GSM is a digital cellular network standard used globally. It was developed to standardize the fragmented cellular technologies that existed before 1982. The GSM network is divided into the mobile station (MS), network switching system (NSS), and base station system (BSS). The MS includes the mobile equipment and subscriber identity module (SIM) card. The NSS includes registers like the home location register (HLR) and visitor location register (VLR), and switches like the mobile switching center (MSC). The BSS provides the connection between the MS and NSS, and includes the base transceiver station (BTS) and base station controller (BSC).

1. INTRODUCTION TO GSM
GSM is the short form of Global for Mobile .GSM is Globally accepted
standard for digital cellular communication. GSM Technology was
established and developed to unify different technologies which were
existing before 1982 by CEPT(Conference of European Posts and
Telecommunications).

2. GSM TECHNOLOGY
The GSM technology was
found to be more advantageous compared to the previous regional based
technologies in the
following aspects:
• Improved spectrum efficiency
• International roaming
• Low-cost mobile sets and base stations
• High-quality speech
• Compatibility with ISDN and other telephone company services
• Support for new services e.g; Internet,Text Messages etc
• Quality of service(QOS

3. GSM NETWORK
GSM Network is divided into three major systems
● i. MOBILE STATION (MS)
● ii. NETWORK SWITCHING SYSTEM (NSS)
● iii. BASE STATION SYSTEM(BSS

4. GSM NETWORK

5. MOBILE STATION(MS)
● This includes all user's equipment and software needed for
communication with a mobile
network. This part of GSM consists of two main parts
● - Mobile Equipment(ME)
● - Subscriber Identity Module(SIM)(Electronic Smart Card)

6. ME
Mobile Equipment contains
IMEI-International Mobile Equipment Identity
● Features of ME
-Maximum Transmission power
-service key Support

7. SIM
SIM contains
-IMSI - International Mobile Subscriber identity
-The subscriber is identified by this number
-Hel the subscriber to make emergency call without SIM
Card
-TMSI-Transparency Mobile Subscriber Identity
-This ensures the privacy of the subscriber
-LAI- Location Area Identity
- Identifies the current location of the subscriber

8. SIM
MSISDN-Mobile Station International Subscriber Directory
Number
This is telephone no of mobile substation.It comprises
of Country Code, Network Code and Subscriber number eg:
+255673789793
+ = International
2 = Africa
55 = Tanzania
0673= Network Code
789793= Subscriber Identity

9. NETWORK SWITCHING
SYSTEM(NSS)
●
Network Switching System(NSS) is responsible for performing call processing and
subscriber-related functions. The switching system includes the following functional unit
●
Home Location Register(HLR) – This is a database which stores the subscriber's
●
parameters including reference data, variation Identification number and address
●
Visitor Location Register(VLR)- This contains selected information from the
●HLR,which is necessary for call control and provision of subscribed services
●Equipment Identity Register(EIR)- This contains a list of all valid mobile equipment
●on the network.
●Mobile Switching Center (MSC)- This is the central of Network Subsystem. MSC
deals with:
- Billing
- Location registration
- Gateway to SMS
- Synchronizing BSS
- Handover management
-Authentication of MS(Done By Authentication Centre (AuC))

10. NSS

11. BASE STATION SYSTEM(BSS)
● The BSS provides a connection between the Ms of a
limited area and the NSS. The BSS consist of two main
elements
● - One or more BTSs (Base Transceiver System/Station)
● -One BSC(Base Switching Controller);

12. BASE SWITCHING
CONTROLLER(BSC)
● The BSC forms the center of the BSS. The BSC connects
many BTSs over the Abis-Interface. The BSC was
● made intentionally to reduce the load from MSC.The
Functions of BSC are:
-Channel Allocation
-Terrestrial Channel Management
-Channel Configuration Management
-Handover Control

13. BASE TRANSCEIVER
SWITCH(BTS)
● The BTS provides the physical connection of MS to the network in form of
Air-Interface.. the
● functions of BTS includes:
-Connects to a number of mobile stations (MSs)
-Formation of cells using appropriately directed antenna
- Processing of signals
-Amplification of signals to acceptable strength so that they can be
transmitted without loss of data
- Channel coding and decoding
-Encryption and decryption of data

14. BTS

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