How much data do DM Devices use?
Table of Contents
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 supply devices globally, but have offices based in the US, The Netherlands, 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!).
This question comes up often, as partners need to choose a SIM data plan to assets costings. However this 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?
Rules of thumb
- Battery powered devices (i.e. Remora2, Oyster2) use about 1 - 3MB of data per month, dependent on settings
- Wired devices (i.e. Dart2, G62, G120) use about 5-10MB per month
Wired device data breakdown:
- Roughly 0.25MB per month for GPS Aiding Data
- About 30kB per hour in-trip, on default settings
- About 2kB per upload in connection overhead, plus any minimum connection charge
- Hard wired devices generally send a lot of updates when driving, so this is quite dependant on how much use the asset sees.
Keep in mind:
- 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.
- 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.
LTE-M vs NB-IoT, what to choose?
- 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
- Your hand may simply be forced as you may only have 1 technology available in your region. Or only one has widespread coverage. In that case go with 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 very long - leaving the modem on for a long time = reduced battery life. So firmware updates to fix bugs are possible, but battery life will take a little bit of a hit (not extreme).
NB-IoT data consumption - our tests
NB-IoT is an emerging technology geared around sending small amounts of data. Like infrequent location updates, temperature readings, or some other sensor values - powering the "Internet of Things", and many millions of interconnected devices.
As of 2020, NB-IoT is being rolled out in many countries, along with data packages and rate plans. 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. In the context of our devices, that might be:
- A Yabby giving 4 location updates per day, this is a good application for NB-IoT
- An Oyster2 on default settings, providing constant trip tracking (i.e 2 min records and uploads every 30 min while on the move) - we should choose LTE-M for this application.
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 cost 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 have clear how much data we expect to use, and test, before rolling out large-scale NB-IoT deployments. Typically it is not easy from a SIM or device level to simply switch to a higher plan, or from NB-IoT to Cat-M1, without retrieving the device and swapping SIMs.
So how much data will I actually use?
The answer really 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
- 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, acknowledgements, and other messages just as part of the actual connection - before we even send any data. This is can often outweigh the actual message payload.
- Firmware updates
- GPS aiding data. Our GPS devices periodically download information from the satellites, which helps
- 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 the 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 just look at the data usage at the end of the month satellite-aiding. We did just that with our Yabbies!
Some Data Usage Tests
Yabby3 Data Usage Test
We set up a Yabby 3 for 4 x Daily heartbeats. However as it is a GPS device, it periodically downloads satellite aiding data, which dramatically increases the overall data usage.
M2M One NB-IoT SIM card, operating on Telstra's NB-IoT network in Perth, Australia
- Average data usage per heartbeat: ~1.5kB
- Average data usage per aiding data download: 50kB
- Aiding data is downloaded once every 4-6 days, let us call this 5 times in a month.
So, we can provide the following rough estimates for NB-IoT
- 1 update per day: ~50kB for heartbeats + 250kB for aiding data = ~300kB/month
- 2 updates per day: ~100kB for heartbeats + 250kB for aiding data = ~350kB/month
- 4 updates per day: ~200kB for heartbeats + 250kB for aiding data = ~450kB/month
For LTE-M, the min connection will apply on the heartbeats (2kb for Telstra in AU) - so the data usage will be higher.
What about the Oyster3 and Remora3?
The above estimates for the Yabby 3 holds for these devices, provided they have the same settings.
Edge Devices (Yabby Edge, Barra Edge and Oyster Edge)
The way in which GNSS and Wi-Fi fixes are obtained on the Yabby Edge is quite different to our other devices. Almanac data is sent to the device but the file size is far smaller, so overall data usage is lower.
A Yabby Edge was configured for 2 x Daily Heartbeats., using a Telstra NB-IoT SIM in Perth, Australia.
- Each heartbeat is approximately 1-1.3kB
- The variance is based upon how many Satellite/WiFi Access points are found and sent to the server, which changes.
- >1-2 times per month, the almanac is downloaded, which is about 5kB
- The total data usage for the month was 74kB
So this gives us the following rough estimates for monthly data
- 1 update per day 35-40kB/month
- >2 updates per day ~75-80kB/month
- 4 updates per day ~145-150kB/month
Can I get this lower? What are my options?
Unfortunately, this is currently the best we can do with the current devices. On GPS devices aiding data downloads can not be disabled in system parameters - and these trade off a little bit of data usage for a battery life gain - as it speeds up GPS fixes, reducing their power consumption. Additionally, the actual payload information (lat/long, voltages etc) is much smaller than the overall data (hundreds of bytes at most). A protocol other than TCP will help cut down on overhead, but it would reduce battery life in the majority of cases.
We are always developing new products, so watch this space for future products, optimised for NB-IoT and getting the data usage to the absolute minimum.
How do I set up my device for NB-IoT?on
Our current range of cellular devices uses the uBlox SARA-R410M modem, which is a Cat-M1/NB-IoT modem. There is nothing particularly special that needs to be done to get online, however, we have noticed that getting online on many NB-IoT networks has proven tricky. However, our Autonet feature aims to make getting online as simple and automatic as possible. So to get online, the steps are:
- Just 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 a specific SIM card 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 Periodic Tracking
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 really is not that hard to test for yourself to know for sure!
However, we can work out some figures roughly.
The above tests done on NB-IoT apply to LTE-M, the difference is that most providers charge a min 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, the partner must log in to OEM and apply them. So you should not be caught by surprise.
- 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.