Reset the retransmission timer when receiving duplicate ACKs.

[utcp] / utcp.c

diff --git a/utcp.c b/utcp.c
index 7c30246cb066d1edccaa1fd5a48a7ec0a0fcedde..ac598ddae28667fd9a40c28ace29255b7dd22f66 100644 (file)
--- a/utcp.c
+++ b/utcp.c
@@ -128,7 +128,7 @@ static void print_packet(struct utcp_connection *c, const char *dir, const void
 }
 
 static void debug_cwnd(struct utcp_connection *c) {
-       debug(c, "snd.cwnd %u snd.ssthresh %u\n", c->snd.cwnd, c->snd.ssthresh);
+       debug(c, "snd.cwnd %u snd.ssthresh %u\n", c->snd.cwnd, ~c->snd.ssthresh ? c->snd.ssthresh : 0);
 }
 #else
 #define debug(...) do {} while(0)
@@ -402,11 +402,7 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
        c->snd.nxt = c->snd.iss + 1;
        c->snd.last = c->snd.nxt;
        c->snd.cwnd = (utcp->mtu > 2190 ? 2 : utcp->mtu > 1095 ? 3 : 4) * utcp->mtu;
-#if UTCP_DEBUG
-       c->snd.ssthresh = c->sndbuf.maxsize;
-#else
        c->snd.ssthresh = ~0;
-#endif
        debug_cwnd(c);
        c->utcp = utcp;
 
@@ -812,27 +808,24 @@ static void retransmit(struct utcp_connection *c) {
                pkt->hdr.seq = c->snd.una;
                pkt->hdr.ack = c->rcv.nxt;
                pkt->hdr.ctl = ACK;
-               uint32_t len = seqdiff(c->snd.last, c->snd.una);
-
-               if(len > utcp->mtu) {
-                       len = utcp->mtu;
-               }
+               uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mtu);
 
                if(fin_wanted(c, c->snd.una + len)) {
                        len--;
                        pkt->hdr.ctl |= FIN;
                }
 
-               c->snd.nxt = c->snd.una + len;
-
                // RFC 5681 slow start after timeout
-               c->snd.ssthresh = max(c->snd.cwnd / 2, utcp->mtu * 2); // eq. 4
+               uint32_t flightsize = seqdiff(c->snd.nxt, c->snd.una);
+               c->snd.ssthresh = max(flightsize / 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, "rtrx", pkt, sizeof(pkt->hdr) + len);
                utcp->send(utcp, pkt, sizeof(pkt->hdr) + len);
+
+               c->snd.nxt = c->snd.una + len;
                break;
 
        case CLOSED:
@@ -855,6 +848,7 @@ static void retransmit(struct utcp_connection *c) {
        }
 
        c->rtt_start.tv_sec = 0; // invalidate RTT timer
+       c->dupack = 0; // cancel any ongoing fast recovery
 
 cleanup:
        free(pkt);
@@ -1464,14 +1458,15 @@ synack:
                        break;
                }
        } else {
-               if(!len && is_reliable(c)) {
+               if(!len && is_reliable(c) && c->snd.una != c->snd.last) {
                        c->dupack++;
                        debug(c, "duplicate ACK %d\n", c->dupack);
 
                        if(c->dupack == 3) {
                                // RFC 5681 fast recovery
                                debug(c, "fast recovery started\n", c->dupack);
-                               c->snd.ssthresh = max(c->snd.cwnd / 2, utcp->mtu * 2); // eq. 4
+                               uint32_t flightsize = seqdiff(c->snd.nxt, c->snd.una);
+                               c->snd.ssthresh = max(flightsize / 2, utcp->mtu * 2); // eq. 4
                                c->snd.cwnd = min(c->snd.ssthresh + 3 * utcp->mtu, c->sndbuf.maxsize);
 
                                if(c->snd.cwnd > c->sndbuf.maxsize) {
@@ -1490,6 +1485,11 @@ synack:
 
                                debug_cwnd(c);
                        }
+
+                       // We got an ACK which indicates the other side did get one of our packets.
+                       // Reset the retransmission timer to avoid going to slow start,
+                       // but don't touch the connection timeout.
+                       start_retransmit_timer(c);
                }
        }