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eSIMs – What and How…

SIM Cards

If you have bought a new iPhone or a smart watch in the last couple of years you may have heard the term eSIM mentioned. This article aims to provide a little background on why eSIMs came to be, how they work and the differences for consumer (e.g. smart phones, etc.) and Machine-2-Machine (M2M, for instance connectected cars, smart energy meters, etc.) devices.

Firstly, let’s briefly cover what a SIM card actually does..

What is a SIM?

A SIM or Subscriber Identity Module is essentially a very small specialised computer used to securely store and manage identity information. While plastic SIM cards have changed size over the years (from credit card size in the early 90s through to the nano format used by Apple, Samsung and others today), the basic principle of how a SIM operates has changed little as 2G, 3G and 4G technologies were developed and established.

Mobile Network Operators (MNOs) typically purchase and own traditional SIM cards. Each SIM has a unique identifier (Integrated Circuit Card Identifier or ICCID) that the MNO maps to a particular customer’s phone number (known as the Mobile Station International Subscriber Directory Number or MSISDN). This mapping can be changed, like for instance if a customer loses their phone and is shipped a new SIM card.

The most important aspect of a traditional SIM card is that the identity (known as a profile) is written to the SIM as it is manufactured and cannot be changed. This was part of the value of a SIM card, its purpose was to ensure a device connecting into a network was authorised.

Why eSIMs?

Some readers may be wondering – what’s the problem with a traditional SIM? There are different issues for both consumer and M2M devices, explained below.

From a consumer perspective, the biggest factor has been the demand to enable smaller devices to connect to into 3/4G networks. The best example of this is the smart watch, which consumers expect to be compact, water-proof and reliable, something quite challenging for manufacturers if they need to fit a removable SIM slot. Even for phones, as more and more functionality is squeezed into shrinking real-estate, maintaining a physical SIM slot is a compromise.

For M2M manufacturers, the challenges presented by physical SIM cards are much greater. As a brief aside here, one thing we didn’t cover earlier is that in addition to plastic SIM cards, versions are also available in chip form that manufacturers can embed into their equipment. Aside from the physical package, a traditional embedded SIM operates in exactly the same way as its plastic counterpart. It has an ICCID and is mapped to a MSISDN by the manufacturer’s chosen MNO. This last point highlights one of the massive barriers to manufacturers – if they fit a traditional SIM into their equipment (e.g. a connected car, smart meter, MRI scanner, etc…) they are committed to a contract with that MNO for the lifetime of the product. Yes, they could fit a removable SIM slot, but doing so presents many challenges (theft of SIM card, outages caused by vibration, etc.).

The net result is that uptake of cellular technology in M2M equipment has been quite low. Over recent years various specialist vendors have produced solutions to the problem – multi-profile SIMs that can be switched from one operator to another after manufacture. They have helped and many of the vending machines, smart meters and similar that are in the wild today use such products. What these solutions share in common is that they are proprietary – while you can change MNO, manufacturers are committed to the vendor of the multi-profile SIM cards for the life of their product.

Standards-Based Solution

The body representing MNOs around the world (GSMA) recognised this barrier to adoption and for over a decade have been developing a more sustainable solution. The goal was to produce an industry standard approach to allow SIM cards to be switched from one MNO to another after manufacture, a process that could be managed over-the-air (OTA) and crucially, one that would not tie manufacturers into a commercial arrangement with any single company.

The initiative took some time to gain momentum – while most MNOs welcomed the opportunity to open up cellular connectivity to new markets, not quite as many were as keen on making it easier for customers to switch away from their incumbent supplier; however the first ratified version of the standard was approved early in 2016, with products arriving in the consumer space later that year.

While the term eSIM is generically used to cover both consumer and M2M implementations, the two are really quite different. The principle difference between the them relates to how profiles are loaded and/or switched on the device, but a fuller explanation is listed below.

eSIM – Consumer

The consumer version is specifically designed to allow control by the device owner. This makes sense and retains exactly the same concepts people will be familiar with today – e.g. you choose your MNO.

The consumer eSIM architecture requires a component referred to as the Local Profile Assistant or LPA, which must be delivered by the device manufacturer and which initiates the process of loading or switching profiles on the eSIM. Apple implement this on the iPhone (XS/R/11) via a QR code supplied by a MNO. Once scanned, the phone is able to download the operators profile securely onto the eSIM and activate it.

The consumer eSIM solution requires many other components to be deployed (either by the manufacturer themselves or a partner) along with commercial agreements with each MNO. This process takes considerable time even for a company such as Apple. For example, the iPhone XS was released in 2018 and initially supported only one UK MNO (EE). Since then only one other major UK MNO (O2) has been added, with both Vodaphone and Three yet to be supported (at the time this article was written!).

It is for this reason that we are likely to continue to see dual-SIM solutions (e.g. devices with both a removable SIM slot and an eSIM) delivered for the foreseeable future.

eSIM – M2M

For the M2M eSIM version, it is the device manufacturer that controls which profiles are loaded and activated. If you think for a moment of a car manufacturer, they could, for instance, specify profiles on a per-country/region basis or even the status of the vehicle (for instance, one profile during manufacture, switching profile during poor coverage, etc…).

The diagram below is taken from the GSMA M2M standard (SGP.02, version 4.0 at the time this article was written) and shows the full architecture:

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Explanations of the key components are listed below:

  • eUICC: This is the physical eSIM module, typically supplied in chip form that is integrated into a device.
  • SM-SR: This component manages the loading and activation of profiles on the eSIM. The SM-SR is typically either owned/operated by the M2M manufacturer or delivered to them by a service provider.
  • SM-DP: This component is responsible for preparing, storing/securing operator profiles and pushing them to eSIMs remotely. The SM-DP is typically owned/operated by the MNO.

Later versions of the GSMA standard for M2M eSIMs focussed not just on remotely switching/managing profiles, but also the ability to make changes to the above architecture. For instance, a manufacturer could initially take a subscription management solution as a service from either their chosen MNO or even an eSIM manufacturer, but later choose to host the SM-SR themselves once their solution matures. While commercial factors may well influence such a decision, the ability to change the SM-SR architecture is crucial.


That brings us to a close and hopefully readers will have gained some insight into why eSIMs will play an increasingly important role in both consumer and M2M devices. With the deployment of 5G, eSIMs should provide a catalyst to enable more and more devices to be connected.

For more information, a whitepaper explaining the eSIM standard in more detail can be found on the GSMA website. Additionally, the latest standards document for the M2M version (4.0 at the time this article was written) can be found here.

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