Each network is set up a little differently, which is a challenge for global connectivity. Planning for network heterogeneity is a great way to ensure your devices have the best chance of finding a successful connection.
Our SIMs are designed with network heterogeneity in mind and follow global telecommunication standards (e.g., GSMA) to ensure that this is possible. Most cellular modules are designed to meet 3GPP standards to ensure they work with the SIMs built according to telecommunication standards.
This should mean that SIMs are already network agnostic. However, within these standards, we have found cellular modules differ in their implementation and can often be optimized for a specific network or SIM type. These nuances are often only discovered after deployment, when there is no access to the device.
Therefore, we recommend that you consider conducting the tests laid out in this article to better understand how they will behave once they're deployed and difficult to access.
What you will need for these tests:
Access to Onomondo (to view the SIM's network logs)
A basic understanding of network logs (see: How do I read network logs?)
3-5 test SIMs
Recommended tests
1. Automatic network selection based on signal strength
Why?
For quality of service reasons, we offer plug-and-play SIMs without specified network steering lists (PLMN preference lists). This allows your device to connect to the first stable connection it finds instead of connecting to a SIM defined “preferred” signal, which might be weaker.
Having a preferred networks list on the SIM could in theory make the initial selection of a network faster, but it comes at the cost of not selecting a network with high-quality radio signal.
Not having a good radio signal can lead to a weak connection which could lead to multiple reconnections and unstable data transmission.
We have seen some modules and pre-configured devices that by default need a preferred network list on the SIM to work.
Test Suggestions
Put an activated SIM into your device, go to the SIM details page on the platform and click the network logs tab (NB all Onomondo SIMs are “active” by default)
Turn on your device and set the APN to onomondo (no caps) and set the device is allowed to use data on roaming networks (only if required)
Check the SIM's network logs
Troubleshooting
There is a GSM attachment but no "data" attachment log (sometimes you will "allowed data" log, sometimes only GSM).
The most common reason for this is that the APN and data roaming is not set. Check these settings on the device. If the APN has been set make sure it is all small letters. If it is a preconfigured device (such as an off the shelf gateway), make sure that the default APN is not still being used. Reset the APN and if that doesn't work, restart the device.
On rare occasions the device throws errors when trying to establish a PDP context. We recommend looking at the logs of the device and check the status of the errors occurring during PDP context activation. For example, using the AT command
AT+CMEE=2
There are no network logs
Unless there are entries in the signaling log, the issue occurs before the device attempts to connect to our network, during communication in the Radio Network, using your own AT command configuration.Check the technology preference and band selection of the modem. For example, if you are in a country with no NB-IoT connections, but NB-IoT is preferred, it will slow down the initial connection (up to 30 minutes/if at all - depending on the device)
Use the technical AT Command connectivity test guide to see if you can establish a connection using these agnostic commands. These can also help show where the device is struggling to connect. If you are unsure what is wrong, you can contact us with the logs for further insight.
There were denials, now we see no new logs
Denials occur when a specific network is not on the whitelist. However, if no networks in the area/country are not on the whitelist the device will try them all. Once they are denied you will need to clear the FPLMN list before the device will see try these networks again. You can see more details under the section below Changing the network whitelist test.Otherwise, you can try adding a PLMN list to a SIM and see if that improves the result.
Adding a PLMN list to the SIM can improve initial connectivity, but overall will result in a lower quality of service, as the device will always select the most preferred network even with a weak signal over a stronger signal that also may be on a whitelist.
2. Deactivating a SIM while it's online
Why?
Sometimes a SIM will drop off a network. E.g., this can occur during planned maintenance periods. We recommend testing how the device responds when it is disconnected to make sure the device is configured to reconnect after getting kicked.
Issue: Not configured properly, some devices require a manual restart. In many IoT situations the device is hard/expensive or impossible to reach once deployed.
Test Suggestions
While your device is online, Toggle the activation of the SIM to deactivated and then activated again.
The RAN will receive signaling from us to CancelLocation of the device currently connected to their infrastructure. The device should go offline and come online again after a short period of time.
3. Changing a network whitelist (PLMN)
Why?
When a device attempts to connect to a network, it will first request permission to attach to that network. When our network receives this request it checks the network whitelist that is attached to the SIM. If the network is on the list, it will be allowed to connect. Otherwise, we will deny the request. This can be seen on the network logs.
When the device is notified, it will write the network to the FPLMN list on the SIM. While the network is on the FPLMN list, the device will not attempt to connect to it in automatic selection mode.
Test how the device records networks to the FPLMN list.
A good failsafe for the device to understand how the device writes to the FPLMN list and adding logic to the device to clear the FPLMN list as back up (for example add it to the device boot up or triggered when the device has failed to attach to network because all networks in range are written to the list.
Test Suggestions
On the SIM you are testing add a network whitelist with limited or no networks in the area.
If you have used this SIM before for testing, make sure to clear any connection to a current network. This can be done toggling the activation toggle to deactivated and back to activated. This will send a CancelLocation request to the network. This will make sure that the device asks for permission again next times it tries to connect to a network.
Once the device has been denied the networks, change the test whitelist so that it only covers networks that have been denied.
Toggle the activation of the SIM off and on again and see if the device attempts to connect to one of the networks.
Troubleshooting
No new network logs
You will need to clear the Forbidden Network (FPLMN) list on the SIM. Once the FPLMN list is cleared, the device should start connecting to the new networks on the whitelist.No new network logs after the FPLMN list is cleared
Modem modules often have a cache including a list of forbidden networks that is cleared when the module/device is reboot.
The FPLMN list is a standard to make connections more effective. We also suggest to consider how this could be implemented in production to make your device more agile. One example is when the module initializing for the first time. Then a reset of the device/module will also clear the FPLMN list.