SIM Cards and Data Usage - Barra GPS
Table of Contents
Disclaimer
This article is intended to assist partners in selecting between LTE-M/NB-IoT, determining costings, and choosing SIM providers.
Advice is general and partners should conduct their own testing and make an informed decision. It should be noted that Digital Matter supplies devices globally but has offices based in the US, South Africa, and Australia.
Our advice/the content of this article may be biased towards certain regions purely because we have more partner feedback from this region around what works.
NB: Cat-M1 and LTE-M are used interchangeably in this article, they mean the same thing. Networks like to change names to make things as confusing as possible! However, more recently LTE-M is the common term (that wasn't what it was when the networks were first launched!).
Introduction
This question comes up often, as partners need to choose a SIM data plan for and determin costings. Choosing a SIM data plan greatly depends on a few factors:
- Device Type: the type of device affects how much data is sent and how often
- Device Setup: what is the device setup to do?
- Network: what is the minimum connection charge?
- Network quality: how often is the device forced to reconnect?
Keep in mind:
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The minimum connection charge has a massive effect on the data usage. Consider Vodacom in South Africa. Each new data connection is charged a minimum of 10kB. The device may send less than 1KB on a heartbeat, but it is still charged for 10kB. With hourly heartbeats, this adds up fast. 10kB per heartbeat x 24 hourly heartbeats x 30 days = 7.2MB. That's just on heartbeats. MTN in South Africa charges a minimum of 25kB per connection. That's 18MB.
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Dropped connections also have an effect: each reconnection could be charged the minimum connection charge.
- Grouped/pooled data plans provide some 'breathing room' for devices that may upload more than planned, since there will be others in the pool which use less data that month.
Rules of thumb
Battery-powered devices typically use about 1 - 3MB of data per month, depending on settings.
1-2 daily updates can bring this down to below 1MB.
LTE-M vs NB-IoT, what to choose?
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For a full overview of the pros/cons of each technology, see 4G Connectivity - Cat-M1 vs NB-IoT, Coverage, Providers and Roaming
- For information on how to select a network, or what SIM providers are available see SIM Providers: LTE-M/Nb-IoT + Roaming, and Setup
Considerations
- You may only have 1 technology available in your region, or only one has widespread coverage. In that case, choose the technology with better coverage.
- LTE-M should be used for hard-wired devices.
- From the plans/costings we have seen, LTE-M overall is more flexible. You may initially be happy with 1 update per day, but if you change your mind later, you can move to a higher plan with ease. This is not generally the case on NB-IoT.
- The NB-IoT pricing structures we have seen are low cost when you are using tiny amounts of data - as soon as you push the update rate up, it is equivalent or more expensive than LTE-M, and doesn't have the benefits of cell tower handover etc.
- Firmware over the air is possible on NB-IoT, but since the data rate is much slower, it takes much longer. Leaving the modem on for a long time = reduced battery life. Firmware updates to fix bugs are possible, but battery life will take a little bit of a hit (not extreme).
NB-IoT data consumption
NB-IoT is geared around sending small amounts of data such as infrequent location updates, temperature readings, or some other sensor values - powering the "Internet of Things", and many millions of interconnected devices.
For a comparison between LTE-M and NB-IoT, along with examples of typical use cases, see 4G Connectivity - Cat-M1 vs NB-IoT, Coverage, Providers and Roaming. In general, NB-IoT is best suited to minimal data usage.
NB-IoT is attractive because the cost can be lower than LTE-M. Even a small saving each month can quickly add up across the lifetime of a device, particularly when rolled out across many thousands of devices. Getting monthly costs down is a key way in which many previously unviable applications are beginning to make cost sense. Now we really can track anything! However, the cost is reflected in the data per plan. E.g. 5MB per year plans aren't uncommon.
It is important to note however that many NB-IoT plans are structured to heavily discourage higher amounts of data usage, at which point they become more expensive than a Cat-M1 plan, so it is important to be clear how much data we expect to use, and test, before rolling out large-scale NB-IoT deployments. Typically you will need to retrieve the device and swap the SIM card if you want to switch to a higher plan, or from NB-IoT to Cat-M1.
So how much data will I actually use?
The answer is 'it depends'. We cannot simply look at the record size sent by our devices and multiply that by the number of uploads. Other things contribute to the overall data use including
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TCP Overhead: Our devices communicate via TCP. TCP is a protocol that establishes and maintains a connection while two parties exchange data. This uses up extra data in sending hellos, acknowledgments, and other messages just as part of the actual connection - before we even send any data. This can often outweigh the actual message payload.
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Firmware updates
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GPS-aiding data: Our GPS devices periodically download information from the satellites, which helps
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Device System Parameters: The configuration of the device will impact the upload size and number of uploads.
- Minimum connection charges typically do not apply on NB-IoT, you're only charged for the data you use, with no rounding up to 1kB, or 2kB for example like on traditional networks. However, this is not a given so be sure to check.
With all these various factors, we can make estimates, but the easiest and most reliable way to work out how much data a device will use is to simply insert the SIM, let it run for a while with the desired settings, and then analyze the data usage at the end of the month.
How do I set up my device for NB-IoT?
The Barra GPS uses the Nordic NRF9160 modem which is a Cat-M1/NB-IoT modem. Our Autonet feature aims to make getting online as simple and automatic as possible. So to get online, the steps are:
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Try inserting the SIM and batteries, if it is a SIM we have added to the Autonet table, it should just do its thing and get online automatically.
- If not, you may need to set some network settings, see the information here - contact our support team if you need assistance:
- Some network operators operate both LTE-M and NB-IoT networks. Typically, they will provide specific SIM cards for each network, but sometimes, an NB-IoT SIM can actually get onto the LTE-M network if the operator hasn't strictly disabled this. In this case, we can configure the Admin Parameters on the device to use NB-IoT only.
Once online, the other setup we must do is simply to make sure we restrict how much data the device will send - i.e. in most cases we would configure the device to only send a couple of updates per day Changing the Update Rate.
LTE-M Data Usage, and how do I get a rough, back-of-the-envelope figure?
This is a reasonable question, but it is important to note that this is not hard to test for yourself to know for sure!
We can work out some figures roughly.
Most providers charge a minimum connection on LTE-M. In Australia, with M2M One SIMs, this is 2kb - it might be similar for your network.
So, for a battery-powered device, we could estimate as follows:
- Number of uploads per month * 2kb
- +250kB aiding data per month
For example, a device updating 4 times per day would equate to 4*30*2kb + 250kB = approx 500kB per month.
Powered devices depend heavily on how long they spend in-trip - so it is best to do your own test. Generally for such devices, we are not trying to work out the cost down to the cent.
What about Firmware Updates?
Firmware updates are not applied automatically, you'll need to log in to OEM and apply them.
Generally, they are around 300-500kB in size.
If you are using a pooled plan, you could update a selection of your devices each month, in a staged process, to stay within your budget.
While extremely rare - critical firmware updates can happen, where all devices need to be immediately updated. In these cases, it just makes sense to accept the cost/risk of overage charges or factor this in initially.
Other Resources
For help in choosing a SIM to get online, see SIM Providers: LTE-M/Nb-IoT + Roaming, and Setup.