The hitchhiker’s guide to IoT roaming

As IoT businesses push for global reach, they often encounter challenges in achieving seamless cellular connectivity abroad. This problem is especially difficult in regions with varying regulatory environments.

Maintaining consistent communication for devices across various geographies can be both technically and logistically challenging, and it’s critical for IoT companies to have a global strategy in place.

In this blog, we explore the fundamentals of SIM technology and cellular networks, explain why roaming restrictions exist, and explore what you can do to successfully navigate these restrictions.

The challenge of global roaming for IoT companies

IoT roaming presents significant complexities and obstacles, especially for global enterprises. To illustrate this, let's consider a scenario featuring a fictional electric vehicle manufacturer named Volt.

Let’s imagine Volt manufactures its vehicles in Germany and intends to ship them globally to sell in different markets worldwide. Integral to these vehicles are telemetry devices designed to monitor battery performance. These devices depend on SIM cards for connectivity to cellular networks, enabling data transmission.

In an ideal world, Volt would embed these SIM cards into the vehicles in the manufacturing process in Germany. Subsequently, the SIM cards would activate upon sale, establishing a connection to the local network in the customer's country.

This process seems straightforward in theory. However, its practical implementation is fraught with challenges.

The core issue lies in the need for a SIM card that can connect to any network worldwide without restriction. Unfortunately, the current regulatory framework governing cellular networks varies significantly across different regions. These differences complicate the pursuit of global cellular connectivity and create a significant logistical challenge for companies like Volt.

Before we can understand the issues and potential solutions companies like Volt can use to overcome the challenges, we need to take a look at some fundamental concepts of SIMs and cellular networks.

The basics of SIM technology

Let's first discuss the anatomy of a SIM from the top down. At the highest level, a SIM is a piece of hardware with memory and a small amount of processing power (like a mini-computer). A SIM can take different physical forms:

• The traditional SIM in a plastic card
• A SIM chip embedded into devices

No matter its physical form, SIMs have the same fundamental functions.

Types of SIMs: UICC vs eUICC

In the same way a desktop computer can have more than one user profile or account, some SIMs can store multiple SIM profiles on the same card. SIMs are either UICC or eUICC.

If the SIM is a UICC, it can store a single SIM profile. If a SIM is an eUICC (​​Embedded Universal Integrated Circuit Card), it can store multiple SIM profiles. eUICC SIMs have this ability thanks to extra built-in technology and software that manages, downloads, enables, and disables SIM profiles. The number of profiles stored on an eUICC SIM is limited only by the memory available in the SIM hardware.

What’s a SIM profile?

The purpose of a SIM profile is to store network-specific information for authentication and identification on cellular networks (more on this later). SIM profiles have a unique identifier called the ICCID (integrated circuit card identifier). The ICCID is essentially the ID number of the SIM profile—internationally unique and identifiable.

SIM profiles on a SIM are analogous to the user profiles on desktop computers. Only one SIM profile can be active at a time to control and use the SIM hardware. And there’s no visibility between profiles. All data is partitioned from others and contained within the profile.

What’s an IMSI?

Moving on to the critical part: the IMSI (International Mobile Subscriber Identity). The IMSI comprises three codes:

1. MCC
2. MNC
3. MSIN

The combination of the MCC and MNC fully identifies the home network of the SIM profile, called the Home Network Identity (HNI). The MSIN is the unique component of the IMSI. It’s what cellular networks use to recognize and verify a SIM profile.

You might think the IMSI sounds similar to the ICCID. However, a crucial difference is key to understanding when navigating roaming restrictions.

ICCID vs. IMSI: What’s the difference?

Think of the ICCID as your fingerprint—unique to you and unchanging. However, when traveling, you don't use your fingerprint for entry at borders. You use your passport. Suppose you have dual citizenship, with passports from both the USA and France. At an airport in the USA, you'd present your US passport. But when entering Europe, you'd use your French passport for a smoother entry.

