tcp_beta.
 * These are conservative: averaging over a long
 * period of time, and allowing for large individual deviations from
 * tp->t_srtt.
 */
#define	TCP_ALPHA	SDIV(9,10)			/*0.9*/
#define	TCP_BETA	SCALE(2)			/*2.0*/
#endif /*OLDHBTCP*/

/*
 * Force a time value to be in a certain range.
 */
#define	TCPT_RANGESET(tv, value, tvmin, tvmax) { \
	(tv) = (value); \
	if ((tv) < (tvmin)) \
		(tv) = (tvmin); \
	if ((tv) > (tvmax)) \
		(tv) = (tvmax); \
}
#ifdef KERNEL
extern int tcp_keepidle;		/*time before keepalive probes begin*/
extern int tcp_keepintvl;		/*time between keepalive probes */
extern int tcp_maxidle;			/*time to drop after starting probes*/
extern int tcp_backoff[];		/*time to live for TCP segs */
#endif /*KERNEL*/
#endif /* _h_TCP_TIMER */
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