• IoT Connectivity

Making the right decision: What is eSIM, eUICC and UICC?

Your understanding of what eSIM offers could limit your global IoT connectivity options.

10 min read


May 9, 2019

You’ve likely heard eUICC, eSIM and embedded SIM used in the IoT and M2M market, but might not know what the differences are. This confusion is completely understandable, as the industry often uses the three terms interchangeably. While they’re all related, there are some critical distinctions that will help you make better decisions for IoT connectivity.

In this article, we’re going to break down what exactly each of these terms mean, what the tech actually does, and how they interact with each other. This will help you make the right decision when it comes to connectivity for your IoT project as well as help you understand how your devices work a little better.

Before getting into exactly how connectivity software works, we’re going to cover the five basic SIM form factors.

Summary: Picking eSIM is not always required.

The term eSIM is confounding the understanding between the embedded sim form factor and the eUICC architecture that allows one to have multiple network profiles on a SIM. Understanding they are separate choices will provide more choices when combining different form factors with either eUICC or UICC, depending on your specific IoT requirements.

Key takeaways:

  • MFF2 is a chip that is embedded/fixed onto a device's circuitboard.
  • eUICC enables multiple network profiles to be stored on a SIM and can be updated using an eSIM management platform.
  • The eSIM management platform currently has limitations in it technical specifications and current business model that lock you in to specific providers.
  • A UICC profile can be updated using a specific Over The Air (OTA) platform.
  • Selecting UICC is a good alternative when one network is enough to meet the specific connectivity requirements.

Understanding SIM form factors.

The differences between SIM cards start with form factor.

Just as with computers and smartphones, SIM cards come in various shapes and sizes, and these different sizes don’t necessarily determine what kind of software the SIM will have implemented.

There are five primary types of SIM cards:

  • Full-Size (FF1).
  • Mini-SIM (FF2).
  • Micro-SIM (FF3).
  • Nano-SIM (FF4).
  • Embedded SIM (MFF2, previously referred to as VQFN-8).

The FF1 SIM card is the oldest of the five and also the biggest. Over the years, the size of SIM cards has gone down, which comes with obvious hardware benefits — such as extra space.

Each SIM size comes with one of three software options:

  • ICC.
  • UICC.
  • eUICC.

Mix and Match these components to meet your specific IoT connectivity needs.

The ICC standard is long outdated and generally out of use. It is only capable of using GSM and 2G, so you’re unlikely to come across it when choosing SIM cards for your IoT system.

UICC and eUICC, on the other hand, are still very much in use. UICC is the more common one at the moment, as it supports GSM/2G, 3G, 4G, and 5G. eUICC is an enhancement upon UICC and is the new standard in SIM cards. Alongside supporting all of the previously supported connectivity options, eUICC cards also support multiple carriers on the same device.

This means that — if it was on your smartphone — you could have AT&T and Vodafone on one phone, switching between the two at will. This is the main difference and biggest advantage that eUICC has over UICC.

Differences between embedded SIM vs. eSIM.

You may have noticed that we mentioned embedded SIMs and eUICC software, but left out eSIMs.

This is because there is a lot of confusion surrounding the term “eSIM” and what it is actually referring to, and searching the internet for answers only adds to the mess. Many think of eSIMs and embedded SIMs as being one and the same, with the “e” in “eSIM” representing “embedded” — “(e)mbedded SIM”. However, this is mostly due to people using these terms interchangeably in marketing and conversation, as well as poor naming conventions on the part of the GSMA. While the GSMA chose the name “eSIM,” to try and market to the IoT industry, it ironically ended up complicating the choices available to IoT customers instead.

Embedded SIM form factor (MFF2) — The hardware.

Embedded SIM refers to the physical form of the SIM itself (MFF2) and has nothing to do with the software on the SIM. The GSMA term “eSIM,” refers to the software architecture eUICC and not the embedded SIM form factor (MFF2) — hence the confusion!

