Add more accurate support for changing capacity in SimulatedNetwork

NetworkBehaviorInterface::RegisterDeliveryTimeChangedCallback
adds support for a network behaviour to reschedule next time DequeueDeliverablePackets should be invoked.

SimulatedNetwork::SetConfig(const BuiltInNetworkBehaviorConfig& config,
                            Timestamp config_update_time)
adds possibility to change the configuration at config_update_time. Delivery time of a packet currently in the narrow section, will depend on the link capacity before and after the update.

Bug: webrtc:14525
Change-Id: I271251992d05c68f9160bb81811ea8f2efe9c921
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/349461
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42243}

api/BUILD.gn

@@ -849,7 +849,10 @@ rtc_source_set("simulated_network_api") {
     "../rtc_base:macromagic",
     "../rtc_base:random",
   ]
-  absl_deps = [ "//third_party/abseil-cpp/absl/types:optional" ]
+  absl_deps = [
+    "//third_party/abseil-cpp/absl/functional:any_invocable",
+    "//third_party/abseil-cpp/absl/types:optional",
+  ]
 }
 
 # TODO(srte): Move to network_emulation sub directory.

api/test/simulated_network.h

@@ -14,10 +14,9 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#include <deque>
-#include <queue>
 #include <vector>
 
+#include "absl/functional/any_invocable.h"
 #include "absl/types/optional.h"
 #include "rtc_base/random.h"
 #include "rtc_base/thread_annotations.h"
@@ -58,8 +57,8 @@ struct BuiltInNetworkBehaviorConfig {
   int queue_delay_ms = 0;
   // Standard deviation of the extra delay.
   int delay_standard_deviation_ms = 0;
-  // Link capacity in kbps.
+  // Link capacity in kbps. Negative number is treated as infinite capacity.
-  int link_capacity_kbps = 0;
+  int link_capacity_kbps = -1;
   // Random packet loss, range 0 to 100.
   double loss_percent = 0.;
   // If packets are allowed to be reordered.
@@ -115,6 +114,14 @@ class NetworkBehaviorInterface {
   // random extra delay), in such case this method should be called again to get
   // the updated estimated delivery time.
   virtual absl::optional<int64_t> NextDeliveryTimeUs() const = 0;
+  // Registers a callback that should be triggered by an implementation if the
+  // next NextDeliveryTimeUs() has changed between a call to NextDeliveryTimeUs
+  // and DequeueDeliverablePackets.
+  // The intended usage is to invoke NextDeliveryTimeUs and reschedule the
+  // DequeueDeliverablePackets call when network parameters (such as link
+  // capacity) changes.
+  virtual void RegisterDeliveryTimeChangedCallback(
+      absl::AnyInvocable<void()> callback) {}
   virtual ~NetworkBehaviorInterface() = default;
 };
 

test/network/BUILD.gn

@@ -95,23 +95,6 @@ rtc_library("emulated_network") {
   ]
 }
 
-rtc_library("network_emulation_unittest") {
-  testonly = true
-  sources = [ "network_emulation_unittest.cc" ]
-  deps = [
-    ":emulated_network",
-    "../:test_support",
-    "../..//test/network:simulated_network",
-    "../../api:simulated_network_api",
-    "../../api/units:time_delta",
-    "../../rtc_base:gunit_helpers",
-    "../../rtc_base:logging",
-    "../../rtc_base:rtc_event",
-    "../../rtc_base:task_queue_for_test",
-    "../../rtc_base/synchronization:mutex",
-  ]
-}
-
 if (rtc_include_tests && !build_with_chromium) {
   rtc_library("network_emulation_pc_unittest") {
     testonly = true
@@ -163,6 +146,26 @@ rtc_library("cross_traffic_unittest") {
 }
 
 if (rtc_include_tests) {
+  rtc_library("network_emulation_unittest") {
+    testonly = true
+    sources = [ "network_emulation_unittest.cc" ]
+    deps = [
+      ":emulated_network",
+      "../:test_support",
+      "../..//test/network:simulated_network",
+      "../../api:create_time_controller",
+      "../../api:simulated_network_api",
+      "../../api/task_queue:task_queue",
+      "../../api/units:time_delta",
+      "../../api/units:timestamp",
+      "../../rtc_base:gunit_helpers",
+      "../../rtc_base:logging",
+      "../../rtc_base:rtc_event",
+      "../../rtc_base:task_queue_for_test",
+      "../../rtc_base/synchronization:mutex",
+    ]
+  }
+
   rtc_library("feedback_generator") {
     testonly = true
     sources = [
@@ -235,6 +238,7 @@ if (rtc_include_tests) {
       "../../api/units:data_rate",
       "../../api/units:data_size",
       "../../api/units:time_delta",
+      "../../api/units:timestamp",
       "//testing/gtest",
     ]
     absl_deps = [ "//third_party/abseil-cpp/absl/algorithm:container" ]

test/network/network_emulation.cc

@@ -311,6 +311,26 @@ EmulatedNetworkNodeStats EmulatedNetworkNodeStatsBuilder::Build() const {
   return stats_;
 }
 
+LinkEmulation::LinkEmulation(
+    Clock* clock,
+    absl::Nonnull<TaskQueueBase*> task_queue,
+    std::unique_ptr<NetworkBehaviorInterface> network_behavior,
+    EmulatedNetworkReceiverInterface* receiver,
+    EmulatedNetworkStatsGatheringMode stats_gathering_mode)
+    : clock_(clock),
+      task_queue_(task_queue),
+      network_behavior_(std::move(network_behavior)),
+      receiver_(receiver),
+      stats_builder_(stats_gathering_mode) {
+  task_queue_->PostTask([&]() {
+    RTC_DCHECK_RUN_ON(task_queue_);
+    network_behavior_->RegisterDeliveryTimeChangedCallback([&]() {
+      RTC_DCHECK_RUN_ON(task_queue_);
+      UpdateProcessSchedule();
+    });
+  });
+}
+
 void LinkEmulation::OnPacketReceived(EmulatedIpPacket packet) {
   task_queue_->PostTask([this, packet = std::move(packet)]() mutable {
     RTC_DCHECK_RUN_ON(task_queue_);
@@ -326,28 +346,8 @@ void LinkEmulation::OnPacketReceived(EmulatedIpPacket packet) {
     }
     if (process_task_.Running())
       return;
-    absl::optional<int64_t> next_time_us =
+
-        network_behavior_->NextDeliveryTimeUs();
+    UpdateProcessSchedule();
-    if (!next_time_us)
-      return;
-    Timestamp current_time = clock_->CurrentTime();
-    process_task_ = RepeatingTaskHandle::DelayedStart(
-        task_queue_,
-        std::max(TimeDelta::Zero(),
-                 Timestamp::Micros(*next_time_us) - current_time),
-        [this]() {
-          RTC_DCHECK_RUN_ON(task_queue_);
-          Timestamp current_time = clock_->CurrentTime();
-          Process(current_time);
-          absl::optional<int64_t> next_time_us =
-              network_behavior_->NextDeliveryTimeUs();
-          if (!next_time_us) {
-            process_task_.Stop();
-            return TimeDelta::Zero();  // This is ignored.
-          }
-          RTC_DCHECK_GE(*next_time_us, current_time.us());
-          return Timestamp::Micros(*next_time_us) - current_time;
-        });
   });
 }
 
