The topic of embedded SIM (eSIM), and its successor, the integrated SIM (iSIM), has been a prominent one in the Internet of Things (IoT) for the last five years, promising a fundamental change in how connectivity is delivered. In this article Matt Hatton, founding partner of Transforma Insights, explores the background to eSIM/iSIM and the implications for IoT adoption, particularly the way in which it has reduced the cost of deploying cellular-based IoT.
There are a number of interlinked technology concepts tied up in the eSIM, involving hardware, software and connectivity. The starting point for any discussion on eSIM is the physical entity. A lot of terms are used interchangeably here. The term ‘SIM card’ is still generally used to refer to the physical integrated circuit that manages the authentication of mobile devices. However, it should be referred to as the universal integrated circuit card (UICC). The UICC is the integrated circuit, including CPU, ROM, RAM, etc., installed on mobile phones or other cellular-connected devices to run the Subscriber Identity Module (SIM) application. The ‘SIM’ is the name that should more accurately be given to the application rather than the physical card. Nevertheless, many commentators refer to the SIM as a physical item.Â
Evolving Form Factors and What It Means for the SIM
The UICC/SIM card has had several different form factors. Each evolution was focused on saving space on devices, getting gradually smaller, but each as a plastic removable card. This changed with the introduction of the machine form factor (MFF) card, which was particularly aimed at better addressing the needs of IoT devices. Unlike the earlier generations of the SIM card, the MFF is not removable. Instead, it is soldered directly onto the circuit board. It is more secure, more ruggedized and better able to withstand extremes of temperature and vibration, making it more appropriate for IoT.
The latest form factor evolution sees the UICC disappear altogether, with the SIM application existing instead as a function (or software, hence ‘Soft SIM’) on another processor. This implementation lacks some of the security advantages of the physical SIM card, whether embedded or removable. That is to be balanced against lower production costs, space savings that can be made within the device and the potential to develop more robust hardware that can be hermetically sealed. The inherent security weakness of the Soft SIM approach, about which mobile network operators (MNOs) were highly sceptical, meant that the concept had to be evolved, specifically to the integrated SIM (iSIM). With iSIM, the SIM functionality is still software-based but is implemented as a secure enclave in a system-on-a-chip (SoC) architecture that integrates the SIM function with a processor and modem. This creates an inherently more secure environment, although not as secure as a dedicated component.
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The embedded SIM MFF provides several benefits in terms of building IoT devices that are smaller, more robust and more secure. However, the biggest implication comes from the fact that the SIM card is not removable. As a result, it was necessary to develop the capability to change the SIM profile through a mechanism other than physically swapping out SIM cards. That mechanism is remote SIM provisioning (RSP). This ability to manage the SIM remotely could be considered another additional benefit of embedded SIM, although it is not an exclusive feature of embedded SIMs. Remote management is a feature that could also be applied to removable form factors too.
The other evolution is that of nuSIM, which Deutsche Telekom pioneered. It was designed in the beginning to work with NB-IoT, and was subsequently packaged with LTE-M. Deutsche Telekom offers it on all LPWA tariffs. Effectively this is a variation on the iSIM concept but designed for very constrained devices, with reduced size, power consumption, processing, memory (the nuSIM profile is only 500 bytes) and cost compared to traditional SIMs and embedded SIMs. There is no capacity for OTA remote SIM provisioning currently with the nuSIM, just a single IMSI. The aim with nuSIM was always to develop a SIM format whose parameters work well with the types of use cases that might be supported by NB-IoT, i.e., for a static connection with the connectivity costs paid for the lifetime of the device. This is envisaged as an open ecosystem that will welcome other operators and promises relatively quick integration for those that decide to adopt, although other MNOs have yet to make any commitments. We expect further developments during 2022 and a ramp-up in adoption.Â
The Future Is Compact
The arrival of the eSIM, iSIM and remote SIM provisioning represents a significant change in how cellular-based IoT connectivity is delivered. It makes for smaller devices with lower requirements for power. It also streamlines the logistics costs by removing the need to send SIM cards to be plugged into the device. Furthermore, it provides a much better guarantee of compliance with local regulations, avoiding the prohibition on using overseas roaming SIM cards in some countries (e.g., Brazil, India and Turkey). It also gives end-users more freedom to change their connectivity provider, which has some potential concerns for network operators.
It also makes for cheaper cellular connectivity, as identified by a recent report published by Transforma Insights titled Using eSIM and iSIM will save money for IoT deploymentsOpens a new window . According to the report, using eSIM or iSIM can save between 8% and 13% on the connectivity cost for an IoT device’s lifetime. While hardware cost may be slightly higher than for plastic SIMs (but falling), and there is a cost associated with the remote SIM provisioning, the savings more than outweigh it, for instance, from optimising data costs through localization and reduced power draw.Â
Innovation and SIMplicity
Overall, eSIM and iSIM, with RSP, will increasingly become the norm for cellular IoT devices. Within five years, we expect the vast majority of new cellular IoT devices to make use of both MFF form-factor and RSP. There are exceptions. Many genuinely roaming devices will continue to use roaming, although the number of applications for which this is true (e.g., shipping containers) is limited. Also, devices intended for deployment only in a single territory will frequently continue to rely on a single pre-set IMSI (or multi-IMSI). Other commercial alternatives such as the use of multi-IMSI SIMs and permanent roaming are also valid alternatives in some circumstances but will see declining popularity.
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