1/* SPDX-License-Identifier: BSD-3-Clause */
2/*
3 * Copyright (c) 1982, 1986, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the University nor the names of its contributors
15 * may be used to endorse or promote products derived from this software
16 * without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 *
30 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
31 * tcp_timer.h,v 1.4 1994/08/21 05:27:38 paul Exp
32 */
33
34#ifndef TCP_TIMER_H
35#define TCP_TIMER_H
36
37/*
38 * Definitions of the TCP timers. These timers are counted
39 * down PR_SLOWHZ times a second.
40 */
41#define TCPT_NTIMERS 4
42
43#define TCPT_REXMT 0 /* retransmit */
44#define TCPT_PERSIST 1 /* retransmit persistence */
45#define TCPT_KEEP 2 /* keep alive */
46#define TCPT_2MSL 3 /* 2*msl quiet time timer */
47
48/*
49 * The TCPT_REXMT timer is used to force retransmissions.
50 * The TCP has the TCPT_REXMT timer set whenever segments
51 * have been sent for which ACKs are expected but not yet
52 * received. If an ACK is received which advances tp->snd_una,
53 * then the retransmit timer is cleared (if there are no more
54 * outstanding segments) or reset to the base value (if there
55 * are more ACKs expected). Whenever the retransmit timer goes off,
56 * we retransmit one unacknowledged segment, and do a backoff
57 * on the retransmit timer.
58 *
59 * The TCPT_PERSIST timer is used to keep window size information
60 * flowing even if the window goes shut. If all previous transmissions
61 * have been acknowledged (so that there are no retransmissions in progress),
62 * and the window is too small to bother sending anything, then we start
63 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
64 * we go to transmit state. Otherwise, at intervals send a single byte
65 * into the peer's window to force him to update our window information.
66 * We do this at most as often as TCPT_PERSMIN time intervals,
67 * but no more frequently than the current estimate of round-trip
68 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
69 * a window update from the peer.
70 *
71 * The TCPT_KEEP timer is used to keep connections alive. If an
72 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
73 * but not yet established, then we drop the connection. Once the connection
74 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
75 * (and keepalives have been enabled on the socket), we begin to probe
76 * the connection. We force the peer to send us a segment by sending:
77 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
78 * This segment is (deliberately) outside the window, and should elicit
79 * an ack segment in response from the peer. If, despite the TCPT_KEEP
80 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
81 * amount of time probing, then we drop the connection.
82 */
83
84/*
85 * Time constants.
86 */
87#define TCPTV_MSL (5 * PR_SLOWHZ) /* max seg lifetime (hah!) */
88
89#define TCPTV_SRTTBASE \
90 0 /* base roundtrip time; \
91 if 0, no idea yet */
92#define TCPTV_SRTTDFLT (3 * PR_SLOWHZ) /* assumed RTT if no info */
93
94#define TCPTV_PERSMIN (5 * PR_SLOWHZ) /* retransmit persistence */
95#define TCPTV_PERSMAX (60 * PR_SLOWHZ) /* maximum persist interval */
96
97#define TCPTV_KEEP_INIT (75 * PR_SLOWHZ) /* initial connect keep alive */
98#define TCPTV_KEEP_IDLE (120 * 60 * PR_SLOWHZ) /* dflt time before probing */
99#define TCPTV_KEEPINTVL (75 * PR_SLOWHZ) /* default probe interval */
100#define TCPTV_KEEPCNT 8 /* max probes before drop */
101
102#define TCPTV_MIN (1 * PR_SLOWHZ) /* minimum allowable value */
103#define TCPTV_REXMTMAX (12 * PR_SLOWHZ) /* max allowable REXMT value */
104
105#define TCP_LINGERTIME 120 /* linger at most 2 minutes */
106
107#define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
108
109
110/*
111 * Force a time value to be in a certain range.
112 */
113#define TCPT_RANGESET(tv, value, tvmin, tvmax) \
114 { \
115 (tv) = (value); \
116 if ((tv) < (tvmin)) \
117 (tv) = (tvmin); \
118 else if ((tv) > (tvmax)) \
119 (tv) = (tvmax); \
120 }
121
122extern const int tcp_backoff[];
123
124struct tcpcb;
125
126void tcp_fasttimo(Slirp *);
127void tcp_slowtimo(Slirp *);
128void tcp_canceltimers(struct tcpcb *);
129
130#endif
131