How Blockcast Works

Network Overview

flowchart TD
    subgraph "Content Origin"
        F1[Upstream CDN /<br>Content Origin]
    end

    subgraph "Blockcast Solution Layer"
        F1 --> F[Upstream CDN Integration]
        F --> G[Crowdsourced<br>Node Network]
        F --> H[CDN<br>Interconnection]
        F --> I[Open<br>Marketplace]
        F --> J[Automatic<br>Multicast]
    end

    subgraph "Blockcast Infrastructure"
        G --> K[Node<br>Registration]
        H --> M[Control Plane<br>Management]
        I --> N[Capacity Contracts<br>& SLA Verification]
        J --> L[Source<br>Authentication]
        K --> O[Solana<br>Blockchain]
        L --> O
        M --> O
        N --> O
    end

CDNs pool bandwidth from points of presence (PoPs) worldwide and contract out their ingress (bandwidth into an on-network ISP) and egress (bandwidth to other networks). While CDNs are distributed networks by definition, they have a single owner, so getting coverage of PoPs deeper in networks and closer to end user is challenging for the following reasons:

1. Capital costs of deploying many nodes

2. Lack of financial incentives to operate nodes for resources provided

3. Bottlenecks on ingress to fill caches where there is no fiber

4. Confidentiality of user data and node operation in untrusted environment

Blockcast enables existing and new CDNs to operate as pools, with a permissionless control plane. It incentivizes node operators to bring and deploy their own hardware and contribute their resources.

Additionally, Blockcast automatically converts unicast requests into multicast between nodes, enabling downstream PoPs to share the same ingress bandwidth resources carrying popular content. RELAY nodes work with CAST nodes to expand the coverage of multicast data services to ISPs that don't peer them.

This tree-structured delivery follows the TreeDN architecture (RFC 9706), combining Source-Specific Multicast (SSM) with AMT tunneling overlays (RFC 7450) and automatic relay discovery (RFC 8777 DRIAD) to deliver content efficiently across both multicast-enabled and unicast-only networks. For the full technical architecture, see TreeDN: Multicast Content Delivery.

This allows the services to be run over bandwidth-constrained networks, including satellite or cellular networks. With nodes that can be run anywhere, with the scalability of television broadcasts, everyone enjoys much better latency, faster download speeds, and lower data costs.

    flowchart TD
    %% Main nodes
    O[Content Origin] --> CDN
    
    subgraph CDN[Upstream Commercial CDN]
        direction LR
        MC[MultiCDN Selector]
    end
    
    subgraph CAST[Cast Group]
        direction LR
        C[Request Router <br \> Topology Monitor]
        D[Mid-Tier Cache <br \> Multicast Sender]
    end
    
    subgraph RELAY[Relay Group]
        direction LR
        R[Edge-Tier Cache<br>Multicast Retransmit]
    end
    
    subgraph RECV[Receiver Group]
        direction LR
        RCV[Personal Cache<br>Multicast Receiver]
    end
    
    %% Connections with annotations
    CDN --> |"Regional CDN Offload"| CAST
    CAST --> |"Edge Distribution"| RELAY
    RELAY --> |"Deep-Edge Distribution"| RECV
    
    %% Simple characteristics
    classDef default fill:#f9f9f9,stroke:#333,stroke-width:2px
    classDef origin fill:#f4f4f4,stroke:#666
    class O origin
    
    %% Notes for each layer
    note1[/"High Capacity<br>Global Distribution"/]
    note2[/"Topology Management<br>Delivery Proofs"/]
    note3[/"Subnet CIDR Unicast Distribution"/]
    note4[/"Self-IP Unicast Distribution"/]
    
    CDN --- note1
    CAST --- note2
    RELAY --- note3
    RECV --- note4
    
    classDef note fill:none,stroke:none
    class note1,note2,note3,note4 note

Content Delivery Flow

sequenceDiagram
    participant CP as Content Provider
    participant CDN as Upstream CDN
    participant CN as Cast Node
    participant RN as Relay Node
    participant RC as Beacon Node
    participant EU as End User

    CP->>CDN: Submit configuration
    CDN->>CN: Delegate coverage
    CN->>RN: Monitor health
    CN->>RC: Monitor health
    
    EU->>CDN: Request content
    alt If request IP matches receiver IP
        CDN->>CN: Request next host
        CN->>CDN: Delegate receiver
        CDN->>EU: Redirect receiver
        EU->>RC: Request data
        RC->>CN: Forward request (on MISS)
        note over CN,RC: === Multicast Transport ===
            alt If not joined multicast group
                RC->>RN: Subscribe to Stream
                CN->>RC: Unicast early media              
            end
            CN->>RN: Response via Multicast
            RN->>RC: Forward Multicast
            alt Multicast loss
              CN->>RC: Unicast Repairs
            end
        RC->>EU: Send response
    else If without personal Beacon but in Relay coverage
        CDN->>CN: Request next host
        CN->>CDN: Delegate relay
        CDN->>EU: Redirect relay
        EU->>RN: Request data
        RN->>CN: Forward request and get data (on MISS)
        RN->>EU: Send response
    else Not in Relay coverage area
        CDN->>EU: Traditional delivery
    end