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33 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
34 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
39 #define max(x,y) ((x) > (y) ? (x) : (y))
40 #define min(x,y) ((x) < (y) ? (x) : (y))
42 int tcp_keepidle = TCPTV_KEEP_IDLE;
43 int tcp_keepintvl = TCPTV_KEEPINTVL;
45 int so_options = DO_KEEPALIVE;
47 struct tcpstat tcpstat; /* tcp statistics */
48 u_int32_t tcp_now; /* for RFC 1323 timestamps */
51 * Fast timeout routine for processing delayed acks
56 register struct socket *so;
57 register struct tcpcb *tp;
59 DEBUG_CALL("tcp_fasttimo");
63 for (; so != &tcb; so = so->so_next)
64 if ((tp = (struct tcpcb *)so->so_tcpcb) &&
65 (tp->t_flags & TF_DELACK)) {
66 tp->t_flags &= ~TF_DELACK;
67 tp->t_flags |= TF_ACKNOW;
68 tcpstat.tcps_delack++;
69 (void) tcp_output(tp);
74 * Tcp protocol timeout routine called every 500 ms.
75 * Updates the timers in all active tcb's and
76 * causes finite state machine actions if timers expire.
81 register struct socket *ip, *ipnxt;
82 register struct tcpcb *tp;
85 DEBUG_CALL("tcp_slowtimo");
87 tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl;
89 * Search through tcb's and update active timers.
94 for (; ip != &tcb; ip = ipnxt) {
99 for (i = 0; i < TCPT_NTIMERS; i++) {
100 if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
102 if (ipnxt->so_prev != ip)
112 tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */
114 if ((int)tcp_iss < 0)
115 tcp_iss = 0; /* XXX */
117 tcp_now++; /* for timestamps */
121 * Cancel all timers for TCP tp.
129 for (i = 0; i < TCPT_NTIMERS; i++)
133 int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
134 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
137 * TCP timer processing.
140 tcp_timers(tp, timer)
141 register struct tcpcb *tp;
146 DEBUG_CALL("tcp_timers");
151 * 2 MSL timeout in shutdown went off. If we're closed but
152 * still waiting for peer to close and connection has been idle
153 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
154 * control block. Otherwise, check again in a bit.
157 if (tp->t_state != TCPS_TIME_WAIT &&
158 tp->t_idle <= tcp_maxidle)
159 tp->t_timer[TCPT_2MSL] = tcp_keepintvl;
165 * Retransmission timer went off. Message has not
166 * been acked within retransmit interval. Back off
167 * to a longer retransmit interval and retransmit one segment.
172 * XXXXX If a packet has timed out, then remove all the queued
173 * packets for that session.
176 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
178 * This is a hack to suit our terminal server here at the uni of canberra
179 * since they have trouble with zeroes... It usually lets them through
180 * unharmed, but under some conditions, it'll eat the zeros. If we
181 * keep retransmitting it, it'll keep eating the zeroes, so we keep
182 * retransmitting, and eventually the connection dies...
183 * (this only happens on incoming data)
185 * So, if we were gonna drop the connection from too many retransmits,
186 * don't... instead halve the t_maxseg, which might break up the NULLs and
193 if (tp->t_maxseg < 32) {
195 * We tried our best, now the connection must die!
197 tp->t_rxtshift = TCP_MAXRXTSHIFT;
198 tcpstat.tcps_timeoutdrop++;
199 tp = tcp_drop(tp, tp->t_softerror);
200 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
201 return (tp); /* XXX */
205 * Set rxtshift to 6, which is still at the maximum
210 tcpstat.tcps_rexmttimeo++;
211 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
212 TCPT_RANGESET(tp->t_rxtcur, rexmt,
213 (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
214 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
216 * If losing, let the lower level know and try for
217 * a better route. Also, if we backed off this far,
218 * our srtt estimate is probably bogus. Clobber it
219 * so we'll take the next rtt measurement as our srtt;
220 * move the current srtt into rttvar to keep the current
221 * retransmit times until then.
223 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
224 /* in_losing(tp->t_inpcb); */
225 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
228 tp->snd_nxt = tp->snd_una;
230 * If timing a segment in this window, stop the timer.
234 * Close the congestion window down to one segment
235 * (we'll open it by one segment for each ack we get).
236 * Since we probably have a window's worth of unacked
237 * data accumulated, this "slow start" keeps us from
238 * dumping all that data as back-to-back packets (which
239 * might overwhelm an intermediate gateway).
241 * There are two phases to the opening: Initially we
242 * open by one mss on each ack. This makes the window
243 * size increase exponentially with time. If the
244 * window is larger than the path can handle, this
245 * exponential growth results in dropped packet(s)
246 * almost immediately. To get more time between
247 * drops but still "push" the network to take advantage
248 * of improving conditions, we switch from exponential
249 * to linear window opening at some threshold size.
250 * For a threshold, we use half the current window
251 * size, truncated to a multiple of the mss.
253 * (the minimum cwnd that will give us exponential
254 * growth is 2 mss. We don't allow the threshold
258 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
261 tp->snd_cwnd = tp->t_maxseg;
262 tp->snd_ssthresh = win * tp->t_maxseg;
265 (void) tcp_output(tp);
269 * Persistence timer into zero window.
270 * Force a byte to be output, if possible.
273 tcpstat.tcps_persisttimeo++;
276 (void) tcp_output(tp);
281 * Keep-alive timer went off; send something
282 * or drop connection if idle for too long.
285 tcpstat.tcps_keeptimeo++;
286 if (tp->t_state < TCPS_ESTABLISHED)
289 /* if (tp->t_socket->so_options & SO_KEEPALIVE && */
290 if ((so_options) && tp->t_state <= TCPS_CLOSE_WAIT) {
291 if (tp->t_idle >= tcp_keepidle + tcp_maxidle)
294 * Send a packet designed to force a response
295 * if the peer is up and reachable:
296 * either an ACK if the connection is still alive,
297 * or an RST if the peer has closed the connection
298 * due to timeout or reboot.
299 * Using sequence number tp->snd_una-1
300 * causes the transmitted zero-length segment
301 * to lie outside the receive window;
302 * by the protocol spec, this requires the
303 * correspondent TCP to respond.
305 tcpstat.tcps_keepprobe++;
308 * The keepalive packet must have nonzero length
309 * to get a 4.2 host to respond.
311 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
312 tp->rcv_nxt - 1, tp->snd_una - 1, 0);
314 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
315 tp->rcv_nxt, tp->snd_una - 1, 0);
317 tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
319 tp->t_timer[TCPT_KEEP] = tcp_keepidle;
323 tcpstat.tcps_keepdrops++;
324 tp = tcp_drop(tp, 0); /* ETIMEDOUT); */