Mobile Behind the scenes EP 1: The 5G PLMN issue (Part 1 of 2)

Disclaimer: All opinions expressed here are solely my own and do not represent the views of my current or past employers.

Deploying 4G/5G private networks comes with unique challenges. Among them lies a lesser-discussed hurdle: the 5G PLMN issue.

What exactly is the 5G PLMN issue? Let’s break it down.

What is a PLMN, and why does it matter?

A PLMN (Public Land Mobile Network) uniquely identifies every mobile carrier. It consists of:

• MCC (Mobile Country Code): A 3-digit code representing the country (e.g., 724 for Brazil).

• MNC (Mobile Network Code): A 2- to 3-digit code identifying the specific mobile carrier within that country.

For example, PLMN 724-05 represents Claro Brazil. Every mobile carrier worldwide has at least one PLMN, and some may have several.

If you search online for “PLMN list” or “MCC-MNC list,” you’ll find databases detailing these codes. But how does this relate to 5G deployment?

The real 5G PLMN issue

You might think the issue is a lack of PLMNs for the growing number of private networks. While that’s a valid concern, there’s a more immediate and practical challenge: connecting 5G-capable devices to your network smoothly.

When deploying a 5G private network, you’d expect your 5G-capable smartphone to connect without issues. However, the reality is often frustratingly different. Why? It all comes down to how the wholesale smartphone market works.

How device certification impacts 5G connectivity

Historically, smartphones were sold primarily by carriers. Over time, wholesalers began selling unlocked devices, giving consumers more flexibility. But device vendors and carriers are cautious by design, especially when it comes to 5G.

Here’s why: device configurations are fine-tuned for each carrier’s network. Whenever a new feature like Uplink Carrier Aggregation or 5G/NR is introduced, device vendors perform a self-certification process to ensure compatibility. This certification happens for each device model and each PLMN.

What does this mean for 5G private networks?

Let’s say you’re using a 5G-capable smartphone (Device Model D1) on a carrier’s network (Carrier C1). If the device vendor successfully certifies Model D1 for Carrier C1’s PLMN, the device’s software enables the 5G stack for that carrier. When you insert a SIM card or activate your eSIM, the device reads the PLMN from the SIM and matches it with its internal configuration. If the PLMN is certified, the device allows 5G connections.

Now, suppose you use the same device with a different carrier (Carrier C2). If Model D1 hasn’t been certified for Carrier C2’s PLMN, the device won’t enable 5G. No 5G toggle, no 5G service—even though the device and network are technically capable.

Why doesn’t this happen with 4G?

4G technology is well-established, having been fine-tuned almost over the past two decades. As a result, most devices are broadly compatible with any carrier’s SIM card. But with 5G being relatively new, device vendors and carriers are still navigating the complexities of certification.

What’s next?

In the next post, we’ll explore practical solutions to this issue and how organizations deploying private 5G networks can overcome these challenges.

Have you faced similar hurdles in your 5G deployments? Share your thoughts below, and stay tuned for Part 2!