This analogy applies to SIM profiles too. A SIM profile has one permanent ICCID—its "fingerprint." But a SIM profile can have multiple IMSIs, acting like different "passports" that can be selected for identification purposes depending on the country and available networks offering the best connectivity.

In short, while the ICCID identifies the SIM profile, IMSIs are used by cellular networks to identify the SIM profile. This difference, as we'll discuss soon, is key to navigating permanent roaming restrictions.

What happens when a SIM goes abroad?

Let's take a look at how cellular networks work and how roaming is enabled. Cellular networks include many different components of network infrastructure, but to understand roaming we just need to mention two of these:

• Home Location Register (HLR) or Home Subscriber Server (HSS)
• Visitor Location Register (VLR) or Mobile Management Entity (MME).

The HLR and HSS have largely the same function, however HLR is the variant for 3G networks. For LTE and beyond, the HSS is used. Similarly, the VLR and MME have the same function. In this case, the VLR is the variant for 3G networks. LTE and beyond use the MME. For the sake of simplicity, we’ll use HSS and MME in the remainder of this article.

Every mobile network operator (MNO) has a database that stores information about all authorized permanent or _home _users. This database is called the HSS. The IMSI is the primary key for each record in the HSS, and each record includes details of the SIM profile identified by that IMSI.

Every MNO has another database that stores information about all active users_ _in the area covered by the network. This database is called the MME, and it contains records of both network “visitors” and "home" users. Visitors have an IMSI with a different country code (MCC) to the visited network.

When a visitor roams onto a network, the MME receives the record with subscriber and authentication information from the visitor's HSS. Each record in the MME is temporary and only exists as long as the user is active on the network. When the user leaves the area, the record is deleted.

How do SIMs connect to cellular networks abroad?

When a SIM attempts to attach to a network in a country other than its "home" (as in, a country with an MCC different from the MCC in the IMSI of the SIM in question), the SIM is said to be "roaming." So, it’s registered as a visitor on any network it connects to in that country. Bear in mind that a SIM can only connect to networks with which its home mobile network operator (MNO) has roaming agreements.

This part is where things get interesting. Some countries have roaming restrictions, meaning a SIM can only “roam” in the country for a certain period before it’s kicked off the network and no longer allowed to connect. A SIM can only reconnect in this scenario if it re-attaches using another IMSI. To avoid getting kicked off again without having to continually re-attach with new IMSIs, you can use an IMSI local to that country (i.e., an IMSI in which the MCC is the MCC of the country in question).

What is permanent roaming?

When the concept of roaming originated, it was intended for humans traveling with mobile devices who typically only stayed roaming on a visited network for a short period of time.

Countries with restrictions only allow roaming for a certain period before the visitor is disconnected from the network. The permitted time is specified by local regulators or MNOs themselves. Permanent roaming is when a user remains active on the visited network for an extended period.

The prevalence of permanent roaming situations has rapidly increased with the exponential increase of IoT adoption worldwide. Deployed IoT devices often remain connected to networks outside their home networks for extended periods, creating issues that weren’t foreseen when the concept of roaming was invented.

The challenges of permanent roaming restrictions

Consider our example, Volt, in which cars are manufactured with SIMs built in Germany and shipped to automotive retailers worldwide. Let’s assume the cars’ SIM profiles are from a German MNO with German IMSIs.

When the cars are purchased in other countries and the SIMs are activated, they attempt to connect to a network where they’re considered "visitors." In this situation, the SIM will inevitably be permanently roaming on the network in the country where the car was purchased. Technically speaking, this would be a viable option as long as the country in question does not have restrictions on permanent roaming.

Many IoT products encounter this situation. Their product lifecycle is global: Devices are manufactured in one location and shipped to multiple markets across the globe. Given the unpredictability of a product's eventual deployment location, SIMs must be integrated during manufacturing. The device automatically connects to the local network as a roamer upon activation. These enterprises rely on permanent roaming.