@@ -385,6 +385,35 @@ void LinkEmulation::Process(Timestamp at_time) {
   }
 }
 
+void LinkEmulation::UpdateProcessSchedule() {
+  RTC_DCHECK_RUN_ON(task_queue_);
+  if (process_task_.Running()) {
+    process_task_.Stop();
+  };
+  absl::optional<int64_t> next_time_us =
+      network_behavior_->NextDeliveryTimeUs();
+  if (!next_time_us)
+    return;
+  Timestamp current_time = clock_->CurrentTime();
+  process_task_ = RepeatingTaskHandle::DelayedStart(
+      task_queue_,
+      std::max(TimeDelta::Zero(),
+               Timestamp::Micros(*next_time_us) - current_time),
+      [this]() {
+        RTC_DCHECK_RUN_ON(task_queue_);
+        Timestamp current_time = clock_->CurrentTime();
+        Process(current_time);
+        absl::optional<int64_t> next_time_us =
+            network_behavior_->NextDeliveryTimeUs();
+        if (!next_time_us) {
+          process_task_.Stop();
+          return TimeDelta::Zero();  // This is ignored.
+        }
+        RTC_DCHECK_GE(*next_time_us, current_time.us());
+        return Timestamp::Micros(*next_time_us) - current_time;
+      });
+}
+
 NetworkRouterNode::NetworkRouterNode(absl::Nonnull<TaskQueueBase*> task_queue)
     : task_queue_(task_queue) {}
 

test/network/network_emulation.h

@@ -150,12 +150,7 @@ class LinkEmulation : public EmulatedNetworkReceiverInterface {
                 absl::Nonnull<TaskQueueBase*> task_queue,
                 std::unique_ptr<NetworkBehaviorInterface> network_behavior,
                 EmulatedNetworkReceiverInterface* receiver,
-                EmulatedNetworkStatsGatheringMode stats_gathering_mode)
+                EmulatedNetworkStatsGatheringMode stats_gathering_mode);
-      : clock_(clock),
-        task_queue_(task_queue),
-        network_behavior_(std::move(network_behavior)),
-        receiver_(receiver),
-        stats_builder_(stats_gathering_mode) {}
   void OnPacketReceived(EmulatedIpPacket packet) override;
 
   EmulatedNetworkNodeStats stats() const;
@@ -167,6 +162,7 @@ class LinkEmulation : public EmulatedNetworkReceiverInterface {
     EmulatedIpPacket packet;
     bool removed;
   };
+  void UpdateProcessSchedule() RTC_RUN_ON(task_queue_);
   void Process(Timestamp at_time) RTC_RUN_ON(task_queue_);
 
   Clock* const clock_;

test/network/network_emulation_unittest.cc

@@ -14,8 +14,11 @@
 #include <memory>
 #include <set>
 
+#include "api/task_queue/task_queue_base.h"
+#include "api/test/create_time_controller.h"
 #include "api/test/simulated_network.h"
 #include "api/units/time_delta.h"
+#include "api/units/timestamp.h"
 #include "rtc_base/event.h"
 #include "rtc_base/gunit.h"
 #include "rtc_base/synchronization/mutex.h"
@@ -76,6 +79,23 @@ class MockReceiver : public EmulatedNetworkReceiverInterface {
   MOCK_METHOD(void, OnPacketReceived, (EmulatedIpPacket packet), (override));
 };
 
+class MockNetworkBehaviourInterface : public NetworkBehaviorInterface {
+ public:
+  MOCK_METHOD(bool, EnqueuePacket, (PacketInFlightInfo), (override));
+  MOCK_METHOD(std::vector<PacketDeliveryInfo>,
+              DequeueDeliverablePackets,
+              (int64_t),
+              (override));
+  MOCK_METHOD(absl::optional<int64_t>,
+              NextDeliveryTimeUs,
+              (),
+              (const override));
+  MOCK_METHOD(void,
+              RegisterDeliveryTimeChangedCallback,
+              (absl::AnyInvocable<void()>),
+              (override));
+};
+
 class NetworkEmulationManagerThreeNodesRoutingTest : public ::testing::Test {
  public:
   NetworkEmulationManagerThreeNodesRoutingTest() {
@@ -672,5 +692,45 @@ TEST(NetworkEmulationManagerTURNTest, ClientTraffic) {
   emulation.time_controller()->AdvanceTime(TimeDelta::Seconds(1));
 }
 
+TEST(LinkEmulationTest, HandlesDeliveryTimeChangedCallback) {
+  constexpr uint32_t kEndpointIp = 0xC0A80011;  // 192.168.0.17
+  NetworkEmulationManagerImpl network_manager(
+      TimeMode::kSimulated, EmulatedNetworkStatsGatheringMode::kDefault);
+  auto mock_behaviour =
+      std::make_unique<::testing::NiceMock<MockNetworkBehaviourInterface>>();
+  MockNetworkBehaviourInterface* mock_behaviour_ptr = mock_behaviour.get();
+  absl::AnyInvocable<void()> delivery_time_changed_callback = nullptr;
+  TaskQueueBase* emulation_task_queue = nullptr;
+  EXPECT_CALL(*mock_behaviour_ptr, RegisterDeliveryTimeChangedCallback)
+      .WillOnce([&](absl::AnyInvocable<void()> callback) {
+        delivery_time_changed_callback = std::move(callback);
+        emulation_task_queue = TaskQueueBase::Current();
+      });
+  LinkEmulation* link =
+      network_manager.CreateEmulatedNode(std::move(mock_behaviour))->link();
+  network_manager.time_controller()->AdvanceTime(TimeDelta::Zero());
+  ASSERT_TRUE(delivery_time_changed_callback);
+
+  EXPECT_CALL(*mock_behaviour_ptr, EnqueuePacket);
+  EXPECT_CALL(*mock_behaviour_ptr, NextDeliveryTimeUs)
+      .WillOnce(::testing::Return(
+          network_manager.time_controller()->GetClock()->TimeInMicroseconds() +
+          10));
+  link->OnPacketReceived(EmulatedIpPacket(
+      rtc::SocketAddress(kEndpointIp, 50), rtc::SocketAddress(kEndpointIp, 79),
+      rtc::CopyOnWriteBuffer(10), Timestamp::Millis(1)));
+  network_manager.time_controller()->AdvanceTime(TimeDelta::Zero());
+
+  // Test that NetworkBehaviour can reschedule time for delivery. When
+  // delivery_time_changed_callback is triggered, LinkEmulation re-query the
+  // next delivery time.
+  EXPECT_CALL(*mock_behaviour_ptr, NextDeliveryTimeUs)
+      .WillOnce(::testing::Return(
+          network_manager.time_controller()->GetClock()->TimeInMicroseconds() +
+          20));
+  emulation_task_queue->PostTask([&]() { delivery_time_changed_callback(); });
+  network_manager.time_controller()->AdvanceTime(TimeDelta::Zero());
+}
+
 }  // namespace test
 }  // namespace webrtc

