With the sunset of 3G networks on the horizon in Australia, there’s growing concern about how the SMS used for basic mobile text messaging will continue to function. Will devices like SMS modems attached to plant and equipment still be able to send SMS alerts once 3G networks are gone? SMS remains a critical communication tool, especially for IoT devices and certain emergency services, even as we shift towards faster 4G and 5G networks.
The most obvious thing you need to do right now is replace all 3G-only devices with 4G capable devices. But there’s more to it than that. 4G networks introduce more complexities, particularly with how SMS messages are transported, starting from the end device, through the 4G network and ultimately to the destination device. Many of these technical details are not well understood, and most telecommunication carriers do not publish comprehensive guides on their websites.
In this article, we’ll explain how SMS is transported across different network generations, and what will happen to SMS functionality after the 3G shutdown.
The evolution of SMS: 2G, 3G and beyond
The evolution of SMS: 2G, 3G and beyond- 2G networks: the birth of SMS
SMS came into existence soon after the launch of 2G (GSM) networks in the early 1990s. SMS was transmitted via the Short Message Service Centre (SMSC), which routed text messages between senders and recipients using a separate signalling channel. This method is simple and reliable, with SMS remaining largely unchanged with the advent of 3G.
- 3G networks: building on 2G
In 3G networks, SMS relies on the same infrastructure as 2G, with the Mobile Switching Centre (MSC) helping to manage voice and SMS traffic. However, 3G introduced improvements in network efficiency and data speeds, making SMS delivery faster and more robust.
- 4G networks (LTE): introducing SMS-over-NAS and SMS-over-IP
4G (LTE) networks mark a major shift. They are designed primarily for high-speed data and do not inherently support traditional voice or SMS services. Early 4G networks used Circuit Switched Fallback (CSFB), meaning that phones had to fall back to 2G/3G networks to make calls or send SMS messages. This caused inefficiencies, especially as SMS traffic was still very high around 2010.
To resolve this, the SGs-AP interface was introduced, allowing SMS to be transported over the Non-Access Stratum (NAS) directly through the 4G core network without needing to fall back to 2G or 3G. This method, often referred to as SMS-over-NAS, sends SMS through a signalling channel, allowing it to coexist with data traffic on 4G networks.
In parallel, 4G introduced SMS-over-IP, a method used in networks that support VoLTE (Voice over LTE). In this system, SMS is delivered via the IP Multimedia Subsystem (IMS) alongside voice and data traffic, removing the need to fall back to older networks. SMS-over-IP enables operators to build purely IP-based networks without needing older circuit-switched infrastructure. However, SMS-over-IP can be less efficient for certain devices, especially those with lower bandwidth needs, such as IoT devices.
- 5G networks: a new frontier for SMS
5G networks offer new ways of handling SMS, but the basic principles from 4G carry over. In 5G, the SMS Function (SMSF) sends SMS messages over the 5G core (5GC), supporting SMS via NAS even without VoNR (Voice over New Radio). This means that even in a 5G standalone network, SMS can still be delivered without needing an IP-based transport method.
Just as with 4G, SMS-over-IP is available for 5G users with VoNR. However, due to the inefficiency of SMS-over-IP, many operators still prefer to use NAS for certain devices, particularly IoT applications, which benefit from its lower bandwidth requirements.
The role of IP networking in voice and SMS over 4G and 5G
A key distinction between SMS-over-IP (as used in 4G/5G) and SMS-over-NAS (from 4G onwards) lies in how the messages are transported.
With SMS-over-IP, SMS is sent through the IP Multimedia Subsystem (IMS), which means that SMS messages (and voice calls via VoLTE) are transmitted over the same network used for data. This requires a full IP data connection to be established. In simple terms, voice and SMS are no longer handled separately but are carried as part of the overall IP data traffic. This convergence of services onto a single IP network is one of the key features of 4G and 5G networks.
By contrast, older technologies like 2G and 3G (and even SMS-over-NAS on 4G) send SMS and voice calls through separate signalling methods. These technologies do not require an IP data network to be established, meaning that SMS and voice calls can function independently of data traffic.
For operators, transitioning to SMS-over-IP and VoLTE means moving to an all-IP architecture, which is more efficient and future-proof, but this also places new demands on devices and network configurations, particularly around the need for data connectivity, which can easily cause loss of connectivity for a range of legacy devices.
What happens after the 3G shutdown?
As Australia moves towards shutting down its 3G networks, operators like Telstra are shifting their focus to 4G and 5G. Here’s what that means for SMS:
- Telstra’s approach to the 3G shutdown: While Telstra plans to shut down its 3G radio network, the core infrastructure, including the Home Location Register (HLR) and Mobile Switching Center (MSC), will remain operational for some time. This means that devices capable of SMS-over-NAS will still be able to send SMS, even without a 3G radio connection.
- Future-proof devices: Newer 4G devices that support VoLTE and SMS-over-IP, such as the Lantronix M114, will also remain functional after the 3G shutdown. These devices are built to handle SMS delivery over IMS, ensuring that they are compatible with the 4G-only networks of the future.
Ensuring devices are configured correctly
After the 3G shutdown, it’s crucial for devices to be configured properly to continue sending SMS over 4G and 5G networks. Specifically, devices need to have their Access Point Name (APN) settings configured correctly. The APN is what allows a device to connect to an operator’s IP data network. Without proper APN configuration, devices will not be able to establish the necessary data connections required for VoLTE, IMS, and SMS-over-IP.
In some cases, you may be able to leave the APN blank, and the device will still send and receive SMS via SMS-over-NAS without using data. However, this approach is less reliable and could lead to issues down the line if operators update their networks or shut down components like the SGS-AP interface. To future-proof your devices, it’s recommended to set the correct APN according to the network and SIM card being used. For instance, Telstra’s standard APN is typically “telstra.internet”.
Proper APN configuration ensures that your devices can access the IP networks necessary for VoLTE and IMS, enabling SMS and voice calls to be transmitted over the IP network. This is especially important as 4G and 5G networks become the primary method of communication, and older 3G methods are phased out.
As Australian networks move toward 4G and 5G, the SMS landscape is changing, but the fundamentals of SMS transport remain intact. Industrial 4G devices like the ETM Purple2, CYCON-1280-4G, ETM9140-3G/4G, and Lantronix M114 are well-positioned to continue sending SMS after the 3G shutdown, whether they rely on SMS-over-NAS or SMS-over-IP.
For businesses that rely on SMS communication, particularly in industrial or IoT settings, it’s important to understand which transport method your devices use and ensure they are configured correctly for the new network environment. This includes setting the correct APN to ensure access to IP networks, which will enable technologies like VoLTE and IMS for SMS-over-IP and voice services. With proper preparation, you can ensure uninterrupted SMS service for years to come.
