1 /* 2 * Copyright (c) 1982, 1986 Regents of the University of California. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms are permitted 6 * provided that the above copyright notice and this paragraph are 7 * duplicated in all such forms and that any documentation, 8 * advertising materials, and other materials related to such 9 * distribution and use acknowledge that the software was developed 10 * by the University of California, Berkeley. The name of the 11 * University may not be used to endorse or promote products derived 12 * from this software without specific prior written permission. 13 */ 14 15 /* 16 * Definitions of the TCP timers. These timers are counted 17 * down PR_SLOWHZ times a second. 18 */ 19 20 #ifndef _NETINET_TCP_TIMER_H 21 #define _NETINET_TCP_TIMER_H 22 23 #pragma ident "%Z%%M% %I% %E% SMI" 24 /* tcp_timer.h 1.13 89/06/16 SMI; from UCB 7.6 6/29/88 */ 25 26 #ifdef __cplusplus 27 extern "C" { 28 #endif 29 30 #define TCPT_NTIMERS 4 31 32 #define TCPT_REXMT 0 /* retransmit */ 33 #define TCPT_PERSIST 1 /* retransmit persistance */ 34 #define TCPT_KEEP 2 /* keep alive */ 35 #define TCPT_2MSL 3 /* 2*msl quiet time timer */ 36 37 /* 38 * The TCPT_REXMT timer is used to force retransmissions. 39 * The TCP has the TCPT_REXMT timer set whenever segments 40 * have been sent for which ACKs are expected but not yet 41 * received. If an ACK is received which advances tp->snd_una, 42 * then the retransmit timer is cleared (if there are no more 43 * outstanding segments) or reset to the base value (if there 44 * are more ACKs expected). Whenever the retransmit timer goes off, 45 * we retransmit one unacknowledged segment, and do a backoff 46 * on the retransmit timer. 47 * 48 * The TCPT_PERSIST timer is used to keep window size information 49 * flowing even if the window goes shut. If all previous transmissions 50 * have been acknowledged (so that there are no retransmissions in progress), 51 * and the window is too small to bother sending anything, then we start 52 * the TCPT_PERSIST timer. When it expires, if the window is nonzero, 53 * we go to transmit state. Otherwise, at intervals send a single byte 54 * into the peer's window to force him to update our window information. 55 * We do this at most as often as TCPT_PERSMIN time intervals, 56 * but no more frequently than the current estimate of round-trip 57 * packet time. The TCPT_PERSIST timer is cleared whenever we receive 58 * a window update from the peer. 59 * 60 * The TCPT_KEEP timer is used to keep connections alive. If a 61 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time, 62 * but not yet established, then we drop the connection. Once the connection 63 * is established, if the connection is idle for TCPTV_KEEP_IDLE time 64 * (and keepalives have been enabled on the socket), we begin to probe 65 * the connection. We force the peer to send us a segment by sending: 66 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> 67 * This segment is (deliberately) outside the window, and should elicit 68 * an ack segment in response from the peer. If, despite the TCPT_KEEP 69 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE 70 * amount of time probing, then we drop the connection. 71 */ 72 73 #define TCP_TTL 60 /* default time to live for TCP segs */ 74 /* 75 * Time constants. 76 */ 77 #define TCPTV_MSL (30*PR_SLOWHZ) /* max seg lifetime (hah!) */ 78 #define TCPTV_SRTTBASE 0 /* base roundtrip time; */ 79 /* if 0, no idea yet */ 80 #define TCPTV_SRTTDFLT (3*PR_SLOWHZ) /* assumed RTT if no info */ 81 82 #define TCPTV_PERSMIN (5*PR_SLOWHZ) /* retransmit persistance */ 83 #define TCPTV_PERSMAX (60*PR_SLOWHZ) /* maximum persist interval */ 84 85 #define TCPTV_KEEP_INIT (75*PR_SLOWHZ) /* initial connect keep alive */ 86 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */ 87 #define TCPTV_KEEPINTVL (75*PR_SLOWHZ) /* default probe interval */ 88 #define TCPTV_KEEPCNT 8 /* max probes before drop */ 89 90 #define TCPTV_MIN (1*PR_SLOWHZ) /* minimum allowable value */ 91 #define TCPTV_REXMTMAX (64*PR_SLOWHZ) /* max allowable REXMT value */ 92 93 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */ 94 95 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */ 96 97 #ifdef TCPTIMERS 98 char *tcptimers[] = 99 { "REXMT", "PERSIST", "KEEP", "2MSL" }; 100 #endif 101 102 /* 103 * Force a time value to be in a certain range. 104 */ 105 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ 106 (tv) = (value); \ 107 if ((tv) < (tvmin)) \ 108 (tv) = (tvmin); \ 109 else if ((tv) > (tvmax)) \ 110 (tv) = (tvmax); \ 111 } 112 113 #ifdef __cplusplus 114 } 115 #endif 116 117 #endif /* _NETINET_TCP_TIMER_H */ 118