test/network/simulated_network.cc

@@ -15,40 +15,45 @@
 #include <cstdint>
 #include <utility>
 
+#include "absl/types/optional.h"
+#include "api/test/simulated_network.h"
 #include "api/units/data_rate.h"
 #include "api/units/data_size.h"
 #include "api/units/time_delta.h"
+#include "api/units/timestamp.h"
 #include "rtc_base/checks.h"
 
 namespace webrtc {
 namespace {
 
-// Calculate the time (in microseconds) that takes to send N `bits` on a
+// Calculate the time that it takes to send N `bits` on a
 // network with link capacity equal to `capacity_kbps` starting at time
-// `start_time_us`.
+// `start_time`.
-int64_t CalculateArrivalTimeUs(int64_t start_time_us,
+Timestamp CalculateArrivalTime(Timestamp start_time,
                                int64_t bits,
                                int capacity_kbps) {
-  // If capacity is 0, the link capacity is assumed to be infinite.
+  // If capacity is negative, the link capacity is assumed to be infinite.
-  if (capacity_kbps == 0) {
+  if (capacity_kbps < 0) {
-    return start_time_us;
+    return start_time;
   }
+  if (capacity_kbps == 0) {
+    return Timestamp::PlusInfinity();
+  }
+
   // Adding `capacity - 1` to the numerator rounds the extra delay caused by
   // capacity constraints up to an integral microsecond. Sending 0 bits takes 0
   // extra time, while sending 1 bit gets rounded up to 1 (the multiplication by
   // 1000 is because capacity is in kbps).
   // The factor 1000 comes from 10^6 / 10^3, where 10^6 is due to the time unit
   // being us and 10^3 is due to the rate unit being kbps.
-  return start_time_us + ((1000 * bits + capacity_kbps - 1) / capacity_kbps);
+  return start_time +
+         TimeDelta::Micros((1000 * bits + capacity_kbps - 1) / capacity_kbps);
 }
 
 }  // namespace
 
 SimulatedNetwork::SimulatedNetwork(Config config, uint64_t random_seed)
-    : random_(random_seed),
+    : random_(random_seed), bursting_(false), last_enqueue_time_us_(0) {
-      bursting_(false),
-      last_enqueue_time_us_(0),
-      last_capacity_link_exit_time_(0) {
   SetConfig(config);
 }
 
@@ -79,6 +84,30 @@ void SimulatedNetwork::SetConfig(const Config& config) {
   }
 }
 
+void SimulatedNetwork::SetConfig(const BuiltInNetworkBehaviorConfig& new_config,
+                                 Timestamp config_update_time) {
+  RTC_DCHECK_RUNS_SERIALIZED(&process_checker_);
+
+  if (!capacity_link_.empty()) {
+    // Calculate and update how large portion of the packet first in the
+    // capacity link is left to to send at time `config_update_time`.
+    const BuiltInNetworkBehaviorConfig& current_config =
+        GetConfigState().config;
+    TimeDelta duration_with_current_config =
+        config_update_time - capacity_link_.front().last_update_time;
+    RTC_DCHECK_GE(duration_with_current_config, TimeDelta::Zero());
+    capacity_link_.front().bits_left_to_send -= std::min(
+        duration_with_current_config.ms() * current_config.link_capacity_kbps,
+        capacity_link_.front().bits_left_to_send);
+    capacity_link_.front().last_update_time = config_update_time;
+  }
+  SetConfig(new_config);
+  UpdateCapacityQueue(GetConfigState(), config_update_time);
+  if (UpdateNextProcessTime() && next_process_time_changed_callback_) {
+    next_process_time_changed_callback_();
+  }
+}
+
 void SimulatedNetwork::UpdateConfig(
     std::function<void(BuiltInNetworkBehaviorConfig*)> config_modifier) {
   MutexLock lock(&config_lock_);
@@ -117,24 +146,31 @@ bool SimulatedNetwork::EnqueuePacket(PacketInFlightInfo packet) {
     return false;
   }
 
-  // If the packet has been sent before the previous packet in the network left
+  // Note that arrival time will be updated when previous packets are dequeued
-  // the capacity queue, let's ensure the new packet will start its trip in the
+  // from the capacity link.
-  // network after the last bit of the previous packet has left it.
+  // A packet can not enter the narrow section before the last packet has exit.
-  int64_t packet_send_time_us = packet.send_time_us;
+  Timestamp enqueue_time = Timestamp::Micros(packet.send_time_us);
-  if (!capacity_link_.empty()) {
+  Timestamp arrival_time =
-    packet_send_time_us =
+      capacity_link_.empty()
-        std::max(packet_send_time_us, capacity_link_.back().arrival_time_us);
+          ? CalculateArrivalTime(
-  }
+                std::max(enqueue_time, last_capacity_link_exit_time_),
-  capacity_link_.push({.packet = packet,
+                packet.size * 8, state.config.link_capacity_kbps)
-                       .arrival_time_us = CalculateArrivalTimeUs(
+          : Timestamp::PlusInfinity();
-                           packet_send_time_us, packet.size * 8,
+  capacity_link_.push(
-                           state.config.link_capacity_kbps)});
+      {.packet = packet,
+       .last_update_time = enqueue_time,
+       .bits_left_to_send = 8 * static_cast<int64_t>(packet.size),
+       .arrival_time = arrival_time});
 
