WebRTC Topology: SFU vs MCU vs P2P

Most teams discover WebRTC through a simple peer-to-peer demo—and then hit a wall the moment real users, real networks, and real scale arrive. The hidden lever is your media topology: P2P, SFU, or MCU. Pick the wrong one and you’ll fight jitter, ballooning CPU bills, or fragile group calls. Pick the right one and you’ll deliver crisp audio/video with predictable costs.

What these terms actually mean

• P2P (peer-to-peer): Each participant sends media to everyone else. Lowest server cost, but uplink bandwidth and device CPU become the bottleneck beyond very small groups.
• SFU (Selective Forwarding Unit): A server forwards media without mixing. Each sender uploads once; the SFU routes/downs the streams to others. Great for multi-party calls with moderate server cost. See how SFUs work in this practical deep dive on webrtcHacks.
• MCU (Multipoint Control Unit): A server mixes multiple streams into one composite. Clients receive a single stream, which helps low-power devices, but server CPU/GPU costs soar.

When to use which

• Two people, tight budget, low complexity → P2P.
• 3–12 people, interactive meetings/classrooms → SFU.
• Large webinars, strict device constraints, recordings with fixed layouts → MCU (or SFU with server-side composition only when needed).

If you’re building a business app, SFU is the default for most real-time use cases because it balances quality, scalability, and cost.

Real-world considerations (and trade-offs)

• Latency: SFUs avoid the mixing delay of MCUs and usually deliver the snappiest interaction.
• Bandwidth: P2P can explode uplink (N-1 uploads). SFU keeps uplink to one copy per sender.
• Server cost: P2P ≈ lowest, SFU ≈ routing/transcoding edges, MCU ≈ highest.
• Recording & compliance: SFU supports server-side recording pipelines; MCU gives “what you see is what you get” composites.
• Network edge cases: Mobile clients on flaky networks benefit from simulcast/SVC and adaptive bitrate—features well supported in mature SFU stacks.

Open technologies to explore

• Jitsi Videobridge (SFU): Long-running, battle-tested project powering many open systems. Explore its architecture here: jitsi.org/jitsi-videobridge.
• mediasoup (SFU): Node/C++ SFU with fine-grained control over RTP, simulcast, and SVC; popular with custom apps. Docs: mediasoup.org.
• LiveKit (SFU): Cloud-friendly SFU with SDKs and server components for fast prototyping to production. Start here: livekit.io.
• Pion WebRTC (library): A Go implementation for those building bespoke media back-ends. Project page: pion.ly/webrtc.
• WebRTC for the Curious (book): A free, implementation-focused guide to the protocols that make WebRTC tick: webrtcforthecurious.com.

A quick decision guide for product teams

1. Target audience size?
   • 2 people → P2P; 3–12 → SFU; Hundreds → SFU + CDN or MCU for broadcast layout.
2. Devices and networks?
   • Low-power/low-bandwidth clients → prefer SFU with aggressive downscaling; MCU only if composite is mandatory.
3. Costs & compliance?
   • Need recordings, moderation, or “director” control? Favour SFU with server-side pipelines (or MCU when composites are a hard requirement).
4. Roadmap risk:
   • Start SFU; add optional server-side composition for webinars. This avoids locking into costly MCU paths too early.

The bottom line

There’s no one-size-fits-all topology. P2P is perfect for minimal pairs, SFU covers the vast middle (meetings, classrooms, support rooms), and MCU wins when a composed stream is non-negotiable. Get the topology right and everything else—quality, cost, and user satisfaction—falls into place.

---

For more articles like this visit SoftpageCMS.