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diff --git a/third_party/libwebrtc/api/test/network_emulation/cross_traffic.h b/third_party/libwebrtc/api/test/network_emulation/cross_traffic.h
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+/*
+ *  Copyright (c) 2021 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.
+ */
+#ifndef API_TEST_NETWORK_EMULATION_CROSS_TRAFFIC_H_
+#define API_TEST_NETWORK_EMULATION_CROSS_TRAFFIC_H_
+
+#include "api/task_queue/task_queue_base.h"
+#include "api/test/network_emulation/network_emulation_interfaces.h"
+#include "api/units/data_rate.h"
+#include "api/units/data_size.h"
+#include "api/units/time_delta.h"
+#include "api/units/timestamp.h"
+
+namespace webrtc {
+
+// This API is still in development and can be changed without prior notice.
+
+// Represents the endpoint for cross traffic that is going through the network.
+// It can be used to emulate unexpected network load.
+class CrossTrafficRoute {
+ public:
+  virtual ~CrossTrafficRoute() = default;
+
+  // Triggers sending of dummy packets with size `packet_size` bytes.
+  virtual void TriggerPacketBurst(size_t num_packets, size_t packet_size) = 0;
+  // Sends a packet over the nodes. The content of the packet is unspecified;
+  // only the size metter for the emulation purposes.
+  virtual void SendPacket(size_t packet_size) = 0;
+  // Sends a packet over the nodes and runs `action` when it has been delivered.
+  virtual void NetworkDelayedAction(size_t packet_size,
+                                    std::function<void()> action) = 0;
+};
+
+// Describes a way of generating cross traffic on some route. Used by
+// NetworkEmulationManager to produce cross traffic during some period of time.
+class CrossTrafficGenerator {
+ public:
+  virtual ~CrossTrafficGenerator() = default;
+
+  // Time between Process calls.
+  virtual TimeDelta GetProcessInterval() const = 0;
+
+  // Called periodically by NetworkEmulationManager. Generates traffic on the
+  // route.
+  virtual void Process(Timestamp at_time) = 0;
+};
+
+// Config of a cross traffic generator. Generated traffic rises and falls
+// randomly.
+struct RandomWalkConfig {
+  int random_seed = 1;
+  DataRate peak_rate = DataRate::KilobitsPerSec(100);
+  DataSize min_packet_size = DataSize::Bytes(200);
+  TimeDelta min_packet_interval = TimeDelta::Millis(1);
+  TimeDelta update_interval = TimeDelta::Millis(200);
+  double variance = 0.6;
+  double bias = -0.1;
+};
+
+// Config of a cross traffic generator. Generated traffic has form of periodic
+// peaks alternating with periods of silence.
+struct PulsedPeaksConfig {
+  DataRate peak_rate = DataRate::KilobitsPerSec(100);
+  DataSize min_packet_size = DataSize::Bytes(200);
+  TimeDelta min_packet_interval = TimeDelta::Millis(1);
+  TimeDelta send_duration = TimeDelta::Millis(100);
+  TimeDelta hold_duration = TimeDelta::Millis(2000);
+};
+
+struct FakeTcpConfig {
+  DataSize packet_size = DataSize::Bytes(1200);
+  DataSize send_limit = DataSize::PlusInfinity();
+  TimeDelta process_interval = TimeDelta::Millis(200);
+  TimeDelta packet_timeout = TimeDelta::Seconds(1);
+};
+
+}  // namespace webrtc
+
+#endif  // API_TEST_NETWORK_EMULATION_CROSS_TRAFFIC_H_