-  // Only update `next_process_time_us_` if not already set (if set, there is no
+  // Only update `next_process_time_` if not already set. Otherwise,
-  // way that a new packet will make the `next_process_time_us_` change).
+  // next_process_time_ is calculated when a packet is dequeued. Note that this
-  if (!next_process_time_us_) {
+  // means that the newly enqueud packet risk having an arrival time before
+  // `next_process_time_` if packet reordering is allowed and
+  // config.delay_standard_deviation_ms is set.
+  // TODO(bugs.webrtc.org/14525): Consider preventing this.
+  if (next_process_time_.IsInfinite()) {
     RTC_DCHECK_EQ(capacity_link_.size(), 1);
-    next_process_time_us_ = capacity_link_.front().arrival_time_us;
+    next_process_time_ = arrival_time;
   }
 
   last_enqueue_time_us_ = packet.send_time_us;
@@ -143,74 +179,82 @@ bool SimulatedNetwork::EnqueuePacket(PacketInFlightInfo packet) {
 
 absl::optional<int64_t> SimulatedNetwork::NextDeliveryTimeUs() const {
   RTC_DCHECK_RUNS_SERIALIZED(&process_checker_);
-  return next_process_time_us_;
+  if (next_process_time_.IsFinite()) {
+    return next_process_time_.us();
+  }
+  return absl::nullopt;
 }
 
 void SimulatedNetwork::UpdateCapacityQueue(ConfigState state,
-                                           int64_t time_now_us) {
+                                           Timestamp time_now) {
-  // If there is at least one packet in the `capacity_link_`, let's update its
+  // Only the first packet in capacity_link_ have a calculated arrival time
-  // arrival time to take into account changes in the network configuration
+  // (when packet leave the narrow section), and time when it entered the narrow
-  // since the last call to UpdateCapacityQueue.
+  // section. Also, the configuration may have changed. Thus we need to
+  // calculate the arrival time again before maybe moving the packet to the
+  // delay link.
   if (!capacity_link_.empty()) {
-    capacity_link_.front().arrival_time_us = CalculateArrivalTimeUs(
+    capacity_link_.front().last_update_time = std::max(
-        std::max(capacity_link_.front().packet.send_time_us,
+        capacity_link_.front().last_update_time, last_capacity_link_exit_time_);
-                 last_capacity_link_exit_time_),
+    capacity_link_.front().arrival_time =
-        capacity_link_.front().packet.size * 8,
+        CalculateArrivalTime(capacity_link_.front().last_update_time,
-        state.config.link_capacity_kbps);
+                             capacity_link_.front().bits_left_to_send,
+                             state.config.link_capacity_kbps);
   }
 
   // The capacity link is empty or the first packet is not expected to exit yet.
   if (capacity_link_.empty() ||
-      time_now_us < capacity_link_.front().arrival_time_us) {
+      time_now < capacity_link_.front().arrival_time) {
     return;
   }
   bool reorder_packets = false;
 
   do {
-    // Time to get this packet (the original or just updated arrival_time_us is
+    // Time to get this packet (the original or just updated arrival_time is
     // smaller or equal to time_now_us).
     PacketInfo packet = capacity_link_.front();
+    RTC_DCHECK(packet.arrival_time.IsFinite());
     capacity_link_.pop();
 
     // If the network is paused, the pause will be implemented as an extra delay
     // to be spent in the `delay_link_` queue.
-    if (state.pause_transmission_until_us > packet.arrival_time_us) {
+    if (state.pause_transmission_until_us > packet.arrival_time.us()) {
-      packet.arrival_time_us = state.pause_transmission_until_us;
+      packet.arrival_time =
+          Timestamp::Micros(state.pause_transmission_until_us);
     }
 
     // Store the original arrival time, before applying packet loss or extra
     // delay. This is needed to know when it is the first available time the
     // next packet in the `capacity_link_` queue can start transmitting.
-    last_capacity_link_exit_time_ = packet.arrival_time_us;
+    last_capacity_link_exit_time_ = packet.arrival_time;
 
     // Drop packets at an average rate of `state.config.loss_percent` with
     // and average loss burst length of `state.config.avg_burst_loss_length`.
     if ((bursting_ && random_.Rand<double>() < state.prob_loss_bursting) ||
         (!bursting_ && random_.Rand<double>() < state.prob_start_bursting)) {
       bursting_ = true;
-      packet.arrival_time_us = PacketDeliveryInfo::kNotReceived;
+      packet.arrival_time = Timestamp::MinusInfinity();
     } else {
       // If packets are not dropped, apply extra delay as configured.
       bursting_ = false;
-      int64_t arrival_time_jitter_us = std::max(
+      TimeDelta arrival_time_jitter = TimeDelta::Micros(std::max(
           random_.Gaussian(state.config.queue_delay_ms * 1000,
                            state.config.delay_standard_deviation_ms * 1000),
-          0.0);
+          0.0));
 
       // If reordering is not allowed then adjust arrival_time_jitter
       // to make sure all packets are sent in order.
-      int64_t last_arrival_time_us =
+      Timestamp last_arrival_time = delay_link_.empty()
-          delay_link_.empty() ? -1 : delay_link_.back().arrival_time_us;
+                                        ? Timestamp::MinusInfinity()
+                                        : delay_link_.back().arrival_time;
       if (!state.config.allow_reordering && !delay_link_.empty() &&
-          packet.arrival_time_us + arrival_time_jitter_us <
+          packet.arrival_time + arrival_time_jitter < last_arrival_time) {
-              last_arrival_time_us) {
+        arrival_time_jitter = last_arrival_time - packet.arrival_time;
-        arrival_time_jitter_us = last_arrival_time_us - packet.arrival_time_us;
       }
-      packet.arrival_time_us += arrival_time_jitter_us;
+      packet.arrival_time += arrival_time_jitter;
 
       // Optimization: Schedule a reorder only when a packet will exit before
       // the one in front.
-      if (last_arrival_time_us > packet.arrival_time_us) {
+      if (last_arrival_time > packet.arrival_time) {
         reorder_packets = true;
       }
     }
@@ -221,23 +265,23 @@ void SimulatedNetwork::UpdateCapacityQueue(ConfigState state,
       break;
     }
     // If instead there is another packet in the `capacity_link_` queue, let's
-    // calculate its arrival_time_us based on the latest config (which might
+    // calculate its arrival_time based on the latest config (which might
     // have been changed since it was enqueued).
-    int64_t next_start = std::max(last_capacity_link_exit_time_,
+    Timestamp next_start = std::max(last_capacity_link_exit_time_,
-                                  capacity_link_.front().packet.send_time_us);
+                                    capacity_link_.front().last_update_time);
-    capacity_link_.front().arrival_time_us = CalculateArrivalTimeUs(
+    capacity_link_.front().arrival_time =
-        next_start, capacity_link_.front().packet.size * 8,
+        CalculateArrivalTime(next_start, capacity_link_.front().packet.size * 8,
-        state.config.link_capacity_kbps);
+                             state.config.link_capacity_kbps);
     // And if the next packet in the queue needs to exit, let's dequeue it.
-  } while (capacity_link_.front().arrival_time_us <= time_now_us);
+  } while (capacity_link_.front().arrival_time <= time_now);
 
   if (state.config.allow_reordering && reorder_packets) {
     // Packets arrived out of order and since the network config allows
-    // reordering, let's sort them per arrival_time_us to make so they will also
+    // reordering, let's sort them per arrival_time to make so they will also
     // be delivered out of order.
     std::stable_sort(delay_link_.begin(), delay_link_.end(),
                      [](const PacketInfo& p1, const PacketInfo& p2) {
-                       return p1.arrival_time_us < p2.arrival_time_us;
+                       return p1.arrival_time < p2.arrival_time;
                      });
   }
 }
@@ -250,27 +294,49 @@ SimulatedNetwork::ConfigState SimulatedNetwork::GetConfigState() const {
 std::vector<PacketDeliveryInfo> SimulatedNetwork::DequeueDeliverablePackets(
     int64_t receive_time_us) {
   RTC_DCHECK_RUNS_SERIALIZED(&process_checker_);
+  Timestamp receive_time = Timestamp::Micros(receive_time_us);
 