Unlike traditional SIM cards, the embedded form factor is more suited for industrial conditions, such as high vibrations or/and temperature range and built to last longer. Making them a suitable choice for IoT applications.

In other words, an “embedded SIM” is one with the MFF2 form factor, and an “eSIM” refers to the eUICC software. This is why understanding the key concepts and jargon of the IoT industry is so important.

Since so many people get these terms confused, they end up thinking that they have to use eUICC if they want embedded SIMs on their devices, or that they can’t get eUICC software if they want to use removable SIMs — when, in fact, neither of these things is true.

Q. Why does the GSMA Embedded SIM Specification use the word ‘Embedded’?

A. Given the focus on M2M it is likely that the SIM will be soldered into the device (an embedded SIM form factor such as MFF1/MFF2), but of course the GSMA Specification also allows the use of removable M2M SIM form factors also.

eUICC — The software.

eUICC — as mentioned previously — is the software profile implemented on a SIM card. eUICC is purely software, and only refers to the OS on the SIM card. It can be used on embedded SIMs and regular SIMs, so having an embedded SIM doesn’t guarantee that you have eUICC, and vice versa. eUICC can connect to GSM/2G, 3G, 4G, and 5G, and its main advantage is its ability to host as many carrier profiles as you want.

An eSIM management platform is used to manage the carrier profiles on the devices over the air (OTA) without physically changing the SIM hardware on the device. This is one of the reasons why the IoT marketing material has often combined the MFF2 chip with the eUICC software. Yet, within the current UICC standard, there is the ability to update devices OTA.

eUICC has been around for a few years now, though it’s really only been used in devices where the carrier isn’t relevant to the user — like connected cars, smart home devices, etc. Because of this, the standards for eUICC are written in a way that creates an eSIM management platform lock-in, limiting your device’s flexibility in the future.

Fortunately, embedded SIMs can have both eUICC software and the more flexible UICC software. Depending on your IoT project, you may find that UICC is more than capable of meeting your needs.

Download our guide to IoT Connectivity to find out what else is important.

Should I select UICC and eUICC for my IoT project?

While the biggest factor separating UICC from eUICC is the ability to host multiple carriers, there are other distinctions between the two that need to be considered when choosing a connectivity provider for your IoT project.


UICC has one network profile, while eUICC can have multiple network profiles.

Option 1: UICC.

UICC is the older of the two, and as such is widely the standard. Its status as the standard means that it has much better implementation than eUICC. It’s more flexible, more easily manageable, and overall more convenient. Any OTA platform that is GSMA/3GPP compliant can access a UICC SIM, which makes it easy to make changes and switch carriers. The network profile on a UICC device can even be updated through a binary SMS. Thanks to these standards, a UICC device isn’t bound to any particular OTA platform.

To achieve this, you are required to have the keys to each SIM provided to you by your current network provider providing they have ownership of their own SIM keys. Once provided, your new provider can use an OTA platform to update the network profile, allowing you the flexibility to change providers in the future if partnership conditions change.

A key focus point to achieve this future flexibility is to make sure SIM key ownership is built into your operator agreements, something that is rarely standard.

Technically, you can use an OTA platform to change network profiles.

Option 2: eUICC.

eUICC is an updated version of UICC that can store multiple network profiles. This is particularly helpful in the IoT market since there are many cases where one carrier doesn’t cover enough area to support a large IoT system. However, choosing a network with global coverage, greater flexibility, and improved features can significantly reduce the necessity of relying on eUICC’s multiple profiles. Let’s go deeper.

What are the existing lock-ins with eUICC?

Unfortunately, due to the current eUICC regulations, using eUICC SIMs can come with the cost of complications — namely, lock-ins.

Technical — The way the eUICC standard is written.

