Global System for Mobile Communication (GSM)

Global System for Mobile Communication (GSM) is an international standard for 2G mobile networks, created to establish a consistent framework for mobile voice and data communication. First launched in the early 1990s, GSM replaced a variety of incompatible analog systems, allowing mobile users to connect across different countries and network providers without changing devices. It uses time division multiple access (TDMA) technology, which splits each frequency channel into time slots so multiple users can share the same channel efficiently.

GSM supports essential services such as voice calls, SMS text messaging, and basic data transfer. It incorporates encryption to protect communications, helping maintain privacy between callers. Subscriber Identity Module (SIM) cards store user credentials, making it easy to move between devices or carriers while keeping the same phone number and service. Over time, GSM has evolved to support newer mobile technologies, forming the foundation for many 3G and 4G systems still operating today.

Key Characteristics

GSM has been one of the most influential technologies in mobile communication, shaping how people connect across the globe for more than three decades. Its widespread adoption created a single, unified standard that replaced fragmented, country-specific systems, making it easier for individuals and businesses to communicate without technical barriers. Understanding GSM’s features helps explain why it became the foundation for modern mobile networks and why it still plays a role in certain markets today.

• Standardized Global Technology: GSM is an internationally recognized standard, enabling compatibility between networks in different countries.
• TDMA-Based Access: Uses Time Division Multiple Access to divide frequency channels into time slots, allowing multiple users to share the same channel efficiently.
• SIM Card Use: Stores subscriber identity and network information, allowing easy device changes without losing service or a phone number.
• Core Services: Supports voice calls, SMS text messaging, and basic mobile data functions.
• Encryption for Privacy: Uses built-in encryption to protect communication between devices and network infrastructure.
• International Roaming: Allows subscribers to use their mobile service when traveling abroad, as long as the destination network also supports GSM.
• Scalability: Designed to serve both small and large user bases, making it adaptable for different network sizes.

Core Components of GSM

GSM networks are built on a structured architecture that divides responsibilities between different systems. Each component plays a specific role in delivering voice, text, and data services to users, ensuring reliable communication across vast geographic areas.

• Mobile Station (MS): The mobile device and SIM card used by the subscriber. The SIM stores identity, authentication data, and contact information, while the device handles communication with the network.
• Base Transceiver Station (BTS): The equipment that communicates directly with mobile devices via radio signals, covering a specific geographic area called a cell.
• Base Station Controller (BSC): Manages multiple BTS units, handling tasks such as frequency allocation, handovers between cells, and controlling radio resources.
• Mobile Switching Center (MSC): Acts as the central hub for call routing, SMS delivery, and connections to other mobile or fixed networks.
• Home Location Register (HLR): A database storing permanent subscriber information, such as phone numbers, services subscribed to, and current location within the network.
• Visitor Location Register (VLR): A temporary database that holds subscriber information when the user is outside their home area, enabling roaming.
• Authentication Center (AUC): Provides security functions, including validating a subscriber’s identity and generating encryption keys for secure communication.
• Equipment Identity Register (EIR): Maintains a list of valid, stolen, or unauthorized devices to prevent fraudulent or unauthorized access to the network.

Security in GSM

Security in GSM was designed to protect both the user’s identity and the confidentiality of their communications. While not perfect by today’s standards, these measures were a major advancement compared to earlier analog systems, which transmitted voice in plain, unprotected form.

• Subscriber Authentication: The network verifies a user’s identity through the SIM card, which stores a unique key shared with the network’s Authentication Center (AUC). This process helps prevent unauthorized network access.
• Encryption of Communications: GSM uses encryption algorithms to scramble voice and data as they travel between the mobile device and the Base Transceiver Station (BTS), making interception more difficult.
• Temporary Identity Assignment: Instead of transmitting the subscriber’s permanent identity (IMSI) over the air, GSM assigns a Temporary Mobile Subscriber Identity (TMSI) to protect privacy.
• Device Validation: The Equipment Identity Register (EIR) keeps track of valid and invalid device IDs, blocking stolen or unauthorized phones from connecting.
• Roaming Security: Authentication and encryption processes are maintained when a user connects to a foreign network, helping keep services secure while traveling