-  UpdateCapacityQueue(GetConfigState(), receive_time_us);
+  UpdateCapacityQueue(GetConfigState(), receive_time);
   std::vector<PacketDeliveryInfo> packets_to_deliver;
 
   // Check the extra delay queue.
   while (!delay_link_.empty() &&
-         receive_time_us >= delay_link_.front().arrival_time_us) {
+         receive_time >= delay_link_.front().arrival_time) {
     PacketInfo packet_info = delay_link_.front();
-    packets_to_deliver.emplace_back(
+    packets_to_deliver.emplace_back(PacketDeliveryInfo(
-        PacketDeliveryInfo(packet_info.packet, packet_info.arrival_time_us));
+        packet_info.packet, packet_info.arrival_time.IsFinite()
+                                ? packet_info.arrival_time.us()
+                                : PacketDeliveryInfo::kNotReceived));
     delay_link_.pop_front();
   }
-
+  // There is no need to invoke `next_process_time_changed_callback_` here since
-  if (!delay_link_.empty()) {
+  // it is expected that the user of NetworkBehaviorInterface calls
-    next_process_time_us_ = delay_link_.front().arrival_time_us;
+  // NextDeliveryTimeUs after DequeueDeliverablePackets. See
-  } else if (!capacity_link_.empty()) {
+  // NetworkBehaviorInterface.
-    next_process_time_us_ = capacity_link_.front().arrival_time_us;
+  UpdateNextProcessTime();
-  } else {
-    next_process_time_us_.reset();
-  }
   return packets_to_deliver;
 }
 
+bool SimulatedNetwork::UpdateNextProcessTime() {
+  Timestamp next_process_time = next_process_time_;
+
+  next_process_time_ = Timestamp::PlusInfinity();
+  for (const PacketInfo& packet : delay_link_) {
+    if (packet.arrival_time.IsFinite()) {
+      next_process_time_ = packet.arrival_time;
+      break;
+    }
+  }
+  if (next_process_time_.IsInfinite() && !capacity_link_.empty()) {
+    next_process_time_ = capacity_link_.front().arrival_time;
+  }
+  return next_process_time != next_process_time_;
+}
+
+void SimulatedNetwork::RegisterDeliveryTimeChangedCallback(
+    absl::AnyInvocable<void()> callback) {
+  RTC_DCHECK_RUNS_SERIALIZED(&process_checker_);
+  next_process_time_changed_callback_ = std::move(callback);
+}
+
 }  // namespace webrtc

test/network/simulated_network.h

@@ -12,6 +12,7 @@
 
 #include <stdint.h>
 
+#include <cstdint>
 #include <deque>
 #include <queue>
 #include <vector>
@@ -19,7 +20,6 @@
 #include "absl/types/optional.h"
 #include "api/sequence_checker.h"
 #include "api/test/simulated_network.h"
-#include "api/units/data_size.h"
 #include "api/units/timestamp.h"
 #include "rtc_base/race_checker.h"
 #include "rtc_base/random.h"
@@ -32,7 +32,8 @@ namespace webrtc {
 //
 // This is a basic implementation of NetworkBehaviorInterface that supports:
 // - Packet loss
-// - Capacity delay
+// - Capacity delay: Delay caused by a narrow section that only allows one
+//                   packet through at the time with a limited capacity.
 // - Extra delay with or without packets reorder
 // - Packet overhead
 // - Queue max capacity
@@ -46,10 +47,20 @@ class RTC_EXPORT SimulatedNetwork : public SimulatedNetworkInterface {
   // EnqueuePacket but also packets in the network that have not left the
   // network emulation. Packets that are ready to be retrieved by
   // DequeueDeliverablePackets are not affected by the new configuration.
-  // TODO(bugs.webrtc.org/14525): Fix SetConfig and make it apply only to the
+  // This method can be invoked directly by tests on any thread/sequence, but is
-  // part of the packet that is currently being sent (instead of applying to
+  // less accurate than the version with timestamp since changes to the
-  // all of it).
+  // configuration does not take affect until the time returned by
+  // NextDeliveryTimeUs has passed.
   void SetConfig(const Config& config) override;
+  // Updates the configuration at a specific time.
+  // Note that packets that have already passed the narrow section constrained
+  // by link capacity will not be affected by the change. If packet re-ordering
+  // is not allowed, packets with new shorter queue delays will arrive
+  // immediately after packets with the old, longer queue delays. Must be
+  // invoked on the same sequence as other methods in NetworkBehaviorInterface.
+  void SetConfig(const BuiltInNetworkBehaviorConfig& config,
+                 Timestamp config_update_time);
+
   void UpdateConfig(std::function<void(BuiltInNetworkBehaviorConfig*)>
                         config_modifier) override;
   void PauseTransmissionUntil(int64_t until_us) override;
@@ -60,12 +71,20 @@ class RTC_EXPORT SimulatedNetwork : public SimulatedNetworkInterface {
       int64_t receive_time_us) override;
 
   absl::optional<int64_t> NextDeliveryTimeUs() const override;
+  void RegisterDeliveryTimeChangedCallback(
+      absl::AnyInvocable<void()> callback) override;
 
  private:
   struct PacketInfo {
     PacketInFlightInfo packet;
+    // Time the packet was last updated by the capacity link.
+    Timestamp last_update_time;
+    // Size of the packet left to send through the capacity link. May differ
+    // from the packet size if the link capacity changes while the packet is in
+    // the capacity link.
+    int64_t bits_left_to_send;
     // Time when the packet has left (or will leave) the network.
-    int64_t arrival_time_us;
+    Timestamp arrival_time;
   };
   // Contains current configuration state.
   struct ConfigState {
@@ -80,8 +99,12 @@ class RTC_EXPORT SimulatedNetwork : public SimulatedNetworkInterface {
     int64_t pause_transmission_until_us = 0;
   };
 
+  // Calculates next_process_time_. Returns true if changed.
+  bool UpdateNextProcessTime() RTC_RUN_ON(&process_checker_);
   // Moves packets from capacity- to delay link.
-  void UpdateCapacityQueue(ConfigState state, int64_t time_now_us)
+  // If `previouse_config` is set, it is the config that was used until
+  // `time_now_us`
+  void UpdateCapacityQueue(ConfigState state, Timestamp time_now)
       RTC_RUN_ON(&process_checker_);
   ConfigState GetConfigState() const;
 
