What is GSM (Global System for Mobile Communications)?

GSM (Global System for Mobile Communications) is the most widely used digital mobile phone system and standard in Europe.

What is GSM (Global System for Mobile Communications)?

GSM System

The GSM system is the 2nd generation digital mobile communication system based on radio cells and was developed to address the problems posed by analog systems.

This system is designed for voice transmission and therefore is based on circuit switching, a feature different from the GPRS (General Packet Radio Service) system.

When performing the transmission via circuit switching, resources are busy throughout the entire communication and therefore pricing is calculated based on elapsed time.


All GSM networks are divided into four basic sections;

  1. MS (Mobile Station)
  2. BSS (Base Station)
  3. NSS (Network and Switching Subsystem)
  4. OSS (Support and Operation Subsystems)

GSM also provides complementary telephony services such as caller ID, call forwarding, call waiting, busy user call termination, and closed user groups.

   1. MS (Mobile Station)

It consists of two basic elements: terminal/mobile equipment on the one hand and SIM or Subscriber Identity Module on the other.

SIM is a small smart card used to describe the features of our terminal. This card is inserted inside the mobile phone and allows the user to access all the services offered by their operator.

Without the SIM card, the terminal will not work because the network will be unavailable.

   2. BSS (Base Station)

In addition to being responsible for transmission and reception, it serves to connect mobile stations to the NSS.

Like MS, these are made up of two different elements.

  1. BTS (Base Transceiver Station)
  2. BSC (Base Station Controller)

   3. NSS (Network and Switching Subsystem)

This system is responsible for managing the communication between different users of the network.

To do this job, NSS is divided into seven different components, each with a role within the network:

1) MSC (Mobile Services Switching Center)

It is the central component of NSS and is responsible for performing switching tasks within the network and providing connectivity to other networks.

2) GMSC (Gateway Mobile Services Switching Center)

A gateway is responsible for connecting two networks and is a translator device, which is software/hardware that allows communication protocols found on both networks to understand each other.

The role of the GMSC is to transform the communication between fixed telephone networks and the GSM network and to provide services.

3) HLR (Home Location Register)

HLR is a database containing information about users connected to a particular MSC. Among the information stored by HLR, there are basically the user’s location and the services they have access to.

4) VLR (Visitor Location Register)

It contains all the information a user needs to access network services and is part of the HLR with which it shares functionality.

5) AuC (Authentication Center)

It provides the necessary parameters for user authentication within the network and is also responsible for supporting encryption functions.

6) EIR (Equipment Identy Register)

EIR is used in GSM networks, but to provide security at the current equipment level and has a database containing all terminals valid for use in the network.

7) GIWU (GSM Interworking Unit)

It acts as a communication interface between different networks for data communication.

   4. OSS (Support and Operation Subsystems)

OSS connects to different NSS and BSCs to control and monitor the entire GSM network.

Pricing System

The charges for the use of the GSM network are made depending on the service and company it supports.

In this way, the pricing system consists of a cost that is a function of the realization of a voice or data communication through this service, a cost of establishing the communication, and the time it remains installed.

Depending on the network operator, this pricing can be determined by factors such as call establishment, establishment fee, set-up fee, and call maintenance.

It can have a fixed cost and a variable duration depending on the time period, and the cost can be variable depending on the time period in question.

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