Cellular devices need specific hardware and software components to connect to cellular networks. These components allow the device to identify and attach to networks owned by specific carriers, enable the network to authenticate the device to ensure it has access (and what kind of access it has), and associate the device and its network usage with a specific account.
As you explore cellular components, at times you may hear several different terms for components that provide the same core function, such as a SIM, eSIM, and iSIM. The difference between these components could have a significant impact on your device’s future functionality, security, and scalability, so it’s important to understand the differences between them.
In this article, we’ll examine each of these components and describe how their differences impact your device.
What is a SIM?
A SIM is a Subscriber Identity Module. It’s an integrated circuit component that has its own operating and filesystem. The SIM securely stores information needed to authenticate and access a mobile network, such as private keys, security algorithms, and identifiers such as the International Mobile Subscriber Identity (IMSI).
While a SIM includes a software component when people say “SIM,” they’re generally referring to the physical hardware that stores it: a SIM card. Standard SIM cards come in traditional form factors mini(2FF), micro(2FF), and nano (4FF) - but there are SIM chips in the embedded form factor (MFF2) - that are often ambiguously called eSIM.
SIM cards require a slot in the device and are removable, which allows someone to reuse their SIM card in another device or install a new card to access different networks. The SIM in the embedded form factor are soldered onto the device or module - and are not removable. When comparing traditional SIM form factors and embedded SIMs - the embedded SIM prevents theft of the SIM, as well as provides better physical characteristics in terms of shock and corrosion resistance. On the other side traditional SIM form factors can be changed in case a SIM swap is required.
Disadvantages of a SIM
Traditional SIMs - no matter if they are embedded or have standard plastic card form factor - have several disadvantages. In cellular IoT, one of the biggest disadvantages of traditional SIMs is that they come pre-programmed with a single identity, with a fixed functionality available on the SIM card at the time of production. While in the consumer case, humans have access to the SIM card and can change it in the case of need, for cellular IoT the devices are usually in the field at a customer site - without an easy possibility to swap SIM cards. So for cellular IoT changes that are happening after the SIM production can impact the service availability, such as the shutdown of radio technologies like 2G, and 3G or changing roaming partnerships and regulations.
All of these problems can be mitigated by using either an eSIM.
What is an eSIM?
An eSIM is a SIM card that can be remotely updated over the Air. With consumer devices such as smartphones and tablets, the eSIM is often referred to as just a software profile that is downloaded via a QR code. For IoT devices the eSIM is still a physical card or embeddable module - so the eSIM comes in all the form factors as standard SIMs. From a technical perspective, the eSIM that is used in typical IoT devices is referred to as M2M eUICC as standardized by the GSMA.
Advantages of an eSIM
eSIMs have several key advantages over traditional SIM cards. First and foremost, they can be provisioned with a new profile OTA. Traditional SIM cards have always been stuck with the existing functionality that was available when they were produced. With the eSIM OTA functionality, the eSIM can receive new profiles with different network coverage, enable in the future new radio technologies like 5G and cellular over satellite (NTN), or additional smart functionality can be updated on the eSIM such as applets or security mechanisms. This vastly improves your device’s ability to adjust to a changing environment and ensures that your SIM is connected for as long as your device's lifetime.
Disadvantages of an eSIM
From a technical perspective, there is no disadvantage of an eSIM compared to a standard SIM - everything a SIM can do - the eSIM can do as well and better. As one of the newest, most advanced SIM technologies, eSIMs are more expensive than traditional SIM cards and not all devices can make use of the over-the-air update capability - e.g. devices that do not allow to receive SMS.
What is an iSIM?
An iSIM is an Integrated Subscriber Identity Module. It’s essentially a more advanced eSIM. It provides the same functionality, but you don’t have to solder it onto the device’s circuit board. Instead, an iSIM has a dedicated space on the System of Chip (SoC), where it’s protected by a Tamper Resistant Element (TRE).
Integrated SIMs continue the tradition of making cellular components smaller and more efficient, and on the wireless module it is just a fraction of the size of an MFF2 (eSIM), which was already substantially smaller than a traditional SIM card.
Advantages of an iSIM
An iSIM has the same advantages as an eSIM: it’s more durable and tamper-proof, it can change carriers OTA (thanks to its eUICC capability), and since it’s even smaller than an eSIM and built right into the SoC, it has virtually no impact on your device’s design.
Since the iSIM is built into the chipset, you don’t actually even have to install it. No soldering necessary. The operator profile will be provisioned on the module during the chipset manufacturing. At scale, this can help you manufacture and deploy devices faster.
Disadvantages of an iSIM
Currently, iSIMs aren’t in widespread use. This is the newest SIM technology on the market, and so the chipsets and modules that are iSIM capable are limited.
Difference between SIM, eSIM, and iSIM
The most obvious difference between the SIM, eSIM, and iSIM is size. Smaller SIM formats give you greater flexibility when it comes to designing your device, and in some applications, building smaller, more discrete devices may be essential (such as surveillance or healthcare).
Additionally, eSIMs and iSIMs are always going to cost more than traditional SIM cards. They’re more complex and advanced, which makes them more expensive to produce and develop with. However, this upfront cost can save you the monumental cost (or disruption to your business) of having to physically replace SIM cards down the road.
Get the SIMs you need with emnify
While the iSIM hasn’t been implemented at scale yet, IoT manufacturers still have a range of options when it comes to SIM form factors. emnify’s global IoT SIMs are available in all traditional form factors, the MFF2 and also in iSIM, and you can add eSIM capabilities to any of them. These network agnostic eSIMs enable your devices to connect to more than 540 networks in over 180 countries.
We’ll even send you test SIMs for free. Request an trial pack, and we’ll send you two of our SIMs in the form factor of your choice with prepaid data plans and 60 days of access to our connectivity platform.
Shannon McCrocklin
Shannon has over seven years of experience communicating with audiences on behalf of businesses. She is passionate about making complex, technical topics easy to understand for readers of all backgrounds.