@@ -96,11 +119,11 @@ class RTC_EXPORT SimulatedNetwork : public SimulatedNetworkInterface {
   // only be able to deliver 1000 bits per second).
   //
   // Invariant:
-  // The head of the `capacity_link_` has arrival_time_us correctly set to the
+  // The head of the `capacity_link_` has arrival_time correctly set to the
   // time when the packet is supposed to be delivered (without accounting
   // potential packet loss or potential extra delay and without accounting for a
   // new configuration of the network, which requires a re-computation of the
-  // arrival_time_us).
+  // arrival_time).
   std::queue<PacketInfo> capacity_link_ RTC_GUARDED_BY(process_checker_);
   // Models the extra delay of the network (see `queue_delay_ms`
   // and `delay_standard_deviation_ms` in BuiltInNetworkBehaviorConfig), packets
@@ -110,8 +133,10 @@ class RTC_EXPORT SimulatedNetwork : public SimulatedNetworkInterface {
   // Represents the next moment in time when the network is supposed to deliver
   // packets to the client (either by pulling them from `delay_link_` or
   // `capacity_link_` or both).
-  absl::optional<int64_t> next_process_time_us_
+  Timestamp next_process_time_ RTC_GUARDED_BY(process_checker_) =
-      RTC_GUARDED_BY(process_checker_);
+      Timestamp::PlusInfinity();
+  absl::AnyInvocable<void()> next_process_time_changed_callback_
+      RTC_GUARDED_BY(process_checker_) = nullptr;
 
   ConfigState config_state_ RTC_GUARDED_BY(config_lock_);
 
@@ -126,7 +151,7 @@ class RTC_EXPORT SimulatedNetwork : public SimulatedNetworkInterface {
   // The last time a packet left the capacity_link_ (used to enforce
   // the capacity of the link and avoid packets starts to get sent before
   // the link it free).
-  int64_t last_capacity_link_exit_time_;
+  Timestamp last_capacity_link_exit_time_ = Timestamp::MinusInfinity();
 };
 
 }  // namespace webrtc

test/network/simulated_network_unittest.cc

@@ -10,6 +10,7 @@
 #include "test/network/simulated_network.h"
 
 #include <algorithm>
+#include <cstdint>
 #include <map>
 #include <optional>
 #include <set>
@@ -19,6 +20,7 @@
 #include "api/test/simulated_network.h"
 #include "api/units/data_rate.h"
 #include "api/units/time_delta.h"
+#include "api/units/timestamp.h"
 #include "test/gmock.h"
 #include "test/gtest.h"
 
@@ -26,6 +28,8 @@ namespace webrtc {
 namespace {
 
 using ::testing::ElementsAre;
+using ::testing::MockFunction;
+using ::testing::SizeIs;
 
 PacketInFlightInfo PacketWithSize(size_t size) {
   return PacketInFlightInfo(/*size=*/size, /*send_time_us=*/0, /*packet_id=*/1);
@@ -194,10 +198,115 @@ TEST(SimulatedNetworkTest,
                   /*receive_time_us=*/TimeDelta::Millis(1100).us())));
 }
 
-TEST(SimulatedNetworkTest, NetworkEmptyAfterLastPacketDequeued) {
+TEST(SimulatedNetworkTest,
+     SetConfigUpdateNextDeliveryTimeIfLinkCapacityChange) {
   // A packet of 125 bytes that gets enqueued on a network with 1 kbps capacity
   // should be ready to exit the network in 1 second.
   SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 1});
+  MockFunction<void()> delivery_time_changed_callback;
+  network.RegisterDeliveryTimeChangedCallback(
+      delivery_time_changed_callback.AsStdFunction());
+  const PacketInFlightInfo packet_1 =
+      PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/1);
+  ASSERT_TRUE(network.EnqueuePacket(packet_1));
+  EXPECT_EQ(network.NextDeliveryTimeUs(), TimeDelta::Seconds(1).us());
+
+  // Since the link capacity changes from 1 kbps to 10 kbps, packets will take
+  // 100 ms each to leave the network. After 500ms, half the packet should have
+  // gone through.
+  EXPECT_CALL(delivery_time_changed_callback, Call).WillOnce([&]() {
+    EXPECT_EQ(network.NextDeliveryTimeUs(), TimeDelta::Millis(500 + 50).us());
+  });
+  network.SetConfig({.link_capacity_kbps = 10},
+                    /*config_update_time*/ Timestamp::Millis(500));
+}
+
+TEST(SimulatedNetworkTest,
+     SetConfigUpdateNextDeliveryTimeIfLinkCapacityChangeFromZero) {
+  SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 0});
+  MockFunction<void()> delivery_time_changed_callback;
+  network.RegisterDeliveryTimeChangedCallback(
+      delivery_time_changed_callback.AsStdFunction());
+  const PacketInFlightInfo packet_1 =
+      PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/1);
+  ASSERT_TRUE(network.EnqueuePacket(packet_1));
+  EXPECT_FALSE(network.NextDeliveryTimeUs().has_value());
+
+  // The link capacity changes from 0 kbps to 10 kbps during 10ms 1/10th of the
+  // packet will be transmitted. (The packet would take 100ms to go through the
+  // network at 10kbps.)
+  ::testing::Sequence s;
+  EXPECT_CALL(delivery_time_changed_callback, Call)
+      .InSequence(s)
+      .WillOnce([&]() {
+        EXPECT_EQ(network.NextDeliveryTimeUs(),
+                  TimeDelta::Millis(500 + 100).us());
+      });
+  EXPECT_CALL(delivery_time_changed_callback, Call)
+      .InSequence(s)
+      .WillOnce(
+          [&]() { EXPECT_FALSE(network.NextDeliveryTimeUs().has_value()); });
+  EXPECT_CALL(delivery_time_changed_callback, Call)
+      .InSequence(s)
+      .WillOnce([&]() {
+        EXPECT_EQ(network.NextDeliveryTimeUs(),
+                  TimeDelta::Millis(610 + 90).us());
+      });
+  network.SetConfig({.link_capacity_kbps = 10},
+                    /*config_update_time*/ Timestamp::Millis(500));
+  network.SetConfig({.link_capacity_kbps = 0},
+                    /*config_update_time*/ Timestamp::Millis(510));
+  network.SetConfig({.link_capacity_kbps = 10},
+                    /*config_update_time*/ Timestamp::Millis(610));
+}
+
+TEST(SimulatedNetworkTest, SetConfigUpdateQueueDelayAfterDelivery) {
+  // A packet of 125 bytes that gets enqueued on a network with 1000 kbps
+  // capacity should be ready to exit the narrow section in 1 ms.
+  SimulatedNetwork network =
+      SimulatedNetwork({.queue_delay_ms = 1000, .link_capacity_kbps = 1000});
+  MockFunction<void()> delivery_time_changed_callback;
+  network.RegisterDeliveryTimeChangedCallback(
+      delivery_time_changed_callback.AsStdFunction());
+  EXPECT_CALL(delivery_time_changed_callback, Call).Times(0);
+  const PacketInFlightInfo packet_1 =
+      PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/1);
+  ASSERT_TRUE(network.EnqueuePacket(packet_1));
+  EXPECT_EQ(network.NextDeliveryTimeUs(), TimeDelta::Millis(1).us());
+  // But no packets is actually delivered. Only moved to the delay link.
+  EXPECT_TRUE(network
+                  .DequeueDeliverablePackets(
+                      /*receive_time_us=*/TimeDelta::Millis(1).us())
+                  .empty());
+  EXPECT_EQ(network.NextDeliveryTimeUs(), TimeDelta::Millis(1000 + 1).us());
+
+  // Changing the queue time does not change the next delivery time.
+  network.SetConfig({.queue_delay_ms = 1, .link_capacity_kbps = 100},
+                    /*config_update_time*/ Timestamp::Millis(500));
+  EXPECT_EQ(network.NextDeliveryTimeUs(), TimeDelta::Millis(1000 + 1).us());
+
+  // A new packet require NextDeliveryTimeUs to change since the capacity
+  // change. But does not affect the delivery time of packet_1.
+  const PacketInFlightInfo packet_2 = PacketInFlightInfo(
+      /*size=*/125, /*send_time_us=*/TimeDelta::Millis(500).us(),
+      /*packet_id=*/2);
+  ASSERT_TRUE(network.EnqueuePacket(packet_2));
+  EXPECT_EQ(network.NextDeliveryTimeUs(), TimeDelta::Millis(1000 + 1).us());
+  // At 100kbps, it will take packet 2 10ms to pass through the narrow section.
+  // Since delay is lower for packet_2, but reordering is not allowed, both
+  // packets are delivered at the same time.
+  std::vector<PacketDeliveryInfo> delivered_packets =
+      network.DequeueDeliverablePackets(
+          /*receive_time_us=*/TimeDelta::Millis(1000 + 1).us());
+  ASSERT_THAT(delivered_packets, SizeIs(2));
+  EXPECT_EQ(delivered_packets[0].receive_time_us,
+            delivered_packets[1].receive_time_us);
+}
+
+TEST(SimulatedNetworkTest, NetworkEmptyAfterLastPacketDequeued) {
+  // A packet of 125 bytes that gets enqueued on a network with 1 kbps
+  // capacity should be ready to exit the network in 1 second.
+  SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 1});
   ASSERT_TRUE(network.EnqueuePacket(PacketWithSize(125)));
 
