Introduction

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:

1. Device Type: the type of device affects how much data is sent and how often
2. Device Setup: what is the device setup to do?
3. Network: what is the minimum connection charge?
4. Network quality: how often is the device forced to reconnect?

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.

NB-IoT SIM Providers, which provider 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

NB-IoT data consumption

NB-IoT is 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. 

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.

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 LTE-M 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 LTE-M, 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
• 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, 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.

Barra Core NB-IoT data use test

A Barra Core was configured for 2 x Daily Heartbeats., using a Telstra NB-IoT SIM in Perth, Australia.

Key Stats:

• Each heartbeat is approximately 1-1.3kB
  • The variance is based on how many WiFi Access points are found and sent to the server, which changes
• The total data usage for the month was 62kB

So this gives us the following rough estimates for monthly data

• 1 update per day ~30-40kB/month
• >2 updates per day ~60-75kB/month
• 4 updates per day ~125-150kB/month

How do I set up my device for NB-IoT

The device uses the Quectel BC660K-GL modem. Which is a 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:

1. 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
2. If not, you may need to set some network settings, see the information here - contact our support team if you need assistance:
   1. 4G APN - How do I set the APN to connect to the network?
   2. 4G Network Settings
   3. Setting the Network Profile - LTE-M/NB-IoT devices
3. Some network operators operate both LTE-M and NB-IoT networks. Typically, they will provide a specific SIM card for each network. For the Barra Core, make sure to purchase an NB-IoT SIM.

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

What about Firmware Updates?

• Firmware updates are not applied automatically, the partner must log in to Device Manager 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.

Other Resources

For help in choosing a SIM to get online, see SIM Providers: LTE-M/Nb-IoT + Roaming, and Setup