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33 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
34 * $FreeBSD: src/sys/netinet/tcp_timer.h,v 1.18.2.1 2002/08/16 22:16:39 dillon Exp $
35 * $DragonFly: src/sys/netinet/tcp_timer.h,v 1.3 2003/08/23 11:18:00 rob Exp $
38 #ifndef _NETINET_TCP_TIMER_H_
39 #define _NETINET_TCP_TIMER_H_
42 * The TCPT_REXMT timer is used to force retransmissions.
43 * The TCP has the TCPT_REXMT timer set whenever segments
44 * have been sent for which ACKs are expected but not yet
45 * received. If an ACK is received which advances tp->snd_una,
46 * then the retransmit timer is cleared (if there are no more
47 * outstanding segments) or reset to the base value (if there
48 * are more ACKs expected). Whenever the retransmit timer goes off,
49 * we retransmit one unacknowledged segment, and do a backoff
50 * on the retransmit timer.
52 * The TCPT_PERSIST timer is used to keep window size information
53 * flowing even if the window goes shut. If all previous transmissions
54 * have been acknowledged (so that there are no retransmissions in progress),
55 * and the window is too small to bother sending anything, then we start
56 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
57 * we go to transmit state. Otherwise, at intervals send a single byte
58 * into the peer's window to force him to update our window information.
59 * We do this at most as often as TCPT_PERSMIN time intervals,
60 * but no more frequently than the current estimate of round-trip
61 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
62 * a window update from the peer.
64 * The TCPT_KEEP timer is used to keep connections alive. If an
65 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
66 * but not yet established, then we drop the connection. Once the connection
67 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
68 * (and keepalives have been enabled on the socket), we begin to probe
69 * the connection. We force the peer to send us a segment by sending:
70 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
71 * This segment is (deliberately) outside the window, and should elicit
72 * an ack segment in response from the peer. If, despite the TCPT_KEEP
73 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
74 * amount of time probing, then we drop the connection.
80 #define TCPTV_MSL ( 30*hz) /* max seg lifetime (hah!) */
81 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
83 #define TCPTV_RTOBASE3 ( 3*hz) /* assumed RTO if no info */
84 #define TCPTV_RTOBASE1 ( 1*hz) /* assumed RTO (RFC 6298) */
85 #define TCPTV_SRTTDFLT ( 3*hz) /* assumed RTT if no info */
87 #define TCPTV_PERSMIN ( 5*hz) /* retransmit persistence */
88 #define TCPTV_PERSMAX ( 60*hz) /* maximum persist interval */
90 #define TCPTV_KEEP_INIT ( 75*hz) /* initial connect keepalive */
91 #define TCPTV_KEEP_IDLE (120*60*hz) /* dflt time before probing */
92 #define TCPTV_KEEPINTVL ( 75*hz) /* default probe interval */
93 #define TCPTV_KEEPCNT 8 /* max probes before drop */
96 * TCPTV_MIN represents the minimum allowed retransmit interval. It
97 * is currently one second but will ultimately be reduced to 3 ticks
98 * for algorithmic stability, leaving the 200ms variance to deal with
99 * delayed-acks, protocol overheads. A 1 second minimum badly breaks
100 * throughput on any network faster then a modem that has minor but
101 * continuous packet loss unrelated to congestion, such as on a wireless
104 #define TCPTV_MIN ( hz/2 ) /* minimum allowable value */
105 #define TCPTV_CPU_VAR ( hz/10) /* cpu variance (100ms) */
106 #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */
108 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
110 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
112 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
114 #define TCPTV_DELACK (hz / PR_FASTHZ / 2) /* 100ms timeout */
117 static const char *tcptimers[] =
118 { "REXMT", "PERSIST", "KEEP", "2MSL" };
122 * Force a time value to be in a certain range.
124 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
125 (tv) = (value) + tcp_rexmit_slop; \
126 if ((u_long)(tv) < (u_long)(tvmin)) \
128 else if ((u_long)(tv) > (u_long)(tvmax)) \
134 #define TCPTV_RTOBASE \
135 (tcp_low_rtobase ? TCPTV_RTOBASE1 : TCPTV_RTOBASE3)
138 struct netmsg_tcp_timer {
139 struct netmsg_base tt_msg;
140 struct tcpcb *tt_tcb;
141 int tt_cpuid; /* owner cpuid */
142 lwkt_port_t tt_msgport; /* owner msgport */
143 uint32_t tt_tasks; /* pending tasks */
144 uint32_t tt_running_tasks; /* running tasks */
145 uint32_t tt_prev_tasks; /* prev pending tasks (debug) */
149 struct callout tc_callout;
150 uint32_t tc_task; /* callout's task id */
153 extern int tcp_keepinit; /* time to establish connection */
154 extern int tcp_keepidle; /* time before keepalive probes begin */
155 extern int tcp_keepintvl; /* time between keepalive probes */
156 extern int tcp_keepcnt; /* maximum number of keepalive probes */
157 extern int tcp_delacktime; /* time before sending a delayed ACK */
158 extern int tcp_maxpersistidle;
159 extern int tcp_rexmit_min;
160 extern int tcp_rexmit_slop;
162 extern int tcp_ttl; /* time to live for TCP segs */
163 extern int tcp_backoff[]; /* rxt backoff for data */
164 extern int tcp_syn_backoff[]; /* rxt backoff for SYN */
165 extern int tcp_syn_backoff_low[]; /* rxt backoff for SYN w/ RFC6298 */
167 void tcp_timer_2msl(void *xtp);
168 void tcp_timer_keep(void *xtp);
169 void tcp_timer_persist(void *xtp);
170 void tcp_timer_rexmt(void *xtp);
171 void tcp_timer_delack(void *xtp);
172 void tcp_inittimers(struct tcpcb *);
175 void tcp_create_timermsg(struct tcpcb *, struct lwkt_port *);
176 void tcp_destroy_timermsg(struct tcpcb *);
180 #endif /* !_NETINET_TCP_TIMER_H_ */