   // Collecting all the delivered packets ...
@@ -211,21 +320,21 @@ TEST(SimulatedNetworkTest, NetworkEmptyAfterLastPacketDequeued) {
 }
 
 TEST(SimulatedNetworkTest, DequeueDeliverablePacketsOnLateCall) {
-  // A packet of 125 bytes that gets enqueued on a network with 1 kbps capacity
+  // A packet of 125 bytes that gets enqueued on a network with 1 kbps
-  // should be ready to exit the network in 1 second.
+  // capacity should be ready to exit the network in 1 second.
   SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 1});
   ASSERT_TRUE(network.EnqueuePacket(
       PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/1)));
 
-  // Enqueue another packet of 125 bytes with send time 1 second so this should
+  // Enqueue another packet of 125 bytes with send time 1 second so this
-  // exit after 2 seconds.
+  // should exit after 2 seconds.
   ASSERT_TRUE(network.EnqueuePacket(
       PacketInFlightInfo(/*size=*/125,
                          /*send_time_us=*/TimeDelta::Seconds(1).us(),
                          /*packet_id=*/2)));
 
-  // Collecting delivered packets after 3 seconds will result in the delivery of
+  // Collecting delivered packets after 3 seconds will result in the delivery
-  // both the enqueued packets.
+  // of both the enqueued packets.
   std::vector<PacketDeliveryInfo> delivered_packets =
       network.DequeueDeliverablePackets(
           /*receive_time_us=*/TimeDelta::Seconds(3).us());
@@ -234,13 +343,13 @@ TEST(SimulatedNetworkTest, DequeueDeliverablePacketsOnLateCall) {
 
 TEST(SimulatedNetworkTest,
      DequeueDeliverablePacketsOnEarlyCallReturnsNoPackets) {
-  // A packet of 125 bytes that gets enqueued on a network with 1 kbps capacity
+  // A packet of 125 bytes that gets enqueued on a network with 1 kbps
-  // should be ready to exit the network in 1 second.
+  // capacity should be ready to exit the network in 1 second.
   SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 1});
   ASSERT_TRUE(network.EnqueuePacket(PacketWithSize(125)));
 
-  // Collecting delivered packets after 0.5 seconds will result in the delivery
+  // Collecting delivered packets after 0.5 seconds will result in the
-  // of 0 packets.
+  // delivery of 0 packets.
   std::vector<PacketDeliveryInfo> delivered_packets =
       network.DequeueDeliverablePackets(
           /*receive_time_us=*/TimeDelta::Seconds(0.5).us());
@@ -251,8 +360,8 @@ TEST(SimulatedNetworkTest,
 }
 
 TEST(SimulatedNetworkTest, QueueDelayMsWithoutStandardDeviation) {
-  // A packet of 125 bytes that gets enqueued on a network with 1 kbps capacity
+  // A packet of 125 bytes that gets enqueued on a network with 1 kbps
-  // should be ready to exit the network in 1 second.
+  // capacity should be ready to exit the network in 1 second.
   SimulatedNetwork network =
       SimulatedNetwork({.queue_delay_ms = 100, .link_capacity_kbps = 1});
   ASSERT_TRUE(network.EnqueuePacket(PacketWithSize(125)));
@@ -283,8 +392,8 @@ TEST(SimulatedNetworkTest,
                         .delay_standard_deviation_ms = 90,
                         .link_capacity_kbps = 1,
                         .allow_reordering = false});
-  // A packet of 125 bytes that gets enqueued on a network with 1 kbps capacity
+  // A packet of 125 bytes that gets enqueued on a network with 1 kbps
-  // should be ready to exit the network in 1 second.
+  // capacity should be ready to exit the network in 1 second.
   ASSERT_TRUE(network.EnqueuePacket(
       PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/1)));
 
@@ -322,8 +431,8 @@ TEST(SimulatedNetworkTest, QueueDelayMsWithStandardDeviationAndReorderAllowed) {
                         .link_capacity_kbps = 1,
                         .allow_reordering = true},
                        /*random_seed=*/1);
-  // A packet of 125 bytes that gets enqueued on a network with 1 kbps capacity
+  // A packet of 125 bytes that gets enqueued on a network with 1 kbps
-  // should be ready to exit the network in 1 second.
+  // capacity should be ready to exit the network in 1 second.
   ASSERT_TRUE(network.EnqueuePacket(
       PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/1)));
 
