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 /**
34  * samkumar: The FreeBSD Operating System uses its callout subsystem to
35  * implement TCP timers. I've removed the relevant definitions/declarations
36  * below, since TCPlp relies on the host system to implement TCP timers. To
37  * save memory, I've removed some configurability (e.g., per-TCB keepalive
38  * parameters) and global statistics (e.g. tcp_keepcnt).
39  */
40 
41 #ifndef TCPLP_NETINET_TCP_TIMER_H_
42 #define TCPLP_NETINET_TCP_TIMER_H_
43 
44 #include "tcp_var.h"
45 
46 /*
47  * The TCPT_REXMT timer is used to force retransmissions.
48  * The TCP has the TCPT_REXMT timer set whenever segments
49  * have been sent for which ACKs are expected but not yet
50  * received.  If an ACK is received which advances tp->snd_una,
51  * then the retransmit timer is cleared (if there are no more
52  * outstanding segments) or reset to the base value (if there
53  * are more ACKs expected).  Whenever the retransmit timer goes off,
54  * we retransmit one unacknowledged segment, and do a backoff
55  * on the retransmit timer.
56  *
57  * The TCPT_PERSIST timer is used to keep window size information
58  * flowing even if the window goes shut.  If all previous transmissions
59  * have been acknowledged (so that there are no retransmissions in progress),
60  * and the window is too small to bother sending anything, then we start
61  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
62  * we go to transmit state.  Otherwise, at intervals send a single byte
63  * into the peer's window to force him to update our window information.
64  * We do this at most as often as TCPT_PERSMIN time intervals,
65  * but no more frequently than the current estimate of round-trip
66  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
67  * a window update from the peer.
68  *
69  * The TCPT_KEEP timer is used to keep connections alive.  If an
70  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
71  * but not yet established, then we drop the connection.  Once the connection
72  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
73  * (and keepalives have been enabled on the socket), we begin to probe
74  * the connection.  We force the peer to send us a segment by sending:
75  *	<SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
76  * This segment is (deliberately) outside the window, and should elicit
77  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
78  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
79  * amount of time probing, then we drop the connection.
80  */
81 
82 #define TT_DELACK	0x0001
83 #define TT_REXMT	0x0002
84 #define TT_PERSIST	0x0004
85 #define TT_KEEP		0x0008
86 #define TT_2MSL		0x0010
87 
88 /*
89  * Time constants.
90  */
91 #define	TCPTV_MSL	( 30*hz)		/* max seg lifetime (hah!) */
92 #define	TCPTV_SRTTBASE	0			/* base roundtrip time;
93 						   if 0, no idea yet */
94 #define	TCPTV_RTOBASE	(  3*hz)		/* assumed RTO if no info */
95 
96 #define	TCPTV_PERSMIN	(  5*hz)		/* retransmit persistence */
97 #define	TCPTV_PERSMAX	( 60*hz)		/* maximum persist interval */
98 
99 #define	TCPTV_KEEP_INIT	( 75*hz)		/* initial connect keepalive */
100 #define	TCPTV_KEEP_IDLE	(120*60*hz)		/* dflt time before probing */
101 #define	TCPTV_KEEPINTVL	( 75*hz)		/* default probe interval */
102 #define	TCPTV_KEEPCNT	8			/* max probes before drop */
103 
104 #define TCPTV_FINWAIT2_TIMEOUT (60*hz)         /* FIN_WAIT_2 timeout if no receiver */
105 
106 /*
107  * Minimum retransmit timer is 3 ticks, for algorithmic stability.
108  * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
109  * the expected worst-case processing variances by the kernels
110  * representing the end points.  Such variances do not always show
111  * up in the srtt because the timestamp is often calculated at
112  * the interface rather then at the TCP layer.  This value is
113  * typically 50ms.  However, it is also possible that delayed
114  * acks (typically 100ms) could create issues so we set the slop
115  * to 200ms to try to cover it.  Note that, properly speaking,
116  * delayed-acks should not create a major issue for interactive
117  * environments which 'P'ush the last segment, at least as
118  * long as implementations do the required 'at least one ack
119  * for every two packets' for the non-interactive streaming case.
120  * (maybe the RTO calculation should use 2*RTT instead of RTT
121  * to handle the ack-every-other-packet case).
122  *
123  * The prior minimum of 1*hz (1 second) badly breaks throughput on any
124  * networks faster then a modem that has minor (e.g. 1%) packet loss.
125  */
126 #define	TCPTV_MIN	( hz/33 )		/* minimum allowable value */
127 #define TCPTV_CPU_VAR	( hz/5 )		/* cpu variance allowed (200ms) */
128 #define	TCPTV_REXMTMAX	( 64*hz)		/* max allowable REXMT value */
129 
130 #define TCPTV_TWTRUNC	8			/* RTO factor to truncate TW */
131 
132 #define	TCP_LINGERTIME	120			/* linger at most 2 minutes */
133 
134 #define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */
135 
136 #define	TCPTV_DELACK	( hz/10 )		/* 100ms timeout */
137 
138 #ifdef	TCPTIMERS
139 static const char *tcptimers[] =
140     { "REXMT", "PERSIST", "KEEP", "2MSL", "DELACK" };
141 #endif
142 
143 int tcp_timer_active(struct tcpcb *tp, uint32_t timer_type);
144 void tcp_timer_activate(struct tcpcb *tp, uint32_t timer_type, uint32_t delta);
145 void tcp_cancel_timers(struct tcpcb* tp);
146 
147 /* I moved the definition of TCPT_RANGESET to tcp_const.h. */
148 
149 static const int	tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
150     { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
151 
152 static const int	tcp_backoff[TCP_MAXRXTSHIFT + 1] =
153     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
154 
155 static const int tcp_totbackoff = 2559;	/* sum of tcp_backoff[] */
156 
157 /*
158  * samkumar: Changed return value to int to indicate whether connection was
159  * dropped or not.
160  */
161 int tcp_timer_delack(struct tcpcb* tp);
162 int tcp_timer_keep(struct tcpcb* tp);
163 int tcp_timer_persist(struct tcpcb* tp);
164 int tcp_timer_2msl(struct tcpcb* tp);
165 int tcp_timer_rexmt(struct tcpcb *tp);
166 int tcp_timer_active(struct tcpcb *tp, uint32_t timer_type);
167 
168 /*
169  * samkumar: Modified to use default keepalive parameters, since we removed
170  * the fields from tcpcb that allow them to be set on a per-connection basis.
171  */
172 #define	TP_KEEPINIT(tp)	(/*(tp)->t_keepinit ? (tp)->t_keepinit :*/ tcp_keepinit)
173 #define	TP_KEEPIDLE(tp)	(/*(tp)->t_keepidle ? (tp)->t_keepidle :*/ tcp_keepidle)
174 #define	TP_KEEPINTVL(tp) (/*(tp)->t_keepintvl ? (tp)->t_keepintvl :*/ tcp_keepintvl)
175 #define	TP_KEEPCNT(tp)	(/*(tp)->t_keepcnt ? (tp)->t_keepcnt :*/ tcp_keepcnt)
176 #define	TP_MAXIDLE(tp)	(TP_KEEPCNT(tp) * TP_KEEPINTVL(tp))
177 
178 /*
179  * samkumar: MOVED NECESSARY EXTERN DECLARATIONS TO TCP_SUBR.C
180  * Removed timer declarations that aren't needed since timers are handled
181  * by the host system (in this case, OpenThread), in TCPlp.
182  */
183 
184 #endif /* !_NETINET_TCP_TIMER_H_ */
185