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 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 14 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 15 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. 16 * 17 * @(#)tcp_timer.h 7.6 (Berkeley) 06/29/88 18 */ 19 20 /* 21 * Definitions of the TCP timers. These timers are counted 22 * down PR_SLOWHZ times a second. 23 */ 24 #define TCPT_NTIMERS 4 25 26 #define TCPT_REXMT 0 /* retransmit */ 27 #define TCPT_PERSIST 1 /* retransmit persistance */ 28 #define TCPT_KEEP 2 /* keep alive */ 29 #define TCPT_2MSL 3 /* 2*msl quiet time timer */ 30 31 /* 32 * The TCPT_REXMT timer is used to force retransmissions. 33 * The TCP has the TCPT_REXMT timer set whenever segments 34 * have been sent for which ACKs are expected but not yet 35 * received. If an ACK is received which advances tp->snd_una, 36 * then the retransmit timer is cleared (if there are no more 37 * outstanding segments) or reset to the base value (if there 38 * are more ACKs expected). Whenever the retransmit timer goes off, 39 * we retransmit one unacknowledged segment, and do a backoff 40 * on the retransmit timer. 41 * 42 * The TCPT_PERSIST timer is used to keep window size information 43 * flowing even if the window goes shut. If all previous transmissions 44 * have been acknowledged (so that there are no retransmissions in progress), 45 * and the window is too small to bother sending anything, then we start 46 * the TCPT_PERSIST timer. When it expires, if the window is nonzero, 47 * we go to transmit state. Otherwise, at intervals send a single byte 48 * into the peer's window to force him to update our window information. 49 * We do this at most as often as TCPT_PERSMIN time intervals, 50 * but no more frequently than the current estimate of round-trip 51 * packet time. The TCPT_PERSIST timer is cleared whenever we receive 52 * a window update from the peer. 53 * 54 * The TCPT_KEEP timer is used to keep connections alive. If an 55 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time, 56 * but not yet established, then we drop the connection. Once the connection 57 * is established, if the connection is idle for TCPTV_KEEP_IDLE time 58 * (and keepalives have been enabled on the socket), we begin to probe 59 * the connection. We force the peer to send us a segment by sending: 60 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> 61 * This segment is (deliberately) outside the window, and should elicit 62 * an ack segment in response from the peer. If, despite the TCPT_KEEP 63 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE 64 * amount of time probing, then we drop the connection. 65 */ 66 67 #define TCP_TTL 30 /* default time to live for TCP segs */ 68 /* 69 * Time constants. 70 */ 71 #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */ 72 #define TCPTV_SRTTBASE 0 /* base roundtrip time; 73 if 0, no idea yet */ 74 #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */ 75 76 #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */ 77 #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */ 78 79 #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */ 80 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */ 81 #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */ 82 #define TCPTV_KEEPCNT 8 /* max probes before drop */ 83 84 #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */ 85 #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */ 86 87 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */ 88 89 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */ 90 91 #ifdef TCPTIMERS 92 char *tcptimers[] = 93 { "REXMT", "PERSIST", "KEEP", "2MSL" }; 94 #endif 95 96 /* 97 * Force a time value to be in a certain range. 98 */ 99 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ 100 (tv) = (value); \ 101 if ((tv) < (tvmin)) \ 102 (tv) = (tvmin); \ 103 else if ((tv) > (tvmax)) \ 104 (tv) = (tvmax); \ 105 } 106 107 #ifdef KERNEL 108 extern int tcp_keepidle; /* time before keepalive probes begin */ 109 extern int tcp_keepintvl; /* time between keepalive probes */ 110 extern int tcp_maxidle; /* time to drop after starting probes */ 111 extern int tcp_ttl; /* time to live for TCP segs */ 112 extern int tcp_backoff[]; 113 #endif 114