A data connection is needed for applications that exchange data with devices where SMS messages are insufficient or not possible. The data connection can be established over a mobile network, WiFi or a fixed link (e.g., ethernet). The data connection service provides a basic API for requesting and releasing a data connection.

The Data Channel Service (DCS) provides an interface for a client application to configure and use the available data channels on its target.

"Data channel" is a generic term meant to include and cover the data "connection", "link", or similiar, named for and established by various connectivity technologies as a communication channel or pipe for sending and receiving data packets on a network or with another endpoint. DCS's currently supported connectivity technologies are cellular and WiFi, both of which would bring up the network layer for their connections and employ IP addressing and routing to communicate.

Note: This interface does not support a data connection over a fixed link.

Warning: The dependency between the cellNetService and dataConnectionService has been removed. A data connection request will no longer ensure that the radio is on, or verify that the SIM is valid and unlocked.

The following diagram illustrates at the overview level where the DCS interfaces are relative to client applications and the physical technologies underneath, as well as what the "channel", "connection", "technology", etc., terminologies refer to.

The Data Channel Service contains two sets of APIs:

le_data.api - legacy API interface that has been supported prior Legato Release 18.10.
le_dcs.api and le_net.api - new API interfaces that are currently in experimental state.

Getting Started

This service is automatically included in the Legato Framework by including default.sdef in your system and the service loads automatically on startup.

The following line in the default.sdef is responsible for adding the Data Channel Service to your system:

apps: {
   $LEGATO_ROOT/apps/platformServices/dataConnectionService
}

le_data vs le_dcs

The new interfaces le_dcs and le_net consist of an expanded architecture for supporting multiple active data channels of the same or different technologies which the legacy le_data interface doesn't have. They offer flexible choices to client applications over which specific technology and data channel to pick, and the querying capability to learn about all the choices available. Unlike them, the legacy le_dcs.api supports only one single channel on a device at any time and offers no choices over which technology and channel to select.

Please refer to the diagram above to see how multiple active data connections can now be supported in the le_dcs architecture.

Warning: Any client application that continues to use the le_data interface needs to beware of the new reality that multiple data channels could have been active if some others have started them via the le_dcs interface. The one that it has started might not have the device's default gateway and DNS server addresses set on its network interface, because although these network configurations would be automatically inserted by the le_data interface, some other data channel that got established later via le_dcs and le_net could have set these configurations onto another network interface instead. Thus, the network admin of any Legato device on which both le_data and le_dcs plus le_net would be used together has to understand the network topology and manage its routing configurations properly at any time.

DCS APIs

The Data Channel Service now provides the following API interfaces for managing and operating over network connections.

API Guide	API Reference	File Name	Description
le_dcs Interface	le_dcs API Reference	`le_dcs.api`	Provides multi-connection data channel services
le_net Interface	le_net API Reference	`le_net.api`	Provides network services to data channels managed by `le_dcs`
le_data Interface	le_data API Reference	`le_data.api`	Provides data channel services to a single data connection

IPC Interface Binding to DCS

For an application to be able to use the le_dcs and le_net APIs, it needs to perform the bindings in the application's .adef as done below:

  bindings:
   {
      clientExe.clientComponent.le_dcs -> dataConnectionService.le_dcs
      clientExe.clientComponent.le_net -> dataConnectionService.le_net
   }

App Implementation

The Data Channel Service is implemented by the dataConnectionService that relies on the following services for connection technologies:

When an application needs to use such connection technologies, it has to create IPC bindings and service connections to them as done in the following sample.

To create IPC bindings:

  bindings:
   {
      clientExe.clientComponent.le_mdc -> modemService.le_mdc
      clientExe.clientComponent.le_wifiClient -> <root>.le_wifiClient
   }

The necessary IPC binding for using le_data is likewise.

To create service connections, in the application's COMPONENT_INIT() code:

    le_mdc_ConnectService();
    le_wifiClient_ConnectService();

How Tos & Samples

Migration tips from le_data to le_dcs.
Sample apps using le_dcs. Please search through the code there for API calls to le_dcs and le_net.
Sample code using le_data.