Android 6.0 and higher include a capability for privileged apps to provide carrier-specific configuration to the platform. This functionality, based on the UICC Carrier Privileges introduced (Lollipop MR1), allows carrier configuration to be moved away from the static configuration overlays and gives carriers and OEMs the ability to dynamically provide carrier configuration to the platform through a defined interface.

A properly signed carrier app can either be preloaded in the system image, installed automatically, or manually installed through an app store. The app is queried by the platform to provide configuration for settings including:

• Roaming/nonroaming networks
• Visual voicemail
• SMS/MMS network settings
• VoLTE/IMS configurations

The determination of what values to return is entirely up to the carrier app and can be dynamic based on detailed information passed to the app through the platform.

The key benefits of this approach are:

• Dynamic configuration – Support for concepts like non-MCCMNC derived configuration, for example, mobile virtual network operators (MVNOs) or customer opt in to extra services.
• Support for devices sold through any channel – For example, an open market phone can be automatically configured with the right settings by downloading an app from an app store.
• Security – Privilege to provide this configuration is given only to apps signed by the carrier.
• Defined API – Previously this configuration was stored mostly in internal XML overlays within the framework and not through a public API. The carrier config API in Android 6.0 is public and well defined.

How it works

Loading the config

The carrier configuration supplied by this feature is a set of key-value pairs that change various telephony-related behaviors in the platform.

The set of values for a particular device is determined by querying the following components in order:

1. The carrier app (this is optional, but it’s the recommended location for additional configuration beyond what exists in the Android Open Source Project (AOSP))
2. The platform config app bundled with the system image
3. Default values, hardcoded into the framework (equivalent to the behavior prior to Android 6.0)

The platform config app

A generic platform config app is bundled with the system image. This app can supply values for any variables that the regular carrier app doesn’t.

This app’s purpose is to provide some per-network configuration when a carrier app isn’t installed, and carriers/OEMs should make only minimal changes to it in their own images. Instead carriers should provide the separate carrier app for carrier customization, allowing updates to be distributed through avenues such as app stores.

How privilege is granted to a carrier app

The carrier app in question must be signed with the same certificate found on the SIM card, as documented in UICC Carrier Privileges.

What information is passed to the carrier app

The carrier app is supplied with the following values, enabling it to make a dynamic decision as to what values to return:

• MCC
• MNC
• SPN
• IMSI
• GID1
• GID2
• Carrier ID

For more information on integrating carrier IDs, see Integrating carrier IDs with CarrierConfig.

When loading the carrier config occurs

The building of the list of key value pairs occurs:

• When the SIM is loaded (boot, or SIM hot swap)
• When the carrier app manually triggers a reload
• When the carrier app gets updated

Using the config

When the configuration is built, the values contained within it are used to set various values of system configuration, including:

• Internal framework telephony settings
• SDK-returned configuration values, for example, in SmsManager
• App settings like VVM connection values in the Dialer

Configuration keys

The list of keys is defined as part of the public SDK and can’t change within the same API level. See the table below for a summary of keys.

Building the app

Declaring a class that overrides android.service.carrier.CarrierService

1. Override onLoadConfig to return the values you wish to supply based on the service.carrier.CarrierIdentifier object passed.
2. Add logic to call notifyConfigChangedForSubId in scenarios where the carrier configuration may change over time (for example, when the user adds extra services to their account).