1.
1
My Perspective
Pion WebRTC (Go implementation)
- Wrote it with servers in mind
- Introduced to the other use cases by contributors
- WebTorrent, Snowflake, IPFS, self-hosted conference.
WebRTC for the Curious
- People don’t really know how WebRTC works!
- Hard to build/debug your cool idea….

2.
WHAT IS WEBRTC?

3.
2
API and a Protocol
API defined by the W3C
- Only available in the browser
Protocol defined by the IETF
- C
- C++
- Python
- Go
- Typescript
- GStreamer
- Erlang (not public)
- Java (not public)

4.
3
WebRTC the Protocol
Multiple Audio/Video Tracks
- Add or Remove them at anytime
Binary Data
- Can be lossy
- Can be unordered
- Multiple distinct DataChannels
Security is Mandatory

5.
4
WebRTC the Protocol
Userland Connectivity Establishment
- UDP or TCP
- You can choose the route
- You can switch at anytime
- P2P or Client/Server
Userland Congestion Control
- Do you prefer latency or loss?
- Sender or receiver can pick bitrate

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Bundle of Protocols
Session Description Protocol (RFC 2327
ICE (RFC 8445)
- STUN (RFC 5389)
- TURN (RFC 5776)
DTLS (RFC 6347)
RTP/RTCP (RFC 1889)
SCTP (RFC 2960)

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WebRTC in Four Steps
Signaling ->
Connecting ->
Securing ->
Communicating

8.
SIGNALING

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7
Minimum Details to start Call
Global state
- ICE Auth and Candidates
- DTLS Role and Fingerprint
Media Sections
- Offer/Answer model
- How many tracks you want to send and receive
- Protocol makes no restriction around codecs

10.
CONNECTING

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Two Roles
- Controlling
- Controlled
Both Sides Have Auth
Both Sides Have Candidates
- Which then create candidate pairs

12.
What is the best pair?
9
Do you take the first connected pair?
Do you wait for the best pair?
What should we measure?
- Round Trip Time
- Packet Loss
- Bandwidth Costs

13.
Stay connected on the move
10
New candidates as you move (Wifi/LTE)
Nominating new candidate pair
Needs to be cheap

14.
SECURING

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11
DTLS Handshake
- Sent over ICE
- Keys extracted to encrypt RTP
Self-signed certs verified via hash
Requires you to trust your signaling

16.
MEDIA COMMUNICATION

17.
Video Basics
12
Constraints
- Bandwidth
- Hardware
- Network (MTU, Loss, Jitter)
- Decoders (Hardware vs Software)
Solutions
- Keyframe Interval
- Coding Complexity
- Bitrate

18.
Not so basic…

19.
RTP
13

20.
Common RTP Problems
14
Jitter
- Add Delay/Re-order
Latency
- Move ahead when possible
Packet Loss
- NACK
- PLI
- FEC

21.
RTP Trade-offs
15
Latency vs quality
Does one track matter more?
Spend bandwidth on FEC?

22.
Receiver Driven Congestion Control
16
Receiver tells sender requested bitrate (REMB)
Really simple, but all state exists on one side.

23.
Sender Driven Congestion Control
17
Receiver sends reception status (TWCC)
Sender then chooses bitrate
Sender is aware of Jitter, PacketLoss and
much more. You can play with algorithm
more.

24.
https://datatracker.ietf.org/wg/rmcat/documents/

25.
DATA COMMUNICATION

26.
DataChannel Basics
18
Multiple Streams
Each have distinct behavior
- ordered
- maxPacketLifetime
- maxRetransmits
Datagram Based

27.
All about Chunks
19
DATA
- Transmission Sequence Number
- Stream Identifier
- Stream Sequence Number
SACK
- What is the last TSN I saw?

28.
Don’t wait on lost data
20
Don’t worry when you lose one part
- Sender skips the TSN ahead
Don’t block on old data
- Why do we care about what happened in the past?

29.
SOLVE UNIQUE PROBLEMS

30.
Problem: Connect two users with no Public IP
21

31.
Solution: NAT Traversal
22

32.
Solution: NAT Traversal
23

33.
Problem: Wi-Fi on Fire
24

34.
Solution: ICE Renomination
25

35.
Problem: What bitrate do I upload?
26

36.
Problem: What bitrate do I upload?
27

37.
Solution: Congestion Control
28

38.
Problem: connect without knowing IP?
29

39.
Solution: mDNS Candidates
30

40.
Problem: Don’t block on the past
1331

41.
Solution: SCTP
1332

42.
WEBRTC IN ACTION

43.
ns-remote
https://github.com/mzyy94/ns-remote
33

44.
CloudRetro.io
34

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Neko
github.com/nurdism/neko

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TelloGo
https://github.com/Ragnar-H/TelloGo

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37
ascii
https://github.com/dialup-inc/ascii

48.
Strive CDN
38

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Protocol Bridge

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40
ssh-p2p
github.com/nobonobo/ssh-p2p

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41
RTCTunnel
github.com/rtctunnel

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42
Snowflake
snowflake.torproject.org

53.
webwormhole.io
43

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Ion
github.com/pion/ion