Dec, 10 2020

What Is Multi-IMSI and How Does It Work?

Quick definition: “Multi-IMSI” is an abbreviation for Multiple International Mobile Subscriber Identities. An IMSI is a unique number that lets Mobile Network Operators authenticate their subscribers so they can access the MNO’s network—and any networks the MNO has established roaming agreements with.

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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 provision a SIM card Over-the-Air (OTA). But doing so with an eUICC can cost tens of thousands of dollars at scale, takes more time, and doesn’t allow data to transfer from one profile to another.


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 you switch between carriers and pause or resume contracts as needed. 


An eUICC is more of a safeguard for 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 an eUICC won’t give you redundant coverage in the same country. (Redundant coverage lets you choose the best network to attach to instead of defaulting to whatever is available.)

This is because the two technologies have fundamentally different architecture. An eUICC can store multiple profiles, but each time you add a new one, your new provider has to integrate with your old one, and the two cellular carriers have to coordinate their various protocols.

With Multi-IMSI, you have a single MNO (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. No need to repeat data transfer attempts. And your device can bring data from one carrier to another—because you’re still just managing one MNO subscription.

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 identifies the MNO the subscriber 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:


Mobile Country Code


United States

Mobile Network Code



Mobile Subscription Identification Number




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.

At any given time, a single IMSI essentially only has one network to choose from: whichever one the MNO works within the particular region the device is in. That means if the network has a poor signal, charges expensive data rates, or experiences a service disruption, the subscriber is out of luck. 

This is most likely to be a problem in the IMSI’s “home network”—the country its primary MNO covers. When the device roams, the carrier may have negotiated agreements with multiple MNOs that have overlapping coverage in another country. But they’re never going to give you access to another network in their home region.

An example of when Multi-IMSI helps

The automotive industry is arguably the sector that IoT has grown fastest in. It’s also an excellent use case for Multi-IMSI technology. Vehicles travel at high speeds and may be highly dependent on low-latency connectivity. You don’t just want to be covered by a network. You want the network with the best coverage. 

Increasingly, car manufacturers and suppliers have been using embedded SIMs so that they can incorporate them into the product earlier in the manufacturing process. Using a connectivity management platform with a Multi-IMSI SIM card makes it easier to deploy on-board units or vehicles globally because the manufacturer doesn’t have to worry about predetermining the deployment region in production. 

EMnify’s Multi-IMSI SIM card ensures that automotive IoT applications like fleet management and smart cars 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 redeploys its device to the UK (MCC 348).
  4. The SIM tries to reach the network in the UK with IMSI #1.
  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 connectivity 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 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.

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