1 /*!\file netinet/tcp_time.h
2 * TCP timer definitions.
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37 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
38 * $Id: tcp_timer.h,v 1.10 1996/09/13 23:51:43 pst Exp $
41 #ifndef __NETINET_TCP_TIMER_H
42 #define __NETINET_TCP_TIMER_H
45 * Definitions of the TCP timers. These timers are counted
46 * down PR_SLOWHZ times a second.
48 #define TCPT_NTIMERS 4
50 #define TCPT_REXMT 0 /* retransmit */
51 #define TCPT_PERSIST 1 /* retransmit persistence */
52 #define TCPT_KEEP 2 /* keep alive */
53 #define TCPT_2MSL 3 /* 2*msl quiet time timer */
56 * The TCPT_REXMT timer is used to force retransmissions.
57 * The TCP has the TCPT_REXMT timer set whenever segments
58 * have been sent for which ACKs are expected but not yet
59 * received. If an ACK is received which advances tp->snd_una,
60 * then the retransmit timer is cleared (if there are no more
61 * outstanding segments) or reset to the base value (if there
62 * are more ACKs expected). Whenever the retransmit timer goes off,
63 * we retransmit one unacknowledged segment, and do a backoff
64 * on the retransmit timer.
66 * The TCPT_PERSIST timer is used to keep window size information
67 * flowing even if the window goes shut. If all previous transmissions
68 * have been acknowledged (so that there are no retransmissions in progress),
69 * and the window is too small to bother sending anything, then we start
70 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
71 * we go to transmit state. Otherwise, at intervals send a single byte
72 * into the peer's window to force him to update our window information.
73 * We do this at most as often as TCPT_PERSMIN time intervals,
74 * but no more frequently than the current estimate of round-trip
75 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
76 * a window update from the peer.
78 * The TCPT_KEEP timer is used to keep connections alive. If an
79 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
80 * but not yet established, then we drop the connection. Once the connection
81 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
82 * (and keepalives have been enabled on the socket), we begin to probe
83 * the connection. We force the peer to send us a segment by sending:
84 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
85 * This segment is (deliberately) outside the window, and should elicit
86 * an ack segment in response from the peer. If, despite the TCPT_KEEP
87 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
88 * amount of time probing, then we drop the connection.
94 #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */
95 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
97 #define TCPTV_RTOBASE ( 3*PR_SLOWHZ) /* assumed RTO if no info */
98 #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */
100 #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistence */
101 #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */
103 #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */
104 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */
105 #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */
106 #define TCPTV_KEEPCNT 8 /* max probes before drop */
108 #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */
109 #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */
111 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
113 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
115 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
118 static char *tcptimers[] =
119 { "REXMT", "PERSIST", "KEEP", "2MSL" };
123 * Force a time value to be in a certain range.
125 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \
127 if ((u_long)(tv) < (u_long)(tvmin)) \
129 else if ((u_long)(tv) > (u_long)(tvmax)) \