yet more lint

[unix-history] / usr / src / sys / netinet / tcp_timer.h

diff --git a/usr/src/sys/netinet/tcp_timer.h b/usr/src/sys/netinet/tcp_timer.h
index f22e634..cc73ea6 100644 (file)
--- a/usr/src/sys/netinet/tcp_timer.h
+++ b/usr/src/sys/netinet/tcp_timer.h
@@ -1,4 +1,4 @@
-/*     tcp_timer.h     4.1     81/11/29        */
+/*     tcp_timer.h     4.2     81/12/02        */

 
 /*
  * Definitions of the TCP timers.  These timers are counted
 
 /*
  * Definitions of the TCP timers.  These timers are counted


@@ -7,25 +7,88 @@
 #define        TCPT_NTIMERS    4
 
 #define        TCPT_REXMT      0               /* retransmit */
 #define        TCPT_NTIMERS    4
 
 #define        TCPT_REXMT      0               /* retransmit */

-#define        TCPT_2MSL       1               /* 2*msl quiet time timer */
-#define        TCPT_PERSIST    2               /* retransmit persistance */
-#define        TCPT_KEEP       3               /* keep alive */
+#define        TCPT_PERSIST    1               /* retransmit persistance */
+#define        TCPT_KEEP       2               /* keep alive */
+#define        TCPT_2MSL       3               /* 2*msl quiet time timer */
+
+/*
+ * The TCPT_REXMT timer is used to force retransmissions.
+ * The TCP has the TCPT_REXMT timer set whenever segments
+ * have been sent for which ACKs are expected but not yet
+ * received.  If an ACK is received which advances tp->snd_una,
+ * then the retransmit timer is cleared (if there are no more
+ * outstanding segments) or reset to the base value (if there
+ * are more ACKs expected).  Whenever the retransmit timer goes off,
+ * we retransmit all unacknowledged segments, and do an exponential
+ * backoff on the retransmit timer.
+ *
+ * The TCPT_PERSIST timer is used to keep window size information
+ * flowing even if the window goes shut.  If an output is attempted when there
+ * is data ready to transmit, but nothing gets sent because the window
+ * is shut, then we start the TCPT_PERSIST timer, and at intervals
+ * send a single byte into the peers window to force him to update
+ * our window information.  We do this at most as often as TCPT_PERSMIN
+ * time intervals, but no more frequently than the current estimate of
+ * round-trip packet time.  The TCPT_PERSIST timer is cleared whenever
+ * we receive a window update from the peer.
+ *
+ * The TCPT_KEEP timer is used to keep connections alive.  If an
+ * connection is idle (no segments received) for TCPTV_KEEP amount of time,
+ * but not yet established, then we drop the connection.  If the connection
+ * is established, then we force the peer to send us a segment by sending:
+ *     <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
+ * This segment is (deliberately) outside the window, and should elicit
+ * an ack segment in response from the peer.  If, despite the TCPT_KEEP
+ * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
+ * amount of time, then we drop the connection.
+ */

 
 #define        TCP_TTL         60              /* time to live for TCP segs */
 /*
 
 #define        TCP_TTL         60              /* time to live for TCP segs */
 /*

- * TCPSC constants give various timeouts in ``slow-clock'' ticks.
+ * Time constants.

  */
  */

-#define        TCPSC_MSL       (120*PR_SLOWHZ)         /* max seg lifetime */
-#define        TCPSC_REXMT     (  1*PR_SLOWHZ)         /* base retransmit time */
-#define        TCPSC_KEEP      (240*PR_SLOWHZ)         /* keep alive */
-#define        TCPSC_PERSIST   (  5*PR_SLOWHZ)         /* retransmit persistance */
+#define        TCPTV_MSL       (120*PR_SLOWHZ)         /* max seg lifetime */
+#define        TCPTV_SRTTBASE  (  1*PR_SLOWHZ)         /* base roundtrip time */
+#define        TCPTV_KEEP      (240*PR_SLOWHZ)         /* keep alive - 4 mins */
+#define        TCPTV_PERSMIN   (  5*PR_SLOWHZ)         /* retransmit persistance */

 
 

-#define        TCPSC_KEEPTTL   (  4*TCPSC_KEEP)        /* keep alive too long */
-#define        TCPSC_2MSL      (  2*TCPSC_MSL)         /* 2*msl quiet time timer */
+#define        TCPTV_MAXIDLE   (  4*TCPTV_KEEP)        /* maximum allowable idle
+                                                  time before drop conn */

 
 

-#define        TCPSC_TOOLONG   (480*PR_SLOWHZ)
+#define        TCPTV_MIN       (  1*PR_SLOWHZ)         /* minimum allowable value */
+#define        TCPTV_MAX       (480*PR_SLOWHZ)         /* maximum allowable value */

 
 #ifdef TCPTIMERS
 char *tcptimers[] =
 
 #ifdef TCPTIMERS
 char *tcptimers[] =

-    { "INIT", "REXMT", "REXMTTL", "KEEP", "KEEPTTL", "PERSIST", "2MSL" };
+    { "REXMT", "KEEP", "PERSIST", "2MSL" };

 #endif
 #endif

+
+/*
+ * Retransmission smoothing constants.
+ * Smoothed round trip time is updated by
+ *    tp->t_srtt = (tcp_alpha * tp->t_srtt) + ((1 - tcp_alpha) * tp->t_rtt)
+ * each time a new value of tp->t_rtt is available.  The initial
+ * retransmit timeout is then based on
+ *    tp->t_timer[TCPT_REXMT] = tcp_beta * tp->t_srtt;
+ * limited, however to be at least TCPTV_REXMTLO and at most TCPTV_REXMTHI.
+ */
+float  tcp_alpha, tcp_beta;
+
+/*
+ * Initial values of tcp_alpha and tcp_beta.
+ * These are conservative: averaging over a long
+ * period of time, and allowing for large individual deviations from
+ * tp->t_srtt.
+ */
+#define        TCP_ALPHA       0.9
+#define        TCP_BETA        2.0
+
+/*
+ * Force a time value to be in a certain range.
+ */
+#define        TCPT_RANGESET(tv, value, tvmin, tvmax) \
+       (tv) = (value); \
+       if ((tv) < (tvmin)) \
+               (tv) = (tvmin); \
+       if ((tv) > (tvmax)) \
+               (tv) = (tvmax);