What Is GSM? From 2G to Today's IoT Networks

This guide explains GSM's network architecture in technical detail, why the SIM model it introduced still underpins every cellular IoT connection today, and exactly what the 2G shutdown timeline in Norway means for a live deployment.

Key takeaways:

• GSM is the 2G standard that introduced digital voice, the removable SIM card, and the subscriber-identity model that every later mobile generation, including 5G, still builds on.
• GSM's network architecture separates the radio access network (BTS and BSC) from the core switching network (MSC, HLR, VLR), a layered design that later generations refined rather than replaced.
• GSM uses TDMA and FDMA together to divide radio spectrum into channels and time slots, a fundamentally different approach from the OFDMA-based access methods used in 4G and 5G.
• Telia has already completed its 2G network shutdown in Norway, finishing in December 2025. Telenor plans to keep 2G running until early 2028.
• Any IoT device still connecting over GSM needs a migration plan to LTE-M, NB-IoT, or standard 4G before its network operator switches 2G off.
• Com4 provisions SIM connectivity across GSM's IoT successors, LTE-M and NB-IoT, and works with businesses to plan and execute 2G migrations before a device goes dark.

What does GSM actually stand for, and what did it introduce?

GSM stands for Global System for Mobile Communications, originally Groupe Spécial Mobile after the European standards group that developed it in the 1980s. Before GSM, mobile networks were a patchwork of incompatible national and regional analog standards, meaning a phone built for one country's network often could not be used in another. GSM changed that by creating a single, common digital standard that let a device, and later a SIM card, work across networks and borders. Two ideas from GSM still define how mobile and IoT connectivity works today:

• The SIM card. GSM introduced the concept of separating a subscriber's identity from the physical device, using a removable Subscriber Identity Module. That same principle underpins every form of IoT SIM connectivity sold today, including eSIM and iSIM, which are really just newer physical and provisioning formats built on GSM's original identity model.

• Digital voice and signaling. GSM moved mobile communication from analog to digital, which improved call quality, made encryption possible, and used network capacity far more efficiently than analog systems, laying the technical foundation every later generation built on.

How does GSM's network architecture actually work?

A GSM network is built from two connected subsystems: the Base Station Subsystem (BSS), which handles the radio connection to devices, and the Network Switching Subsystem (NSS), which handles authentication, routing, and call switching.

• BTS (Base Transceiver Station). This is the physical radio tower or antenna a device connects to. The BTS handles the radio interface directly, including channel coding and encryption on that link.
• BSC (Base Station Controller). One BSC typically controls multiple BTS units, managing radio resources, handovers between towers, and power control across the cells it oversees.
• MSC (Mobile Switching Center). The MSC is the core switching node, responsible for call routing, registration, authentication, and handovers at the network level, not just within a single cell.
• HLR (Home Location Register). The HLR is the master subscriber database, storing permanent information about every SIM registered on the network, including its identity and service permissions.
• VLR (Visitor Location Register). The VLR is a temporary database tracking subscribers currently active in a given area, updated as devices move between locations.

This layered BSS-and-NSS architecture, radio access separated from core switching, is the same basic pattern later generations refined. 4G's eNodeB and EPC, covered in Com4's guide to LTE, are a direct architectural descendant of GSM's BTS, BSC, and MSC, just consolidated and rebuilt around all-IP data instead of circuit-switched voice.

What access technology does GSM use, and how is it different from 4G?

GSM combines two radio access techniques to share spectrum across many simultaneous users:

• FDMA (Frequency Division Multiple Access) divides the available radio spectrum into separate frequency channels, each roughly 200 kHz wide in GSM's case.
• TDMA (Time Division Multiple Access) then divides each of those frequency channels into eight time slots, letting up to eight separate calls or connections share the same frequency channel by taking turns in rapid succession.

