# Raw RPC Format (legacy)

> Wire-level reference for the legacy voice-RPC envelope. New code uses MoQT.

> **NOTE:**
> **This section documents the legacy voice-RPC wire format.** It's kept for
> reference and backwards compatibility — new code should use the
> [modality clients](/modalities/overview) over MoQT instead. The Voice
> modality (`clutchcall.voice`, `@@clutchcall/sdk/voice`, etc.) replaces
> every `method_id` RPC documented here with a typed surface that runs over
> the same MoQT relay mesh as streams, robotics, games, and data.
> 
> See [Architecture](/concepts/architecture) for how the legacy envelope and
> MoQT coexist today.

The ClutchCall gateway's original control plane was a binary RPC protocol
over QUIC. The legacy SDK surface (`ClutchCallClient.dial`, `hangup`,
`barge`, `push_audio`, …) wraps it; nothing is hidden. If you have a QUIC
client and a serializer for little-endian primitives, you can talk to the
gateway directly.

## Read these in order

  1. **Envelope Format**
Byte layout of a single RPC frame on the wire — length prefix, method id,
    serde envelope body, field encoding. [→ Envelope Format](/rpc/envelope-format)
  2. **Method IDs**
The full table of `method_id` constants and their request/response DTOs.
    [→ Method IDs](/rpc/method-ids)
  3. **Types**
Field-level breakdown of every DTO (`OriginateRequest`, `CallEvent`, etc).
    [→ Types](/rpc/types)
  4. **Audio Frames**
How outbound and inbound `AudioFrame` envelopes are framed on uni-streams.
    [→ Audio Frames](/rpc/audio-frames)
  5. **Events**
Server-pushed `CallEvent` semantics, ordering, and reconnect behaviour.
    [→ Events](/rpc/events)

## Endpoint

```
quic://engine.clutchcall.dev:9090   (ALPN: h3)
```

In the browser, the same gateway is reachable via WebTransport:

```
https://engine.clutchcall.dev:9090
```

## Stream model

Connection setup uses one bidirectional stream for the initial JWT
handshake (the SDK does this for you). After that:

| Stream type   | Direction       | Carries                               |
| ------------- | --------------- | ------------------------------------- |
| Bidirectional | client → server | A single RPC envelope; close-on-write |
| Unidirectional | client → server | `AudioFrame` stream (mic → trunk)     |
| Unidirectional | server → client | `CallEvent` and `AudioFrame` (trunk → app) |

Every frame, regardless of stream, follows the [envelope format](/rpc/envelope-format).

## Versioning

Each serde envelope carries a 1-byte `version` and a 1-byte `compat_version`.
The gateway accepts envelopes whose `compat_version ≤ server_current_version`.
Adding fields is backwards-compatible; removing or reordering them is not —
do that with a new method id, not a version bump.