# MQTT over TCP Bridge

The MQTT over TCP Bridge is a key feature of EMQX Edge that enables reliable, bi-directional communication between your local edge broker and remote MQTT brokers using standard TCP connections. This bridge is especially suited for IoT edge-to-cloud scenarios, ensuring data reliability, message integrity, and connectivity across network boundaries such as firewalls or proxies.

## What Is MQTT over TCP Bridge?

The MQTT over TCP Bridge establishes an outbound connection from EMQX Edge to a remote MQTT broker such as [EMQX Platform](https://www.emqx.com/en/platform), using the MQTT protocol over TCP or TLS.

This bridge allows you to:

- Forward MQTT messages from local topics to the cloud or another broker.
- Receive messages from remote topics into local topics.
- Maintain QoS-based message delivery even across unstable networks.
- Configure message caching and automatic resend when reconnecting.

## Key Features

- **Protocol Support**: MQTT v3.1, v3.1.1, and v5.0 over TCP or TLS.
- **Bi-directional Bridging**: Both publish (forward) and subscribe (receive) across brokers.
- **Automatic Reconnect**: Handles disconnection and reconnection with optional message buffering.
- **Parallel Connections**: Support for concurrent parallel processes to improve throughput.
- **Full Dashboard Integration**: Configure, monitor, and manage bridges through a visual UI.

## How It Works

The MQTT over TCP Bridge consists of three components:

1. **Connector**: Establishes the connection to the remote MQTT broker using TCP or TLS.
2. **Forwards**: Rules for sending messages from local topics to remote topics.
3. **Subscriptions**: Rules for receiving messages from remote topics to local topics.

The bridge manages message queues, QoS levels, and connection lifecycles internally to ensure reliability even in challenging network environments.

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## What's Next

- Follow the [Quick Start Guide](./tcp-bridge-quick-start.md) to create your first MQTT over TCP bridge.
- Explore the [Advanced Configuration Guide](./tcp-bridge-advanced.md) to learn about topic mapping, hybrid bridging, message caching, and more.