Add AlrDetector

webrtc/modules/pacing/alr_detector.cc

+/*
+ *  Copyright (c) 2016 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 "webrtc/modules/pacing/alr_detector.h"
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+
+namespace {
+
+// Time period over which outgoing traffic is measured and considered a single
+// data point.
+constexpr int kMeasurementPeriodMs = 100;
+
+// Minimum number of consecutive measurements over |kMeasurementPeriodMs| time
+// that indicate sending rate is below |kUsagePercent| to consider being
+// application limited.
+constexpr int kApplicationLimitedThreshold = 5;
+
+// Sent traffic percentage as a function of network capaicty to consider traffic
+// as application limited.
+// NOTE: This is intentionally conservative at the moment until BW adjustments
+// of application limited region is fine tuned.
+constexpr int kUsagePercent = 30;
+
+}  // namespace
+
+namespace webrtc {
+
+AlrDetector::AlrDetector()
+    : total_bytes_sent_(0),

[philipel, 2016/09/15 15:00:20]

I think |total_bytes_sent_| is not really correct, something like 
|measurement_interval_bytes_sent_| maybe?

Same for |total_elapsed_time_ms_|

WDYT?

[Irfan, 2016/09/19 06:51:13]

Done.

+      total_elapsed_time_ms_(0),
+      estimated_bitrate_bps_(0),
+      application_limited_count_(0) {}
+
+AlrDetector::~AlrDetector() {}
+
+void AlrDetector::ReportElapsedTime(int64_t delta_time_ms) {
+  RTC_DCHECK(delta_time_ms);

[philipel, 2016/09/15 15:00:20]

RTC_DCHECK_GT(delta_time_ms, 0);

[Irfan, 2016/09/19 06:51:13]

Done.

+  if (total_elapsed_time_ms_ > kMeasurementPeriodMs) {
+    RTC_DCHECK(estimated_bitrate_bps_);
+    int max_bytes =
+        (total_elapsed_time_ms_ * estimated_bitrate_bps_) / (8 * 1000);
+    int utilization = (total_bytes_sent_ * 100) / max_bytes;
+    if (utilization < kUsagePercent) {
+      application_limited_count_++;
+      if (application_limited_count_ == kApplicationLimitedThreshold)
+        LOG(LS_INFO) << "ALR start";
+    } else {
+      if (application_limited_count_ >= kApplicationLimitedThreshold)
+        LOG(LS_INFO) << "ALR stop";
+      application_limited_count_ = 0;
+    }
+    total_elapsed_time_ms_ = delta_time_ms;
+    total_bytes_sent_ = 0;
+  }
+  total_elapsed_time_ms_ += delta_time_ms;
+}
+
+void AlrDetector::ReportBytesSent(size_t bytes) {
+  RTC_DCHECK(bytes);
+  RTC_DCHECK(estimated_bitrate_bps_);
+  total_bytes_sent_ += bytes;

[philipel, 2016/09/15 15:00:20]

I think we should combine ReportBytesSent and ReportElapsedTime so that every
time we report that more bits have been sent we also calculate the accumulated
possible bits sent and then use that value to calculate the utilization.

[Irfan, 2016/09/19 06:51:13]

Done.

+}
+
+void AlrDetector::SetEstimatedBitrate(int bitrate_bps) {
+  RTC_DCHECK(bitrate_bps);
+  estimated_bitrate_bps_ = bitrate_bps;
+}
+
+bool AlrDetector::InApplicationLimitedRegion() {
+  return application_limited_count_ >= kApplicationLimitedThreshold;
+}
+
+}  // namespace webrtc