Implement slow start threshold according to RFC 5681.

diff --git a/utcp.c b/utcp.c
index d2a777ce00ed9b1d9ea18a622f1ab1523dcc74b5..7aeb2d358cf7b3157672f8bb2f25b488b9a40606 100644 (file)
--- a/utcp.c
+++ b/utcp.c
@@ -54,6 +54,10 @@
        } while (0)
 #endif
 
+static inline size_t min(size_t a, size_t b) {
+       return a < b ? a : b;
+}
+
 static inline size_t max(size_t a, size_t b) {
        return a > b ? a : b;
 }
@@ -113,9 +117,14 @@ static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, si
 
        debug("\n");
 }
+
+static void debug_cwnd(struct utcp_connection *c) {
+       debug("snd.cwnd = %u\n", c->snd.cwnd);
+}
 #else
 #define debug(...) do {} while(0)
 #define print_packet(...) do {} while(0)
+#define debug_cwnd(...) do {} while(0)
 #endif
 
 static void set_state(struct utcp_connection *c, enum state state) {
@@ -383,7 +392,9 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
        c->snd.una = c->snd.iss;
        c->snd.nxt = c->snd.iss + 1;
        c->snd.last = c->snd.nxt;
-       c->snd.cwnd = utcp->mtu;
+       c->snd.cwnd = (utcp->mtu > 2190 ? 2 : utcp->mtu > 1095 ? 3 : 4) * utcp->mtu;
+       c->snd.ssthresh = ~0;
+       debug_cwnd(c);
        c->utcp = utcp;
 
        // Add it to the sorted list of connections
@@ -506,19 +517,18 @@ void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 
 static void ack(struct utcp_connection *c, bool sendatleastone) {
        int32_t left = seqdiff(c->snd.last, c->snd.nxt);
-       int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
-       debug("cwndleft = %d\n", cwndleft);
+       int32_t cwndleft = min(c->snd.cwnd, c->snd.wnd) - seqdiff(c->snd.nxt, c->snd.una);
 
        assert(left >= 0);
 
-       if(cwndleft <= 0) {
-               cwndleft = 0;
-       }
-
-       if(cwndleft < left) {
+       if(cwndleft < 0) {
+               left = 0;
+       } else if(cwndleft < left) {
                left = cwndleft;
        }
 
+       debug("cwndleft = %d, left = %d\n", cwndleft, left);
+
        if(!left && !sendatleastone) {
                return;
        }
@@ -744,7 +754,12 @@ static void retransmit(struct utcp_connection *c) {
                }
 
                c->snd.nxt = c->snd.una + len;
-               c->snd.cwnd = utcp->mtu; // reduce cwnd on retransmit
+
+               // RFC 5681 slow start after timeout
+               c->snd.ssthresh = max(c->snd.cwnd / 2, utcp->mtu * 2); // eq. 4
+               c->snd.cwnd = utcp->mtu;
+               debug_cwnd(c);
+
                buffer_copy(&c->sndbuf, pkt->data, 0, len);
                print_packet(c->utcp, "rtrx", pkt, sizeof(pkt->hdr) + len);
                utcp->send(utcp, pkt, sizeof(pkt->hdr) + len);
@@ -1332,12 +1347,20 @@ synack:
                c->snd.una = hdr.ack;
 
                c->dupack = 0;
-               c->snd.cwnd += utcp->mtu;
+
+               // Increase the congestion window according to RFC 5681
+               if(c->snd.cwnd < c->snd.ssthresh) {
+                       c->snd.cwnd += min(advanced, utcp->mtu); // eq. 2
+               } else {
+                       c->snd.cwnd += max(1, (utcp->mtu * utcp->mtu) / c->snd.cwnd); // eq. 3
+               }
 
                if(c->snd.cwnd > c->sndbuf.maxsize) {
                        c->snd.cwnd = c->sndbuf.maxsize;
                }
 
+               debug_cwnd(c);
+
                // Check if we have sent a FIN that is now ACKed.
                switch(c->state) {
                case FIN_WAIT_1:
@@ -1370,6 +1393,7 @@ synack:
                                //Reset the congestion window so we wait for ACKs.
                                c->snd.nxt = c->snd.una;
                                c->snd.cwnd = utcp->mtu;
+                               debug_cwnd(c);
                                start_retransmit_timer(c);
                        }
                }

diff --git a/utcp_priv.h b/utcp_priv.h
index c23279d82c4c4369a0de076a65c9d86d408e4687..5ed0344a45fce589963253eafe5ec11bbcdfc937 100644 (file)
--- a/utcp_priv.h
+++ b/utcp_priv.h
@@ -125,6 +125,7 @@ struct utcp_connection {
 
                uint32_t last;
                uint32_t cwnd;
+               uint32_t ssthresh;
        } snd;
 
        struct {