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Understanding IoT SIMs


What are SIM form factors

The size and form of a physical SIM is known as its form factor (FF). Removable SIMs are available in a range of standard sizes ranging from 1FF, the first and largest SIM to be developed, to 4FF or nano-SIM, the latest and smallest SIM. There are also embedded SIM options—the MFF2 and USON-8.

Typical sizes of SIM form factors:

  • 1FF: 85.6mm × 53.98mm × 0.76mm (not used in modern IoT devices)
  • 2FF (Mini): 25mm x 15mm x 0.76mm
  • 3FF (Micro): 15mm x 12mm x 0.76mm
  • 4FF (Nano): 12.3mm × 8.8mm × 0.67mm
  • MFF2 (Embedded, M2M): 5mm x 6 mm x 0.9mm
  • USON-8 (Embedded): 2mm x 2mm x 0.5mm
  • iSIM (Integrated): Less than 1sq mm

A triple-cut card contains 2FF, 3FF and 4FF form factors for the SIM. The required sized SIM can be snapped out.

The history of SIMs

The first SIM – introduced in the early 1990s – was the size of a credit card, had little memory and required a 5V voltage supply.

In response to requirements for ever-smaller, more efficient devices, new versions of the SIM shrank in form factor from Mini to Micro to Nano. The new versions offered better performance, functionality and security – and a reduced voltage requirement of 1.8V.

In the early 2010s, the embedded SIM was introduced to overcome issues with removable SIMs. Issues included the space required on devices for the socket, the potential for damage or theft and the cost and complexity in managing SIMs separately to the devices.

The iSIM is the next step on this evolutionary path – completely removing the requirement for a separate SIM (card or chip) by integrating the SIM functionality into a System-on-Chip (SoC).

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eSIM: the foundation for iSIM

The introduction of embedded SIMs was a step change for IoT but it intensified the need to manage SIMs remotely – if you want to change to a different network, you can’t just swap one embedded SIM for another.

In response, the GSMA developed the eSIM specification. This introduces the eUICC SIM, which can store multiple operator profiles, and a Remote SIM Provisioning (RSP) solution to enable connectivity providers and end users to manage SIMs remotely.

As the eSIM specifications are designed for both embedded and integrated SIMs, the foundations are already in place for iSIMs to provide the seamless connectivity that’s essential for IoT deployments. The same RSP network components can be used to manage embedded SIMs and iSIMs.

Choosing a SIM for your device

Although the physical size differs, the capabilities of each form factor are the same.

The choice of form factor depends on considerations such as the amount of space available for the SIM and the environment in which the devices will be used. Prior to the introduction of remote network switching, removable SIMs had to be used in order to switch to a different network operator.

The removable form factors, 2FF–4FF, are available in consumer or industrial-grade quality. Industrial-grade SIMs come with a thicker pin plating to safeguard devices from corrosion, vibrations, and other environmental factors, such as extreme temperature conditions (typically between -40°C and +105°C).

The MFF2 SIM is an integrated circuit that’s designed to be permanently soldered into an IoT device. It has eight electrical pins, which are the same as the eight gold contacts on removable SIMs.

The USON-8 is a plastic ultra-thin small outline no-lead package with 8 connectors. USON-8 chips are built into cellular modules or modems.

Benefits of embedded SIMs

Embeddable SIMs are often the best choice for IoT devices for a number of reasons:

  • The chips can be hermetically sealed and soldered onto a circuit board. This reduces failures from shock, corrosion, and other environmental factors and makes them a better option for outdoor locations.
  • The expected lifetime is much longer than other form factors, so the SIMs are likely to outlast the devices in which they’re embedded.
  • Physical security is improved as it’s much harder for anyone tampering with the device to remove the SIM.
  • Without the need for an external-facing SIM slot, there’s more scope in device design for improved aesthetics and smaller sizes.

SIM terminology and functionality

UICC (Universal Integrated Circuit Card)

The Universal Integrated Circuit Card (UICC) is the hardware containing the SIM software and applications that enable a device to access cellular networks. A UICC contains a computer or microprocessor, its own data storage and software.

SIM (Subscriber Identity Module)

SIM stands for Subscriber Identity Module. Although it’s often used to mean the whole physical card or chip, a SIM is technically one part of the UICC. It’s responsible for securely storing data, including:

  • The Integrated Circuit Card Identifier (ICCID), which identifies the physical SIM itself
  • The International Mobile Subscriber Identity (IMSI), which identifies the mobile network to which the SIM is subscribed
  • Credentials and cryptographic security keys that identify and authenticate a subscriber on a network

A SIM passes identity and authentication information to a cellular modem. The modem performs the actual connection to the network.

IMSI (International Mobile Subscriber Identifier)

An International Mobile Subscriber Identifier (IMSI) identifies a user or device on a particular network. The IMSI is one of the key data items stored on a SIM.

Traditional SIMs contain a single IMSI, provided by the selected network operator. The IMSI is installed onto the SIM during manufacture and ties the SIM to the operator’s network (the home network). Depending on the roaming agreements that the operator has in place, devices can roam onto other networks, but the only way to change network operator or service provider is to physically replace the SIM with a SIM from a new provider.

