Transport

Meshtastic communicates between the app and radio hardware through multiple transport mechanisms.

Transport Abstraction

The transport layer is abstracted through interfaces in core/network and core/ble, allowing the app to work identically regardless of the underlying connection type.

App ← RadioController → Transport (BLE | Serial | TCP)

Bluetooth Low Energy (BLE)

Module: core:ble
Platforms: Android, Desktop (JVM via Kable), iOS (planned)

The primary transport for mobile devices and also available on desktop:

  • Service discovery for Meshtastic GATT services
  • Characteristic-based read/write for protobuf packets
  • Connection state management and automatic reconnection
  • MTU negotiation for optimal packet sizes

Key Classes

  • core/ble/ — BLE scanning, connection, and GATT operations
  • Platform-specific implementations in androidMain and jvmMain (Kable)

USB Serial

Module: core:network
Platforms: Android (OTG), Desktop

Serial communication over USB:

  • Uses usb-serial-for-android library on Android
  • Direct serial port access on Desktop (JVM)
  • Probe table for supported USB vendor/product IDs
  • Automatic detection when USB device is connected

Key Classes

  • Serial prober and transport factory in core/network
  • Desktop-specific serial in desktopApp/src/main/kotlin/.../radio/

TCP/IP

Module: core:network
Platforms: Android, Desktop, iOS

Network-based transport for WiFi-enabled radios:

  • TCP socket connection to radio’s IP address
  • Default port: 4403
  • Used for development with simulated radios
  • Available when BLE/USB is impractical

Transport Factory

The RadioTransportFactory interface abstracts transport creation:

interface RadioTransportFactory {
    val supportedDeviceTypes: List<DeviceType>
    fun createTransport(address: String, service: RadioInterfaceService): RadioTransport
    fun isMockTransport(): Boolean
    fun isAddressValid(address: String?): Boolean
    fun toInterfaceAddress(interfaceId: InterfaceId, rest: String): String
}

Platform-specific implementations:

  • Android: Supports BLE + USB + TCP
  • Desktop: Supports BLE (Kable) + USB + TCP
  • iOS: Planned BLE + TCP

Connection Lifecycle

  1. Discovery — Scan for available radios (BLE scan / USB detect / manual TCP)
  2. Connection — Establish link to selected radio
  3. Handshake — Exchange node info and configuration
  4. Active — Normal message exchange
  5. Disconnection — Clean teardown or error recovery

Adding a New Transport

  1. Implement RadioTransport interface
  2. Register in platform-specific RadioTransportFactory
  3. Add connection UI in feature:connections
  4. Update DI bindings for the platform