1780620 - Research why we calculate negative feedback_rtt in GoogCcNetworkController::OnTransportPacketsFeedback

Status: NEW

(Core :: WebRTC, task)

Description

[Michael Froman [:mjf]]

Currently, we're calculating feedback_rtt in GoogCcNetworkController::OnTransportPacketsFeedback:

    TimeDelta feedback_rtt =
        report.feedback_time - feedback.sent_packet.send_time;

This number can be negative (and probably shouldn't be allowed). A negative number causes an assert in GoogCcNetworkController::UpdateCongestionWindowSize here:

  DataSize data_window = last_loss_based_target_rate_ * time_window;

We currently don't call UpdateCongestionWindowSize because we have no QueueSize set in the field trial string. Prior to the fast-forward work, there was no default congestion window trial string, so we also never called UpdateCongestionWindowSize.