So what's the problem? Due to the lack of clarity about the duration of stay and resource usage of devices engaging in permanent roaming, many operators and regulatory bodies worldwide are growing skeptical and increasingly resistant to allowing IoT devices to roam indefinitely on their networks. For this reason, a number of countries have implemented permanent roaming restrictions, and some have entirely banned permanent roaming.

Roaming restrictions are a big concern for businesses operating in the global IoT sector. They exemplify the fact that roaming was geared toward smartphones and tablets and was designed for travel, not IoT.

How can IoT companies overcome the challenges of permanent roaming restrictions?

In countries where permanent roaming isn’t possible, companies like Volt have some options to make sure their devices stay connected:

1. Use SIMs from local MNOs in the devices shipped to the country in question

This solution introduces another level of complexity to the manufacturing process, making inventory management a logistical nightmare. The company must forecast where each manufactured device will go, and inventory can’t later be moved between countries if needed.

It also means the company needs to establish technical and commercial relationships with multiple MNOs, which can delay market entry and adversely affect profit margins. The limited access to IoT devices after deployment means changing SIM cards and providers on the go is a difficult—if not impossible—undertaking. But it's understandably tricky to plan for the entire lifespan of your device when markets and technology evolve so quickly.

2. Use eUICC SIMs with multiple profiles to store local profiles on the SIMs

If a device is deployed in a country with permanent roaming restrictions, you can activate an eUICC profile of a local operator so the device can connect to a local network. It is not considered to be roaming in this scenario. There are drawbacks to this solution, however. For example, there’s limited storage on SIMs, so depending on the number of countries that require local profiles, there may not be space for them all on the same SIM. If different profiles are stored on different SIMs for different regions, you’re back to the original problem of increased logistical overhead.

3. Alternate among several roaming profiles

If your device is deployed in a country with permanent roaming restrictions and for which your eUICC SIM does not have a local profile (but has more than one profile), you can change profiles periodically (e.g., every 90 or 45 days) to comply with regulations. In this scenario, you periodically change profiles before the maximum roaming time limit is reached so that you never achieve permanent roaming status.

4. Multi-IMSI solutions

The optimal solution to overcome permanent roaming restrictions is to leverage multi-IMSI technology. Also known as localization, the process involves switching the IMSI to that of a local network operator.

Localization

As we talked about earlier, a single SIM profile can have multiple IMSIs associated with it, like a person traveling with multiple passports. Multi-IMSI SIM profiles use an intelligent applet that selects the most appropriate IMSI for each location. So when a SIM enters a new country, it will use an IMSI for a local network—if it has one—for connecting. This solution means the IMSI will be stored in the HSS of that network (as opposed to the MME) and won't appear to be roaming at all. And no roaming means no roaming restrictions.

IMSI rotation

Another related solution is IMSI rotation. This solution might be applicable in a situation where a SIM profile has multiple IMSIs, but none are local to the country where the device is deployed. IMSIs are rotated so that, within the restriction window, the IMSI is switched to another, thus appearing as a completely different user to the local network. This rotation continues on a defined schedule.

Using SIMs equipped with multi-IMSI technology is a modern solution to the modern problem of IoT device roaming. To leverage this technology, you need to choose a provider that has experience supporting successful global IoT deployments.

Successfully navigate IoT roaming with Telnyx

Understanding the intricacies of global IoT connectivity is crucial for IoT businesses. The challenges of permanent roaming restrictions and the quest for seamless global connectivity underscore the importance of choosing the right technology partner.

Telnyx IoT is designed with the future of IoT in mind. It offers a robust foundation for overcoming the hurdles of roaming. Telnyx IoT SIM cards are eUICC-enabled with multi-IMSI technology. With Telnyx, you can unlock the full potential of your IoT devices, leveraging our global network for unparalleled connectivity.