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Works with Super SIM

Works with Super SIM is a collaborative program between cellular module manufacturers and Twilio to ensure device designers have an optimal experience when using Super SIM and our vendor partners’ modules. Featured modems have been certified to support the functionality required for Super SIM’s multi-IMSI applet and the over-the-air updates used to ensure Super SIMs always offer the latest features and improvements. To learn more about the testing performed to ensure certification, please refer to the section below.

For each featured module, we provide a guide for using it with Super SIM which includes useful commands such as setting the APN, enabling roaming, and establishing a data connection. The guides also include a step-by-step walkthrough for getting started with the module’s primary developer kit.

Featured cellular modules

Super SIM functionality testing

The multi-IMSI applet

Each Super SIM holds multiple IMSIs (International Mobile Subscriber Identities) that allow it to access different networks around the world. These IMSIs are managed by an applet that will, under certain conditions, switch to the IMSI that should be used to connect. For an optimal experience when using Super SIM, it’s critical that the module supplies the information the applet requires to determine which IMSI to use, and that the module responds to commands issued by the applet.

For more detailed information on IMSIs and the Super SIM IMSI-switching tool, see Super SIM’s Multi-IMSI Applet.

Our Works with Super SIM tests verify that program modules perform the following tasks.

Switches to the preferred IMSI

Each IMSI may offer access to different networks and the best IMSI to use in one country may be different from that required in another country. If the multi-IMSI applet detects that another IMSI should be used to connect, it will update the local files that contain the subscriber information needed to connect to the networks. It will then issue a command to the module to reread those files. If the module does not respond to these commands, you may not be able to access all the networks available to you and the time to initially connect may be longer than intended.

Modules certified as Works with Super SIM have been tested to confirm that the location information required by the multi-IMSI applet to determine if a different IMSI should be used is quickly passed by the module to the Super SIM and that the module quickly uses the new IMSI issued by the Super SIM to connect. To test this, we connect a Super SIM with the module in a country where the preferred IMSI is different than the IMSI that the Super SIM first presents. We verify that Super SIM quickly changes to the expected IMSI and that the module is able to successfully connect to the cellular network within an appropriate amount of time.

Switches IMSIs when unable to connect

Super SIM’s multi-IMSI approach also allows other IMSIs to be used if your device can’t connect. This allows your device to try to connect to different networks or to connect to the same networks but through different downstream network partners, giving your devices redundant paths to get connected.

If the module is unable to connect to a cellular network, Super SIM will enter Limited Service mode. After being in this mode for a period of time, the multi-IMSI applet will switch IMSIs and issue a command to the module to reread the local files, which it just updated. The module should then try to connect with the new IMSI. This process repeats until your device is able to connect to a cellular network. If the module does not send the events needed to determine when to switch, or does not respond to the commands from the Super SIM, then your device may not be able to connect or may have longer-than-necessary recovery times in the event of a network outage.

Modules certified as Works with Super SIM have been tested to ensure that they change IMSIs within an appropriate amount of time if they are unable to connect. To test this, the network permissions for a Super SIM are modified so that it will be rejected by all networks and therefore will be unable to connect. Using logs emitted by the Twilio Mobile Core, we monitor which IMSI is used each time the module tries to connect and verify that it iterates through each IMSI as expected and within an appropriate amount of time. We then verify that the module is able to successfully connect to the cellular network after the Super SIM’s network permissions have again been modified, to allow it to connect.

Over-the-air updates

Super SIMs will be periodically updated over the air to add additional IMSIs, alter which IMSI is preferred for certain countries, modify other settings on the SIM, or receive updates to the applets running onboard. This allows your Super SIMs to continue to improve over time as we add more networks or make improvements to the platform that require changes to the SIM.

Modules certified as Works with Super SIM have been tested to ensure that they allow the Super SIM applets to contact the necessary downstream services and can receive over-the-air updates. To perform this test, we stage an update to the multi-IMSI applet’s settings, verify that the update has been successfully retrieved, and that the behavior between the Super SIM and the module reflects the expected behavior imposed by the new settings.

For more detailed information on how Super SIM updates work, see Super SIM Over-the-Air Updates.

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