# Stream channels (/en/realtime-media/rtm/build/work-with-channels/stream-channel/windows)

> For AI agents: see the complete documentation index at [llms.txt](/llms.txt).

Stream channels are based on the room model. In Signaling, communication through stream channels requires use of specific APIs. This page shows you how to join, leave, and send messages in stream channels.

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

    To use stream channels, you first create a stream channel object instance. The channel instance gives you access to all stream channel management methods. Use the stream channel instance to:

    * Join and leave a channel
    * Join and leave topics
    * Subscribe to and unsubscribe from topics
    * Send messages
    * Destroy the channel instance

    After joining a stream channel, you listen to event notifications in the channel. To send and receive messages in the channel, you use [topics](topics). Signaling allows thousands of stream channels to exist simultaneously in your app. However, due to client-side performance and bandwidth limitations, a single client may only join a limited number of channels concurrently. For details, see [API usage restrictions](../../reference/limitations).

    ## Prerequisites [#prerequisites-5]

    Ensure that you have:

    * Integrated the Signaling SDK in your project, and implemented the framework functionality from the [SDK quickstart](../../quickstart) page.

    * Activated the stream channel capability.

      <CalloutContainer type="warning">
        <CalloutTitle>
          Important
        </CalloutTitle>

        <CalloutDescription>
          **Stream channel activation requirements**

          Please note that the activation of Stream Channel functionality in Signaling directly depends on the activation of the 128-host feature in Real-Time Communication (RTC). To ensure proper activation:

          * Submit a formal request to [support@agora.io](mailto\:support@agora.io).
          * Specifically request activation of the 128-host feature.
          * Wait for confirmation before implementing Stream Channel features.

          For further assistance or questions regarding this requirement, please contact [Agora Support](mailto\:support@agora.io).
        </CalloutDescription>
      </CalloutContainer>

    ## Implement communication in a stream channel [#implement-communication-in-a-stream-channel-5]

    This section shows you how to use the Signaling SDK to implement stream channel communication in your app.

    ### Create a stream channel [#create-a-stream-channel-5]

    To use stream channel functionality, call `createStreamChannel` to create an `IStreamChannel` object instance.

    ```cpp
    int errorCode = 0;
    IStreamChannel* stream_channel = rtm_client->createStreamChannel("channel_name", errorCode);
    if (stream_channel == nullptr || errorCode != 0) {
        printf("create stream channel failed");
    } else {
        printf("create stream channel success");
    }
    ```

    This method creates only one `IStreamChannel` instance at a time. If you need to create multiple instances, call the method multiple times.

    ```cpp
    int errorCode = 0;
    IStreamChannel* stream_channel1 = rtm_client->createStreamChannel("chat_room1", errorCode);
    if (stream_channel1 == nullptr || errorCode != 0) {
        printf("create stream channel failed");
    } else {
        printf("create stream channel success");
    }

    IStreamChannel* stream_channel2 = rtm_client->createStreamChannel("chat_room2", errorCode);
    if (stream_channel2 == nullptr || errorCode != 0) {
        printf("create stream channel failed");
    } else {
        printf("create stream channel success");
    }
    ```

    <CalloutContainer type="info">
      <CalloutDescription>
        Signaling enables you to create unlimited stream channel instances in a single app. However, best practice is to create channels based on your actual requirements to maintain optimal client-side performance. For instance, if you hold multiple stream channel instances, destroy the ones that are no longer in use to prevent resource blocking, and recreate them when they are needed again.
      </CalloutDescription>
    </CalloutContainer>

    ### Join a stream channel [#join-a-stream-channel-5]

    Call the `join` method on the `IStreamChannel` instance with appropriate options as follows:

    ```cpp
    JoinChannelOptions options;
    options.token = "your_token";

    uint64_t requestId;
    stream_channel->join(options, requestId);
    ```

    When joining a channel, set the `token` parameter in `JoinChannelOptions` with a temporary token from Agora Console. When you call this method, the SDK triggers the `onJoinResult` callback and returns the call result.

    ```cpp
    // Triggered when you call the join method
    class RtmEventHandler : public IRtmEventHandler {
        void onJoinResult(const uint64_t requestId, const char *channelName, const char *userId, RTM_ERROR_CODE errorCode) {
            if (errorCode != RTM_ERROR_OK) {
                printf("join rtm channel failed error is %d reason is %s\n", errorCode, getErrorReason(errorCode));
            } else {
                printf("join rtm channel %s success\n", channelName);
            }
        }
    };
    ```

    When joining a channel, set the notification subscription parameters in `JoinChannelOptions`:

    ```cpp
    JoinChannelOptions options;
    options.token = "your_token";
    options.withLock = false;  // Disable lock event notifications
    options.withMetadata = false; // Disable storage event notifications
    options.withPresence = true; // Subscribe to presence event notifications

    uint64_t requestId;
    stream_channel->join(options, requestId);
    ```

    In stream channels, message flow is managed using topics. Even if you configure a global message listener, you must still join a topic to send messages. Similarly, to receive messages you must subscribe to a topic. See [Topics](topics) for more information.

