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33 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
37 #ifndef _NETINET_TCP_TIMER_H_
38 #define _NETINET_TCP_TIMER_H_
41 * Definitions of the TCP timers. These timers are counted
42 * down PR_SLOWHZ times a second.
44 #define TCPT_NTIMERS 4
46 #define TCPT_REXMT 0 /* retransmit */
47 #define TCPT_PERSIST 1 /* retransmit persistance */
48 #define TCPT_KEEP 2 /* keep alive */
49 #define TCPT_2MSL 3 /* 2*msl quiet time timer */
52 * The TCPT_REXMT timer is used to force retransmissions.
53 * The TCP has the TCPT_REXMT timer set whenever segments
54 * have been sent for which ACKs are expected but not yet
55 * received. If an ACK is received which advances tp->snd_una,
56 * then the retransmit timer is cleared (if there are no more
57 * outstanding segments) or reset to the base value (if there
58 * are more ACKs expected). Whenever the retransmit timer goes off,
59 * we retransmit one unacknowledged segment, and do a backoff
60 * on the retransmit timer.
62 * The TCPT_PERSIST timer is used to keep window size information
63 * flowing even if the window goes shut. If all previous transmissions
64 * have been acknowledged (so that there are no retransmissions in progress),
65 * and the window is too small to bother sending anything, then we start
66 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
67 * we go to transmit state. Otherwise, at intervals send a single byte
68 * into the peer's window to force him to update our window information.
69 * We do this at most as often as TCPT_PERSMIN time intervals,
70 * but no more frequently than the current estimate of round-trip
71 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
72 * a window update from the peer.
74 * The TCPT_KEEP timer is used to keep connections alive. If an
75 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
76 * but not yet established, then we drop the connection. Once the connection
77 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
78 * (and keepalives have been enabled on the socket), we begin to probe
79 * the connection. We force the peer to send us a segment by sending:
80 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
81 * This segment is (deliberately) outside the window, and should elicit
82 * an ack segment in response from the peer. If, despite the TCPT_KEEP
83 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
84 * amount of time probing, then we drop the connection.
90 #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */
91 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
93 #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */
95 #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */
96 #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */
98 #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */
99 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */
100 #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */
101 #define TCPTV_KEEPCNT 8 /* max probes before drop */
103 #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */
104 #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */
106 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
108 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
110 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
114 { "REXMT", "PERSIST", "KEEP", "2MSL" };
118 * Force a time value to be in a certain range.
120 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \
122 if ((u_long)(tv) < (u_long)(tvmin)) \
124 else if ((u_long)(tv) > (u_long)(tvmax)) \
129 extern int tcp_keepidle
; /* time before keepalive probes begin */
130 extern int tcp_keepintvl
; /* time between keepalive probes */
131 extern int tcp_maxidle
; /* time to drop after starting probes */
132 extern int tcp_ttl
; /* time to live for TCP segs */
133 extern int tcp_backoff
[];