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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 * The TCPT_REXMT timer is used to force retransmissions.
42 * The TCP has the TCPT_REXMT timer set whenever segments
43 * have been sent for which ACKs are expected but not yet
44 * received. If an ACK is received which advances tp->snd_una,
45 * then the retransmit timer is cleared (if there are no more
46 * outstanding segments) or reset to the base value (if there
47 * are more ACKs expected). Whenever the retransmit timer goes off,
48 * we retransmit one unacknowledged segment, and do a backoff
49 * on the retransmit timer.
51 * The TCPT_PERSIST timer is used to keep window size information
52 * flowing even if the window goes shut. If all previous transmissions
53 * have been acknowledged (so that there are no retransmissions in progress),
54 * and the window is too small to bother sending anything, then we start
55 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
56 * we go to transmit state. Otherwise, at intervals send a single byte
57 * into the peer's window to force him to update our window information.
58 * We do this at most as often as TCPT_PERSMIN time intervals,
59 * but no more frequently than the current estimate of round-trip
60 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
61 * a window update from the peer.
63 * The TCPT_KEEP timer is used to keep connections alive. If an
64 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
65 * but not yet established, then we drop the connection. Once the connection
66 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
67 * (and keepalives have been enabled on the socket), we begin to probe
68 * the connection. We force the peer to send us a segment by sending:
69 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
70 * This segment is (deliberately) outside the window, and should elicit
71 * an ack segment in response from the peer. If, despite the TCPT_KEEP
72 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
73 * amount of time probing, then we drop the connection.
79 #define TCPTV_MSL ( 30*hz) /* max seg lifetime (hah!) */
80 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
82 #define TCPTV_RTOBASE ( 3*hz) /* assumed RTO if no info */
83 #define TCPTV_SRTTDFLT ( 3*hz) /* assumed RTT if no info */
85 #define TCPTV_PERSMIN ( 5*hz) /* retransmit persistence */
86 #define TCPTV_PERSMAX ( 60*hz) /* maximum persist interval */
88 #define TCPTV_KEEP_INIT ( 75*hz) /* initial connect keepalive */
89 #define TCPTV_KEEP_IDLE (120*60*hz) /* dflt time before probing */
90 #define TCPTV_KEEPINTVL ( 75*hz) /* default probe interval */
91 #define TCPTV_KEEPCNT 8 /* max probes before drop */
93 #define TCPTV_MIN ( 1*hz) /* minimum allowable value */
94 #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */
96 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
98 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
100 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
102 #define TCPTV_DELACK (hz / PR_FASTHZ) /* 200ms timeout */
105 static char *tcptimers[] =
106 { "REXMT", "PERSIST", "KEEP", "2MSL" };
110 * Force a time value to be in a certain range.
112 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
114 if ((u_long)(tv) < (u_long)(tvmin)) \
116 else if ((u_long)(tv) > (u_long)(tvmax)) \
121 extern int tcp_keepinit; /* time to establish connection */
122 extern int tcp_keepidle; /* time before keepalive probes begin */
123 extern int tcp_keepintvl; /* time between keepalive probes */
124 extern int tcp_maxidle; /* time to drop after starting probes */
125 extern int tcp_delacktime; /* time before sending a delayed ACK */
126 extern int tcp_maxpersistidle;
128 extern int tcp_ttl; /* time to live for TCP segs */
129 extern int tcp_backoff[];
131 void tcp_timer_2msl __P((void *xtp));
132 void tcp_timer_keep __P((void *xtp));
133 void tcp_timer_persist __P((void *xtp));
134 void tcp_timer_rexmt __P((void *xtp));
135 void tcp_timer_delack __P((void *xtp));
139 #endif /* !_NETINET_TCP_TIMER_H_ */