Seamless IoT connectivity relies on successful mobile network registration, a complex process involving IoT modems, SIM cards, and mobile network operators (MNOs). When a device powers on, its modem, armed with a SIM card, initiates a conversation with the network, ensuring secure authentication and reliable service.
Understanding how this works helps businesses deploy IoT solutions more efficiently while troubleshooting connectivity issues when they arise.
How Mobile Network Registration Works
Step 1: Initiating the Connection
When a device is powered on, the modem communicates with the SIM card to retrieve critical authentication credentials (IMSI, security keys, etc.). These are then sent to the network’s core infrastructure to initiate registration.
Step 2: Authentication and Validation
The network verifies the device’s credentials against the Home Location Register (HLR). If authentication succeeds, the SIM is authorized for network access.
Step 3: Location Update
After authentication, the device informs the network of its location, which is stored in the Visitor Location Register (VLR). This ensures that services like calls, SMS, and data are properly routed.
Step 4: Receiving Network Information
The device receives key identifiers, including:
- Mobile Country Code (MCC) and Mobile Network Code (MNC), which define the Public Land Mobile Network (PLMN).
- Temporary Mobile Subscriber Identity (TMSI) for better security.
Step 5: Establishing a Data Session
If internet access is required, the device initiates a Packet Data Protocol (PDP) context, enabling it to use data services.
Key Signaling Events in Mobile Network Registration
During the registration process, various signaling messages are exchanged between the device and network. The following table outlines these key events:
| Event | Purpose | When It Happens |
|---|---|---|
| Send Authentication Info | Sends security credentials to the HLR for verification. | Before a device can access the network. |
| Authentication Failure Report | Indicates that authentication failed due to mismatched security keys. | If the SIM’s authentication fails. |
| Update Location | Updates the device’s location in the VLR to ensure proper routing. | When a device moves between cells or registers anew. |
| Cancel Location | Forces the SIM to re-register by clearing its session in the network. | Used for troubleshooting or network reassignments. |
| Insert Subscriber Data | Updates subscriber information, such as plan changes or new permissions. | When an operator modifies the user’s subscription. |
| Purge MS | Notifies the HLR that the subscriber is no longer active on the network. | When the network cannot reach the device (e.g., APN issue). |
Factors Affecting Network Registration
- Signal Strength
A poor signal can prevent network registration. Signal strength is measured in decibels (dBm), with values affecting registration as follows:
| Signal Strength (dBm) | Quality | Impact on Registration |
|---|---|---|
| -120 to -100 dBm | Poor / No Signal | Registration likely to fail. |
| -100 to -80 dBm | Weak Signal | Unstable connection, potential issues. |
| -80 to -65 dBm | Good Signal | Reliable network registration. |
| -65 to -50 dBm | Excellent Signal | Ideal for smooth, fast registration. |
- SIM Card Issues
- Authentication failures can prevent registration.
- Physical damage or dirt on the SIM can impact connectivity.
- Network Compatibility
- Some networks may block certain SIMs due to steering rules.
- Roaming devices must connect to a partner network under the correct roaming agreement.
- APN (Access Point Name) Settings
- Incorrect APN configurations can prevent devices from establishing a data session.
- Ensure that no unnecessary username or password is used.
- Blacklisting and Whitelisting
- Some devices may be blacklisted on a network due to security policies.
- Whitelisting allows only approved devices to connect.
Troubleshooting Registration Issues
If a device fails to register, follow these steps:
| Issue | Possible Cause | Solution |
|---|---|---|
| No Network Detected | Poor signal strength, SIM issue | Move to an area with better coverage. |
| Authentication Failure | Incorrect security keys, SIM card problem | Try another SIM or check operator compatibility. |
| Stuck in “Searching” Mode | Blocked by network steering, APN misconfiguration | Check PLMN lists and APN settings. |
| Dropped Registration | Weak signal, network congestion | Reboot device, relocate, or try manual selection. |
| No Data Connection | Incorrect APN settings | Ensure proper APN configuration. |
If problems persist, remote SIM reset via the ‘Cancel Location’ command can force re-registration.
Impact of Network Registration on IoT Connectivity
- Data Sessions: A properly registered device can establish a PDP context for seamless data connectivity.
- SMS Services: The device must be registered on a 2G network to send/receive SMS.
- Billing & Session Management: Networks track registration timestamps for billing and usage calculations.
Pre-Deployment Planning for Reliable Connectivity
- Verify network availability before deploying IoT devices.
- Ensure SIMs are programmed with the correct network access rules.
- Check that operators in the target region support your SIM profiles.
Once devices are deployed, changing settings remotely can be difficult or impossible—so proactive planning is essential.
As stated by Luigi Capobianco from our partner floLIVE: “Building connectivity into the design phase of an IoT (Internet of Things) project is crucial for ensuring reliable and efficient communication between devices, network, and the application layer. Defining project requirements and choosing the appropriate connectivity technologies will help determine security requirements, optimize for performance and power consumption, design for future scalability and flexibility and meet compliance requirements.” Read more here https://flolive.net/blog/building-connectivity-into-the-design-stage/
In closing, mobile network registration is a multi-step process that depends on the interplay between modems, SIM cards, and mobile networks. By understanding the signaling events, key factors, and troubleshooting steps, businesses can ensure seamless, uninterrupted IoT connectivity.
Are you ready to optimize your IoT device and its connectivity? Contact CommsCloud today for a consultation and learn how we can help you ensure your IoT deployments are equipped with the right connectivity solutions tailored to your needs.
CommsCloud IoT Connectivity Solutions | Empowering Your Business to Connect, Grow, and Thrive—Contact Us | +27 21 551 5526 or Get in Touch. Follow our journey across Africa with the social media links below.