    ### Send a message [#send-a-message-5]

    To send a message to a stream channel:

    * Create an `IStreamChannel` instance.
    * Use the `join` method to join a channel.
    * Call `joinTopic` to register as a message publisher for the specified topic. See [Topics](topics).

    Call `publishTopicMessage` to publish a message to a topic. This method sends a message to a single topic at a time. To deliver messages to multiple topics, call the method separately for each topic.

    Refer to the following sample code for sending messages:

    * String message

      ```cpp
      // Sending a string message
      std::string message = "Hello Agora!";
      TopicMessageOptions options;
      options.messageType = RTM_MESSAGE_TYPE_STRING;
      options.customType = "PainTxt";
      uint64_t requestId;
      streamChannel.publishTopicMessage("topicName", message.c_str(), message.size(), options, requestId);
      ```

    * Binary message

      ```cpp
      // Sending a binary message
      char message[5] = {0x00, 0x01, 0x02, 0x03, 0x04};

      TopicMessageOptions options;
      options.messageType = RTM_MESSAGE_TYPE_BINARY;
      options.customType = "ByteArray";
      uint64_t requestId;
      streamChannel.publishTopicMessage("topicName", message, 5, options, requestId);
      ```

    When you this method, the SDK triggers the `onPublishTopicMessageResult` callback and returns the API call result.

    ```cpp
    // Asynchronous callback
    class RtmEventHandler : public IRtmEventHandler {
        void onPublishTopicMessageResult(const uint64_t requestId, const char* channelName, const char* topic, RTM_ERROR_CODE errorCode) override {
            if (errorCode != RTM_ERROR_OK) {
                // publish topic message failed
            } else {
                // publish topic message success
            }
        }
    };
    ```

    In Signaling, a user may register as a message publisher for up to 8 topics concurrently. However, there are no limitations on the number of users a single topic can accommodate. You can achieve a message transmission frequency to a topic of up to 120 QPS. This capability is useful in use-cases that demand high-frequency and high-concurrency data processing, such as Metaverse location status synchronization, collaborative office sketchpad applications, and parallel control operation-instructions transmission.

    ### Leave a stream channel [#leave-a-stream-channel-5]

    To leave a channel, call the `leave` method on the `IStreamChannel` instance:

    ```cpp
    // Leave the channel
    uint64_t requestId;
    streamChannel->leave(requestId);
    ```

    When you call this method, the SDK triggers the `onLeaveResult` callback and returns the call result.

    ```cpp
    // Triggered when you call the leave method
    class RtmEventHandler : public IRtmEventHandler {
        void onLeaveResult(const uint64_t requestId, const char *channelName, const char *userId, RTM_ERROR_CODE errorCode) {
            if (errorCode != RTM_ERROR_OK) {
                printf("leave rtm channel failed error is %d reason is %s\n", errorCode, getErrorReason(errorCode));
            } else {
                printf("leave rtm channel %s success\n", channelName);
            }
        }
    };
    ```

    To rejoin a stream channel, call the `join` method again. You can join and leave as long as the corresponding `IStreamChannel` instance remains active and has not been destroyed.

    ### Destroy the stream channel instance [#destroy-the-stream-channel-instance-4]

    To destroy a stream channel instance, call `release`:

    ```cpp
    stream_channel->release();
    stream_channel = null;
    ```

    <CalloutContainer type="info">
      <CalloutDescription>
        Destroying a stream channel removes the `IStreamChannel` instance from your app. This action is local to your app and does not affect other users or the Signaling channel.
      </CalloutDescription>
    </CalloutContainer>

    ## 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.

    ### Message packet size [#message-packet-size-5]

    Signaling SDK imposes size limits on message payload packets sent in message type channels and stream type channels: 32 KB for message type channels and 1 KB for stream type channels. The message payload packet size includes the message payload itself plus the size of the customType field. If the message payload package size exceeds the limit, you will receive an error message.

    To avoid sending failure due to message payload packet size exceeding the limit, check the packet size before sending.

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

    * [`createStreamChannel `](/en/api-reference/api-ref/signaling#channelcreatepropsag_platform)
    * [`join`](/en/api-reference/api-ref/signaling#channeljoinpropsag_platform)
    * [`publishTopicMessage`](/en/api-reference/api-ref/signaling#topicpublishpropsag_platform)
    * [`leave`](/en/api-reference/api-ref/signaling#channelleavepropsag_platform)
    * [`release`](/en/api-reference/api-ref/signaling#channelreleasepropsag_platform)