NB-IoT and LTE-M on eSIM – alternative technologies

It’s been a year since we last posted on the status of Mobile IoT technology. As time has progressed, so has the evolution of these industry-specific connectivity technologies.

Here is our current take on Mobile IoT and LPWA. This time the emphasis is on the eSIM for M2M Remote Subscription Management context.

We’re focussing on the two leading Mobile IoT technologies of NB-IoT and LTE-M. Both are 3GPP standardised and radio spectrum licensed technologies.

General Overview

NB-IoT (also called LTE Cat NB1 and LTE Cat NB2) and LTE-M (also known as LTE Cat M1 and LTE Cat M2) were established around the same time (2015 - 2016) as new cellular radio access technologies. Their dedicated features and functions were introduced in 3GPP Release 13 specifications (published in 2016).

By now both technologies are enhanced further with 3GPP specifications Release 14 (published in 2017) and Release 15 (published in 2018).

The focus of those revisions has been put on the functionalities ensuring low power and wide-area connectivity.

Today, that first set of goals has been achieved thanks to:

• a wide range of NB-IoT and LTE-M capable IoT modules available from various vendors (for more details on this and test reports on IoT devices verified in our 1oT Lab, please refer to the 1oT’s eSIM Test Report);

• mobile network operators have their core networks upgraded to support Mobile IoT requirements.

The next steps for Mobile IoT deployments will be achieving the proper functionality of these technologies in global roaming scenarios. Including interoperability of IoT devices and interconnectivity of IoT networks.

These should be assured directly at the level of data architecture and the support of key features.

Deploying compatible features, including standard spectrum bands and a consistent set of configurations must be coordinated between mobile network operators, device vendors and application service providers.

The description of features available in different releases of 3GPP specifications and industry recommendations for both NB-IoT and LTE-M technologies have been analysed in two deployment guidelines by GSMA. They are also promised to be updated regularly, considering the advancement of technology and global installations:

• NB-IoT Deployment Guide Release 3 (the latest version from July 2019)

• LTE-M Deployment Guide Release 3 (the newest version from July 2019)

Considerations for eSIM

International Roaming

In the M2M variant of the eSIM Remote Subscription Management solution, the first use of the service requires cellular connectivity between a newly registered eUICC and a mobile network.

It is achieved with an eSIM Bootstrap Profile, which is personalised on an eUICC at the time of manufacturing. The Bootstrap Profile allows for a first cellular connection. Even before an Operational eSIM Profile will be ready for use.

Today, commercially available roaming agreements for LPWA are still a work in progress. Over the last year, several new roaming initiatives have been signed between mobile network operators belonging to the same carrier group or by forming partnerships between key players in a region. These were:

• June 2019 - LTE-M roaming agreement between AT&T, KPN, Orange and Swisscom, and covering United States, Mexico, several European countries - the Netherlands, Switzerland, France, Romania, Spain, Belgium, Poland and Slovakia;

• September 2019 - LTE-M roaming launch between TELUS and AT&T, between Canada and the United States;

• October 2019 - NB-IoT roaming agreement of AT&T and Vodafone, signed between the USA and five European countries - Spain, Germany, Italy, UK and the Netherlands;

• April 2020 - NB-IoT roaming agreements of Deutsche Telekom with several European partners - Vodafone, Telia and Swisscom, covering in total 18 mobile network operators across Europe.

For all these organisations, expanding their NB-IoT and LTE-M roaming footprints globally shows the desire to have Mobile IoT / LPWA on a similar global scale to 4G technology. NB-IoT and LTE-M are also expected to be included in the future global standards for 5G massive IoT.

SMS Support

SMS is one of the supported transport channels between an eUICC and the Remote Subscription Management SM-SR platform. Even when it is replaced with a higher bandwidth - data transport channel BIP/HTTPS or BIP/CAT-TP, there is always a need for an MT Push SMS as a trigger for BIP channel opening (between the eUICC and the IoT device) before any eSIM Profile management operation can take place.

With the current state of NB-IoT technology as standardised in 3GPP specifications, there is no place for support of SMS communication.

A potential workaround solution to this omission of SMS could be the use of an IoT module supporting other RAN technologies that are SMS capable (including 2G, 3G, 4G), and allowing for a fallback to one of them for the execution of eSIM M2M Remote Subscription Management related operations.

Similarly, in NB-IoT there is no option for an Over-the-Air (OTA) SMS remote access to eSIM Profiles of eUICC (or a classical SIM).

The only existing alternative could be the use of IP based data communication but for an IoT device, this is used for Firmware Over-the-Air (FOTA) related updates.

