What Is A Multi-IMSI SIM? – IoT Uncovered


For most IoT deployments, zero-touch, out-of-the-box connectivity is essential. Devices might be installed in remote, inhospitable terrain or hidden within a car dashboard or retail vending machine. Requiring users to enter networks details and credentials would create significant logistical and security issues. In this article, we explore the importance of roaming and the benefits that come when a SIM can flexibly connect to a local network to achieve an optimum connection.

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 such as a vending machine, can’t connect in foreign countries, even with a roaming agreement in place. These issues can take months to resolve – especially for smaller operators. So, if a SIM has only one bootstrap network (called an IMSI), out-of-the-box connectivity can’t be guaranteed.

IMSI: An International Mobile Subscriber Identifier identifies the user on the network. A traditional SIM contains one network profile with one IMSI. This IMSI is tied to a single network provider.

When roaming works, it can be invaluable for IoT deployments. As discussed, if a SIM can’t connect to a local network when a device starts up, it can roam onto another network. And devices that move – for example, tracking devices in vehicles – can roam onto different networks as they change regions or countries, so they are always connected.

Did you know that in some countries, permanent roaming is not permitted? After a certain length of time, roaming devices must connect to a local network or risk being disconnected. 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 network 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.

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

Localising or changing networks

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

  • Avoid permanent roaming restrictions
  • Use a service with better connectivity
  • Change from a provider who is sunsetting a service that you need (such as 2G or 3G)
  • Achieve a better deal or service from another provider

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

  • With eUICC, you can switch to a different network provider (usually only once for standard eUICC SIMs) and depending on the solution provider, you also may have the option to localise the device to an approved network
  • With a multi-IMSI SIM, you can switch networks as many times as you like but remain with your current connectivity provider

What can multi-IMSI SIMs offer?

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.

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. So, 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.

Secure solution

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.

Taking multi-IMSI SIMs to a new level

As we’ve explored, multi-IMSI SIMs help to answer some of the main problems that IoT devices face when being deployed in multiple geographies; however, to achieve truly ubiquitous, global connectivity a more robust and flexible solution is required. Stay tuned for next week when we delve into the GSMA’s new eUICC standard.

If you’re interested in finding more about our intelligent IoT connectivity, head to our Solutions page where we walk through our unique capabilities.

Latest news

The Myth Behind Network Coverage: Mobile Operators Not-Spots in the UK

The Current State of Mobile Network Connectivity Coverage The rivalry between mobile network operators over network coverage availability...

How to Supercharge eUICC for IoT? – IoT Uncovered

Over the last two blogs, we explored What is a Multi-IMSI SIM and What is eUICC....

Are vending machines the new retail?

Retail has taken a substantial hit in 2020 and is among one of the most severe...