01 July 2020
Reading Time: 5 mins
01 July 2020
Reading Time: 5 mins
An IMSI (International Mobile Subscriber Identity) is a globally unique number that cellular networks use to identify and authenticate every user and/or device on a GSM or UMTS network. IMSIs are used in any network that connects with another and are stored on the SIM card.
A multi-IMSI SIM contains many IMSIs, each of which can connect to a different network. There is usually one bootstrap IMSI that comes pre-loaded, although more advanced SIMs can accommodate multiple bootstraps, and some SIMs can be updated with additional IMSIs over-the-air.
For most IoT deployments, a single MNO doesn’t provide the flexibility to handle global installations and single SKU products, mobile devices, gaps in coverage, roaming restrictions, and changes in the commercial and service landscape in mobile telecommunications. Managed connectivity solutions with multi-IMSI SIMs can address these requirements.
They are able to offer a fallback solution because there are multiple bootstrap IMSI profiles – and connection options – stored on a single SIM. This means that it can maintain high levels of connectivity and device uptime across multiple regions and countries, and switch networks to respond to circumstances like network failures and roaming restrictions to ensure the IoT device remains connected to the best available network.
Using SIMs pre-loaded with bootstrap IMSIs from Tier 1 providers – well-established network providers with extensive, verified roaming agreements – provides the best guarantee that every device will connect out-of-the-box, anywhere in the world.
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 Remote SIM Provisioning system (RSP) 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. Some multi-IMSI SIMs may need to use a different pre-configured bootstrap IMSI depending on where the device is installed.
The Multi-IMSI SIM is configured to dynamically determine which IMSI is best to use from its available bootstrap IMSIs. That way it can connect even if it encounters unexpected problems – without any external intervention.
If a device modem loses connection or fails to connect to a network, after a set period of time a SIM application automatically rotates the SIM onto the next IMSI and presents the alternative to the modem. The modem is refreshed to use the alternative settings.
The length of time taken for an IMSI to rotate, either on the device or OTA, depends on the following factors:
You can usually manage configurations and optimise timing using your connectivity management platform.
Be careful! Not all multi-IMSI SIMs are equal. Some provide a limited capability to swap IMSIs based on pre-configured rules. Others provide a fully functional solution that ensures devices can connect out-of-the-box and remain connected for their lifetimes.
Multi-IMSI is a concept with no defined specification and is not governed by a global standard or certification system, whereas eUICC is a GSMA standard for Remote SIM Provisioning (RSP) used with eSIMs.
Both multi-IMSI SIMs and eSIMs can be in any form factor, store multiple IMSI profiles and enable the switching from one network to another, but there are some key differences:
Some network operators don’t provide IMSIs to third parties for security reasons but will supply eSIM network profiles to their partners. For some IoT deployments requiring specific MNO connectivity, this prohibits the use of a multi-IMSI solution where IMSIs are preloaded onto the SIM.
Profiles supplied for a multi-IMSI solution can be preloaded onto the SIM as bootstraps for automatic rotation and then updated via SMS whereas eSIM profiles must be requested from the MNOs SM-DP or loaded into your own SM-DP at the point of switching.
eUICC SIMs don’t use automatic rotation of bootstrap profiles. Once switched, the new eUICC profile is the primary operator on the SIM and if configured, the SIM will fallback to another profile. This can result in the device being offline for up to 25 minutes before the fallback is activated.
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.
For solutions that do offer it, updating IMSIs over-the-air requires the IoT device to be online for the duration of the update. This can take anything from 10 minutes to a couple of hours which is particularly difficult for battery-powered devices or those that connect intermittently. Updates must be planned to coincide with the device’s connectivity patterns and the impact on battery life should be carefully considered.
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 guarantee that different parties can or will operate together.
IoT devices often operate in various locations globally. Multi-IMSI SIM cards allow these devices to connect to multiple mobile networks, ensuring reliable connectivity across borders. This is especially valuable for IoT applications that involve tracking, monitoring, or managing assets in different countries.
Multi-IMSI SIMs can maintain high connectivity by switching networks in response to circumstances such as roaming restrictions, fluctuations in network quality, faults or outages. Multi-IMSI SIMs can switch to alternative networks automatically, providing network redundancy and ensuring continuous operation even in the face of network issues.
Almost every mobile network provider claims to have hundreds of roaming agreements with other providers to give them global coverage. But data rates for roaming can be costly. Multi-IMSI SIM cards can help optimise roaming costs by selecting the most cost-effective network available in a specific location. This can be crucial for managing operational expenses in IoT deployments.
IoT applications may have varying requirements for data speed, latency, or reliability. Multi-IMSI SIM cards can enable intelligent network selection, allowing devices to choose the most suitable network based on performance metrics or cost considerations.
For most IoT deployments, zero-touch, out-of-the-box connectivity is essential. SIMs must be able to connect to a network from any location. If deploying in multiple countries or regions, the use of a single multi-IMSI SIM card can simplify logistics of deployment and device management. Multi-IMSI SIMS enable a single-SKU solution reducing manufacturing complexity and cost.
As IoT deployments scale, managing connectivity across different networks and regions can become complex. Multi-IMSI SIM cards provide a scalable solution, allowing for streamlined management and connectivity as the number of deployed devices increases.
Since 2007, we have been pioneers in cellular IoT hardware, connectivity and SIM technology. Our multi-award-winning AnyNet+ SIM, is available in a wide choice of form factors with access to a choice of over 700 mobile networks across 190+ countries.
Deploy your multi-IMSI SIMs anywhere in the world with your preferred pre-loaded IMSIs and manage connectivity over-the-air for the lifetime of your device with our IoT connectivity management platform.
Paul is one of Eseye’s co-founders. With a background in senior design engineering, Paul’s focus is on ensuring his development, operations and support teams deliver solutions that work faultlessly in the field.
Paul was co-founder of CompXs, with Ian Marsden, and developed the world’s first IEEE 802.15.4 radio. Before CompXs, Paul was in senior radio design at Philips.
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