How do you find the ICCID number?
Since you need the ICCID number to manage a specific SIM card, it’s important to know how to find it. (Especially if you use multiple prepaid SIM cards for the same device.) As mentioned earlier, you can usually find the code on the card itself, or on the packaging.
But that’s not always convenient. Thankfully, there’s another way to find it. You can insert the SIM card into a device, and then use the device to query the ICCID number. In a cell phone, you can find the ICCID in your settings menu.
With an IoT device, you need to issue an AT command. The exact command depends on your device’s module, but it will look something like this:
- “AT+CCID=?” for SIMCOM modules
- “AT#CCID=?” for Telit modules
- “AT+QCCID=?” for Quectel modules
How MNOs use ICCID numbers
After you insert a SIM card into a device that uses cellular connectivity, it searches for any available cellular networks, then uses the ICCID number and IMSI to determine if the device has rights to access the network.
Here’s how it works.
When a device attaches to a “visiting” network (meaning not its home network), that network sends an authentication request to the device’s home network. The home network sends what basically amounts to a riddle that only the device can solve. The network generates a random number and shares it with the device, then uses an algorithm and a shared secret key to produce a new number based on the random one. If the device produces the same number, it proves it has the same secret key and with that it’s authorized to use the network.
If the SIM card doesn’t have the correct key to access the network, the device can only use the network to call emergency services. (Devices can even use this service without a SIM.)
ICCID vs. IMSI vs. IMEI
In addition to the ICCID, there are two other mobile network identifiers you should be familiar with: IMSI and IMEI. While the ICCID identifies your SIM card, IMSI identifies the specific subscriber, and IMEI identifies the specific device.
IMSI stands for "International Mobile Subscriber Identity." It’s a mobile subscriber’s unique identification number. Like an ICCID, an IMSI is saved on the SIM card. Most SIM cards only store a single IMSI, which is associated with a list of networks the subscriber is authorized to access. EMnify’s SIMs, however, are Multi-IMSI, meaning they store multiple subscriber identities. This allows the SIM to change identities to access more networks and select the one with the best coverage.
An IMSI is not the same as a telephone number. The IMSI number has up to 15 digits and consists of three parts:
- The first three digits are the Mobile Country Code (MCC). This can be used to determine the home country of the operator that issued the SIM card. The IMSI of European countries always starts with the number 2.
- The following two or three digits are the Mobile Network Code, which represents the network the user is active in. For example, the number 01 represents Deutsche Telekom.
- All subsequent numbers are specifically assigned to the user, and no two users share the same IMSI number.
The International Mobile Station Equipment Identity, or IMEI for short, is one unique 15-digit serial number that can be used to uniquely identify each mobile radio terminal (your device). It includes four parts:
- The first two digits indicate the reporting body identifier showing Type Allocation Code (TAC) by GSMA approval group.
- The next six digits are the TAC.
- The six digits after that uniquely identify the individual device.
- The final number is the check digit, which helps prevent errors in equipment databases.
There are also “software versions” of IMEIs, referred to as IMEISVs. In an IMEISV, there is no check digit, and the last two digits represent the Software Version Number (SVN).
Understanding cellular connectivity
There are many identifiers for cellular technology. While they all impact connectivity, they don’t necessarily impact the end user. If you want to learn more about how cellular connectivity works with the Internet of Things, check out our guide to cellular IoT, or explore how a cloud native approach to development and connectivity could benefit your business.