tcp_timer.h revision 112009
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: head/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 126static 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 142extern int tcp_keepinit; /* time to establish connection */ 143extern int tcp_keepidle; /* time before keepalive probes begin */ 144extern int tcp_keepintvl; /* time between keepalive probes */ 145extern int tcp_maxidle; /* time to drop after starting probes */ 146extern int tcp_delacktime; /* time before sending a delayed ACK */ 147extern int tcp_maxpersistidle; 148extern int tcp_rexmit_min; 149extern int tcp_rexmit_slop; 150extern int tcp_msl; 151extern int tcp_ttl; /* time to live for TCP segs */ 152extern int tcp_backoff[]; 153 154struct tcptw; 155 156void tcp_timer_init(void); 157void tcp_timer_2msl(void *xtp); 158struct tcptw * 159 tcp_timer_2msl_tw(int _reuse); /* XXX temporary */ 160void tcp_timer_2msl_reset(struct tcptw *_tw, int _timeo); 161void tcp_timer_2msl_stop(struct tcptw *_tw); 162void tcp_timer_keep(void *xtp); 163void tcp_timer_persist(void *xtp); 164void tcp_timer_rexmt(void *xtp); 165void tcp_timer_delack(void *xtp); 166 167#endif /* _KERNEL */ 168 169#endif /* !_NETINET_TCP_TIMER_H_ */ 170