Watt-32 tcp/ip  2.2 dev-rel.10
tcp_time.h
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1 
5 /*
6  * Copyright (c) 1982, 1986, 1993
7  * The Regents of the University of California. All rights reserved.
8  *
9  * Redistribution and use in source and binary forms, with or without
10  * modification, are permitted provided that the following conditions
11  * are met:
12  * 1. Redistributions of source code must retain the above copyright
13  * notice, this list of conditions and the following disclaimer.
14  * 2. Redistributions in binary form must reproduce the above copyright
15  * notice, this list of conditions and the following disclaimer in the
16  * documentation and/or other materials provided with the distribution.
17  * 3. All advertising materials mentioning features or use of this software
18  * must display the following acknowledgement:
19  * This product includes software developed by the University of
20  * California, Berkeley and its contributors.
21  * 4. Neither the name of the University nor the names of its contributors
22  * may be used to endorse or promote products derived from this software
23  * without specific prior written permission.
24  *
25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28  * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35  * SUCH DAMAGE.
36  *
37  * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
38  * $Id: tcp_timer.h,v 1.10 1996/09/13 23:51:43 pst Exp $
39  */
40 
41 #ifndef __NETINET_TCP_TIMER_H
42 #define __NETINET_TCP_TIMER_H
43 
44 /*
45  * Definitions of the TCP timers. These timers are counted
46  * down PR_SLOWHZ times a second.
47  */
48 #define TCPT_NTIMERS 4
49 
50 #define TCPT_REXMT 0 /* retransmit */
51 #define TCPT_PERSIST 1 /* retransmit persistence */
52 #define TCPT_KEEP 2 /* keep alive */
53 #define TCPT_2MSL 3 /* 2*msl quiet time timer */
54 
55 /*
56  * The TCPT_REXMT timer is used to force retransmissions.
57  * The TCP has the TCPT_REXMT timer set whenever segments
58  * have been sent for which ACKs are expected but not yet
59  * received. If an ACK is received which advances tp->snd_una,
60  * then the retransmit timer is cleared (if there are no more
61  * outstanding segments) or reset to the base value (if there
62  * are more ACKs expected). Whenever the retransmit timer goes off,
63  * we retransmit one unacknowledged segment, and do a backoff
64  * on the retransmit timer.
65  *
66  * The TCPT_PERSIST timer is used to keep window size information
67  * flowing even if the window goes shut. If all previous transmissions
68  * have been acknowledged (so that there are no retransmissions in progress),
69  * and the window is too small to bother sending anything, then we start
70  * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
71  * we go to transmit state. Otherwise, at intervals send a single byte
72  * into the peer's window to force him to update our window information.
73  * We do this at most as often as TCPT_PERSMIN time intervals,
74  * but no more frequently than the current estimate of round-trip
75  * packet time. The TCPT_PERSIST timer is cleared whenever we receive
76  * a window update from the peer.
77  *
78  * The TCPT_KEEP timer is used to keep connections alive. If an
79  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
80  * but not yet established, then we drop the connection. Once the connection
81  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
82  * (and keepalives have been enabled on the socket), we begin to probe
83  * the connection. We force the peer to send us a segment by sending:
84  * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
85  * This segment is (deliberately) outside the window, and should elicit
86  * an ack segment in response from the peer. If, despite the TCPT_KEEP
87  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
88  * amount of time probing, then we drop the connection.
89  */
90 
91 /*
92  * Time constants.
93  */
94 #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */
95 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
96  if 0, no idea yet */
97 #define TCPTV_RTOBASE ( 3*PR_SLOWHZ) /* assumed RTO if no info */
98 #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */
99 
100 #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistence */
101 #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */
102 
103 #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */
104 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */
105 #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */
106 #define TCPTV_KEEPCNT 8 /* max probes before drop */
107 
108 #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */
109 #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */
110 
111 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
112 
113 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
114 
115 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
116 
117 #ifdef TCPTIMERS
118 static char *tcptimers[] =
119  { "REXMT", "PERSIST", "KEEP", "2MSL" };
120 #endif
121 
122 /*
123  * Force a time value to be in a certain range.
124  */
125 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \
126  (tv) = (value); \
127  if ((u_long)(tv) < (u_long)(tvmin)) \
128  (tv) = (tvmin); \
129  else if ((u_long)(tv) > (u_long)(tvmax)) \
130  (tv) = (tvmax); \
131  }
132 
133 #endif