GSM NETWORK BASICS Lesson Note
Learning Objectives
This SS2 Computer Hardware & GSM Repair lesson note covers GSM NETWORK BASICS for First Term, Week 5.
Lesson Note
Learning Objectives
By the end of the lesson, students should be able to:
1. Define GSM.
2. Explain the meaning of a mobile communication network.
3. Describe the basic principles of GSM communication.
4. Identify the major components of a GSM network.
5. Explain the functions of a SIM card.
6. Explain the meaning and importance of a mobile cell.
7. Differentiate between 2G, 3G, 4G and 5G mobile networks.
8. Explain the functions of a Base Transceiver Station (BTS).
9. Identify common GSM network problems.
10. Explain basic methods of troubleshooting GSM network problems.
CONTENT
MEANING OF GSM
GSM stands for Global System for Mobile Communications. It is a standard originally developed for digital mobile cellular communication.
GSM technology became widely used for mobile voice calls, text messaging and other mobile communication services.
GSM networks traditionally provided services such as:
- Voice calls
- SMS (Short Message Service)
- Basic data communication
- Subscriber identification
- Mobile roaming
Although newer mobile technologies such as 3G, 4G and 5G are widely used today, GSM remains an important concept in understanding the development and operation of mobile communication networks.
MEANING OF A GSM NETWORK
A GSM network is a cellular communication system that allows mobile phones and other compatible devices to communicate through radio signals and network infrastructure.
When a person makes a call, sends an SMS or uses a mobile service, the mobile device communicates wirelessly with a nearby cellular base station. The network then handles the communication and connects the user to the intended destination or service.
Simple Communication Flow
Mobile Phone → BTS → Network System → Other Network/User
The exact network architecture is more complex, but this gives a basic idea of how a mobile device communicates with a network.
BASIC PRINCIPLE OF CELLULAR NETWORKS
A mobile network divides a geographical area into smaller areas called cells.
Each cell is served by one or more radio base stations.
The use of cells allows network operators to reuse radio frequencies in different locations and serve many users efficiently.
ADVANTAGES OF CELLULAR NETWORKS
1. Allows many users to communicate.
2. Provides wide geographical coverage.
3. Allows frequencies to be reused in different areas.
4. Supports mobility as users move from one area to another.
5. Makes efficient use of available radio spectrum.
MAJOR COMPONENTS OF A GSM NETWORK
A traditional GSM network can be understood through four major parts:
1. Mobile Station (MS)
2. Base Station Subsystem (BSS)
3. Network and Switching Subsystem (NSS)
4. Operations and Support Subsystem (OSS)
MOBILE STATION (MS)
The Mobile Station (MS) refers to the mobile equipment used by a subscriber together with the SIM-related subscriber identity.
A mobile station includes the mobile device and its subscriber identity information.
Examples of Mobile Equipment
- Mobile phone
- Compatible cellular device
Functions
1. Sends and receives radio signals.
2. Allows the user to make calls.
3. Allows the user to send and receive messages.
4. Provides access to supported mobile services.
5. Communicates with the cellular network.
SIM CARD
SIM stands for Subscriber Identity Module.
A SIM is a small integrated circuit used to securely store subscriber-related information and support authentication on mobile networks.
Functions of a SIM
1. Identifies the subscriber to the mobile network.
2. Supports subscriber authentication.
3. Stores certain subscriber-related information.
4. Enables a compatible mobile device to access the subscriber’s mobile service.
5. Contains information associated with the subscriber’s network account.
IMPORTANT SIM TERMS
IMSI
IMSI stands for International Mobile Subscriber Identity.
It is an identifier associated with a mobile subscriber and is used by the network for subscriber identification.
PIN
A Personal Identification Number (PIN) may be used to protect access to the SIM.
PUK
A Personal Unblocking Key (PUK) can be required to unlock a SIM after too many incorrect PIN attempts.
IMEI
IMEI stands for International Mobile Equipment Identity.
It is a number used to identify a mobile device on cellular networks.
Difference Between SIM and IMEI
SIM| IMEI
Relates primarily to the subscriber/service identity| Identifies the mobile equipment
Stored on/in the SIM| Associated with the mobile device
Used in subscriber authentication and network access| Used to identify the equipment
Can be moved to another compatible phone| Belongs to the particular equipment
A technician may need to understand both concepts when diagnosing mobile network or device-related problems.
