Main Entities of GSM Architecture.

GSM is used to mean Global System for Mobile communications. GSM was designed as a circuit-switched system with the following four subsystems.

-Mobile Station (MS): carried by the subscriber

-Base Station Subsystem (BSS): radio network

-Network Station Subsystem (NSS): switched network

-Network Management System (NMS) or Operation Station Subsystem (OSS).


Portable, vehicle mounted, hand held device .MS contains Mobile Equipment (ME) the terminal and Subscriber Identity Module (SIM). As we require mobility of a user which is main aim of wireless technology. It is first part.


It is radio part, we have controller. In BSS have divided into two main parts,

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


It’s a core of network. It manage the entire network. It contains databases which are;

  1. Mobile Switching Center (MSC)
  2. Home Location Register (HLR)
  3. Visitor Location Register (VLR)
  4. Authentication Center (AUC)
  5. Equipment Identity Register (EIR)
  6. Intelligent Network (IN)
  7. Gateway Mobile Switching Center (GMSC)
  8. Short Message Service Center (SMSC)


Any fault of any configuration relative problems, we require OSS or NMS. It divided into two main parts.

  1. Operational Maintenance Center for Radio (OMC-R)
  2. Operation Maintenance Center for Switch (OMC-S)


1. Mobile Station (MS)

MS is connected to BTS with help of antenna to path a signal from MS to BTS. The connection part between MS and BTS is air interface or (sometimes is called Uu: User to user interface).

2. Base Transceiver Station (BTS)

A unit that can transmit and receive is known as transceiver. BTS has the following functions;

         -Frequency hopping

         -Communicates with Mobile station and BSC

         -Mobile station signals are received by BTS.

3. Base Station Controller (BSC)

          -BSC manages all BTS in a particular area

          -All BTS signals in a particular area are managed by BSC

          -Handover for each MS

          -Radio Power control 

          -Assigns Frequency and time slots for all MS’s in its area

          -All signals from BSC will be forwarded to MSC

4. Mobile Switching Center (MSC)

It is a heart of a network (core of a network).

   -All BSS are controlled by MSC

  -All switching functionality, authentications, verification as well as security purpose are performed in MSC

   -Has a number of databases attached to it which are, HLR, VLR, EIR, IN, AUC, GMSC, SMSC.

Home Location Register (HLR)

  -Its permanent database. It stores permanent location of a user.  For example, when I go to purchase SIM (Subscriber Identity Module), I require address prove, according to my location, locate me to a particular cell. Cell allocated me will be my home (house number is not my home).

  -All numbers are defined according to HLR.

Visitor Location Register (VLR)

  -Temporary database which updates whenever new MS enters its area, by HLR database.

  -Deals with change in location, i.e. Handover as you move from one place to another, all locations are stored in VLR.

Equipment Identity Register (EIR)

Made up of three sub-classes:

  1. The White List, Are mobile users who communicate.
  2. The Black List, Total number of users who blocked by a network, i.e. particular numbers are blocked by a network.
  3. The Gray List, Are services denied users i.e. blocked incoming call or blocked out coming call.

EIR, checks all numbers either in white list, black list or gray list

Authentication Center (AUC)

   -Deals with verifications. The same key stored in SIM, the same key stored in AUC database. If the key matches, the user key is authenticated.

     -Protects against intruders in air interface.

Intelligent Network (IN)

All bills are checked in IN. Example pre-paid bills and all added values services are recorded in IN.

Short Message Service Center (SMSC)

It works for both store and forward short message. SMSC has address of a particular SMS.

Gateway Mobile Switching Center (GMSC)

GMSC is used when we require to connect a number of MSC together. GMSC makes possible for international call. Example when you want to communicate with someone outside of your country (India and Canada).i.e. Gateway of India will contact with gateway of Canada.

Public Switched Telephone Network (PSTN)

Landlines connections.

5. Network Management Subsystem or Operation Station Subsystem (NMS / OSS)

Deals with monitoring, configuration management and performance management. (NMS / OSS) is divided into two parts;

  1. OMC-R; Operation Maintenance Center for Radio (BSS part).
  2. OMC-S; Operation Maintenance Center for Switch (NSS part).



Login to comment