Peer: Exchange Guide

Both clients listen for each other’s Offer and Answer messages at the relay service. Once the Deep Link is received, the Offer client proves its identity using the Liquid Extension then sends an Offer message to the Answer client. The Answer client then sends an Answer message to the Offer client.

sequenceDiagram
    participant A as Answer Client
    participant C as Liquid Service
    participant B as Offer Client
    A->>A: Present QR Code
    B->>A: Scan QR Code
    A-->>B: Receive Origin and RequestId
    B->>C: Authenticate/Register
    C->>C: Validate Signatures
    C->>C: Join Clients to Room
    C-->>B: Ok Response
    B->>C: Emit Offer to Origin
    C-->>A: Emit Offer to Client
    A->>C: Emit Answer to Origin
    C-->>B: Emit Answer to Client

ICE Candidates

The clients exchange ICE candidates to establish a connection. The ICE candidates are used to determine the best path for the data to travel between the clients. The clients exchange ICE candidates over the signaling server via WebSockets.

sequenceDiagram
    participant A as Answer Client
    participant C as Liquid Service
    participant B as Offer Client
    A->>A: Gather ICE Candidates
    A->>C: Send ICE Candidates
    C->>B: Send ICE Candidates
    B->>B: Gather ICE Candidates
    B->>C: Send ICE Candidates
    C->>A: Send ICE Candidates

Candidate Discovery

STUN and TURN servers are used as a fallback when a local connection cannot be established on the LAN. The STUN server is used to discover the client’s public IP address, while the TURN server is used to relay data if a direct connection to public IP cannot be established.

The following diagram shows the exchange of STUN/TURN candidates with a client.

sequenceDiagram
    participant A as Peer A
    participant B as STUN Service
    participant C as TURN Service
    A->>A: Get Local Candidates
    A->>B: Get STUN Candidates
    B-->>A: Send STUN Candidates
    A->>C: Get TURN Relay Candidates
    C-->>A: Send TURN Relay Candidates