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 /* 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_ */ 166