1 files changed, 156 insertions, 0 deletions
diff --git a/libtransport/src/protocols/rtc_data_path.cc b/libtransport/src/protocols/rtc_data_path.cc
new file mode 100644
index 000000000..30644e939
--- /dev/null
+++ b/libtransport/src/protocols/rtc_data_path.cc
@@ -0,0 +1,156 @@
+/*
+ * Copyright (c) 2017-2019 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <protocols/rtc_data_path.h>
+
+#include <cfloat>
+#include <chrono>
+
+#define MAX_ROUNDS_WITHOUT_PKTS 10  // 2sec
+
+namespace transport {
+
+namespace protocol {
+
+RTCDataPath::RTCDataPath()
+    : min_rtt(UINT_MAX),
+      prev_min_rtt(UINT_MAX),
+      min_owd(INT_MAX),  // this is computed like in LEDBAT, so it is not the
+                         // real OWD, but the measured one, that depends on the
+                         // clock of sender and receiver. the only meaningful
+                         // value is is the queueing delay. for this reason we
+                         // keep both RTT (for the windowd calculation) and OWD
+                         // (for congestion/quality control)
+      prev_min_owd(INT_MAX),
+      avg_owd(0.0),
+      queuing_delay(DBL_MAX),
+      lastRecvSeq_(0),
+      lastRecvTime_(0),
+      avg_inter_arrival_(DBL_MAX),
+      received_nacks_(false),
+      received_packets_(false),
+      rounds_without_packets_(0),
+      RTThistory_(HISTORY_LEN),
+      OWDhistory_(HISTORY_LEN){};
+
+void RTCDataPath::insertRttSample(uint64_t rtt) {
+  // for the rtt we only keep track of the min one
+  if (rtt < min_rtt) min_rtt = rtt;
+}
+
+void RTCDataPath::insertOwdSample(int64_t owd) {
+  // for owd we use both min and avg
+  if (owd < min_owd) min_owd = owd;
+
+  if (avg_owd != DBL_MAX)
+    avg_owd = (avg_owd * (1 - ALPHA_RTC)) + (owd * ALPHA_RTC);
+  else {
+    avg_owd = owd;
+  }
+
+  // owd is computed only for valid data packets so we count only
+  // this for decide if we recevie traffic or not
+  received_packets_ = true;
+}
+
+void RTCDataPath::computeInterArrivalGap(uint32_t segmentNumber) {
+  // got packet in sequence, compute gap
+  if (lastRecvSeq_ == (segmentNumber - 1)) {
+    uint64_t now = std::chrono::duration_cast<std::chrono::milliseconds>(
+                       std::chrono::steady_clock::now().time_since_epoch())
+                       .count();
+    uint64_t delta = now - lastRecvTime_;
+    lastRecvSeq_ = segmentNumber;
+    lastRecvTime_ = now;
+    if (avg_inter_arrival_ == DBL_MAX)
+      avg_inter_arrival_ = delta;
+    else
+      avg_inter_arrival_ =
+          (avg_inter_arrival_ * (1 - ALPHA_RTC)) + (delta * ALPHA_RTC);
+    return;
+  }
+
+  // ooo packet, update the stasts if needed
+  if (lastRecvSeq_ <= segmentNumber) {
+    lastRecvSeq_ = segmentNumber;
+    lastRecvTime_ = std::chrono::duration_cast<std::chrono::milliseconds>(
+                        std::chrono::steady_clock::now().time_since_epoch())
+                        .count();
+  }
+}
+
+void RTCDataPath::receivedNack() { received_nacks_ = true; }
+
+double RTCDataPath::getInterArrivalGap() {
+  if (avg_inter_arrival_ == DBL_MAX) return 0;
+  return avg_inter_arrival_;
+}
+
+bool RTCDataPath::isActive() {
+  if (received_nacks_ && rounds_without_packets_ < MAX_ROUNDS_WITHOUT_PKTS)
+    return true;
+  return false;
+}
+
+void RTCDataPath::roundEnd() {
+  // reset min_rtt and add it to the history
+  if (min_rtt != UINT_MAX) {
+    prev_min_rtt = min_rtt;
+  } else {
+    // this may happen if we do not receive any packet
+    // from this path in the last round. in this case
+    // we use the measure from the previuos round
+    min_rtt = prev_min_rtt;
+  }
+
+  if (min_rtt == 0) min_rtt = 1;
+
+  RTThistory_.pushBack(min_rtt);
+  min_rtt = UINT_MAX;
+
+  // do the same for min owd
+  if (min_owd != INT_MAX) {
+    prev_min_owd = min_owd;
+  } else {
+    min_owd = prev_min_owd;
+  }
+
+  if (min_owd != INT_MAX) {
+    OWDhistory_.pushBack(min_owd);
+    min_owd = INT_MAX;
+
+    // compute queuing delay
+    queuing_delay = avg_owd - getMinOwd();
+
+  } else {
+    queuing_delay = 0.0;
+  }
+
+  if (!received_packets_)
+    rounds_without_packets_++;
+  else
+    rounds_without_packets_ = 0;
+  received_packets_ = false;
+}
+
+double RTCDataPath::getQueuingDealy() { return queuing_delay; }
+
+uint64_t RTCDataPath::getMinRtt() { return RTThistory_.begin(); }
+
+int64_t RTCDataPath::getMinOwd() { return OWDhistory_.begin(); }
+
+}  // end namespace protocol
+
+}  // end namespace transport