BASE TRANSCEIVER STATION (BTS)
A Base Transceiver Station (BTS) is the radio equipment that communicates wirelessly with mobile devices within a cell.
It contains equipment such as radio transmitters, receivers and antennas.
Functions of a BTS
1. Communicates with mobile phones through radio signals.
2. Transmits radio signals to mobile devices.
3. Receives radio signals from mobile devices.
4. Provides radio coverage for a cell.
5. Helps establish and maintain wireless communication.
Simple Representation
Mobile Phone ⇄ Radio Signal ⇄ BTS
BASE STATION CONTROLLER (BSC)
The Base Station Controller (BSC) is a network component used in traditional GSM architecture to control and manage multiple BTS sites.
Functions of a BSC
1. Controls multiple base stations.
2. Manages radio resources.
3. Helps manage handovers between cells.
4. Controls allocation of radio channels.
5. Coordinates communication between BTS equipment and the core network.
MOBILE SWITCHING CENTRE (MSC)
The Mobile Switching Centre (MSC) is a major component of traditional GSM core-network architecture responsible for switching and managing mobile communications.
Functions
1. Handles mobile voice call switching.
2. Connects calls to other networks.
3. Supports mobility management.
4. Helps manage subscriber communication.
5. Supports services such as roaming and call routing.
HOME LOCATION REGISTER (HLR)
The Home Location Register (HLR) is a database used in traditional GSM networks to store important information about subscribers.
Information May Include
- Subscriber identity
- Subscription information
- Service information
- Current location-related information used for routing
Function
The HLR helps the network determine information about a subscriber and how communication should be handled.
VISITOR LOCATION REGISTER (VLR)
The Visitor Location Register (VLR) is a database associated with an MSC that temporarily stores information about subscribers currently being served in an area.
Functions
1. Stores temporary subscriber information.
2. Supports mobility management.
3. Helps the network provide services to visiting subscribers.
4. Works with the HLR and MSC.
AUTHENTICATION CENTRE (AuC)
The Authentication Centre (AuC) is a network component associated with subscriber authentication and security.
Functions
1. Helps authenticate subscribers.
2. Supports protection of mobile communication services.
3. Provides information used in security procedures.
EQUIPMENT IDENTITY REGISTER (EIR)
The Equipment Identity Register (EIR) is a database associated with GSM networks that can contain information about mobile equipment identities.
It may help networks identify equipment that is:
- Authorized
- Suspected of being unauthorized
- Reported as lost or stolen
OPERATIONS AND SUPPORT SUBSYSTEM
The Operations and Support Subsystem (OSS) refers to systems used by network operators to monitor, manage and maintain network equipment and services.
Functions
1. Monitors network performance.
2. Helps identify faults.
3. Supports network maintenance.
4. Assists network management.
5. Helps technicians monitor network equipment.
GSM FREQUENCY BANDS
GSM networks operate using radio-frequency bands assigned by regulators and network operators.
Different countries and operators may use different frequency bands.
Examples of GSM bands historically used in different regions include:
- 850 MHz
- 900 MHz
- 1800 MHz
- 1900 MHz
The exact bands available depend on the country, operator and network technology.
GSM CHANNELS
A mobile network needs radio channels to allow many users to communicate.
GSM uses techniques that divide available radio resources among users.
Two important concepts associated with traditional GSM are:
FDMA
Frequency Division Multiple Access (FDMA) divides available spectrum into frequency channels.
TDMA
Time Division Multiple Access (TDMA) divides communication into time slots so that multiple users can share a radio channel.
GSM traditionally combines frequency and time-based access techniques to efficiently support multiple users.
HANDOVER
Handover is the process of transferring an ongoing mobile connection from one cell or base station to another as the user moves.
Example
A person travelling in a vehicle may move away from one cell and enter another. The network can transfer the connection to another cell to maintain communication.
Importance of Handover
1. Maintains calls while users move.
2. Improves network continuity.
3. Supports mobile users.
4. Helps manage network resources.
ROAMING
Roaming allows a mobile subscriber to use mobile services outside the normal coverage area of their home network, where an agreement exists between networks.
