commit 6dcdf10c76d68459758a6503d9874d76ed1473e5
author gnish <gnish@webrtc.org> Mon Jun 05 13:01:26 2017
committer Commit Bot <commit-bot@chromium.org> Mon Jun 05 13:01:26 2017
tree 53fe1b7c4c93922c16aa0f727f126f6f735064b7
parent 59ee91b68a44104b9aec7b34ac67a215bbf84f85

This is an initial cl, which contains small amount of implemented functions, and large amount of unimplemented ones.

Code should implement BBR which is the congestion controlling algorithm. BBR tries to estimate two values bottle-neck bandwidth(bw) and round trip time(rtt),then use these two values to set two control parameters pacing rate(pacing_rate),the rate at which data should be sent and congestion window size (cwnd), cwnd is the upper bound for data in flight,data_in_flight <= cwnd at all time.
BBR has four modes:
1)Startup-ramping up throughput discovering estimated bw.
2)Drain-after Startup decrease throughput to drain queues.
3)Probe Bandwidth-most of the time BBR should be in this mode,
sending data at the rate of estimated bw, while sometimes trying to discover new bandwidth.
4)Probe Rtt-in this mode BBR tries to discover new rtt for the connection.

The key moment in BBR is when we receive feedback from the receiver,as this is the only moment which should effect our two estimators. At this moment all the switches between modes should happen, except switch to ProbeRtt mode (switching to ProbeRtt mode should happen when current min_rtt value expires).

This cl serves to emphasize the structure of Bbr, when switches happen and what key classes/functions should be implemented for proper functionality.

BUG=webrtc:7713
NOTRY=True

Review-Url: https://codereview.webrtc.org/2904183002
Cr-Commit-Position: refs/heads/master@{#18444}