@@ -356,7 +465,8 @@ TEST(SimulatedNetworkTest, QueueDelayMsWithStandardDeviationAndReorderAllowed) {
 
 TEST(SimulatedNetworkTest, PacketLoss) {
   // On a network with 50% probablility of packet loss ...
-  SimulatedNetwork network = SimulatedNetwork({.loss_percent = 50});
+  SimulatedNetwork network =
+      SimulatedNetwork({.loss_percent = 50}, /*random_seed =*/1);
 
   // Enqueueing 8 packets ...
   for (int i = 0; i < 8; i++) {
@@ -379,9 +489,49 @@ TEST(SimulatedNetworkTest, PacketLoss) {
   EXPECT_EQ(lost_packets, 4);
 }
 
+TEST(SimulatedNetworkTest, NextDeliveryTimeSetAfterLostPackets) {
+  // On a network with 50% probablility of packet loss ...
+  SimulatedNetwork network = SimulatedNetwork(
+      {.queue_delay_ms = 10, .link_capacity_kbps = 1000, .loss_percent = 50},
+      /*random_seed =*/1);
+  // Enqueueing 8 packets at the same time. It should take 1ms to pass through
+  // the capacity limited section per packet, it total adding 8ms delay to the
+  // last packet. Since queue delay is 10ms, multiple packets will be in the
+  // delay queue at the same time.
+  for (int i = 0; i < 8; i++) {
+    ASSERT_TRUE(network.EnqueuePacket(PacketInFlightInfo(
+        /*size=*/125, /*send_time_us=*/0, /*packet_id=*/i + 1)));
+  }
+  int64_t time_us = 0;
+  std::vector<PacketDeliveryInfo> delivered_packets;
+  // This assumes first packet is lost and last packet is delivered....
+  while (delivered_packets.size() != 8) {
+    ASSERT_TRUE(network.NextDeliveryTimeUs().has_value());
+    time_us = *network.NextDeliveryTimeUs();
+    std::vector<PacketDeliveryInfo> packets =
+        network.DequeueDeliverablePackets(time_us);
+    delivered_packets.insert(delivered_packets.end(), packets.begin(),
+                             packets.end());
+  }
+  // Results in the loss of 4 of them.
+  int lost_packets = 0;
+  int received_packets = 0;
+  for (const auto& packet : delivered_packets) {
+    if (packet.receive_time_us == PacketDeliveryInfo::kNotReceived) {
+      lost_packets++;
+    } else {
+      received_packets++;
+    }
+  }
+  EXPECT_EQ(delivered_packets.back().receive_time_us,
+            Timestamp::Millis(10 + 8).us());
+  EXPECT_EQ(lost_packets, 4);
+  EXPECT_EQ(received_packets, 4);
+}
+
 TEST(SimulatedNetworkTest, PacketLossBurst) {
-  // On a network with 50% probablility of packet loss and an average burst loss
+  // On a network with 50% probablility of packet loss and an average burst
-  // length of 100 ...
+  // loss length of 100 ...
   SimulatedNetwork network = SimulatedNetwork(
       {.loss_percent = 50, .avg_burst_loss_length = 100}, /*random_seed=*/1);
 
@@ -412,8 +562,9 @@ TEST(SimulatedNetworkTest, PacketLossBurst) {
 }
 
 TEST(SimulatedNetworkTest, PauseTransmissionUntil) {
-  // 3 packets of 125 bytes that gets enqueued on a network with 1 kbps capacity
+  // 3 packets of 125 bytes that gets enqueued on a network with 1 kbps
-  // should be ready to exit the network after 1, 2 and 3 seconds respectively.
+  // capacity should be ready to exit the network after 1, 2 and 3 seconds
+  // respectively.
   SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 1});
   ASSERT_TRUE(network.EnqueuePacket(
       PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/1)));
@@ -443,8 +594,8 @@ TEST(SimulatedNetworkTest, PauseTransmissionUntil) {
   // delivery time of the next packet which accounts for the network pause.
   EXPECT_EQ(network.NextDeliveryTimeUs(), TimeDelta::Seconds(6).us());
 
-  // And 2 seconds after the exit of the first enqueued packet, the following 2
+  // And 2 seconds after the exit of the first enqueued packet, the following
-  // packets are also delivered.
+  // 2 packets are also delivered.
   delivered_packets = network.DequeueDeliverablePackets(
       /*receive_time_us=*/TimeDelta::Seconds(7).us());
   EXPECT_EQ(delivered_packets.size(), 2ul);
@@ -453,8 +604,8 @@ TEST(SimulatedNetworkTest, PauseTransmissionUntil) {
 TEST(SimulatedNetworkTest, CongestedNetworkRespectsLinkCapacity) {
   SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 1});
   for (size_t i = 0; i < 1'000; ++i) {
-    ASSERT_TRUE(network.EnqueuePacket(
+    ASSERT_TRUE(network.EnqueuePacket(PacketInFlightInfo(
-        PacketInFlightInfo(/*size=*/125, /*send_time_us=*/0, /*packet_id=*/i)));
+        /*size=*/125, /*send_time_us=*/0, /*packet_id=*/i)));
   }
   PacketDeliveryInfo last_delivered_packet{
       PacketInFlightInfo(/*size=*/0, /*send_time_us=*/0, /*packet_id=*/0), 0};
@@ -474,10 +625,10 @@ TEST(SimulatedNetworkTest, CongestedNetworkRespectsLinkCapacity) {
 }
 
 TEST(SimulatedNetworkTest, EnqueuePacketWithSubSecondNonMonotonicBehaviour) {
-  // On multi-core systems, different threads can experience sub-millisecond non
+  // On multi-core systems, different threads can experience sub-millisecond
-  // monothonic behaviour when running on different cores. This test checks that
+  // non monothonic behaviour when running on different cores. This test
-  // when a non monotonic packet enqueue, the network continues to work and the
+  // checks that when a non monotonic packet enqueue, the network continues to
-  // out of order packet is sent anyway.
+  // work and the out of order packet is sent anyway.
   SimulatedNetwork network = SimulatedNetwork({.link_capacity_kbps = 1});
   ASSERT_TRUE(network.EnqueuePacket(PacketInFlightInfo(
       /*size=*/125, /*send_time_us=*/TimeDelta::Seconds(1).us(),

test/scenario/network_node.cc

@@ -24,7 +24,7 @@ constexpr char kDummyTransportName[] = "dummy";
 SimulatedNetwork::Config CreateSimulationConfig(
     NetworkSimulationConfig config) {
   SimulatedNetwork::Config sim_config;
-  sim_config.link_capacity_kbps = config.bandwidth.kbps_or(0);
+  sim_config.link_capacity_kbps = config.bandwidth.kbps_or(-1);
   sim_config.loss_percent = config.loss_rate * 100;
   sim_config.queue_delay_ms = config.delay.ms();
   sim_config.delay_standard_deviation_ms = config.delay_std_dev.ms();