For example, a subscriber may use their mobile service while travelling to another country if their operator supports international roaming.
SMS
SMS stands for Short Message Service.
It allows users to send and receive short text messages through a mobile network.
Uses of SMS
- Sending text messages
- Receiving notifications
- Receiving service information
- Two-factor authentication in supported services
- Mobile alerts
MOBILE DATA
Mobile networks can provide data communication in addition to voice and SMS.
Different generations of mobile technology provide different capabilities.
Examples
- GPRS/EDGE — associated with 2G networks
- 3G — improved mobile data services
- 4G LTE — much faster mobile broadband
- 5G — newer generation with higher capacity and lower latency in suitable deployments
GENERATIONS OF MOBILE NETWORKS
1G
1G refers to the first generation of cellular networks.
Characteristics
- Mainly analogue voice communication.
- Limited capacity compared with later generations.
- Limited security and data capabilities.
2G
2G introduced widespread digital cellular communication.
Characteristics
- Digital voice services.
- SMS.
- Improved security compared with analogue systems.
- Basic mobile data services.
- GSM became one of the major 2G technologies.
3G
3G provided improved mobile data capabilities compared with traditional 2G services.
Features
- Faster data communication.
- Mobile Internet.
- Multimedia services.
- Improved support for video communication.
4G
4G provides much faster mobile broadband and is designed primarily around packet-based data communication.
Features
- High-speed Internet.
- Video streaming.
- Online communication.
- Mobile applications.
- Improved network capacity.
LTE (Long-Term Evolution) is a widely deployed 4G technology.
5G
5G is a newer generation of cellular technology.
Features
- Higher potential data speeds.
- Lower latency in suitable conditions.
- Greater network capacity.
- Support for large numbers of connected devices.
- Applications involving advanced mobile broadband and connected devices.
COMPARISON OF MOBILE NETWORK GENERATIONS
Generation| Main Characteristic
1G| Analogue mobile voice
2G| Digital voice and SMS
3G| Improved mobile data
4G| High-speed mobile broadband
5G| Higher capacity, speed and lower latency in suitable conditions
GSM NETWORK COVERAGE
Network coverage refers to the geographical area where a mobile device can successfully communicate with the mobile network.
Coverage depends on factors such as:
- Number of base stations
- Distance from a base station
- Terrain
- Buildings and obstacles
- Frequency band
- Network design
- Environmental conditions
- Network load
SIGNAL STRENGTH
Signal strength refers to the strength of the radio signal received by a mobile device from the cellular network.
A strong signal generally makes communication more reliable, although network quality depends on more than signal strength alone.
Factors Affecting Signal Strength
1. Distance from a base station.
2. Buildings and walls.
3. Mountains and other geographical features.
4. Trees and other obstacles.
5. Frequency being used.
6. Antenna location.
7. Interference.
COMMON GSM NETWORK PROBLEMS
A mobile phone may experience different network problems.
No Network Signal
The phone displays no network or cannot connect to the mobile network.
Possible Causes
- Poor coverage
- SIM problem
- Network outage
- Airplane mode enabled
- Device network settings problem
- Faulty antenna or radio hardware
Weak Network Signal
The phone receives a weak signal.
Possible Causes
- Distance from the base station
- Buildings or physical obstacles
- Poor coverage
- Network congestion
- Device-related problems
Call Failure
A call may fail to connect.
Possible causes include:
- Poor network coverage
- Network congestion
- Account/service restrictions
- SIM problems
- Temporary network fault
Dropped Calls
A call may disconnect unexpectedly.
Possible causes include:
- Weak or changing signal
- Network problems
- Handover problems
- Device faults
- Network congestion
SMS Failure
A message may fail to send or receive.
Possible causes include:
- Poor signal
- Incorrect message centre configuration where applicable
- Network problems
- SIM/service issues
- Temporary congestion
BASIC GSM NETWORK TROUBLESHOOTING
A technician or user can follow a systematic procedure when investigating network problems.
Step 1: Check Signal Strength
Look at the network signal indicator on the phone.
Check Airplane Mode
Ensure that airplane mode is not unnecessarily enabled.
Step 3: Check the SIM
Make sure the SIM is properly inserted and recognized by the phone.
Step 4: Restart the Device
Restarting the phone can sometimes resolve temporary network registration problems.
