Meshtastic-Android/docs/en/developer/transport.md

title, parent, nav_order, last_updated, description, aliases

title	parent	nav_order	last_updated	description	aliases
Transport	Developer Guide	5	2026-08-29	The BLE, USB serial, and TCP transports behind the RadioTransport abstraction — which module owns each, and how to add a new one.	ble serial tcp radio-transport

Transport

The app talks to the radio over three transports — BLE, USB serial, and TCP — behind one abstraction.

Transport Abstraction

The transport layer is abstracted through interfaces defined in core:repository (RadioTransport, RadioTransportFactory, RadioInterfaceService). Each transport's concrete implementation lives in core:network: BleRadioTransport (BLE), TcpRadioTransport (TCP), and SerialRadioTransport (Android USB serial), alongside MockRadioTransport and ReplayRadioTransport for development. core:ble supplies the lower-level BLE connection primitives (scanning, GATT, Kable wiring) that BleRadioTransport builds on — it does not implement RadioTransport itself. This lets the app work identically regardless of the underlying connection type.

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

Bluetooth Low Energy (BLE)

Module: core:network (the BleRadioTransport implementation) built on core:ble (BLE connection primitives)
Platforms: Android, Desktop (JVM via Kable); code compiles for iOS, but no iOS app ships

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

Where the Code Lives

• BleRadioTransport (core:network) — the RadioTransport implementation for BLE
• core:ble — BLE scanning, connection, and GATT operations (BleScanner, BluetoothRepository, KableBleConnection), which BleRadioTransport consumes
• 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

Where the Code Lives

• SerialRadioTransport (core:network, androidMain) — the Android RadioTransport implementation
• SerialTransport (core:network, jvmMain) — the shared serial-port transport Desktop builds on
• DesktopRadioTransportFactory (desktopApp) — wires Desktop's jSerialComm-based serial connection

TCP/IP

Module: core:network
Platforms: Android, Desktop (iOS: code compiles, but there's no iOS app target or RadioTransportFactory — see Transport Factory)

Network-based transport for Wi-Fi-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>

    /** Whether the virtual demo transports (`m` mock / `r` replay) may be offered right now. */
    val mockTransportEnabled: StateFlow<Boolean>

    /** Whether this build ships a packet capture to replay, rather than degrading to plain mock. */
    val isReplayTransportAvailable: Boolean

    fun createTransport(address: String, service: RadioInterfaceService): RadioTransport
    fun isAddressValid(address: String?): Boolean
    fun toInterfaceAddress(interfaceId: InterfaceId, rest: String): String
}

mockTransportEnabled is a flow, not a one-shot check: the Android Demo Mode gesture (five taps on the Settings app-version row) unlocks the demo transports mid-session, and the device list has to notice. Every consumer must read that one flow — the visibility path and the isAddressValid admission path have to agree, or the demo entry appears and then refuses to connect.

Platform-specific implementations:

• Android: Supports BLE + USB + TCP
• Desktop: Supports BLE (Kable) + USB + TCP
• iOS: Code compiles for BLE and TCP, but no RadioTransportFactory implementation exists and no iOS app ships

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