> ## Documentation Index
> Fetch the complete documentation index at: https://docs.decdn.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Architecture

> The node, client, and origin-backend roles, plus the full path of a paid delivery — discovery, selection, channel open, streamed bytes, vouchers.

## System diagram

```mermaid theme={null}
graph TD
    subgraph Nodes
        N1["Node (cached)"]
        N2["Node (origin-backed)"]
        N3["Node (cached)"]
    end

    subgraph Clients
        C1[Client]
        C2[Client]
        C3[Client]
    end

    subgraph "Provider Infrastructure (external)"
        S3[("Hidden Origin Backend<br/>S3 / R2 / B2")]
    end

    N1 <-->|"paid delivery"| N2
    N2 <-->|"paid delivery"| N3
    N1 <-->|"paid delivery"| N3

    C1 -->|"paid delivery"| N1
    C2 -->|"paid delivery"| N2
    C3 -->|"paid delivery"| N3

    N2 -.->|opaque fetch| S3

    N1 <-.->|"gossip"| N2
    N2 <-.->|"gossip"| N3
```

## Participant roles

| Role                     | Operated by                                      | Participates in CDN?                                      |
| ------------------------ | ------------------------------------------------ | --------------------------------------------------------- |
| **Node (pure cache)**    | Independent node operator                        | Yes — bonds, gossips, probes, delivers                    |
| **Node (origin-backed)** | Content provider *or* node operator with storage | Yes — same protocol, plus a DAO-recognized origin backend |
| **Client**               | End-user or application                          | Pays for bytes; subscribes to gossip but does not publish |

See [Participants](/overview/participants) for a deeper breakdown per role.

## Life of a paid delivery

1. **Client bootstrap** — client generates a keypair, queries the on-chain registry, seeds a peer table, and subscribes to regional + global gossip topics.
2. **Discovery** — client probes its known peers for a blob hash. On miss, any peer performs a DHT lookup to locate holders.
3. **Selection** — returned candidates are scored by price, latency, and reputation; lowest cost wins.
4. **Payment channel open** — client opens a USDC payment channel with the selected node on-chain ([payments](/protocol/payments)).
5. **Streaming + vouchers** — node streams to the client; client signs off-chain vouchers as bytes flow.
6. **Cache-miss fan-out** — if the node doesn't have the blob, it pulls from another peer (paid). Every byte delivered in the network is paid.
7. **Channel close** — either party initiates settlement on-chain, with a dispute window for stale closes.

## Key invariants

* No external origin URL exists — content enters the network through origin-backed nodes whose backends are hidden.
* A node cannot earn without delivering verifiable bytes — hash mismatch voids payment.
* A node cannot join the mesh without bonding — registration enforces a capacity bond (`bond = k × Mbps^α`) scaled to declared bandwidth, rather than a flat minimum.
* A node cannot register an identity it does not control — both keys must sign at registration.
* Safety bounds on all governable parameters are hardcoded — governance cannot set fees to 100% or push the operator revenue share below its floor.
* Being recognized as an origin is DAO-governed — configuring an origin backend locally without authorization means the node's bytes are served only as cache.
* A node cannot serve a blacklisted hash after the compliance window — doing so is slashable.

## Non-goals

* DRM or content protection
* Content transcoding or adaptive format conversion
* Search, discovery, or recommendation
* Mobile or web clients
* Erasure coding — full replication only