LTE-M, in contrast to NB-IoT, is fully capable of SMS support in both MO and MT directions, introduced in 3GPP Release 13. It can be deployed consistently with the existing implementation of SMS over legacy and LTE networks (2G, 3G, 4G). In deployments that are also supporting Voice over LTE (VoLTE being another feature existing in LTE-M specifications and inherited from its LTE predecessor), SMS over IMS (IP Multimedia Subsystem) could be a viable option.

SMS support significantly promotes LTE-M as a more suitable technology for eSIMs and M2M Remote Subscription Management deployments.

PSM and eDRX Configuration

Power Saving Mode (PSM) and Extended Discontinuous Reception (eDRX) are the key features of both Mobile IoT technologies introduced in 3GPP Release 13. They are designed to help IoT devices save and conserve battery power and potentially achieve a 10-year battery lifespan.

PSM allows the device to turn off its radio module while at the same time remain registered to the network. eDRX deactivates a device from listening to the network. Besides, with the eDRX feature enabled, the IoT device may also deactivate the eUICC, thus reducing power consumption even further (this must be configured first in eSIM settings).

Both features were described in more detail in one of our earlier blog posts. This time we focus on their impact on eSIM M2M Remote Subscription Management solutions.

Unfortunately, these features bring a drawback as an IoT device in PSM or eDRX mode can not be contacted from the network side. In such situations, mobile operators may choose between:

• storing incoming MT SMS messages or data packets on their SMSC platform or

• buffering them within their core mobile network,

and forward them to the IoT device only when it wakes up.

A workable solution to this problem might be a synchronisation of active and asleep/hibernate times between eSIM M2M Remote Subscription Management platform and operator’s network infrastructure.

Additionally, due to SMS message’s expiration timer (typically set to 7 days) and mobile operator’s SMSC storage being cleared of such MT SMS messages after their timer expired, to prevent loss of SMS data, IoT devices with PSM/eDRX features should be configured with a lower value than the SMS message expiry timer.

Because of these existing limitations, it is not recommended to store MT SMS while an IoT device is in the PSM/eDRX mode and instead utilise a workaround method.

It is called a pull model for MT data, and it is the responsibility of the IoT device to firstly perform a mobile originating (MO) SMS to the backend infrastructure. That would trigger a response from the application server directly back to the device containing a mobile terminating (MT) SMS message.

MSISDN Availability

Looking more into future IoT deployments, there is a risk of a shortage of MSISDN mobile phone numbers will become a new reality because of the continuous growth of IoT devices worldwide.

One of the solutions designed for mitigating such a risk was prepared in 3GPP Release 11, where legacy MSISDN had been replaced with a newly introduced External Identifier (in the format of <LocalIdentifier>@<DomainIdentifier>).

With other parts of subscription data (ICCID, IMSI), it will allow for mobile core network-related operations, including voice and data.

Yet, other services like eSIM M2M Remote Subscription Management or OTA SMS Configuration that does not support operations without MSISDN must be taken into consideration too.

Devices Mobility

Perhaps not directly linked with the eSIM M2M Remote Subscription Management solution, but considering the deployment of IoT devices like trackers, wearables that are suitable for mobility scenarios, they all require frequent cell reselections and cell handovers to be able to maintain a stable network connection.

In such situations, LTE-M becomes the preferred technology, equipped with a Connected Mode Mobility (CMM) feature, introduced in 3GPP Release 13.

NB-IoT, in contrast, which is missing this feature, is designed for more stationary IoT devices. In case of a moving NB-IoT device, data sessions might get dropped and the device might have to reconnect.

BEST Feature

BEST stands for Battery Efficiency Secure Transport and it is the feature introduced in 3GPP Release 15 for both NB-IoT and LTE-M technologies. This new feature provides end-to-end security between IoT devices and the application server, considering the very low bandwidth of Mobile IoT technologies. It introduces an extra layer of security to data traffic with data payload encryption.

This solution leverages existing eSIM Profile configuration and uses the core functionality of an eUICC operating system for securing the communication channel.

The algorithm that is applied for BEST key generation reuses existing network authentication algorithms (standardised Milenage or proprietary implementations), and together with their secret key K, a new BEST session key is generated. That way, there is no need for additional requirements for a dedicated SIM Applet or SIM functionality.

Conclusion

Currently, there are two emerging technologies that, when brought together, make the delivery of a proven and reliable solution even more difficult.

1oT offers a GSMA certified M2M Remote Subscription Management solution. It is supported with dedicated eUICC products available in plastic and industrial form factors, and range of eSIM Profiles from our carrier roaming partners.

Many of these carrier partners (and eSIM Profiles) can offer NB-IoT or LTE-M type of connectivity within their home networks or are making progress towards establishing global roaming standards.

Stay tuned for our Part 2 of the NB-IoT and LTE-M on eSIM blog post, where we will review and look closer at real-life Mobile IoT deployment examples.