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 * 3. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
34 * $FreeBSD: releng/5.1/sys/netinet/tcp_timer.h 112009 2003-03-08 22:06:20Z jlemon $
35 */
36
37 #ifndef _NETINET_TCP_TIMER_H_
38 #define _NETINET_TCP_TIMER_H_
39
40 /*
41 * The TCPT_REXMT timer is used to force retransmissions.
42 * The TCP has the TCPT_REXMT timer set whenever segments
43 * have been sent for which ACKs are expected but not yet
44 * received. If an ACK is received which advances tp->snd_una,
45 * then the retransmit timer is cleared (if there are no more
46 * outstanding segments) or reset to the base value (if there
47 * are more ACKs expected). Whenever the retransmit timer goes off,
48 * we retransmit one unacknowledged segment, and do a backoff
49 * on the retransmit timer.
50 *
51 * The TCPT_PERSIST timer is used to keep window size information
52 * flowing even if the window goes shut. If all previous transmissions
53 * have been acknowledged (so that there are no retransmissions in progress),
54 * and the window is too small to bother sending anything, then we start
55 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
56 * we go to transmit state. Otherwise, at intervals send a single byte
57 * into the peer's window to force him to update our window information.
58 * We do this at most as often as TCPT_PERSMIN time intervals,
59 * but no more frequently than the current estimate of round-trip
60 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
61 * a window update from the peer.
62 *
63 * The TCPT_KEEP timer is used to keep connections alive. If an
64 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
65 * but not yet established, then we drop the connection. Once the connection
66 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
67 * (and keepalives have been enabled on the socket), we begin to probe
68 * the connection. We force the peer to send us a segment by sending:
69 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
70 * This segment is (deliberately) outside the window, and should elicit
71 * an ack segment in response from the peer. If, despite the TCPT_KEEP
72 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
73 * amount of time probing, then we drop the connection.
74 */
75
76 /*
77 * Time constants.
78 */
79 #define TCPTV_MSL ( 30*hz) /* max seg lifetime (hah!) */
80 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
81 if 0, no idea yet */
82 #define TCPTV_RTOBASE ( 3*hz) /* assumed RTO if no info */
83 #define TCPTV_SRTTDFLT ( 3*hz) /* assumed RTT if no info */
84
85 #define TCPTV_PERSMIN ( 5*hz) /* retransmit persistence */
86 #define TCPTV_PERSMAX ( 60*hz) /* maximum persist interval */
87
88 #define TCPTV_KEEP_INIT ( 75*hz) /* initial connect keepalive */
89 #define TCPTV_KEEP_IDLE (120*60*hz) /* dflt time before probing */
90 #define TCPTV_KEEPINTVL ( 75*hz) /* default probe interval */
91 #define TCPTV_KEEPCNT 8 /* max probes before drop */
92
93 /*
94 * Minimum retransmit timer is 3 ticks, for algorithmic stability.
95 * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
96 * the expected worst-case processing variances by the kernels
97 * representing the end points. Such variances do not always show
98 * up in the srtt because the timestamp is often calculated at
99 * the interface rather then at the TCP layer. This value is
100 * typically 50ms. However, it is also possible that delayed
101 * acks (typically 100ms) could create issues so we set the slop
102 * to 200ms to try to cover it. Note that, properly speaking,
103 * delayed-acks should not create a major issue for interactive
104 * environments which 'P'ush the last segment, at least as
105 * long as implementations do the required 'at least one ack
106 * for every two packets' for the non-interactive streaming case.
107 * (maybe the RTO calculation should use 2*RTT instead of RTT
108 * to handle the ack-every-other-packet case).
109 *
110 * The prior minimum of 1*hz (1 second) badly breaks throughput on any
111 * networks faster then a modem that has minor (e.g. 1%) packet loss.
112 */
113 #define TCPTV_MIN ( 3 ) /* minimum allowable value */
114 #define TCPTV_CPU_VAR ( hz/5 ) /* cpu variance allowed (200ms) */
115 #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */
116
117 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
118
119 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
120
121 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
122
123 #define TCPTV_DELACK (hz / PR_FASTHZ / 2) /* 100ms timeout */
124
125 #ifdef TCPTIMERS
126 static const char *tcptimers[] =
127 { "REXMT", "PERSIST", "KEEP", "2MSL" };
128 #endif
129
130 /*
131 * Force a time value to be in a certain range.
132 */
133 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
134 (tv) = (value) + tcp_rexmit_slop; \
135 if ((u_long)(tv) < (u_long)(tvmin)) \
136 (tv) = (tvmin); \
137 else if ((u_long)(tv) > (u_long)(tvmax)) \
138 (tv) = (tvmax); \
139 } while(0)
140
141 #ifdef _KERNEL
142 extern int tcp_keepinit; /* time to establish connection */
143 extern int tcp_keepidle; /* time before keepalive probes begin */
144 extern int tcp_keepintvl; /* time between keepalive probes */
145 extern int tcp_maxidle; /* time to drop after starting probes */
146 extern int tcp_delacktime; /* time before sending a delayed ACK */
147 extern int tcp_maxpersistidle;
148 extern int tcp_rexmit_min;
149 extern int tcp_rexmit_slop;
150 extern int tcp_msl;
151 extern int tcp_ttl; /* time to live for TCP segs */
152 extern int tcp_backoff[];
153
154 struct tcptw;
155
156 void tcp_timer_init(void);
157 void tcp_timer_2msl(void *xtp);
158 struct tcptw *
159 tcp_timer_2msl_tw(int _reuse); /* XXX temporary */
160 void tcp_timer_2msl_reset(struct tcptw *_tw, int _timeo);
161 void tcp_timer_2msl_stop(struct tcptw *_tw);
162 void tcp_timer_keep(void *xtp);
163 void tcp_timer_persist(void *xtp);
164 void tcp_timer_rexmt(void *xtp);
165 void tcp_timer_delack(void *xtp);
166
167 #endif /* _KERNEL */
168
169 #endif /* !_NETINET_TCP_TIMER_H_ */
Cache object: 1ced21ac52e913f05d28c66dfa99ef18
|