xref: /freebsd/sys/netinet/tcp_timer.h (revision 78007886c995898a9494648343e5236bca1cbba3)
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  * $FreeBSD$
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 #define	TCPTV_INFLIGHT_RTTTHRESH (10*hz/1000)	/* below which inflight
90 						   disengages, in msec */
91 
92 #define TCPTV_FINWAIT2_TIMEOUT (60*hz)         /* FIN_WAIT_2 timeout if no receiver */
93 
94 /*
95  * Minimum retransmit timer is 3 ticks, for algorithmic stability.
96  * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
97  * the expected worst-case processing variances by the kernels
98  * representing the end points.  Such variances do not always show
99  * up in the srtt because the timestamp is often calculated at
100  * the interface rather then at the TCP layer.  This value is
101  * typically 50ms.  However, it is also possible that delayed
102  * acks (typically 100ms) could create issues so we set the slop
103  * to 200ms to try to cover it.  Note that, properly speaking,
104  * delayed-acks should not create a major issue for interactive
105  * environments which 'P'ush the last segment, at least as
106  * long as implementations do the required 'at least one ack
107  * for every two packets' for the non-interactive streaming case.
108  * (maybe the RTO calculation should use 2*RTT instead of RTT
109  * to handle the ack-every-other-packet case).
110  *
111  * The prior minimum of 1*hz (1 second) badly breaks throughput on any
112  * networks faster then a modem that has minor (e.g. 1%) packet loss.
113  */
114 #define	TCPTV_MIN	( 3 )			/* minimum allowable value */
115 #define TCPTV_CPU_VAR	( hz/5 )		/* cpu variance allowed (200ms) */
116 #define	TCPTV_REXMTMAX	( 64*hz)		/* max allowable REXMT value */
117 
118 #define TCPTV_TWTRUNC	8			/* RTO factor to truncate TW */
119 
120 #define	TCP_LINGERTIME	120			/* linger at most 2 minutes */
121 
122 #define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */
123 
124 #define	TCPTV_DELACK	(hz / PR_FASTHZ / 2)	/* 100ms timeout */
125 
126 #ifdef	TCPTIMERS
127 static const char *tcptimers[] =
128     { "REXMT", "PERSIST", "KEEP", "2MSL" };
129 #endif
130 
131 /*
132  * Force a time value to be in a certain range.
133  */
134 #define	TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
135 	(tv) = (value) + tcp_rexmit_slop; \
136 	if ((u_long)(tv) < (u_long)(tvmin)) \
137 		(tv) = (tvmin); \
138 	if ((u_long)(tv) > (u_long)(tvmax)) \
139 		(tv) = (tvmax); \
140 } while(0)
141 
142 #ifdef _KERNEL
143 
144 struct tcp_timer {
145 	struct callout	tt_timer;
146 	int		tt_nextc;	/* next callout time in time_uptime */
147 	int		tt_active;	/* engaged callouts */
148 #define TT_DELACK	0x01
149 #define TT_REXMT	0x02
150 #define TT_PERSIST	0x04
151 #define TT_KEEP		0x08
152 #define TT_2MSL		0x10
153 	int             tt_delack;
154 	int             tt_rexmt;
155 	int             tt_persist;
156 	int             tt_keep;
157 	int             tt_2msl;
158 };
159 
160 extern int tcp_keepinit;		/* time to establish connection */
161 extern int tcp_keepidle;		/* time before keepalive probes begin */
162 extern int tcp_keepintvl;		/* time between keepalive probes */
163 extern int tcp_maxidle;			/* time to drop after starting probes */
164 extern int tcp_delacktime;		/* time before sending a delayed ACK */
165 extern int tcp_maxpersistidle;
166 extern int tcp_rexmit_min;
167 extern int tcp_rexmit_slop;
168 extern int tcp_msl;
169 extern int tcp_ttl;			/* time to live for TCP segs */
170 extern int tcp_backoff[];
171 
172 struct tcptw;
173 
174 extern int tcp_finwait2_timeout;
175 extern int tcp_fast_finwait2_recycle;
176 
177 void	tcp_timer_init(void);
178 struct tcptw *
179 	tcp_timer_2msl_tw(int _reuse);		/* XXX temporary */
180 void	tcp_timer_2msl_reset(struct tcptw *_tw, int rearm);
181 void	tcp_timer_2msl_stop(struct tcptw *_tw);
182 
183 #endif /* _KERNEL */
184 
185 #endif /* !_NETINET_TCP_TIMER_H_ */
186