WebRTC using an SFU (Selective Forwarding Unit)

This shows how you scale beyond the pure peer-to-peer model (where each participant connects to every other participant). SFUs relay streams between peers, reducing load on clients.

flowchart LR
    subgraph Client1["Client 1"]
        C1A[WebRTC API]
        C1B[App Logic]
        C1B --> C1A
    end

    subgraph Client2["Client 2"]
        C2A[WebRTC API]
        C2B[App Logic]
        C2B --> C2A
    end

    subgraph Client3["Client 3"]
        C3A[WebRTC API]
        C3B[App Logic]
        C3B --> C3A
    end

    subgraph SFU["SFU (Selective Forwarding Unit)"]
        S1[Media Router / Forwarder]
    end

    subgraph Signaling["Signaling Server"]
        Sig[Coordinate Session Setup]
    end

    subgraph STUN_TURN["STUN / TURN Servers"]
        N1[NAT Traversal / Relay if Needed]
    end

    %% Connections
    C1A <--> |"Signaling"| Sig
    C2A <--> |"Signaling"| Sig
    C3A <--> |"Signaling"| Sig

    C1A <--> |"Media / Data"| S1
    C2A <--> |"Media / Data"| S1
    C3A <--> |"Media / Data"| S1

    C1A <--> N1
    C2A <--> N1
    C3A <--> N1

    %% Styles
    style Client1 fill:#f0f9ff,stroke:#0369a1,stroke-width:2px,rounded-corners:5px
    style Client2 fill:#ede9fe,stroke:#6d28d9,stroke-width:2px,rounded-corners:5px
    style Client3 fill:#fff7ed,stroke:#c2410c,stroke-width:2px,rounded-corners:5px
    style SFU fill:#fde68a,stroke:#b45309,stroke-width:2px,rounded-corners:5px
    style Signaling fill:#fef9c3,stroke:#ca8a04,stroke-width:2px,rounded-corners:5px
    style STUN_TURN fill:#dcfce7,stroke:#15803d,stroke-width:2px,rounded-corners:5px

SFU-Based WebRTC Architecture (Scalability)

• Clients (1,2,3…) send their audio/video streams to the SFU.
• The SFU forwards each stream to the other clients, without mixing them (lightweight compared to MCU mixing).
• Signaling server is still used for session setup (e.g., exchanging SDP & ICE candidates).
• STUN/TURN servers may be needed for NAT traversal or relaying in restrictive networks.

Benefits of SFU:

• Each client uploads their media once (instead of N times in pure P2P).
• SFU handles redistribution, keeping CPU/bandwidth low for clients.
• Works well for group calls, webinars, multi-user streaming.