A key advantage of cellular IoT is that the infrastructure to support global deployment is already in place. The installed cellular network comprises robust, proven network technology that covers most of the populated regions of the globe.
Because cellular spectrum allocations are licensed and regulated, devices must be identified and authorized before accessing these networks. Most mobiles use a Subscriber Identity Module (SIM) for this purpose. SIMs were originally developed by the European Telecommunications Standards Institute (ETSI) for GSM networks. Today, SIMs are used by almost all mobile devices that connect to LTE (4G) networks.
Future cellular IoT devices will also require identification and authorization, but alternative technology is required because the conventional physical SIM is not a practical solution for billions of remotely deployed devices.
A SIM securely stores an International Mobile Subscriber Identity (IMSI) number, a 15-digit code uniquely identifying the card (and mobile) on the operator’s network. SIMs are typically associated with the company that issued the card and that operator deals with the access request even if the user wants to use a different operator’s network in, for example, another country.
When network access is requested, the IMSI and a one-time-use 128-bit authentication key (Ki) are relayed to the network for operator verification; the operator then authorizes the connection.
There are two major disadvantages of this system for cellular IoT deployment. The first occurs because conventional SIMs are discrete cards that plug in to the mobile device; that means they take up space, the mobile device needs a port (increasing costs and providing an ingress for dust and water), and if a SIM upgrade is required each card must be replaced – something that’s hardly practical for potentially millions of devices, many of which will be in inaccessible locations.
The second problem arises because of the SIM’s association with a single operator: While a SIM covered by a roaming contract can theoretically provide near global coverage by accessing local networks, the actual coverage depends on the number of roaming relationships the “home” operator has negotiated.
It also means paying the high data charges incurred while roaming. Because it stores only a single set of operator credentials, a conventional SIM becomes impractical for a cellular IoT device that is required to operate anywhere in the world. For example, in some regions, permanent roaming authorized by a remote operator is not allowed under local regulations, limiting the cellular IoT device’s usefulness.
An embedded SIM (eSIM) overcomes these problems. The device is no longer a separate, relatively large external plug-in; rather, as the name suggests, it comes in the form of a chip (known as an embedded Universal Integrated Circuit Card (eUICC)) that becomes part of the cellular device’s electronic assembly. That means it can be made tiny — an important consideration for compact cellular IoT devices — and removes the cost and vulnerability of an external port. (An eSIM can also be supplied in conventional micro- or nano-SIM card formats allowing use in older devices that feature a port and don’t have a built-in eSIM.)
An eSIM holds multiple local network operator credentials (in contrast to a conventional SIM card that can only hold one). An eSIM can also be “remotely provisioned” (reprogrammed over the air). Such capabilities not only allow for future technology enhancements but also repeated updates with profiles suitable for the local network – eliminating the regulatory challenges that come from constant roaming and allowing the connected device to take advantage of local (typically cheaper) data charges.
There are advantages for the networks too: Remotely provisioned eSIMs enable mobile operators to seamlessly add cellular IoT devices and apply data charges that would otherwise be directed to the home operator.
Cellular IoT solution providers such as Nordic Semiconductor are embracing eSIMs, and as a result, cellular IoT customers receive global connectivity without the considerable hassle of negotiating and managing relationships with network operators around the world.
Further, eSIMs also ensure local network connectivity out-of-the-box, resulting in operational efficiency and rapidly scalable IoT deployments.