diff --git a/common/rfb/Congestion.cxx b/common/rfb/Congestion.cxx
new file mode 100644
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+++ b/common/rfb/Congestion.cxx
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+/* Copyright 2009-2015 Pierre Ossman for Cendio AB
+ * 
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ * 
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+/*
+ * This code implements congestion control in the same way as TCP in
+ * order to avoid excessive latency in the transport. This is needed
+ * because "buffer bloat" is unfortunately still a very real problem.
+ *
+ * The basic principle is TCP Congestion Control (RFC 5618), with the
+ * addition of using the TCP Vegas algorithm. The reason we use Vegas
+ * is that we run on top of a reliable transport so we need a latency
+ * based algorithm rather than a loss based one.
+ */
+
+#include <sys/time.h>
+
+#include <rfb/Congestion.h>
+#include <rfb/util.h>
+
+// Debug output on what the congestion control is up to
+#undef CONGESTION_DEBUG
+
+using namespace rfb;
+
+// This window should get us going fairly fast on a decent bandwidth network.
+// If it's too high, it will rapidly be reduced and stay low.
+static const unsigned INITIAL_WINDOW = 16384;
+
+// TCP's minimal window is 3*MSS. But since we don't know the MSS, we
+// make a guess at 4 KiB (it's probably a bit higher).
+static const unsigned MINIMUM_WINDOW = 4096;
+
+// The current default maximum window for Linux (4 MiB). Should be a good
+// limit for now...
+static const unsigned MAXIMUM_WINDOW = 4194304;
+
+struct Congestion::RTTInfo {
+  struct timeval tv;
+  int offset;
+  unsigned inFlight;
+};
+
+Congestion::Congestion() :
+    baseRTT(-1), congWindow(INITIAL_WINDOW),
+    ackedOffset(0), sentOffset(0),
+    minRTT(-1), seenCongestion(false),
+    congestionTimer(this)
+{
+}
+
+Congestion::~Congestion()
+{
+}
+
+
+void Congestion::sentPing(int offset)
+{
+  struct RTTInfo rttInfo;
+
+  if (ackedOffset == 0)
+    ackedOffset = offset;
+
+  memset(&rttInfo, 0, sizeof(struct RTTInfo));
+
+  gettimeofday(&rttInfo.tv, NULL);
+  rttInfo.offset = offset;
+  rttInfo.inFlight = rttInfo.offset - ackedOffset;
+
+  pings.push_back(rttInfo);
+
+  sentOffset = offset;
+
+  // Let some data flow before we adjust the settings
+  if (!congestionTimer.isStarted())
+    congestionTimer.start(__rfbmin(baseRTT * 2, 100));
+}
+
+void Congestion::gotPong()
+{
+  struct RTTInfo rttInfo;
+  unsigned rtt, delay;
+
+  if (pings.empty())
+    return;
+
+  rttInfo = pings.front();
+  pings.pop_front();
+
+  rtt = msSince(&rttInfo.tv);
+  if (rtt < 1)
+    rtt = 1;
+
+  ackedOffset = rttInfo.offset;
+
+  // Try to estimate wire latency by tracking lowest seen latency
+  if (rtt < baseRTT)
+    baseRTT = rtt;
+
+  if (rttInfo.inFlight > congWindow) {
+    seenCongestion = true;
+
+    // Estimate added delay because of overtaxed buffers
+    delay = (rttInfo.inFlight - congWindow) * baseRTT / congWindow;
+
+    if (delay < rtt)
+      rtt -= delay;
+    else
+      rtt = 1;
+
+    // If we underestimate the congestion window, then we'll get a latency
+    // that's less than the wire latency, which will confuse other portions
+    // of the code.
+    if (rtt < baseRTT)
+      rtt = baseRTT;
+  }
+
+  // We only keep track of the minimum latency seen (for a given interval)
+  // on the basis that we want to avoid continuous buffer issue, but don't
+  // mind (or even approve of) bursts.
+  if (rtt < minRTT)
+    minRTT = rtt;
+}
+
+bool Congestion::isCongested(int offset, unsigned idleTime)
+{
+  // Idle for too long? (and no data on the wire)
+  //
+  // FIXME: This should really just be one baseRTT, but we're getting
+  //        problems with triggering the idle timeout on each update.
+  //        Maybe we need to use a moving average for the wire latency
+  //        instead of baseRTT.
+  if ((sentOffset == ackedOffset) && (idleTime > 2 * baseRTT)) {
+
+#ifdef CONGESTION_DEBUG
+    if (congWindow > INITIAL_WINDOW)
+      fprintf(stderr, "Reverting to initial window (%d KiB) after %d ms\n",
+              INITIAL_WINDOW / 1024, sock->outStream().getIdleTime());
+#endif
+
+    // Close congestion window and allow a transfer
+    // FIXME: Reset baseRTT like Linux Vegas?
+    congWindow = __rfbmin(INITIAL_WINDOW, congWindow);
+
+    return false;
+  }
+
+  // FIXME: Should we compensate for non-update data?
+  //        (i.e. use sentOffset instead of offset)
+  if ((offset - ackedOffset) < congWindow)
+    return false;
+
+  // If we just have one outstanding "ping", that means the client has
+  // started receiving our update. In order to not regress compared to
+  // before we had congestion avoidance, we allow another update here.
+  // This could further clog up the tubes, but congestion control isn't
+  // really working properly right now anyway as the wire would otherwise
+  // be idle for at least RTT/2.
+  if (pings.size() == 1)
+    return false;
+
+  return true;
+}
+
+bool Congestion::handleTimeout(Timer* t)
+{
+  unsigned diff;
+
+  if (!seenCongestion)
+    return false;
+
+  // The goal is to have a slightly too large congestion window since
+  // a "perfect" one cannot be distinguished from a too small one. This
+  // translates to a goal of a few extra milliseconds of delay.
+
+  diff = minRTT - baseRTT;
+
+  if (diff > __rfbmin(100, baseRTT)) {
+    // Way too fast
+    congWindow = congWindow * baseRTT / minRTT;
+  } else if (diff > __rfbmin(50, baseRTT/2)) {
+    // Slightly too fast
+    congWindow -= 4096;
+  } else if (diff < 5) {
+    // Way too slow
+    congWindow += 8192;
+  } else if (diff < 25) {
+    // Too slow
+    congWindow += 4096;
+  }
+
+  if (congWindow < MINIMUM_WINDOW)
+    congWindow = MINIMUM_WINDOW;
+  if (congWindow > MAXIMUM_WINDOW)
+    congWindow = MAXIMUM_WINDOW;
+
+#ifdef CONGESTION_DEBUG
+  fprintf(stderr, "RTT: %d ms (%d ms), Window: %d KiB, Bandwidth: %g Mbps\n",
+          minRTT, baseRTT, congWindow / 1024,
+          congWindow * 8.0 / baseRTT / 1000.0);
+#endif
+
+  minRTT = -1;
+  seenCongestion = false;
+
+  return false;
+}
+