Design video conferencing signalling like Zoom
PremiumReal-timeMedium
- WebRTC signalling
- SFU
- ICE STUN TURN
Quick answer
This real-time interview question asks you to design video conferencing signalling like Zoom. Aim for a design that delivers updates to many users with low delay, then explain connections, fan-out, ordering and trade-offs. Interviewers want to see how you keep latency low, handle reconnects and stay correct under load.
The problem
Design the signalling system for a video conferencing app like Zoom or Google Meet. Signalling is everything except the media bytes: joining meetings, negotiating WebRTC media with SFUs, keeping the roster (muted, hand raised, sharing, speaking) in sync and recovering dropped connections, for meetings of up to 1,000 people.
The media itself flows through media servers (SFUs) that forward audio and video streams; you must decide how signalling tells clients and SFUs about each other.
What must the system do?
- Create and join: A host creates a meeting; participants join with a link, wait in a lobby if required, and are admitted by the host.
- Media negotiation: On join, the client and the SFU exchange the descriptions and network candidates needed to set up media; later, new streams (camera on, screen share) are negotiated without rejoining.
How well must it do it?
- Join time: From clicking the link to seeing and hearing others in under 3 seconds on a good network.
- Latency: Control events (mute, hand raise) reach all participants within 500 ms.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- WebRTC signalling
- SFU
- ICE STUN TURN
- Session state
- WebSocket
- Reconnect resume
How you’ll practise
- Requirements
- Estimate
- Connections
- Message flow
- Delivery guarantees
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any real-time design round.
- Clarifies latency, ordering and delivery guarantees
- Chooses a connection model with reasons
- Explains fan-out to many receivers
- Handles reconnects, missed messages and duplicates
- Plans for hot spots and sudden traffic spikes
- States trade-offs between consistency and speed
Questions people ask about this interview question
- Which design type is this question?
- It is a real-time question. You design video conferencing signalling like Zoom and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Medium. Entry-level engineers can practise it, but it expects you to reason about requirements and trade-offs, not only list components.
- What should I cover first?
- Start with who sends and receives updates, how fast they must arrive and what order matters. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team