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/*
* Copyright (c) 2025 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.
*/
#include "modules/congestion_controller/scream/scream_network_controller.h"
#include <algorithm>
#include <optional>
#include <utility>
#include "api/transport/network_control.h"
#include "api/transport/network_types.h"
#include "api/units/data_rate.h"
#include "api/units/time_delta.h"
#include "api/units/timestamp.h"
#include "modules/congestion_controller/scream/scream_v2.h"
#include "rtc_base/logging.h"
namespace webrtc {
static constexpr DataRate kDefaultStartRate = DataRate::KilobitsPerSec(300);
ScreamNetworkController::ScreamNetworkController(NetworkControllerConfig config)
: env_(config.env),
params_(env_.field_trials()),
default_pacing_window_(config.default_pacing_time_window),
current_pacing_window_(config.default_pacing_time_window),
scream_(std::in_place, env_),
target_rate_constraints_(config.constraints),
last_padding_interval_started_(Timestamp::Zero()) {
if (config.constraints.min_data_rate.has_value() ||
config.constraints.max_data_rate.has_value()) {
scream_->SetTargetBitrateConstraints(
config.constraints.min_data_rate.value_or(DataRate::Zero()),
config.constraints.max_data_rate.value_or(DataRate::PlusInfinity()));
}
}
NetworkControlUpdate ScreamNetworkController::OnNetworkAvailability(
NetworkAvailability msg) {
RTC_LOG(LS_INFO) << " OnNetworkAvailability network_available:"
<< msg.network_available;
if (msg.network_available) {
// TODO: bugs.webrtc.org/447037083 - rtt must currently be set on every
// update. But here it is not yet known.
return CreateUpdate(
msg.at_time,
target_rate_constraints_.starting_rate.value_or(kDefaultStartRate),
/*rtt=*/TimeDelta::Zero());
}
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnNetworkRouteChange(
NetworkRouteChange msg) {
RTC_LOG(LS_INFO) << " OnNetworkRouteChange, resetting ScreamV2.";
target_rate_constraints_ = msg.constraints;
scream_.emplace(env_);
// TODO: bugs.webrtc.org/447037083 - We should use the minimum rate from
// constraints, REMB and remote network state estimates.
scream_->SetTargetBitrateConstraints(
target_rate_constraints_.min_data_rate.value_or(DataRate::Zero()),
target_rate_constraints_.max_data_rate.value_or(
DataRate::PlusInfinity()));
// TODO: bugs.webrtc.org/447037083 - rtt must currently be set on every
// update. But here it is not yet known.
return CreateUpdate(
msg.at_time,
target_rate_constraints_.starting_rate.value_or(kDefaultStartRate),
/*rtt=*/TimeDelta::Zero());
}
NetworkControlUpdate ScreamNetworkController::OnProcessInterval(
ProcessInterval msg) {
// Scream currently has no need for periodic processing.
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnRemoteBitrateReport(
RemoteBitrateReport msg) {
// TODO: bugs.webrtc.org/447037083 - Implement;
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnRoundTripTimeUpdate(
RoundTripTimeUpdate msg) {
// Scream uses Smoothed RTT from TransportFeedback.
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnSentPacket(SentPacket msg) {
// Scream does not have to know about sent packets.
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnReceivedPacket(
ReceivedPacket msg) {
// Scream does not have to know about received packets.
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnStreamsConfig(
StreamsConfig msg) {
streams_config_ = msg;
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnTargetRateConstraints(
TargetRateConstraints msg) {
target_rate_constraints_ = msg;
// TODO: bugs.webrtc.org/447037083 - We should use the minimum rate from
// constraints, REMB and remote network state estimates.
scream_->SetTargetBitrateConstraints(
target_rate_constraints_.min_data_rate.value_or(DataRate::Zero()),
target_rate_constraints_.max_data_rate.value_or(
DataRate::PlusInfinity()));
// No need to change target rate immediately. Wait until next feedback.
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnTransportLossReport(
TransportLossReport msg) {
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnNetworkStateEstimate(
NetworkStateEstimate msg) {
// TODO: bugs.webrtc.org/447037083 - Implement;
RTC_LOG_F(LS_INFO) << "Not implemented";
return NetworkControlUpdate();
}
NetworkControlUpdate ScreamNetworkController::OnTransportPacketsFeedback(
TransportPacketsFeedback msg) {
DataRate target_rate = scream_->OnTransportPacketsFeedback(msg);
return CreateUpdate(msg.feedback_time, target_rate, msg.smoothed_rtt);
}
NetworkControlUpdate ScreamNetworkController::CreateUpdate(Timestamp now,
DataRate target_rate,
TimeDelta rtt) {
TargetTransferRate target_rate_msg;
target_rate_msg.at_time = now;
target_rate_msg.target_rate = target_rate;
target_rate_msg.network_estimate.at_time = now;
target_rate_msg.network_estimate.round_trip_time = rtt;
// TODO: bugs.webrtc.org/447037083 - bwe_period must currently be set but
// it seems like it is not used for anything sensible. Try to remove it.
target_rate_msg.network_estimate.bwe_period = TimeDelta::Millis(25);
NetworkControlUpdate update;
update.target_rate = target_rate_msg;
update.pacer_config = CreatePacerConfig(target_rate);
return update;
}
PacerConfig ScreamNetworkController::CreatePacerConfig(DataRate target_rate) {
constexpr double kPacingRateFactor = 1.5;
// Time window used for calculating pacing window if target rate is
// constrained by CE markings.
constexpr TimeDelta kReducedPacingWindow = TimeDelta::Millis(10);
// Threshold used for guessing if target rate is constrained due to CE
// marking.
constexpr double kL4sAlphaThreshold = 0.01;
DataRate max_needed_rate =
streams_config_.max_total_allocated_bitrate.value_or(DataRate::Zero());
DataRate padding_rate = DataRate::Zero();
Timestamp now = env_.clock().CurrentTime();
if (target_rate < max_needed_rate * kPacingRateFactor &&
target_rate < target_rate_constraints_.max_data_rate.value_or(
DataRate::PlusInfinity())) {
// Periodically allow padding to be used to reach a target rate close to
// kPacingRateFactor*max_needed_rate.
if (params_.periodic_padding_interval->IsFinite() &&
(now - last_padding_interval_started_ >
params_.periodic_padding_interval.Get())) {
last_padding_interval_started_ = now;
}
if (now - last_padding_interval_started_ <
params_.periodic_padding_duration.Get()) {
padding_rate = target_rate;
}
}
if (current_pacing_window_ == default_pacing_window_ &&
target_rate < max_needed_rate &&
scream_->l4s_alpha() > kL4sAlphaThreshold) {
// Do stricter pacing if target rate is lower than what is needed and it
// seems like L4S is enabled. Note that once stricter pacing is enabled, it
// is not stopped.
current_pacing_window_ =
std::min(default_pacing_window_, kReducedPacingWindow);
}
return PacerConfig::Create(now, target_rate * kPacingRateFactor, padding_rate,
current_pacing_window_);
}
} // namespace webrtc