Paul Marshall

Founder & CCO

What is a multi-IMSI SIM

Multi-IMSI SIMs contain many IMSIs, each of which can connect to a different network. There is usually one bootstrap IMSI that comes pre-loaded, although more advanced SIMs can accommodate multiple bootstraps, and some SIMs can be updated with additional IMSIs over-the-air.

Benefits of multi-IMSI IoT SIMs

For most IoT deployments, zero-touch, out-of-the-box connectivity is essential. SIMs must be able to connect to a network from any location and if they can’t connect to a local network, they should be able to roam onto another network. Almost every mobile network provider claims to have hundreds of roaming agreements with other providers to give them global coverage. But not every roaming arrangement works in practice.

Problems may only be discovered when IoT devices, particularly static devices can’t connect in foreign countries, even with a roaming agreement in place. These issues can take months to resolve – especially for smaller operators.

A key capability of multi-IMSI SIMs is that they can maintain high connectivity by switching networks in response to circumstances such as network faults and roaming restrictions.

Switching IMSIs doesn’t change from the current service provider but allows the SIM to localise to another network to which the provider has access, either by agreement or through interconnects.

But not all multi-IMSI SIMs are equal. Some provide a limited capability to swap IMSIs based on pre-configured rules. Others provide a fully functional solution that ensures devices can connect out-of-the-box and remain connected for their lifetimes.

Bootstrap options

No single IMSI can connect everywhere in the world. Devices either need different SIMs for different locations, or SIMs must be pre-loaded with multiple bootstrap IMSIs. Some multi-IMSI SIMs use a different pre-configured bootstrap IMSI depending on where the device is installed.

A better solution is for the SIM to dynamically determine which IMSI is best to use from its available bootstrap IMSIs. That way it can connect even if it encounters unexpected problems – without any external intervention.

Using bootstrap IMSIs from Tier 1 providers – well-established network providers with extensive, verified roaming agreements – provides the best guarantee that every device will connect out-of-the-box, anywhere in the world.

Intelligent connectivity

IoT SIMs should connect to the network that provides the highest level of connectivity. This means that a SIM might need to switch networks to avoid permanent roaming restrictions, or in the event of network faults or poor service.

Ideally, the SIM should have built-in intelligence so it can switch autonomously to another network when required. It should also be capable of receiving new IMSIs and commands to enable, disable and delete IMSIs from the connectivity management platform.

If a SIM fails to connect to a new network, there must be a way to recover or the device will remain unconnected. The SIM should have a fallback capability so that it can always revert to an IMSI that can connect, such as one of the bootstrap IMSIs.

Improved IoT security

Some providers use a single security domain on their multi-IMSI SIMs, with the same access keys used for all IMSIs.

A more secure method is to use separate security domains and keys by downloading and storing complete profiles for each network rather than just the IMSIs. This is possible if the provider has interconnects to the networks.

The SIM should be capable of receiving software and security updates over-the-air so that security can be managed centrally and maintained throughout the IoT estate.

The risks of IoT roaming

When a device is roaming, its communications are backhauled to the local (home) network. These long distances between the local and roaming networks can introduce significant latency to the connection, not to mention mounting costs. Given the additional components and complexity, there’s more chance of things going wrong. Problems with either the local or roaming networks can cause communications to be lost. Unpredictable roaming charges and the risk that regulations may be added or changed at any time leads to an uncertain operating environment.

Permanent roaming

When roaming works, it can be invaluable for IoT deployments. But when a device continually uses a roaming nework for connectivity, it is considered to be “permanently roaming” which in some countries is not permitted. After a certain length of time, roaming devices must connect to a local network or risk being disconnected.

Localising your SIM

To avoid the issues that come with roaming, IoT devices need to swap to a local network, a process called localisation.

You might want an IoT SIM to change networks several times during its lifespan. For example, you might want to:

There are two ways to change networks on an IoT device:

Paul Marshall

Founder & CCO


Paul is one of Eseye’s co-founders. With a background in senior design engineering, Paul’s focus is on ensuring his development, operations and support teams deliver solutions that work faultlessly in the field.

Paul was co-founder of CompXs, with Ian Marsden, and developed the world’s first IEEE 802.15.4 radio. Before CompXs, Paul was in senior radio design at Philips.

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