David Evans, IoT Solution Architect, Robustel delves into issues with roaming SIMs, the solutions and how smart roaming technology helps
“This SIM will go to the best network”
This soundbite is one of the greatest fallacies to have propagated throughout the IoT industry over the last 10+ years.
It’s a convenient nugget that encapsulates why someone should buy a roaming SIM.
It’s also fundamentally wrong – and therein lies the problem!
Those helping to spread this story are generally not malicious, more likely misinformed & inadvertent victims of the ‘echo chamber effect’ – if enough people say something enough times – especially if it makes for a good and logical story – it becomes the truth.
So, if a roaming SIM doesn’t go to the best network, what does it do?
In this context, nothing. A SIM itself does not make network selection decisions*, that is a function of the hardware into which it’s placed, be it a vehicle tracker, smart meter, 4G router or similar IoT device.
What the SIM does do is to hold a repository of files that help the hardware decide what type of connection can be built & to which network(s) it can connect.
The hardware (with typically an IoT cellular module at its heart) then carries out the network selection process using “Automatic” or “Manual” network selection
(* – SIM cards running a SIM applet can take more active participation in the process but are not mainstream at the time of writing)
Why should I care? It will just work, right?
Wrong.
Most IoT devices employ Automatic network selection which is fundamentally not fit for purpose for modern data-centric (ie. using mobile data instead of voice or SMS) applications using roaming SIMs. This can leave Tech Support teams scratching heads, trying to explain what’s going on & in more serious cases, loss of connectivity with commercial ramifications.
The full technical detail is beyond the scope of this article but the more curious reader should download specification TS 3GPP 23.122 & search for the section entitled – “Automatic Network Selection Mode Procedure.”
This Document clearly highlights that network selection is “at random”, and introduces the concept of the last known good network (RPLMN) & Forbidden networks (FPLMN), all of which can dictate the success or failure of a cellular internet connection.
Another critical challenge with Automatic network selection is the fact that it uses signal strength alone to determine if a network is good or bad.
As cellphone users, we know that full signal strength doesn’t always correlate with a good service, or even any service at all. This is because there’s much more than just the radio connection in the end to end journey of your IoT data. Looking at the time it takes for your data to get to a server and back (round trip time), or a simple speedtest can be much better indicators of connection health than signal strength alone, but unfortunately, such metrics do not feature in the Automatic network selection process.
OK – so what’s the solution?
Fundamentally, to achieve the best possible reliability, your IoT device needs some extra software smarts to work round the vagaries of Automatic network selection with roaming SIMs. Implementing good connection logic and with expert use of ‘AT Commands’, smart software can babysit your cellular connection forcing instant changes/improvements if problems are detected.
Below are some more detailed solutions to fit your specific circumstance:
If you are a design house building custom devices with cellular modules:
Prioritise “connection control” with the help of a module vendor that gives expert advice on this process. If you are still unsure, employ a consultant that is demonstrably an expert in this field – ascertaining the framework wont take too long, coders just need to know what to code!
End user putting SIMs into off the shelf devices like meters/telecare devices:
This can be one of the more challenging scenarios as you will typically have no control over how the hardware does “connection control”. In fact, some can do it so badly that they become self-defeating. An in-depth conversation with the manufacturer will quickly tell you whether smart connection control of roaming SIMs is baked into the product design or not.
Mobile applications such as vehicle trackers:
Think carefully when using roaming SIMs in mobile applications!
A moving vehicle means a rapidly changing RF environment that needs different rules to a static IoT device. It’s a big topic, well beyond the scope of this short article.
Using 4G or 5G routers as a building block in your system:
Many IoT systems use a 4G or 5G router to provide a simple, scalable, manageable method of connecting devices like DVRs / Industrial Controllers / Solar inverters to the internet. Some router manufacturers provide advanced connectivity control to get to the best possible ‘estate uptime’.
Robustel Technologies is an example of such a manufacturer with their proprietary “Smart Roaming” technology. Available in most 4G and 5G routers, Smart Roaming is designed to solve many of the problems associated with Roaming SIMs.
The whitepaper for Smart Roaming can be found here.
David has 20 years of experience in technical sales and marketing with a focus in industrial and wireless automation. Much of this experience has been gained working on projects in the IoT / M2M space across a multitude of vertical markets.
Author: David Evans, IoT Solution Architect, Robustel
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