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 this notice is preserved and that due credit is given 7 * to the University of California at Berkeley. The name of the University 8 * may not be used to endorse or promote products derived from this 9 * software without specific prior written permission. This software 10 * is provided ``as is'' without express or implied warranty. 11 * 12 * @(#)tcp_timer.h 7.4 (Berkeley) 12/07/87 13 */ 14 15 /* 16 * Definitions of the TCP timers. These timers are counted 17 * down PR_SLOWHZ times a second. 18 */ 19 #define TCPT_NTIMERS 4 20 21 #define TCPT_REXMT 0 /* retransmit */ 22 #define TCPT_PERSIST 1 /* retransmit persistance */ 23 #define TCPT_KEEP 2 /* keep alive */ 24 #define TCPT_2MSL 3 /* 2*msl quiet time timer */ 25 26 /* 27 * The TCPT_REXMT timer is used to force retransmissions. 28 * The TCP has the TCPT_REXMT timer set whenever segments 29 * have been sent for which ACKs are expected but not yet 30 * received. If an ACK is received which advances tp->snd_una, 31 * then the retransmit timer is cleared (if there are no more 32 * outstanding segments) or reset to the base value (if there 33 * are more ACKs expected). Whenever the retransmit timer goes off, 34 * we retransmit one unacknowledged segment, and do a backoff 35 * on the retransmit timer. 36 * 37 * The TCPT_PERSIST timer is used to keep window size information 38 * flowing even if the window goes shut. If all previous transmissions 39 * have been acknowledged (so that there are no retransmissions in progress), 40 * and the window is too small to bother sending anything, then we start 41 * the TCPT_PERSIST timer. When it expires, if the window is nonzero, 42 * we go to transmit state. Otherwise, at intervals send a single byte 43 * into the peer's window to force him to update our window information. 44 * We do this at most as often as TCPT_PERSMIN time intervals, 45 * but no more frequently than the current estimate of round-trip 46 * packet time. The TCPT_PERSIST timer is cleared whenever we receive 47 * a window update from the peer. 48 * 49 * The TCPT_KEEP timer is used to keep connections alive. If an 50 * connection is idle (no segments received) for TCPTV_KEEP amount of time, 51 * but not yet established, then we drop the connection. If the connection 52 * is established, then we force the peer to send us a segment by sending: 53 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> 54 * This segment is (deliberately) outside the window, and should elicit 55 * an ack segment in response from the peer. If, despite the TCPT_KEEP 56 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE 57 * amount of time, then we drop the connection. 58 */ 59 60 #define TCP_TTL 30 /* default time to live for TCP segs */ 61 int tcp_ttl; /* time to live for TCP segs */ 62 /* 63 * Time constants. 64 */ 65 #define TCPTV_MSL ( 15*PR_SLOWHZ) /* max seg lifetime */ 66 #define TCPTV_SRTTBASE 0 /* base roundtrip time; 67 if 0, no idea yet */ 68 #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */ 69 70 #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */ 71 #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */ 72 73 #define TCPTV_KEEP ( 75*PR_SLOWHZ) /* keep alive - 75 secs */ 74 #define TCPTV_MAXIDLE ( 8*TCPTV_KEEP) /* maximum allowable idle 75 time before drop conn */ 76 77 #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */ 78 #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */ 79 80 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */ 81 82 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */ 83 84 #ifdef TCPTIMERS 85 char *tcptimers[] = 86 { "REXMT", "PERSIST", "KEEP", "2MSL" }; 87 #endif 88 89 /* 90 * Force a time value to be in a certain range. 91 */ 92 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ 93 (tv) = (value); \ 94 if ((tv) < (tvmin)) \ 95 (tv) = (tvmin); \ 96 else if ((tv) > (tvmax)) \ 97 (tv) = (tvmax); \ 98 } 99 100 #ifdef KERNEL 101 extern int tcp_backoff[]; 102 #endif 103