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Glossary

WebRTC

Also called: Web Real-Time Communication

WebRTC (Web Real-Time Communication) is an open standard, built into modern browsers and available to native apps, for sending audio, video and data between devices in real time without plugins.

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What WebRTC includes

WebRTC is two sets of standards working together: browser APIs from the W3C and network protocols from the IETF. In practice it gives you:

  • Capture: access to the camera and microphone (getUserMedia).
  • Connections: RTCPeerConnection, which handles codecs, bandwidth adaptation and network traversal through ICE, STUN and TURN servers.
  • Data channels for sending arbitrary data — chat, files, game state — over the same connection.
  • Mandatory encryption: media is encrypted with DTLS-SRTP. There is no unencrypted mode.

How a WebRTC call is set up

  1. 1

    Signaling

    The caller creates an offer describing its media (SDP) and sends it through the app's own server — often a WebSocket. WebRTC deliberately doesn't define this part.

  2. 2

    Answer

    The other device replies with an answer. Both now agree on codecs and formats.

  3. 3

    ICE

    Both sides gather candidate addresses and test pairs, preferring a direct peer-to-peer route and falling back to a TURN relay.

  4. 4

    Media flows

    A DTLS handshake sets up encryption keys, and encrypted audio and video start flowing.

Group calls: mesh, SFU and MCU

Three ways to build a group call on WebRTC
Mesh
How it works:Every participant sends their stream to every other participant
Trade-off:No media server, but upload grows with each person; suits small calls
SFU
How it works:Each person sends one stream to a server that forwards it to the others
Trade-off:Scales well; the server handles media
MCU
How it works:A server mixes all streams into one
Trade-off:Easy on devices, heavy on servers; adds delay

On Asyncbit

Asyncbit's voice and video calls are built on WebRTC, connecting directly where the network allows and relaying through TURN when it doesn't, so calls connect on mobile data and restrictive networks. You start a call from a chat, 1:1 or group, in the browser or the Android app (which supports picture-in-picture). Group calls hold up to 8 people, with video for up to 4; larger calls continue as audio. Call history and a summary line in the chat record each call.

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