---
title: "External Relay"
slug: "dataflow-nodes-external-relay"
updated: 2025-04-30T09:58:18Z
published: 2025-04-30T09:58:18Z
---

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

# External Relay

Entry point of events that are sent by external sources.

In a typical use case, a client starts an operation with Data Flow and any event it sends enter the project through the Entry node. In some use cases (eg. Voice Biometrics), you may want to send some extra information to an existing Data Flow session from an another service.

Data Flow provides a way to send events to existing sessions through its http API. These events enter the project through External Relay. Note that there can be at most one External node in a project.

## Parameters

none

## Inputs

### Audio

None

### Events

All

## Outputs

### Audio

None

### Events

All

## Remarks

Data Flow provides `sessions` http endpoint for sending events to existing sessions. The user must send a POST request to this endpoint. A header with name `SessionId` should contain the id of the session that the contents of this request will be delivered to.

`Content-Type` should be `application/json` and http message content should contain an event. eg.

```
 {
    "Event":
    {
        "StartMsec": 0,
        "EndMsec": 0,
        "Channel": "0",
        "Name": "GreatEvent",
        "Data":
        {
            "ImportantInfo": "whatever",
            "SomeOtherInfo": 9
        },
        "GroupId": "rher456"
    }
}
```

### Retrieving Session Id

#### From Websocket Response

In order to send events to External Node one needs a SessionId. Session Id is provided to the client in the StartResponse message, so the client may share Session Id with a useful external service.

#### From Custom nodes

Custom nodes can access Session Id by using `SessionInfo.id()`.

### Project Structure

External Relay can be used just like the [Entry](/v1/docs/dataflow-nodes-entry) node. However, it can only be used for raising `Event`'s. Which means it can be used as a substitute for almost any node. In the case below, it is used for raising `Language Change` events during runtime.

<center data-tomark-pass="">
<p><img src="https://cdn.document360.io/9bca2910-6a3b-4224-9470-43f91f9a6d57/Images/Documentation/image%28882%29.png" alt="image.png"></p>
</center>

In the example below, External Relay is used to transmit `VBStreamState` event to [VB Realtime](/v1/docs/dataflow-nodes-vb-realtime). This is a prerequisite for VB Realtime to work.

<center data-tomark-pass="">
<p><img src="https://cdn.document360.io/9bca2910-6a3b-4224-9470-43f91f9a6d57/Images/Documentation/image%28883%29.png" alt="image.png"></p>
</center>

### Supported flow types

Stream, Batch

## Release Notes

        

****v3.5.0****

            
            

- Now supports "Update" message as well.

    
    

****v3.1.0****

        
        

- Now supports multi-channel output.

    
    

****v3.0.0****

        
        

- Introduced node.