This FDMA-plus-TDMA approach was well suited to GSM's original purpose, digital voice calls, but it is far less spectrally efficient than the OFDMA-based access methods used in 4G and 5G, which is a core reason later generations deliver dramatically higher data throughput from the same amount of spectrum. In most of Europe, including Norway, GSM operated primarily in the 900 MHz and 1800 MHz bands, spectrum that operators are now progressively repurposing for 4G and 5G as 2G networks are switched off.

GSM's role in the network generations

"GSM" is sometimes used loosely to mean 2G networks in general, and sometimes to describe the broader family of standards, including 3G's UMTS, that trace their core architecture and subscriber-identity model back to GSM. Either way, GSM is the common ancestor of the SIM-based connectivity model every generation since has used, which is exactly why understanding it still matters, even as the network itself is retired.

Why does GSM still come up in IoT conversations today?

Two reasons GSM remains a live topic, even as operators actively shut down 2G networks across Norway and the wider Nordic region:

1. Legacy devices. A meaningful amount of older IoT hardware, particularly in industrial equipment, utility metering, and alarm systems, was deployed on GSM/2G years ago and needs migrating to LTE-M, NB-IoT, or standard 4G before its local 2G network is switched off.
2. The SIM model. Every SIM-based IoT connection today, whether running on 4G, LTE-M, NB-IoT, or 5G, still relies on the subscriber-identification model GSM introduced, now implemented through physical SIM, eSIM, or iSIM form factors. Com4's guide to IoT SIM cards, eSIM, and iSIM covers how that identity model has evolved into today's formats.

When is the 2G shutdown happening in Norway?

The 2G shutdown in Norway is already underway, not a future event to plan around in the abstract. Telia began shutting down its GSM network in Norway in August 2025 and completed the process in December 2025, meaning Telia's 2G network is no longer operating. Telenor has taken a slower path and currently plans to keep its 2G network running until the end of 2027, with a full shutdown expected in early 2028. Regulators in Norway have been actively urging businesses and consumers to move off 2G ahead of these dates, and similar shutdown timelines are playing out across Sweden and much of the rest of the Nordic region. In practical terms, this means any device still connecting over Telia's network needs to have already migrated, and any device on Telenor's 2G network has a defined, non-negotiable window left to do the same.

What are the risks of staying on GSM too long?

Delaying a 2G migration carries a specific, well-understood risk profile for IoT operators:

• Sudden loss of connectivity. Once an operator switches off 2G, devices still provisioned on that network go dark immediately, with no gradual degradation to signal the change is coming.
• Hardware incompatibility. Many GSM-only modems cannot be reconfigured over the air to use a different network generation, meaning migration often requires a physical hardware or SIM change, not just a software update.
• Field service costs at scale. For deployments spanning hundreds or thousands of devices in hard-to-reach locations, from utility meters to remote sensors, a reactive, post-shutdown migration is far more expensive than a planned one carried out ahead of the deadline.
• Compressed migration timelines. Businesses that wait until close to a confirmed shutdown date compete for the same installer and hardware capacity as everyone else in the same position, which tends to push out lead times right when they matter most.

GSM vs LTE-M vs NB-IoT: choosing where to migrate

For most GSM-based IoT devices being migrated today, the choice comes down to whether the device moves and how much data it sends. Mobile or portable equipment generally maps to LTE-M, while simple, stationary sensors reporting small amounts of data are usually a better fit for NB-IoT. Com4's guide to LTE and the 2G shutdown migration guide both go deeper on making that specific decision.

How does Com4 help with GSM and 2G migration?

Com4 provisions SIM connectivity across LTE-M and NB-IoT, the two network generations purpose-built to receive migrating GSM devices, alongside standard 4G and 5G. For businesses still running deployments on 2G, Com4 works through the practical side of the migration: confirming which devices and hardware need replacing versus reconfiguring, sequencing the rollout ahead of each operator's confirmed shutdown date, and provisioning replacement connectivity so devices move across with minimal downtime. Because Com4 SIMs already switch automatically across more than 750 networks in over 190 countries, a device migrated off GSM today is also positioned to keep switching to whichever network generation makes sense for years to come, rather than facing the same forced migration again at the next generational shift.