1 /*-
2 * Copyright (c) 1982, 1986, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 4. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 *
29 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
30 * $FreeBSD: releng/6.0/sys/netinet/tcp_timer.h 139823 2005-01-07 01:45:51Z imp $
31 */
32
33 #ifndef _NETINET_TCP_TIMER_H_
34 #define _NETINET_TCP_TIMER_H_
35
36 /*
37 * The TCPT_REXMT timer is used to force retransmissions.
38 * The TCP has the TCPT_REXMT timer set whenever segments
39 * have been sent for which ACKs are expected but not yet
40 * received. If an ACK is received which advances tp->snd_una,
41 * then the retransmit timer is cleared (if there are no more
42 * outstanding segments) or reset to the base value (if there
43 * are more ACKs expected). Whenever the retransmit timer goes off,
44 * we retransmit one unacknowledged segment, and do a backoff
45 * on the retransmit timer.
46 *
47 * The TCPT_PERSIST timer is used to keep window size information
48 * flowing even if the window goes shut. If all previous transmissions
49 * have been acknowledged (so that there are no retransmissions in progress),
50 * and the window is too small to bother sending anything, then we start
51 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
52 * we go to transmit state. Otherwise, at intervals send a single byte
53 * into the peer's window to force him to update our window information.
54 * We do this at most as often as TCPT_PERSMIN time intervals,
55 * but no more frequently than the current estimate of round-trip
56 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
57 * a window update from the peer.
58 *
59 * The TCPT_KEEP timer is used to keep connections alive. If an
60 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
61 * but not yet established, then we drop the connection. Once the connection
62 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
63 * (and keepalives have been enabled on the socket), we begin to probe
64 * the connection. We force the peer to send us a segment by sending:
65 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
66 * This segment is (deliberately) outside the window, and should elicit
67 * an ack segment in response from the peer. If, despite the TCPT_KEEP
68 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
69 * amount of time probing, then we drop the connection.
70 */
71
72 /*
73 * Time constants.
74 */
75 #define TCPTV_MSL ( 30*hz) /* max seg lifetime (hah!) */
76 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
77 if 0, no idea yet */
78 #define TCPTV_RTOBASE ( 3*hz) /* assumed RTO if no info */
79 #define TCPTV_SRTTDFLT ( 3*hz) /* assumed RTT if no info */
80
81 #define TCPTV_PERSMIN ( 5*hz) /* retransmit persistence */
82 #define TCPTV_PERSMAX ( 60*hz) /* maximum persist interval */
83
84 #define TCPTV_KEEP_INIT ( 75*hz) /* initial connect keepalive */
85 #define TCPTV_KEEP_IDLE (120*60*hz) /* dflt time before probing */
86 #define TCPTV_KEEPINTVL ( 75*hz) /* default probe interval */
87 #define TCPTV_KEEPCNT 8 /* max probes before drop */
88
89 /*
90 * Minimum retransmit timer is 3 ticks, for algorithmic stability.
91 * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
92 * the expected worst-case processing variances by the kernels
93 * representing the end points. Such variances do not always show
94 * up in the srtt because the timestamp is often calculated at
95 * the interface rather then at the TCP layer. This value is
96 * typically 50ms. However, it is also possible that delayed
97 * acks (typically 100ms) could create issues so we set the slop
98 * to 200ms to try to cover it. Note that, properly speaking,
99 * delayed-acks should not create a major issue for interactive
100 * environments which 'P'ush the last segment, at least as
101 * long as implementations do the required 'at least one ack
102 * for every two packets' for the non-interactive streaming case.
103 * (maybe the RTO calculation should use 2*RTT instead of RTT
104 * to handle the ack-every-other-packet case).
105 *
106 * The prior minimum of 1*hz (1 second) badly breaks throughput on any
107 * networks faster then a modem that has minor (e.g. 1%) packet loss.
108 */
109 #define TCPTV_MIN ( 3 ) /* minimum allowable value */
110 #define TCPTV_CPU_VAR ( hz/5 ) /* cpu variance allowed (200ms) */
111 #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */
112
113 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
114
115 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
116
117 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
118
119 #define TCPTV_DELACK (hz / PR_FASTHZ / 2) /* 100ms timeout */
120
121 #ifdef TCPTIMERS
122 static const char *tcptimers[] =
123 { "REXMT", "PERSIST", "KEEP", "2MSL" };
124 #endif
125
126 /*
127 * Force a time value to be in a certain range.
128 */
129 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
130 (tv) = (value) + tcp_rexmit_slop; \
131 if ((u_long)(tv) < (u_long)(tvmin)) \
132 (tv) = (tvmin); \
133 else if ((u_long)(tv) > (u_long)(tvmax)) \
134 (tv) = (tvmax); \
135 } while(0)
136
137 #ifdef _KERNEL
138 extern int tcp_keepinit; /* time to establish connection */
139 extern int tcp_keepidle; /* time before keepalive probes begin */
140 extern int tcp_keepintvl; /* time between keepalive probes */
141 extern int tcp_maxidle; /* time to drop after starting probes */
142 extern int tcp_delacktime; /* time before sending a delayed ACK */
143 extern int tcp_maxpersistidle;
144 extern int tcp_rexmit_min;
145 extern int tcp_rexmit_slop;
146 extern int tcp_msl;
147 extern int tcp_ttl; /* time to live for TCP segs */
148 extern int tcp_backoff[];
149
150 struct tcptw;
151
152 void tcp_timer_init(void);
153 void tcp_timer_2msl(void *xtp);
154 struct tcptw *
155 tcp_timer_2msl_tw(int _reuse); /* XXX temporary */
156 void tcp_timer_2msl_reset(struct tcptw *_tw, int _timeo);
157 void tcp_timer_2msl_stop(struct tcptw *_tw);
158 void tcp_timer_keep(void *xtp);
159 void tcp_timer_persist(void *xtp);
160 void tcp_timer_rexmt(void *xtp);
161 void tcp_timer_delack(void *xtp);
162
163 #endif /* _KERNEL */
164
165 #endif /* !_NETINET_TCP_TIMER_H_ */
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