There are two kinds of lock-ins with eUICC, the first being technical lock-ins. Technical lock-ins are unavoidable when using eUICC, meaning that any eUICC user will be subject to this kind of lock-in.

eUICC SIMs require a record. This record contains information like the IP address of the eSIM platform, granting it access to that platform. This record, however, cannot be changed once it’s been implemented. So your eUICC SIM will be locked to the first management platform you set it up with. This means that you’ll be locked to that platforms features — or lack thereof — for as long as you are using the SIM.

For example, say that you come across a platform that offers better features than your current one, and you decide you want to switch to it. The only way to do so is by physically swapping out the SIMs — even if they’re embedded — of all of your IoT devices. The larger your IoT network, the more difficult this is going to be.

Commercial — Watch out for the terms and conditions.

The second kind of lock-in is a commercial lock-in. A commercial lock-in is where your connectivity provider forces you to maintain bootstrap network profile on your SIMs, forcing you to pay connection costs even when you aren’t using the profile or hindering you in switching it after initial deployment. Bootstrap profiles are a way for your device to connect to any network available without needing to be established. They’re generally only meant to be used when first setting up your device or as a global backup profile if your device moves out of the coverage area of the active profile, allowing you to set the device up without having to connect to wifi or a network before interacting with the device.

When you are commercially locked-in, however, the cost of a bootstrap profile can needlessly increase your overhead, especially in large scale IoT projects.

Understanding the eUICC specifications.

When you get your eUICC SIM, the first thing that’ll happen is filling out the records. Your records are what allow you to connect to an eSIM management platform, and with eUICC, only one set of records is allowed (a.k.a., a technical lock-in). This record contains information like IP address, port number, and encryption. The technical name for these records is the Issuer Security Domain-Root — or ISD-R, for short.

Not only are you only allowed one set of records, but once they are filled out, they cannot be changed. Once an eUICC is assigned to one set of records, that’s the set of records it will always have. After you’ve set up your records, you can start adding network profiles to your SIM. If your SIM comes with a bootstrap profile, it will be set to Key 0. Ideally, you would have the choice to remove the bootstrap profile once you added your network profiles to the SIM, though some commercial agreements restrict this (a.k.a., a commercial lock-in).

To update your network profiles OTA, eUICC standards require you to use binary SMS to establish a connection with the network. From there, HTTPS protocol will use the IP address in your records to update your network profile.

For more technical information see the GSMA standards:

Deciding which is best for your IoT project.

In general, UICC and eUICC can both be implemented on all SIM form factors. So you have a lot of flexibility when deciding between the two.

It’s important to remember that while eUICC is an upgrade to UICC, the only real advantage it has is the ability to have multiple carriers on one device and switch between them in a more streamlined way, which is useful for frequent network changes But with that advantage comes the complication of lock-ins.

So unless you need to have multiple profiles on your devices, UICC could still very well be the way to go. Just remember to include future flexibility with the right to obtain the SIM keys in all commercial agreements with your operator.

If you need to have multiple profiles on your devices, then going with eUICC can be much more convenient than having some devices on one network and others on another network.

Keep in mind, though, that the management platform you choose when setting up your SIMs is the one you’ll be stuck with — unless you are willing to exchange all of the SIMs in all of your devices.

Can you manage with one network?

Understanding the differences between the connectivity options available will help you make the best decision when establishing your IoT project. IoT projects are typically long-term endeavours, so being educated and making wise decisions up front will have long-lasting benefits.

Always opt for global networks that don’t have any hidden lock-ins or costs, as it will keep your project flexible the changing market of IoT.

Onomondo is one example of such a global network with the addition of providing setup agnostic IoT connectivity, able to supply both UICC and eUICC solutions and offering the necessary flexibility of SIM key ownership in all commercial agreements.

By building a global network specifically for the IoT industry, with the specific mindset to limit the complexities of managing large scale and international IoT cases Onomondo is reducing the burden of managing commercial agreements with many network providers. This one network covers 180+ countries, most with two or more networks per country as well as permanent roaming. As a result, many businesses that would have to use eUICC could instead solely use Onomondo’s global network.

Want to consider all possibilities for your IoT cellular connectivity?

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