Allow FakeNetworkPipe to drop packets in bursts.

webrtc/test/fake_network_pipe.h

 /*
  *  Copyright (c) 2012 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 62 matching lines @@
     // Delay in addition to capacity induced delay.
     int queue_delay_ms = 0;
     // Standard deviation of the extra delay.
     int delay_standard_deviation_ms = 0;
     // Link capacity in kbps.
     int link_capacity_kbps = 0;
     // Random packet loss.
     int loss_percent = 0;
     // If packets are allowed to be reordered.
     bool allow_reordering = false;
+    // The average length of a burst of lost packets.
+    int avg_burst_loss_length = -1;

[terelius, 2016/05/30 16:26:32]

I think it would be good to make it a double. There doesn't seem to be any
particular reason why the average burst loss should be an integer.

[philipel, 2016/05/30 16:29:25]

I guess it makes more sense to use a double here instead, but I think it would
be better with a follow-up CL where I change that (and maybe loss_percent as
well) instead.

[mflodman, 2016/05/31 07:42:02]

Do we really need this as a double? I think int precision is fine in this case.

[philipel, 2016/05/31 08:39:00]

Don't think we need this as a double, just something that might have been nice.
If anyone needs it they can easily change it...

   };
 
   FakeNetworkPipe(Clock* clock, const FakeNetworkPipe::Config& config);
   FakeNetworkPipe(Clock* clock,
                   const FakeNetworkPipe::Config& config,
                   uint64_t seed);
   ~FakeNetworkPipe();
 
   // Must not be called in parallel with SendPacket or Process.
   void SetReceiver(PacketReceiver* receiver);
@@ skipping 33 matching lines @@
   std::multiset<NetworkPacket*, PacketArrivalTimeComparator> delay_link_;
 
   // Link configuration.
   Config config_;
 
   // Statistics.
   size_t dropped_packets_;
   size_t sent_packets_;
   int64_t total_packet_delay_;
 
+  // Are we currently dropping a burst of packets?
+  bool bursting_;
+
+  // The probability to drop the packet if we are currently dropping a
+  // burst of packet
+  double prob_loss_bursting_;
+
+  // The probability to drop a burst of packets.

[mflodman, 2016/05/31 07:42:02]

It would be good to add something telling the model, e.g. "according to
gilbert-elliot model."

[philipel, 2016/05/31 08:39:00]

Done kind of. I added a comment to the .cc file since we configure
|prob_loss_bursting_| and |prob_start_bursting_| differently depending on which
type of loss we want.

+  double prob_start_bursting_;
+
   int64_t next_process_time_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(FakeNetworkPipe);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_TEST_FAKE_NETWORK_PIPE_H_