Millions of Phones Use GSM ... Meaning What, Exactly?

By: Marie Look  | 
It would be a lot harder to enjoy that phone call without GSM technology. shapecharge / Getty Images

If you've ever wondered how millions of cell phones across the globe are able to transmit voice, text and other data in an organized and efficient way, the answer has to do with GSM, meaning (or rather, standing for) global system for mobile communications.

This cornerstone of modern communication underpins the way mobile phones around the world operate.


What Is GSM?

GSM is the international standard for mobile communication. It enables users to transmit data, make phone calls and exchange text messages seamlessly.

GSM operates within a framework of radio channels and cellular technology, allowing multiple users to access the same bandwidth simultaneously. In Europe and many other parts of the world, GSM is the only type of cellular service available.


Origins of the GSM System

Developed by the European Telecommunications Standards Institute (ETSI), GSM emerged as a pan-European mobile technology in the 1980s.

Originally, the acronym GSM stood for Groupe Spécial Mobile. The Conference of European Posts and Telegraphs (CEPT) formed the group in 1982 to research the merits of a European standard for mobile telecommunications.


Commercial service using the GSM system did not actually start until 1991. Instead of using analog service, GSM was developed as a digital system using Time Division Multiple Access (TDMA) technology.

How Does GSM Work?

At the core of GSM networks are base transceiver stations (BTS) and base station controllers (BSC), which facilitate communication between mobile devices and the network's core infrastructure.

Division by Region

GSM systems divide geographic areas into cells, each served by a BTS, ensuring coverage across various regions. These cells vary in size, from large umbrella cells covering wide areas to smaller cells catering to dense urban environments.


SIM Cards

When a mobile device enters a cell, it connects to the nearest BTS, registering its presence with the network's Home Location Register (HLR). A subscriber identity module (SIM) card, a small electronic chip containing specific information about the user and their mobile services, facilitates this process.

GSM Frequency Bands

Different parts of the world use different GSM frequency bands, per designations by the International Telecommunication Union (ITU).

The following parts of the world use the GSM-900 and GSM-1800 bands:

  • Africa
  • Asia
  • Europe
  • Middle East
  • Oceania
  • South America (eastern countries)

Meanwhile, other parts of the world use GSM-850 and GSM-1900:

  • Central America
  • North America
  • South America (western countries)


GSM and TDMA Technology

The GSM system uses TDMA to split a frequency into time slots.

If you've ever wondered how millions of people can send text messages at the same time with all of those texts finding their way to the correct destination, the answer has to do, at least in part, with time division multiple access.

Various wireless communication systems, including 2G cellular networks like GSM, use TDMA as the access method for voice and data transmission. In addition to GSM phones, digital radio systems, satellite communication, certain types of wireless LANs (Local Area Networks), and other applications use TDMA.


Communication Time Slots

TDMA systems divide transmission times into discrete intervals or time slots, with each user assigned one or more for their communication needs. These time slots are typically very short, often just milliseconds, and are synchronized across all users within the system.

During each time slot, the user can transmit their data, whether it be voice, text, or multimedia, without interference from other users sharing the same channel.

By ensuring each user has exclusive access to the channel for a fraction of the total transmission time, it minimizes conflicts and collisions between transmissions.

The TDMA Advantage

A major plus of TDMA technology is its ability to support multiple users on the same frequency band simultaneously. Dividing the available time into slots allows for higher capacity and increased data throughput compared to other access methods.


5 Key Features of GSM

From its inception as a European standard to its status as a worldwide model, GSM has shaped the landscape of mobile communications, enabling seamless voice calls, text messages and data exchanges across borders and continents. Here are five characteristics that have made it a success:

  1. Acceptance as a global standard: The widespread acceptance of GSM technology facilitates interoperability, enabling users to use the same mobile phones in different regions without compatibility issues.
  2. Multiple access technologies: GSM utilizes multiple access technologies, including time division multiple access (TDMA) and code division multiple access (CDMA), to accommodate multiple users on the same radio channel simultaneously.
  3. Roaming agreements: GSM network operators often establish roaming agreements with other carriers, allowing users to access cellular services while traveling abroad to ensure continuity of service.
  4. Secure wireless system: With features like encryption and authentication, GSM offers a secure platform for transmitting digital information. This ensures the privacy and integrity of voice calls, text messages and data exchanges over the network.
  5. Short message service (SMS): One of GSM's most popular features is the short message service (SMS), which enables users to exchange texts quickly and efficiently. SMS messaging has become a part of everyday communication, offering both convenience and practicality for many people.


GSM vs. CDMA Networks

GSM utilizes TDM technology rather than code division multiple access (CDMA) technology, which other communication frameworks rely on. While GSM and CDMA technologies serve similar purposes in mobile communications, they differ in their approach to network architecture and operation.

Unlike TDMA, which divides the transmission time into discrete time slots, CDMA networks assign a unique code to each user and spread the signal across the entire frequency band. But similar to TDMA, CDMA allows multiple users with CDMA phones to transmit and receive data concurrently without interfering with each other.


In the United States, the major carriers are divided between TDMA and CDMA. For example, AT&T and Mobile use the GSM system (and therefore TDMA), while T-Mobile, US Cellular and Verizon use CDMA.

We created this article in conjunction with AI technology, then made sure was fact-checked and edited by a HowStuffWorks editor.



What are GSM devices?
The Global System for Mobile communications (GSM) is an international standard for mobile telecommunications. If you travel in Europe or any other parts of the world, GSM is the only type of cellular service that is available.
Do GSM phones work in the U.S.?
GSM operates in Europe and Asia, as well as in the United States in the 1900 MHz (sometimes referred to as 1.9 GHz) band.
What year did the GSM become the global system for mobile communication?
Initially, the acronym GSM stood for Groupe Spécial Mobile, which was a group formed by the Conference of European Posts and Telegraphs (CEPT) in 1982 to research the merits of a European standard for mobile telecommunications. However, it wasn't until 1991 that a commercial service using the GSM system began operating globally.