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29 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
33 #ifndef _NETINET_TCP_TIMER_H_
34 #define _NETINET_TCP_TIMER_H_
37 * The TCPT_REXMT timer is used to force retransmissions.
38 * The TCP has the TCPT_REXMT timer set whenever segments
39 * have been sent for which ACKs are expected but not yet
40 * received. If an ACK is received which advances tp->snd_una,
41 * then the retransmit timer is cleared (if there are no more
42 * outstanding segments) or reset to the base value (if there
43 * are more ACKs expected). Whenever the retransmit timer goes off,
44 * we retransmit one unacknowledged segment, and do a backoff
45 * on the retransmit timer.
47 * The TCPT_PERSIST timer is used to keep window size information
48 * flowing even if the window goes shut. If all previous transmissions
49 * have been acknowledged (so that there are no retransmissions in progress),
50 * and the window is too small to bother sending anything, then we start
51 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
52 * we go to transmit state. Otherwise, at intervals send a single byte
53 * into the peer's window to force him to update our window information.
54 * We do this at most as often as TCPT_PERSMIN time intervals,
55 * but no more frequently than the current estimate of round-trip
56 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
57 * a window update from the peer.
59 * The TCPT_KEEP timer is used to keep connections alive. If an
60 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
61 * but not yet established, then we drop the connection. Once the connection
62 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
63 * (and keepalives have been enabled on the socket), we begin to probe
64 * the connection. We force the peer to send us a segment by sending:
65 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
66 * This segment is (deliberately) outside the window, and should elicit
67 * an ack segment in response from the peer. If, despite the TCPT_KEEP
68 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
69 * amount of time probing, then we drop the connection.
75 #define TCPTV_MSL ( 30*hz) /* max seg lifetime (hah!) */
76 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
78 #define TCPTV_RTOBASE ( 3*hz) /* assumed RTO if no info */
79 #define TCPTV_SRTTDFLT ( 3*hz) /* assumed RTT if no info */
81 #define TCPTV_PERSMIN ( 5*hz) /* retransmit persistence */
82 #define TCPTV_PERSMAX ( 60*hz) /* maximum persist interval */
84 #define TCPTV_KEEP_INIT ( 75*hz) /* initial connect keepalive */
85 #define TCPTV_KEEP_IDLE (120*60*hz) /* dflt time before probing */
86 #define TCPTV_KEEPINTVL ( 75*hz) /* default probe interval */
87 #define TCPTV_KEEPCNT 8 /* max probes before drop */
89 #define TCPTV_INFLIGHT_RTTTHRESH (10*hz/1000) /* below which inflight
90 disengages, in msec */
93 * Minimum retransmit timer is 3 ticks, for algorithmic stability.
94 * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
95 * the expected worst-case processing variances by the kernels
96 * representing the end points. Such variances do not always show
97 * up in the srtt because the timestamp is often calculated at
98 * the interface rather then at the TCP layer. This value is
99 * typically 50ms. However, it is also possible that delayed
100 * acks (typically 100ms) could create issues so we set the slop
101 * to 200ms to try to cover it. Note that, properly speaking,
102 * delayed-acks should not create a major issue for interactive
103 * environments which 'P'ush the last segment, at least as
104 * long as implementations do the required 'at least one ack
105 * for every two packets' for the non-interactive streaming case.
106 * (maybe the RTO calculation should use 2*RTT instead of RTT
107 * to handle the ack-every-other-packet case).
109 * The prior minimum of 1*hz (1 second) badly breaks throughput on any
110 * networks faster then a modem that has minor (e.g. 1%) packet loss.
112 #define TCPTV_MIN ( 3 ) /* minimum allowable value */
113 #define TCPTV_CPU_VAR ( hz/5 ) /* cpu variance allowed (200ms) */
114 #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */
116 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
118 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
120 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
122 #define TCPTV_DELACK (hz / PR_FASTHZ / 2) /* 100ms timeout */
125 static const char *tcptimers[] =
126 { "REXMT", "PERSIST", "KEEP", "2MSL" };
130 * Force a time value to be in a certain range.
132 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
133 (tv) = (value) + tcp_rexmit_slop; \
134 if ((u_long)(tv) < (u_long)(tvmin)) \
136 if ((u_long)(tv) > (u_long)(tvmax)) \
141 extern int tcp_keepinit; /* time to establish connection */
142 extern int tcp_keepidle; /* time before keepalive probes begin */
143 extern int tcp_keepintvl; /* time between keepalive probes */
144 extern int tcp_maxidle; /* time to drop after starting probes */
145 extern int tcp_delacktime; /* time before sending a delayed ACK */
146 extern int tcp_maxpersistidle;
147 extern int tcp_rexmit_min;
148 extern int tcp_rexmit_slop;
150 extern int tcp_ttl; /* time to live for TCP segs */
151 extern int tcp_backoff[];
155 void tcp_timer_init(void);
156 void tcp_timer_2msl(void *xtp);
158 tcp_timer_2msl_tw(int _reuse); /* XXX temporary */
159 void tcp_timer_2msl_reset(struct tcptw *_tw, int rearm);
160 void tcp_timer_2msl_stop(struct tcptw *_tw);
161 void tcp_timer_keep(void *xtp);
162 void tcp_timer_persist(void *xtp);
163 void tcp_timer_rexmt(void *xtp);
164 void tcp_timer_delack(void *xtp);
168 #endif /* !_NETINET_TCP_TIMER_H_ */