# Join multiple channels (/en/realtime-media/broadcast-streaming/build/connect-across-channels/join-multiple-channels/react-native)

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Agora Video SDK enables you to simultaneously join multiple channels. This capability allows you to receive and publish audio and video streams across multiple channels concurrently.

      
  
      
  
      
  
      
  
      
  
      
    ## Understand the tech [#understand-the-tech-5]

    Video SDK's multi-channel functionality is based on two key components:

    * `RtcConnection`

      The `RtcConnection` object identifies a connection. It contains the following information:

      * Channel name
      * User ID of the local user

      You create multiple `RtcConnection` objects, each with a different channel name and user ID. Each `RtcConnection` instance can independently publish multiple audio streams and a single video stream.

    * `IRtcEngineEx`

      The class contains methods tailored for interacting with a designated `RtcConnection` object.

      To join multiple channels, you call `joinChannelEx` method in the `IRtcEngineEx` class multiple times, using a different `RtcConnection` instance each time.

    When joining multiple channels:

    * Ensure that the user ID for each `RtcConnection` object is unique and nonzero.

    * Configure publishing and subscribing options for the `RtcConnection` object in `joinChannelEx`.

    * Use the `connection` parameter in each callback to identify the corresponding channel.

    ## Prerequisites [#prerequisites-5]

    Ensure that you have implemented the [SDK quickstart](../../index) in your project.

    ## Implementation [#implementation-5]

    This section explains how to join a second channel as a host after you have already joined the first channel.

    1. Join the second channel

    Call `joinChannelEx` to join a secondary channel by specifying the `RtcConnection` object and using a random user ID.

    ```javascript
    let token2 = "token2";
    const channelId2 = "channel2";
    let uid2 = 321;

    // Join multiple channels
    rtcEngine.joinChannelEx(
      token2,
      // RtcConnection
      {
        channelId: channelId2,
        localUid: uid2,
      },
      // ChannelMediaOptions
      {
        clientRoleType: ClientRoleType.ClientRoleBroadcaster,
        publishMicrophoneTrack: false,
        publishCameraTrack: false,
        autoSubscribeAudio: false,
        autoSubscribeVideo: false,
        publishSecondaryCameraTrack: true,
      }
    );
    ```

    2. Set up remote user video

    Listen to the `onUserJoined` callback and set the remote video.

    ```tsx
    // Register callback for when a remote user joins the current channel
    agoraEngine.registerEventHandler(
      {
        onUserJoined: (_connection: RtcConnection, uid: number) => {
          showMessage("remote user " + uid + " added");
          setRemoteUid(uid);
        },
      }
    );

    // Creating a Remote View Using RtcSurfaceView
    <RtcSurfaceView
      canvas={
        {
          uid: remoteUid,
          sourceType: VideoSourceType.VideoSourceRemote,
        }
      }
      style={styles.videoView}
    />;
    ```

    ## Reference [#reference-5]

    This section contains content that completes the information on this page, or points you to documentation that explains other aspects to this product.

    ### Sample project [#sample-project-5]

    Agora provides the [JoinMultipleChannel](https://github.com/AgoraIO-Extensions/react-native-agora/blob/main/example/src/examples/advanced/JoinMultipleChannel/JoinMultipleChannel.tsx) open-source sample project for your reference. Download the project or view the source code for a more detailed example.

    ### API reference [#api-reference-5]

    * [`IRtcEngineEx`](https://api-ref.agora.io/en/video-sdk/react-native/4.x/API/class_irtcengineex.html#class_irtcengineex)
    * [`RtcConnection`](https://api-ref.agora.io/en/video-sdk/react-native/4.x/API/class_rtcconnection.html)
    * [`joinChannelEx`](https://api-ref.agora.io/en/video-sdk/react-native/4.x/API/class_irtcengineex.html#api_irtcengineex_joinchannelex)
    * [`onUserJoined`](https://api-ref.agora.io/en/video-sdk/react-native/4.x/API/class_irtcengineeventhandler.html#callback_irtcengineeventhandler_onuserjoined)