***

title: Overview
subtitle: Ultravox in VoxEngine
-------------------------------

## Benefits

Voximplant includes a native Ultravox connector so you can bridge live phone calls to Ultravox’s WebSocket API with minimal setup.

<Info title="Note">
  Ultravox also has a direct SIP integration with Voximplant, which makes it easy to bring PSTN/SIP calls into Ultravox from Voximplant’s telephony stack.
  See the Voximplant announcement and Ultravox SIP docs for details:
  [https://voximplant.com/blog/ultravox-adds-sip-to-its-voice-ai-services-using-voximplant](https://voximplant.com/blog/ultravox-adds-sip-to-its-voice-ai-services-using-voximplant)
</Info>

## Architecture

A VoxEngine scenario answers or places a call, creates an Ultravox WebSocket session, and bridges audio both ways via `VoxEngine.sendMediaBetween`.

```mermaid
%%{init: { "flowchart": { "nodeSpacing": 60, "rankSpacing": 80 }, "themeVariables": { "fontSize": "16px" } }}%%
graph LR
  Caller[PSTN/SIP/WhatsApp/WebRTC] <-->|Media & call control| VoxEngine[VoxEngine Scenario]
  VoxEngine <-->|WebSocket: Config, Audio & Events| Ultravox[Ultravox WebSocket API]
```

## Development notes

* **Native VoxEngine module**: load with `require(Modules.Ultravox)` and create a `Ultravox.WebSocketAPIClient` via `Ultravox.createWebSocketAPIClient(...)`.
* **Session setup**: choose `Ultravox.HTTPEndpoint.CREATE_CALL` (or `CREATE_AGENT_CALL`) and provide `authorizations` (for example `X-API-Key`) plus a request `body` with `systemPrompt`, `model`, and `voice`.
* **Audio bridge**: connect the call and Ultravox using `VoxEngine.sendMediaBetween(call, voiceAIClient)`.
* **Transcripts**: `Ultravox.WebSocketAPIEvents.Transcript` contains `role` plus `text`/`delta` fields; use it for logging and barge‑in logic.
* **Tool invocations**: handle `Ultravox.WebSocketAPIEvents.ClientToolInvocation` and respond with `voiceAIClient.clientToolResult(...)`.
* **Barge‑in**: call `voiceAIClient.clearMediaBuffer()` when you detect user speech or when the server requests buffer clearing.

## Examples

* [Example: Answering an incoming call](ultravox-voice-ai-example-answering-incoming-call)
* [Example: Placing an outbound call](ultravox-voice-ai-example-placing-outbound-call)
* [Example: Function calling](ultravox-voice-ai-example-function-calling)

## Links

### Voximplant

* Ultravox SIP integration announcement: [https://voximplant.com/blog/ultravox-adds-sip-to-its-voice-ai-services-using-voximplant](https://voximplant.com/blog/ultravox-adds-sip-to-its-voice-ai-services-using-voximplant)
* Voice AI product overview: [https://voximplant.ai/](https://voximplant.ai/)

### Ultravox

* Voximplant integration guide: [https://docs.ultravox.ai/integrations/voximplant](https://docs.ultravox.ai/integrations/voximplant)
* SIP integration: [https://docs.ultravox.ai/telephony/sip](https://docs.ultravox.ai/telephony/sip)
* Data messages reference (transcripts, tool invocation, etc.): [https://docs.ultravox.ai/apps/datamessages](https://docs.ultravox.ai/apps/datamessages)