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Multiple Transports Configuration

General Description

The multiple transports feature allows apps connected to Core to start another connection over a different transport for certain services (for example, an app connected over bluetooth using WiFi as a secondary transport for video streaming). This guide will walk you through how to configure the multiple transports feature using the smartDeviceLink.ini file.


  • After Proxy is connected to Core, it initiates another connection over a different transport.
  • Core tells Proxy which transport can be used as Secondary Transport.
  • The services that are allowed on the Secondary Transport are specified by Core.

RPC and Hybrid services only run on the Primary Transport

There are three protocol control frames which are used in the implementation of multiple transports

StartService ACK

        audioServiceTransports : [1, 2]
        videoServiceTransports : [1, 2]
        secondaryTransports : [TCP_WIFI]

Core responds to the proxy's StartService request with additional parameters audioServiceTransports, videoServiceTransports and secondaryTransports.

  • The secondaryTransports contains an array of the allowed secondary transports for the current primary transport.
  • audioServiceTransports and videoServiceTransports describe which services are allowed to run on which transports (Primary, Secondary, or both). The Proxy uses this information and starts services only on allowed transports.
  • Since RPC and Hybrid services always run on Primary Transport, only Video and Audio services are configurable.


    tcpIpAddress :
    tcpPort : 12345

Core sends a TransportEventUpdate to the proxy to provide additional information required to connect over the TCP transport

  • If the tcpIpAddress field is empty, the secondary transport is unavailable and proxy will not send a RegisterSecondaryTransport request


Using the information in the StartService ACK and TransportEventUpdate frames, the proxy sends a RegisterSecondary transport request over the secondary transport.

  • If Core sends back a RegisterSecondaryTransport ACK, the proxy can start services over the secondary transport

Operation Examples

Setting up multiple transports

Getting started

Add the following lines to smartDeviceLink.ini

  • To enable multiple transports in Core
MultipleTransportsEnabled = true
  • To set the available Secondary Transport types for a given Primary transport
SecondaryTransportForBluetooth = WiFi
;SecondaryTransportForUSB =
;SecondaryTransportForWiFi =

The values which can be used in the SecondaryTransportFor configuration are WiFi, Bluetooth and USB

Audio and Video streaming

Modify the services map in smartdeviceLink.ini to restrict video and audio streaming services to specific transport types.

AudioServiceTransports = TCP_WIFI
VideoServiceTransports = TCP_WIFI, AOA_USB
  • Transports are listed in preffered order
  • If a transport is not listed, then the service is not allowed to run on that transport
  • If the AudioServiceTransports/VideoServiceTransports line is omitted, service will be allowed to run on the primary transport

List of secondary transport types

String Description
IAP_BLUETOOTH iAP over Bluetooth
IAP_USB iAP over USB, and Core cannot distinguish between Host Mode and Device Mode.
IAP_USB_HOST_MODE iAP over USB, and the phone is running as host
IAP_USB_DEVICE_MODE iAP over USB, and the phone is running as device
IAP_CARPLAY iAP over Carplay wireless
SPP_BLUETOOTH Bluetooth SPP. Either legacy SPP or SPP multiplexing.
AOA_USB Android Open Accessory
TCP_WIFI TCP connection over Wi-Fi
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