Replacing a SIM in a device is often not practical in IoT. Devices may:

  • Be located in inaccessible places
  • Be part of a deployment of hundreds of thousands (or more) devices
  • Use SIMs that are soldered into the devices

Some providers offer multi-IMSI SIMs to offer more flexibility in connecting to different networks.


A Multi-IMSI SIM can store multiple IMSIs, enabling devices to switch to different networks without physically changing the SIM.

Connectivity providers offer multi-IMSI solutions with different levels of sophistication, functionality, and security. Some solutions can use over-the-air updates to download additional IMSIs and remotely manage the IMSIs on a SIM.

Despite the benefits of multi-IMSI solutions over traditional SIMs, they have some disadvantages:

  • Solutions that can’t download additional IMSIs over-the-air may not be able to provide optimum connectivity for the devices over their lifetime
  • Many network operators don’t want to provide their IMSIs to a 3rd party, particularly if the solution uses the same security credentials across all IMSIs
  • With no global standards and certification in place, there’s no


To provide a more robust and standardised method for remote global SIM provisioning, the GSMA introduced eSIM. This solution is designed to meet the needs of industries where fast time-to-market, low operational costs, low complexity, and high reliability are critical to successful deployments.

In the GSMA definition, eSIM stands for embedded SIM and refers to the Embedded SIM Remote Provisioning Architecture, introduced around 2013. The GSMA definition of eSIM encompasses the SIM itself and the systems required to provision and manage network profiles.

eSIM technology provides the same functionality and security as conventional SIMs, with enhancements that enable:

  • Secure, over-the-air updates for remote provisioning and management of profiles
  • Storage of multiple network profiles on the SIM

The GSMA chose to use the word embedded on the basis that this architecture was designed primarily to support devices with fixed SIMs. However, many IoT devices use removable SIMs and it’s as important to manage connectivity remotely for these devices as it is for fixed SIM devices. Fortunately, SIMs of all form factors can be enabled to use eSIM.


iSIM stands for integrated SIM. An iSIM is a non-removable eUICC SIM that is integrated into a secure enclave alongside the processor and modem on a system on a chip (SoC). The iSIM offers the potential for lower power consumption, footprint, and manufacturing costs over traditional SIMs.

eUICC (embedded Universal Integrated Circuit Card)

eUICC stands for embedded Universal Integrated Circuit Card (eUICC). It refers to the software component of eSIM that runs on a UICC and provides the capability to store multiple network profiles that can be provisioned and managed over-the-air (OTA). The term eUICC is often used to mean the whole physical card or chip.

Although it was envisaged that eUICC SIMs would primarily be in the form of soldered chips or implemented within a system on a chip (SOC), eUICC SIMs can be any form factor.


The term eSIM is often used to mean an embedded SIM (such as the MFF2), regardless of whether it is an eUICC-enabled SIM. Therefore, to avoid confusion, the term eUICC is often used instead of eSIM to refer to the GSMA eSIM architecture and solutions.

Remote SIM Provisioning (RSP)

Remote SIM Provisioning (RSP) is the secure management of network profiles on eUICC-enabled devices using over-the-air commands.

RSP uses secure communication channels to download, install, activate, and delete network profiles on devices. To ensure security and interoperability, all eUICCs and RSP systems must achieve GSMA certification to operate within the eSIM ecosystem.

RSP consists of two key elements:

  • Subscription Management – Data Preparation (SM-DP) – responsible for securely storing network profiles.
  • Subscription Management – Secure Routing (SM-SR) – responsible for managing over-the-air provisioning.

The SM-DP and SM-SR systems may be implemented separately or in a single platform.

Network Profiles

A network profile contains the operator subscription data, including the authentication credentials, as well as SIM-based software and applications. The Trusted Connectivity Alliance (formally the SIM alliance) has defined the content and structure for eSIM profiles to ensure interoperability between all parties in the eSIM ecosystem.

eUICC SIMs can hold multiple profiles, with each profile acting as a virtual SIM within the physical SIM container. Only one profile can be active (or enabled) at any time.

Two types of profile are used:

Bootstrap Profiles

A bootstrap profile (also known as a provisioning profile) enables a device – at a minimum – to access a cellular network in order to communicate with the RSP system when it first starts up. The RSP system can then download and activate an operational profile for the device to use.

Most providers supply an IMSI in the bootstrap profile that provides access to the operator’s network and roaming agreements. This enables the device to connect as soon as it starts up.

Step 2 Profiles

An operational profile (also known as a step 2 profile) provides a device with full access to the operator’s network.

Downloading and enabling a new operational profile means a device can switch to a different network operator without the need to physically change the SIM.

While an eUICC is an integral part of a device, each profile stored in the eUICC remains the property of the operator and is supplied under licence.

The number of profiles that can be stored on an eUICC is limited only by the memory available and the size of each operator’s profile. eUICCs require a minimum memory capacity of 512kb but some have a capacity of several megabytes.

eUICC Manufacturer (EUM)

eUICCs can only be manufactured by accredited organisations. An eUICC manufacturer (EUM) uses data from the operator and creates a personalised profile for each eUICC.

Disclaimer – This post has only been shared for an educational and knowledge-sharing purpose related to Technologies. Information was obtained from the source above source. All rights and credits are reserved for the respective owner(s).

Keep learning 📚 and keep growing 📈

Source: Eseye

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