/*
 * Copyright (c) 1982, 1986 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *      @(#)tcp_timer.h 7.6 (Berkeley) 6/29/88
 */

/*
 * 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_INIT amount of time,
 * but not yet established, then we drop the connection.  Once the connection
 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
 * (and keepalives have been enabled on the socket), we begin to probe
 * the connection.  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 probing, then we drop the connection.
 */

#define TCP_TTL         30              /* default time to live for TCP segs */
/*
 * Time constants.
 */
#define TCPTV_MSL       ( 30*PR_SLOWHZ)         /* max seg lifetime (hah!) */
#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_INIT ( 75*PR_SLOWHZ)         /* initial connect keep alive */
#define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ)      /* dflt time before probing */
#define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ)         /* default probe interval */
#define TCPTV_KEEPCNT   8                       /* max probes before drop */

#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_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_ttl;                     /* time to live for TCP segs */
extern int tcp_backoff[];
#endif