--- /dev/null
+/*!\file netinet/tcp_time.h
+ * TCP timer definitions.
+ */
+
+/*
+ * Copyright (c) 1982, 1986, 1993
+ * The Regents of the University of California. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ * must display the following acknowledgement:
+ * This product includes software developed by the University of
+ * California, Berkeley and its contributors.
+ * 4. Neither the name of the University nor the names of its contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
+ * $Id: tcp_timer.h,v 1.10 1996/09/13 23:51:43 pst Exp $
+ */
+
+#ifndef __NETINET_TCP_TIMER_H
+#define __NETINET_TCP_TIMER_H
+
+/*
+ * 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 persistence */
+#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.
+ */
+
+/*
+ * 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_RTOBASE ( 3*PR_SLOWHZ) /* assumed RTO if no info */
+#define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */
+
+#define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistence */
+#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 TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
+
+#define TCP_LINGERTIME 120 /* linger at most 2 minutes */
+
+#define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
+
+#ifdef TCPTIMERS
+static 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 ((u_long)(tv) < (u_long)(tvmin)) \
+ (tv) = (tvmin); \
+ else if ((u_long)(tv) > (u_long)(tvmax)) \
+ (tv) = (tvmax); \
+ }
+
+#endif
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