Measure packet loss so we can use it to select ICE candidate pairs.

webrtc/p2p/base/port.cc

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 114 matching lines @@
 //   characteristics.  Foundations are used in the frozen algorithm.
 static std::string ComputeFoundation(const std::string& type,
                                      const std::string& protocol,
                                      const std::string& relay_protocol,
                                      const rtc::SocketAddress& base_address) {
   std::ostringstream ost;
   ost << type << base_address.ipaddr().ToString() << protocol << relay_protocol;
   return rtc::ToString<uint32_t>(rtc::ComputeCrc32(ost.str()));
 }
 
+PacketLossEstimator::PacketLossEstimator(int64_t expire_after)
+    : expire_after_(expire_after) {}
+
+void PacketLossEstimator::ExpectResponse(std::string id, int64_t sent_time) {
+  outstanding_packets_.emplace_back(id, sent_time);
+}
+
+void PacketLossEstimator::ReceivedResponse(std::string id,
+                                           int64_t received_time) {
+  auto iter =
+      std::find_if(outstanding_packets_.begin(), outstanding_packets_.end(),
+                   [id](const PacketInfo& packet) { return packet.id == id; });
+
+  // There are several reasons we might not find id:
+  // 1) We already expired this packet (and responses_expected_ was already
+  // incremented).
+  // 2) We already received (and counted) a response with this id.
+  // 3) we never expected to see this id (something else went wrong).

[Taylor Brandstetter, 2017/03/01 02:26:12]

nit: Capitalization of "we"

[Zach Stein, 2017/03/02 00:02:23]

Done.

+
+  if (iter != outstanding_packets_.end()) {
+    responses_expected_ += 1;
+    if (!IsExpired(*iter, received_time)) {
+      responses_received_ += 1;
+    }
+    outstanding_packets_.erase(iter);
+  }
+
+  RemoveExpiredPackets(received_time);
+}
+
+void PacketLossEstimator::RemoveExpiredPackets(int64_t now) {
+  auto iter = outstanding_packets_.begin();
+  while (iter != outstanding_packets_.end() && IsExpired(*iter, now)) {
+    responses_expected_ += 1;
+    ++iter;
+  }
+  outstanding_packets_.erase(outstanding_packets_.begin(), iter);
+
+  UpdateResponseRate();
+}
+
+void PacketLossEstimator::UpdateResponseRate() {
+  response_rate_ =
+      static_cast<double>(responses_received_) / responses_expected_;

[Taylor Brandstetter, 2017/03/01 02:26:12]

Divide by zero?

[Zach Stein, 2017/03/02 00:02:23]

Done.

+}
+
+bool PacketLossEstimator::IsExpired(const PacketInfo& packet,
+                                    int64_t received_time) const {
+  return packet.sent_time < received_time - expire_after_;
+}
+
 Port::Port(rtc::Thread* thread,
            const std::string& type,
            rtc::PacketSocketFactory* factory,
            rtc::Network* network,
            const rtc::IPAddress& ip,
            const std::string& username_fragment,
            const std::string& password)
     : thread_(thread),
       factory_(factory),
       type_(type),
@@ skipping 733 matching lines @@
       connected_(true),
       pruned_(false),
       use_candidate_attr_(false),
       remote_ice_mode_(ICEMODE_FULL),
       requests_(port->thread()),
       rtt_(DEFAULT_RTT),
       last_ping_sent_(0),
       last_ping_received_(0),
       last_data_received_(0),
       last_ping_response_received_(0),
+      packet_loss_estimator_(kPortTimeoutDelay),

[Taylor Brandstetter, 2017/03/01 02:26:12]

This value recently became very large (~45 seconds), so it probably won't be
very useful.

Maybe we should have two time thresholds?

Threshold A (RTT and change): Response is counted as lost, but still remembered
in case a response arrives later than expected.

Threshold B (~45 seconds): Response completely forgotten.

[Zach Stein, 2017/03/02 00:02:23]

I like this idea. As is, we probably won't get a useful signal until long after
a connection has been established. I would like to start with the simplest
possible implementation so that we have something to measure though.

       reported_(false),
       state_(IceCandidatePairState::WAITING),
       receiving_timeout_(WEAK_CONNECTION_RECEIVE_TIMEOUT),
       time_created_ms_(rtc::TimeMillis()) {
   // All of our connections start in WAITING state.
   // TODO(mallinath) - Start connections from STATE_FROZEN.
   // Wire up to send stun packets
   requests_.SignalSendPacket.connect(this, &Connection::OnSendStunPacket);
   LOG_J(LS_INFO, this) << "Connection created";
 }
@@ skipping 332 matching lines @@
   UpdateReceiving(now);
   if (dead(now)) {
     Destroy();
   }
 }
 
 void Connection::Ping(int64_t now) {
   last_ping_sent_ = now;
   ConnectionRequest *req = new ConnectionRequest(this);
   pings_since_last_response_.push_back(SentPing(req->id(), now, nomination_));
+  packet_loss_estimator_.ExpectResponse(req->id(), now);
   LOG_J(LS_VERBOSE, this) << "Sending STUN ping "
                           << ", id=" << rtc::hex_encode(req->id())
                           << ", nomination=" << nomination_;
   requests_.Send(req);
   state_ = IceCandidatePairState::IN_PROGRESS;
   num_pings_sent_++;
 }
 
 void Connection::ReceivedPing() {
   last_ping_received_ = rtc::TimeMillis();
@@ skipping 134 matching lines @@
     std::string pings;
     PrintPingsSinceLastResponse(&pings, 5);
     LOG_JV(sev, this) << "Received STUN ping response"
                       << ", id=" << rtc::hex_encode(request->id())
                       << ", code=0"  // Makes logging easier to parse.
                       << ", rtt=" << rtt
                       << ", pings_since_last_response=" << pings;
   }
   ReceivedPingResponse(rtt, request->id());
 
+  int64_t time_received = rtc::TimeMillis();
+  packet_loss_estimator_.ReceivedResponse(request->id(), time_received);
+
   stats_.recv_ping_responses++;
 
   MaybeUpdateLocalCandidate(request, response);
 }
 
 void Connection::OnConnectionRequestErrorResponse(ConnectionRequest* request,
                                                   StunMessage* response) {
   const StunErrorCodeAttribute* error_attr = response->GetErrorCode();
   int error_code = STUN_ERROR_GLOBAL_FAILURE;
   if (error_attr) {
@@ skipping 208 matching lines @@
     RTC_DCHECK(sent < 0);
     error_ = port_->GetError();
     stats_.sent_discarded_packets++;
   } else {
     send_rate_tracker_.AddSamples(sent);
   }
   return sent;
 }
 
 }  // namespace cricket