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29 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
30 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
35 static struct tcpcb
*tcp_timers(register struct tcpcb
*tp
, int timer
);
38 * Fast timeout routine for processing delayed acks
41 tcp_fasttimo(Slirp
*slirp
)
43 register struct socket
*so
;
44 register struct tcpcb
*tp
;
46 DEBUG_CALL("tcp_fasttimo");
48 so
= slirp
->tcb
.so_next
;
50 for (; so
!= &slirp
->tcb
; so
= so
->so_next
)
51 if ((tp
= (struct tcpcb
*)so
->so_tcpcb
) &&
52 (tp
->t_flags
& TF_DELACK
)) {
53 tp
->t_flags
&= ~TF_DELACK
;
54 tp
->t_flags
|= TF_ACKNOW
;
55 (void) tcp_output(tp
);
60 * Tcp protocol timeout routine called every 500 ms.
61 * Updates the timers in all active tcb's and
62 * causes finite state machine actions if timers expire.
65 tcp_slowtimo(Slirp
*slirp
)
67 register struct socket
*ip
, *ipnxt
;
68 register struct tcpcb
*tp
;
71 DEBUG_CALL("tcp_slowtimo");
74 * Search through tcb's and update active timers.
76 ip
= slirp
->tcb
.so_next
;
79 for (; ip
!= &slirp
->tcb
; ip
= ipnxt
) {
84 for (i
= 0; i
< TCPT_NTIMERS
; i
++) {
85 if (tp
->t_timer
[i
] && --tp
->t_timer
[i
] == 0) {
87 if (ipnxt
->so_prev
!= ip
)
97 slirp
->tcp_iss
+= TCP_ISSINCR
/PR_SLOWHZ
; /* increment iss */
98 slirp
->tcp_now
++; /* for timestamps */
102 * Cancel all timers for TCP tp.
105 tcp_canceltimers(struct tcpcb
*tp
)
109 for (i
= 0; i
< TCPT_NTIMERS
; i
++)
113 const int tcp_backoff
[TCP_MAXRXTSHIFT
+ 1] =
114 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
117 * TCP timer processing.
119 static struct tcpcb
*
120 tcp_timers(register struct tcpcb
*tp
, int timer
)
124 DEBUG_CALL("tcp_timers");
129 * 2 MSL timeout in shutdown went off. If we're closed but
130 * still waiting for peer to close and connection has been idle
131 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
132 * control block. Otherwise, check again in a bit.
135 if (tp
->t_state
!= TCPS_TIME_WAIT
&&
136 tp
->t_idle
<= TCP_MAXIDLE
)
137 tp
->t_timer
[TCPT_2MSL
] = TCPTV_KEEPINTVL
;
143 * Retransmission timer went off. Message has not
144 * been acked within retransmit interval. Back off
145 * to a longer retransmit interval and retransmit one segment.
150 * XXXXX If a packet has timed out, then remove all the queued
151 * packets for that session.
154 if (++tp
->t_rxtshift
> TCP_MAXRXTSHIFT
) {
156 * This is a hack to suit our terminal server here at the uni of canberra
157 * since they have trouble with zeroes... It usually lets them through
158 * unharmed, but under some conditions, it'll eat the zeros. If we
159 * keep retransmitting it, it'll keep eating the zeroes, so we keep
160 * retransmitting, and eventually the connection dies...
161 * (this only happens on incoming data)
163 * So, if we were gonna drop the connection from too many retransmits,
164 * don't... instead halve the t_maxseg, which might break up the NULLs and
171 if (tp
->t_maxseg
< 32) {
173 * We tried our best, now the connection must die!
175 tp
->t_rxtshift
= TCP_MAXRXTSHIFT
;
176 tp
= tcp_drop(tp
, tp
->t_softerror
);
177 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
178 return (tp
); /* XXX */
182 * Set rxtshift to 6, which is still at the maximum
187 rexmt
= TCP_REXMTVAL(tp
) * tcp_backoff
[tp
->t_rxtshift
];
188 TCPT_RANGESET(tp
->t_rxtcur
, rexmt
,
189 (short)tp
->t_rttmin
, TCPTV_REXMTMAX
); /* XXX */
190 tp
->t_timer
[TCPT_REXMT
] = tp
->t_rxtcur
;
192 * If losing, let the lower level know and try for
193 * a better route. Also, if we backed off this far,
194 * our srtt estimate is probably bogus. Clobber it
195 * so we'll take the next rtt measurement as our srtt;
196 * move the current srtt into rttvar to keep the current
197 * retransmit times until then.
199 if (tp
->t_rxtshift
> TCP_MAXRXTSHIFT
/ 4) {
200 tp
->t_rttvar
+= (tp
->t_srtt
>> TCP_RTT_SHIFT
);
203 tp
->snd_nxt
= tp
->snd_una
;
205 * If timing a segment in this window, stop the timer.
209 * Close the congestion window down to one segment
210 * (we'll open it by one segment for each ack we get).
211 * Since we probably have a window's worth of unacked
212 * data accumulated, this "slow start" keeps us from
213 * dumping all that data as back-to-back packets (which
214 * might overwhelm an intermediate gateway).
216 * There are two phases to the opening: Initially we
217 * open by one mss on each ack. This makes the window
218 * size increase exponentially with time. If the
219 * window is larger than the path can handle, this
220 * exponential growth results in dropped packet(s)
221 * almost immediately. To get more time between
222 * drops but still "push" the network to take advantage
223 * of improving conditions, we switch from exponential
224 * to linear window opening at some threshold size.
225 * For a threshold, we use half the current window
226 * size, truncated to a multiple of the mss.
228 * (the minimum cwnd that will give us exponential
229 * growth is 2 mss. We don't allow the threshold
233 u_int win
= min(tp
->snd_wnd
, tp
->snd_cwnd
) / 2 / tp
->t_maxseg
;
236 tp
->snd_cwnd
= tp
->t_maxseg
;
237 tp
->snd_ssthresh
= win
* tp
->t_maxseg
;
240 (void) tcp_output(tp
);
244 * Persistence timer into zero window.
245 * Force a byte to be output, if possible.
250 (void) tcp_output(tp
);
255 * Keep-alive timer went off; send something
256 * or drop connection if idle for too long.
259 if (tp
->t_state
< TCPS_ESTABLISHED
)
262 if ((SO_OPTIONS
) && tp
->t_state
<= TCPS_CLOSE_WAIT
) {
263 if (tp
->t_idle
>= TCPTV_KEEP_IDLE
+ TCP_MAXIDLE
)
266 * Send a packet designed to force a response
267 * if the peer is up and reachable:
268 * either an ACK if the connection is still alive,
269 * or an RST if the peer has closed the connection
270 * due to timeout or reboot.
271 * Using sequence number tp->snd_una-1
272 * causes the transmitted zero-length segment
273 * to lie outside the receive window;
274 * by the protocol spec, this requires the
275 * correspondent TCP to respond.
277 tcp_respond(tp
, &tp
->t_template
, (struct mbuf
*)NULL
,
278 tp
->rcv_nxt
, tp
->snd_una
- 1, 0);
279 tp
->t_timer
[TCPT_KEEP
] = TCPTV_KEEPINTVL
;
281 tp
->t_timer
[TCPT_KEEP
] = TCPTV_KEEP_IDLE
;
285 tp
= tcp_drop(tp
, 0);