What Is Multi-IMSI and How Does It Work?

An IMSI is a key component of a Subscriber Identity Module (SIM) profile, which is stored on a SIM card. Each one allows a device to connect to a limited number of networks. When a SIM card holds multiple IMSIs, it enables subscribers to switch carriers as needed and connect to significantly more networks.

Multi-IMSI technology is essential for cellular IoT manufacturers that plan on deploying globally or creating mobile applications. You want your device to have service wherever your customers use it—not just wherever a particular carrier has coverage or roaming agreements with other MNOs.

The difference between Multi-IMSI and eUICC

Like Multi-IMSI, an Embedded Universal Integrated Circuit Card (eUICC) allows you to change carriers and store multiple MNO profiles. But the process (and cost) of switching between carriers with these technologies is fundamentally different.

Integration

An eUICC for M2M can store multiple profiles, but each time you add a new one, your new provider has to integrate their SM-SR and SM-DP with your old provider’s Subscription Manager Secure Routing (SM-SR) and Subscription Manager Data Preparation (SM-DP), and the two cellular carriers have to coordinate their various protocols.

Switching profiles with an eUICC also means you’re “leaving” your original provider and cancelling your contract. And since you’re completely changing providers, you’ll have to use the new operator’s portal, tools, and API. You’ll also get a new MSISDN for each device. 

With Multi-IMSI, you have a single service provider (such as emnify), but multiple subscriber identities, each of which can connect to a limited number of carriers. (This is the “allowed network coverage” list.) When your device needs to connect to a carrier that isn’t on the list, it automatically changes IMSIs to get a new list of approved networks. 

There’s no need for OTA provisioning, new integration, new APIs, or new portals. And your device can bring data from one carrier to another—because you’re still just managing one MNO subscription.

Network selection

Multi-IMSI SIM cards can be configured to automatically select the network with the strongest signal or lowest costs, and it can be preloaded with several subscriber identities, which lets your device switch between carriers and pause or resume contracts as needed. 

An eUICC is more of a safeguard if your carrier goes out of business or you need to deploy somewhere that requires a local carrier (such as Brazil or India) . Switching between profiles with an eUICC is far less cost effective than using Multi-IMSI, and you need to download and activate the new profile manually when you deploy to a new country..

Note: An eUICC can store a profile for a Multi-IMSI provider, combining the benefits of these two technologies and giving you greater flexibility.

The components of an IMSI

The International Telecommunication Union (ITU) has standardized IMSI numbers, so it’s easy to identify what country and MNO a given subscriber should be associated with. IMSIs usually have 15 digits, but it varies depending on the country and provider. Those digits are divided into three sets, each of which communicates a different piece of information:

1. The first set of digits is the Mobile Country Code (MCC), which defines the country a subscriber primarily operates within. This is always either two or three digits.
2. The second set of digits is the Mobile Network Code (MNC), which represents the MNO the subscriber identify is associated with. This is between one and three digits.
3. The final set of digits is the Mobile Subscription Identification Number, which is unique to the subscriber. (This is typically nine or ten digits.)

For example, here’s what MNOs knows from information the IMSI number, 310005987654321:

As you can see, a single IMSI is connected to a specific geographic region and associated with a particular MNO. When the device roams outside of the country the MNO covers, it has to connect to another MNO on its list of network roaming partners. 

A single IMSI may have redundant coverage in some places, enabling the device to access multiple operators in the same country. But this rarely happens in the IMSI’s “home network”—the country its primary MNO covers. Redundant coverage in the primary operator’s home country is known as “national roaming,” and most operators don’t provide this.

With a Multi-IMSI, however, the device will often have redundant coverage because it can access multiple lists of approved networks—one list per IMSI. When the first IMSI doesn’t have any networks available, the Multi-IMSI applet switches to another IMSI and attempts to connect to the networks associated with the new MNO profile.

An example of when Multi-IMSI helps

Telematics is one of the industries where IoT has grown fastest in. It’s also an excellent use case for Multi-IMSI technology. Vehicles traveling across several borders may need GPS trackers and Onboard Diagnostics devices to operate in countries where they need to switch profiles to stay connected.

In a single trip, the vehicle may need to switch to one or more different carriers and switch back to the original carrier on the trip back. With a Multi-IMSI SIM card, your service provider manages all of these transitions, and you never have to change portals or MSISDNs, and changing profiles doesn’t require new integration or additional costs.

emnify’s Multi-IMSI SIM card ensures that automotive IoT applications always connect to the network with the strongest signal and lowest costs. Plus, when you deploy globally, you can always have a profile for a local carrier if you need it.

How changing IMSIs works

Let’s say you have a vehicle using a cellular IoT device in its onboard entertainment system. Using emnify’s SIM card, it connects to one of emnify’s US network partners through a specific IMSI (IMSI #1). 

But the manufacturer also wants to deploy in the UK. In this new deployment, the device connects to one of emnify’s UK network partners with a new IMSI (IMSI #2). Here’s how the process of swapping IMSIs works:

1. A SIM is initially provisioned with IMSI #1 active.
2. The SIM attaches to the US Network (MCC 310).
3. The manufacturer ships its device to the UK (MCC 348).
4. The SIM tries to reach the network in the UK with IMSI A
5. IMSI #1 doesn’t have any UK MNOs on its list of approved network partners, so the cellular network rejects it. (Remember, each IMSI can only have a limited number of network roaming partners.) 
6. On emnify’s user interface, the manufacturer receives a message: "Location update rejected from VLR 34656022000 for IMSI 310005987654321. This operator is currently not supported for this IMSI. A different IMSI or operator will be used for the network registration."
7. The SIM’s applet finds UK (MCC 348) as the new location.
8. The SIM’s applet overwrites the active IMSI and replaces IMSI #1 with IMSI #2, according to the IMSI selection table.
9. The SIM sends a refresh command to the device and attaches to a new network with IMSI #2.
10. The SIM connects to one of emnify’s network partners in the UK. 

And this all happens automatically. emnify’s communication management platform clarifies what’s happening, but you don’t have to manually select a network unless you want to.

emnify’s Multi-IMSI solution

Our Multi-IMSI connectivity platform means services are instantly available in over 180 countries and 540+ mobile networks. If you deploy in a country with a pre-configured IMSI that doesn’t have a roaming agreement with a local network operator, our SIMs will swap IMSIs to use one that has an existing roaming agreement.

You can manage your Multi-IMSI and network roaming partners through a single interface, and you can update them OTA to add or remove IMSIs as needed throughout your SIMs lifetime.