Cellular Connectivity Basics

While Soracom Air for Cellular generally provides a frustration-free experience for enabling cellular connectivity for IoT or M2M devices, in some cases there may be differences in how a device or local network behaves which can result in unpredictable or unreliable cellular network connectivity. In these situations, without the ability to inspect the cellular network itself, it's often difficult to identify the specific issue that might be causing connection problems. However, some basic knowledge of what typically occurs between powering on a device and sending data over a cellular connection can be helpful with understanding where a connectivity issue might be occurring.

Basic Requirements

Before a cellular-enabled device can connect to Soracom, it needs to be set up and configured. The amount of set up will vary depending on your device: some devices may already be set up out of the box and simply need a SIM card and APN settings, while others may require additional configuration. However, in general you will want to make sure that the following items are properly set up:

Soracom provides setup guides for reference devices, which include more detailed instructions. Refer to the Developer Guides section for more information.

Hardware Check

Device Configuration

SIM Activation

Finally, when your device attempts to connect to a cellular network, Soracom will check the SIM's Subscriber Status in order to determine whether or not your device should be allowed to connect, and will then approve or reject the connection accordingly. To connect to a cellular network, your SIM should be in one of the following statuses:

For more details about each status, refer to the Subscriber Status documentation.

Connection Process

Once your device is set up and configured, you can power it on in order to connect to a cellular network. In general, there are three main steps involved durng the cellular connection process:

Basic Connectivity

Requesting Network Registration

During the network registration process, a modem will first discover what networks are available in the vicinity of the device, and will attempt to communicate with a cellular network. This lets the network know that the device is located in the area, and to begin setting up the cellular connection. The network registration process consists of the following steps:

  1. The modem scans for nearby radio towers and checks which network operators they belong to.

    When using a brand new Soracom SIM card, or when your device has moved from one country or region to another, this step may take several minutes to complete. The duration of this network scan procedure depends on several factors, such as how many radio technologies and frequency bands the modem needs to scan, and how many different network operators are in the area. It is important that the modem is not interrupted during this process, otherwise it may have difficulty continuing to the next step.

    Note that while 3GPP-compliant modems should handle this process automatically, some devices may override the standard behavior and interrupt the modem if the modem has not finished registering in a short amount of time. If you notice that your device is having trouble registering to a network when using a new Soracom SIM, or when moving between countries or regions, you may need to check with the device manufacturer if the device is mistakenly interrupting the network scan procedure.

  2. For each network operator detected, the modem checks if it is allowed to register to the network. During this step, the network will request the subscriber (SIM) details from the modem, and then check with Soracom whether to allow or disallow network registration.

    If the subscriber status is Suspended, Soracom will notify the local network that the subscriber is not allowed to register to the network, even if the local network is one of Soracom's supported carriers.

  3. Once the modem has found a suitable network where it is allowed to register, the modem will request network registration, and the local network will complete the registration process.

Once the modem has registered to a network, SMS and USSD services will be available (where supported). If using a device that shows network status information (such as a smartphone or a gateway that reports the cellular network status), you should be able to see the name of the local network operator, as well as the signal strength.

However, at this stage, a data connection has not been established, so your device will not yet be able to send or receive data. On devices that show the network status, you may see an icon indicating that data communication is not available.

If your SIM's subscriber status is in the Ready or Standby status, Soracom will automatically change the status to Active as soon as your modem has registered to a network. While you should be able to check the User Console to see that the subscriber status has changed to Active, the data connection status will still appear as Offline at this point.

Requesting Data Session

Next, the modem will continue to the following steps in order to establish a data connection:

  1. The modem sends a request to the local network operator to create a data session with the configured APN settings.

    Typically this step should occur automatically. However, in some devices, if data roaming is disabled, the device will actively prevent the modem from sending this request.

  2. The local network uses the APN details to forward the create data session request to Soracom.

  3. Once Soracom receives the create data session request, Soracom will assign an IP address to the modem, send the IP address and DNS server details back to modem, and finish setting up the data connection.

    When a session is created a subnet mask is not assigned by Soracom

Once the data session has been created, the modem will be able to begin sending and receiving data using the cellular connection.

At the same time, Soracom will update the subscriber status from Offline to Online, and you will be able to check this status from the User Console. Additionally a data session log will be recorded in the SIM's Session details.

Sending and Receiving Data

Finally, with a data connection established, your device can use the cellular connection provided by the modem to send and receive data:

  1. Your device sends IP packets to the Soracom platform, a cloud endpoint, or other Internet service using the modem's cellular data connection, or receives IP packets in similar fashion.

  2. As data is transferred over the data connection, Soracom will record the data usage amount.

When sending or receiving data, you can check the data usage to help narrow down potential connectivity issues. For example, when your device sends data to a server but you are unable to see the data arriving at your server, the data usage history can give you a better idea of where an error may be occurring: