1 /* 2 * Copyright (c) 1982, 1986 Regents of the University of California. 3 * All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 * 7 * @(#)tcp_timer.h 7.8 (Berkeley) 06/28/90 8 */ 9 10 /* 11 * Definitions of the TCP timers. These timers are counted 12 * down PR_SLOWHZ times a second. 13 */ 14 #define TCPT_NTIMERS 4 15 16 #define TCPT_REXMT 0 /* retransmit */ 17 #define TCPT_PERSIST 1 /* retransmit persistance */ 18 #define TCPT_KEEP 2 /* keep alive */ 19 #define TCPT_2MSL 3 /* 2*msl quiet time timer */ 20 21 /* 22 * The TCPT_REXMT timer is used to force retransmissions. 23 * The TCP has the TCPT_REXMT timer set whenever segments 24 * have been sent for which ACKs are expected but not yet 25 * received. If an ACK is received which advances tp->snd_una, 26 * then the retransmit timer is cleared (if there are no more 27 * outstanding segments) or reset to the base value (if there 28 * are more ACKs expected). Whenever the retransmit timer goes off, 29 * we retransmit one unacknowledged segment, and do a backoff 30 * on the retransmit timer. 31 * 32 * The TCPT_PERSIST timer is used to keep window size information 33 * flowing even if the window goes shut. If all previous transmissions 34 * have been acknowledged (so that there are no retransmissions in progress), 35 * and the window is too small to bother sending anything, then we start 36 * the TCPT_PERSIST timer. When it expires, if the window is nonzero, 37 * we go to transmit state. Otherwise, at intervals send a single byte 38 * into the peer's window to force him to update our window information. 39 * We do this at most as often as TCPT_PERSMIN time intervals, 40 * but no more frequently than the current estimate of round-trip 41 * packet time. The TCPT_PERSIST timer is cleared whenever we receive 42 * a window update from the peer. 43 * 44 * The TCPT_KEEP timer is used to keep connections alive. If an 45 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time, 46 * but not yet established, then we drop the connection. Once the connection 47 * is established, if the connection is idle for TCPTV_KEEP_IDLE time 48 * (and keepalives have been enabled on the socket), we begin to probe 49 * the connection. We force the peer to send us a segment by sending: 50 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> 51 * This segment is (deliberately) outside the window, and should elicit 52 * an ack segment in response from the peer. If, despite the TCPT_KEEP 53 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE 54 * amount of time probing, then we drop the connection. 55 */ 56 57 #define TCP_TTL 60 /* default time to live for TCP segs */ 58 /* 59 * Time constants. 60 */ 61 #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */ 62 #define TCPTV_SRTTBASE 0 /* base roundtrip time; 63 if 0, no idea yet */ 64 #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */ 65 66 #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */ 67 #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */ 68 69 #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */ 70 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */ 71 #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */ 72 #define TCPTV_KEEPCNT 8 /* max probes before drop */ 73 74 #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */ 75 #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */ 76 77 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */ 78 79 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */ 80 81 #ifdef TCPTIMERS 82 char *tcptimers[] = 83 { "REXMT", "PERSIST", "KEEP", "2MSL" }; 84 #endif 85 86 /* 87 * Force a time value to be in a certain range. 88 */ 89 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ 90 (tv) = (value); \ 91 if ((tv) < (tvmin)) \ 92 (tv) = (tvmin); \ 93 else if ((tv) > (tvmax)) \ 94 (tv) = (tvmax); \ 95 } 96 97 #ifdef KERNEL 98 extern int tcp_keepidle; /* time before keepalive probes begin */ 99 extern int tcp_keepintvl; /* time between keepalive probes */ 100 extern int tcp_maxidle; /* time to drop after starting probes */ 101 extern int tcp_ttl; /* time to live for TCP segs */ 102 extern int tcp_backoff[]; 103 #endif 104