Pion's Bandwidth Estimation Journey

This talk is the story/evolution of my understanding of Congestion Control. When I started Pion the only thing I understood was 'UDP can drop packets'. We then went through the steps of

* Implementing Feedback
* Implementing Congestion Control Algorithms
* Designing one for SFUs

Transcript

1. P I O N
2. Thank You Aaron France Adam Kiss Aleksandr Razumov Alex Browne Alex Harford AlexWoo(武杰) Antoine Baché Ato Araki Atsushi Watanabe Brendan Rius Cecylia Bocovich Chao Yuan Chris Hiszpanski Christopher Fry CloudWebRTC Daniele Sluijters Denis Gareth Hayes Guilherme Hongchao Ma Hugo Arregui Igor German Ingmar Wittkau Jadon Bennett Jake B Jason Maldonis John Bradley Justin Okamoto Konstantin Itskov Lander Noterman Lukas Herman Lukas Rezek Luke Curley Marouane Max Hawkins Michael MacDonald Michiel De Backker Mike Coleman Mészáros Mihály Oleg Kovalov Rafael Viscarra Raphael Derosso Pereira Raphael Randschau Robert Eperjesi RunningMan Ryan Gordon Sean DuBois Sebastian Waisbrot Slugalisk Stefan Tatschner Steve Suhas Gaddam Tobias Fridén Vicken Simonian Will Watson Woodrow Douglass Yutaka Takeda Zizheng Tai adwpc chenkaiC4 earle feixiao frank igolaizola imalic3 jinleileiking jose nazario mchlrhw mxmCherry notedit rob-deutsch ronan simonacca-fotokite songjiayang spaceCh1mp sylba2050 wattanakorn495 xsbchen zigazeljko Clayton McCray Hendrik Hofstadt Luke S Bao Nguyen Konstantin Chugalinskiy
3. 1 What is this talk Go programmer fi guring out real-time networking This is the evolution of my understanding If you are familiar with these topics please reach out! I still have a lot to learn
4. 2 What is WebRTC RTP (rfc1889) over ICE (rfc8445) Media packetized for UDP Datagrams Needs to be sub-second, minimal bu ff ering
5. PION PRE-BANDWIDTH ESTIMATION
6. 3 Avoiding The Problem WebRTC can mostly be implemented via RFCs - SDP, ICE, SRTP, RTP/RTCP all in IETF Bandwidth Estimation isn’t as clear IETF RMCAT exists, but didn’t fi nd a conclusion Space is still evolving/more complicated problem?
7. 4 Pion doesn’t work in X network Users are complaining sharing screenshots of broken video. At this point all I knew was ‘UDP drops packets’
8. RTP 5
9. RTCP 6
10. libwebrtc does the work 7 libwebrtc sends ‘Receiver Estimated Max Bitrate’ Pion can read that packet and act upon it Great all fi xed….
11. Only solves half the problem 8 What if Chrome is sending the video? I don’t know what numbers to send in a REMB
12. libwebrtc does all the work (again) 9 Use RTCP to send ‘Receiver Reports’ - Number of Packets Lost - Jitter (Is one way trip time smooth) If we generate Chrome adjusts as a Sender
13. It is slow 10 Pion Google Meet
14. Transport Wide Congestion Control 11
15. Transport Wide Congestion Control 12 Sender knows how long it took for each packet Users are ‘mostly’ happy
16. PION BANDWIDTH ESTIMATION
17. False Starts 13 Was told that GCC is best thing to use - Spec was out of date - SCReAM and NADA are not ‘as good’? Maybe BBR is better since it is documented/widely implemented? I have no idea what I am doing….
18. Experts get involved 14
19. Only possible because of NLNet 15
20. Built by Mathis 16 github.com/mengelbart
21. Watch his talk 17 Bandwidth Estimation from Scratch - Mathis Engelbart https://www.youtube.com/watch?v=zQsJeHUc2TQ
22. GCC State Machine 18
23. Increase/Decrease Test 19 Loss-Based - Loss < 2% Increase Bitrate - Loss > 10% Decrease Bitrate Delay-based - Delay Increasing, Delay Bitrate - Delay Decreasing, Increase Bitrate
24. Try it out! 20 We have a easy to use example - bandwidth-estimation-from-disk Code is in pion/interceptor - Needs things like fast start, but works!
25. CLIENTS VS SERVERS
26. Simulcast 21
27. Server Running GCC 3 Times? 22 Publisher 1 Publisher 2 Publisher 3 Viewer Server
28. GCC on Simulcast 23 Can’t adjust the encoder - We can add probing packets Do we run the state machine per publisher? - Large CPU overhead - Large network overhead
29. Congestion Control for Servers 24 github.com/aalekseevx
30. Packing Problem (thank you Varun) 25
31. THAT WAS A LOT!
32. 26 Pion needs you Empower those helping the internet! Gain deep WebRTC knowledge A fun challenge where you pick the goals
33. 27 webrtcforthecurious.com github.com/pion pion.ly/slack twitter.com/_pion sean@pion.ly https://www.linkedin.com/in/sean-dubois/