Step 5: Check Network Selection
Check whether the phone is set to an appropriate automatic or manual network selection mode.
Step 6: Check Network Mode
Ensure that the device supports and is configured for a network mode available in the area.
Step 7: Test the SIM in Another Compatible Phone
This can help determine whether the problem is related to the SIM/service or the original phone.
Step 8: Test Another SIM in the Phone
This can help determine whether the phone itself has a network-related fault.
Step 9: Check for Network Outage
The mobile network operator may be experiencing a temporary service problem.
Step 10: Seek Technical Assistance
If the problem continues, the device or SIM may require professional diagnosis.
IMPORTANCE OF GSM NETWORKS
GSM and related mobile networks are important because they:
1. Enable mobile communication.
2. Support voice calls.
3. Support text messaging.
4. Provide mobile Internet services.
5. Support communication over large geographical areas.
6. Enable mobile users to communicate while travelling.
7. Support businesses and organizations.
8. Provide emergency and public communication services where available.
9. Support mobile banking and other digital services.
10. Provide connectivity for various mobile applications.
IMPORTANCE OF GSM KNOWLEDGE TO A REPAIR TECHNICIAN
A GSM repair technician needs basic network knowledge because some mobile-phone problems are not caused by damaged hardware.
Understanding GSM networks helps a technician distinguish between:
- SIM problems
- Network-service problems
- Software/configuration problems
- Antenna problems
- Radio-frequency hardware problems
- Network coverage problems
This prevents unnecessary replacement of working components.
SUMMARY
GSM means Global System for Mobile Communications and is an important digital cellular communication standard.
A GSM network consists of mobile devices, radio base stations and network components that work together to provide communication services.
Important GSM components include the Mobile Station, BTS, BSC, MSC, HLR, VLR, AuC and EIR.
A mobile network divides an area into cells to provide coverage and efficiently reuse radio resources. Handover allows an active connection to move from one cell to another as a user travels.
Mobile network generations have developed from 1G to 5G, with improvements in digital communication, data speed, capacity and network capabilities.
Knowledge of GSM network basics is important to GSM repair technicians because it helps them identify whether a problem is caused by the mobile device, SIM card, configuration, network coverage or the network operator.
Evaluation
OBJECTIVE QUESTIONS
Choose the correct answer from options A–D.
1. What does GSM stand for?
A. Global System for Mobile Communications
B. General System for Machine Communication
C. Global Service Machine
D. General Signal Mobile
2. Which component communicates directly with mobile phones through radio signals in a traditional GSM network?
A. BTS
B. Printer
C. Keyboard
D. Scanner
3. What does SIM stand for?
A. Subscriber Identity Module
B. System Internet Machine
C. Signal Identification Memory
D. Subscriber Internet Machine
4. Which of the following is mainly used to identify mobile equipment?
A. IMEI
B. PIN
C. SMS
D. HLR
5. What is the main purpose of dividing a mobile network into cells?
A. To reduce the size of mobile phones
B. To improve the efficient use of radio resources and provide coverage
C. To increase the weight of phones
D. To prevent users from making calls
6. Which generation of mobile technology is associated with widespread digital voice and SMS?
A. 1G
B. 2G
C. 4G
D. 5G
7. What is handover in a mobile network?
A. Removing a SIM card
B. Transferring a connection from one cell to another
C. Switching off a phone
D. Formatting a phone
8. Which of the following is a common symptom of poor GSM network coverage?
A. Weak signal
B. Larger screen
C. Faster keyboard
D. More storage space
9. Which device is used to identify a subscriber’s mobile service?
A. SIM card
B. Monitor
C. Keyboard
D. Printer
10. Which of the following is a basic step when troubleshooting a mobile network problem?
A. Remove the motherboard immediately
B. Check the signal and SIM connection
C. Break the phone casing
D. Replace the screen first
THEORY QUESTIONS
1a. What is GSM? Explain the meaning and importance of a GSM network.
1b. State and explain the functions of any five major components of a GSM network.
2a. What is a cellular network? Explain how cells help in providing mobile communication services.
2b. Differentiate between 2G, 3G, 4G and 5G mobile networks.
2c. State five common GSM network problems and explain the basic steps for troubleshooting them.