GSM Network Architecture Quiz

GSM Network Architecture

The architecture of the GSM network consists of the mobile station (MS), the base transceiver station (BTS), the base station controller (BSC), the mobile switching center (MSC), the home location register (HLR), and the visitor location register (VLR).
The MS is the mobile phone, and it connects to the network through the BTS.
BTSs are grouped together and controlled by the BSC.
The MSC is the central switching center for the GSM network.
The HLR stores information about subscribers, such as their phone number, location, and service features.
The VLR stores information about subscribers who are currently roaming in the network.

Mobile Station (MS)

The mobile phone is the MS, and connects to the network through the BTS.
Has a Subscriber Identity Module (SIM), which stores the customer's personal information.
It has an International Mobile Equipment Identity (IMEI) (15 Digit Number), which uniquely identifies each device.
It features a Terminal Module and Controller.
It has a Switch Matrix to switch between different channels.
It includes Operation and Maintenance features.

Base Transceiver Station (BTS)

BTS are responsible for transmitting and receiving radio signals.
BTS can be configured in different ways, including:
- Star Cell Configuration: The BTS is at the center of the cell and all MSs connect directly to it.
- Umbrella Cell Configuration: The BTS has a wider coverage area.
- Sectorized Cell Configuration: The BTS is divided into sectors with different coverage areas.
Each BTS has an International Cell Global Identity (CGI) and a Base Station Identity Code (BSIC).
The BTS has different critical elements:
- DXU – Distribution Switch Unit
- TRU – Transceiver Unit
- CDU – Combining and Distribution Unit
- ECU – Energy Control Unit
  - PSU: Power Supply Unit
  - BFU: Battery Fuse Unit

Base Station Controller (BSC)

The BSC is responsible for controlling the BTSs.
Its functions include paging, channel allocation, dynamic power control, handover, and frequency hopping.

Mobile Switching Center (MSC)

The MSC is the central switching center for the GSM network.
It is responsible for:
- Channel Assignment
- Inter-MSC handover
- Gateways to other networks

Handover

There are different handovers in GSM networks:
- Mobile-controlled Handoff: the MS monitors signals around BS and issues a handoff
- Network-controlled Handoff: BS measure the MS signal and issue a handoff request
- Mobile-assisted Handoff: The network asks the MS to measure the BS signal
- Inter-Base Station Handoff: MS will issue a request by using a free channel
- Inter-System Handoff: BTS are connected to 2 different MSCs - Verify RF line

Identity Numbers

Several types of identity numbers are used in GSM networks:
- Mobile Station ISDN (MSISDN)
- International Mobile Subscriber Identity (IMSI)
- International Mobile Station Equipment Identity (IMEI)
- Mobile Station Roaming Number (MSRN)
- Temporary Mobile Subscriber Identity Number (TMSI)

Additional Components of the GSM Network

Trans-coding Rate and Adaptation Unit (TRAU): Compresses/Decompresses speech & uses Regular Pulse Excitation
Home Location Register (HLR): Authentication and Security; fixed reference point of the current mobile user location
Visitor Location Register (VLR): Dynamic user info. & parameters
Equipment Identity Register (EIR): White, black and gray lists to prevent illegal mobile phone use
Gateway Mobile Switching Center (GMSC): Connects to other networks
Operation Subsystem (OSS): Network management and maintenance

5G Technology

5G technology is the latest telecommunication network that replaces earlier technologies like 3G and 4G.
It creates a more reliable and faster connection for users.
It is expected to have more capacity and efficiency than its predecessors.

Public Land Mobile Network (PLMN)

Mobile Station (MS): The device used by the subscriber to make and receive calls.
Subscriber Identity Module (SIM): A microchip in the MS that stores subscriber information and authentication data.
Base Transceiver Station (BTS): The physical antenna that communicates with the MS.
- Star Cell Configuration: One BTS at the center communicating with multiple MSs.
- Umbrella Cell Configuration: A larger cell covering a wider area, usually with more than one BTS.
- Sectorized Cell Configuration: Multiple sectors within a cell, each with its own BTS for improved coverage and capacity.
Base Station Controller (BSC): Manages multiple BTSs, controlling handover, resource management, and channel assignment.
Mobile Switching Center (MSC): The central switch that handles call routing, registration, and handover between BTSs.
Trans-coding Rate and Adaptation Unit (TRAU): Compresses and decompresses speech signals for efficient bandwidth usage.
Home Location Register (HLR): Stores permanent information about subscribers like their phone number and subscription details.
Visitor Location Register (VLR): Stores temporary information of a subscriber when they are roaming in a different network.
Equipment Identity Register (EIR): Maintains a database of valid and invalid IMEI numbers for security purposes.
Gateway Mobile Switching Center (GMSC): Connects the GSM network with external networks like the public switched telephone network (PSTN) and other mobile networks.
Operation Subsystem (OSS): Responsible for network management, maintenance, and monitoring.

GSM Network Architecture

Handoffs: Mechanisms for smoothly transferring calls from one cell to another as the MS moves.
- Mobile Controlled Handoff: The MS monitors signal strength and initiates the handover.
- Network Controlled Handoff: The network monitors signal strength and initiates the handover.
- Mobile Assisted Handoff: The network requests the MS to measure signal strength and provide feedback.
- Inter-Base Station Handoff: Handover between BTSs within the same MSC.
- Inter-System Handoff: Handover between BTSs that are connected to different MSCs.

The Mobile Station

Mobile Equipment: The physical device, featuring an IMEI (International Mobile Equipment Identity) - a unique 15-digit number.
Subscriber Identity Module (SIM): A microchip containing information specific to the subscriber, including their IMSI (International Mobile Subscriber Identity).

5 Types of Identity Numbers

Mobile Station ISDN (MSISDN): The subscriber's phone number.
International Mobile Subscriber Identity (IMSI): A unique identification number associated with the subscriber's SIM card.
International Mobile Station Equipment Identity (IMEI): A unique identification number associated with the mobile device.
Mobile Station Roaming Number (MSRN): A temporary number used during roaming.
Temporary Mobile Subscriber Identity Number (TMSI): Temporary identity number assigned by the network to enhance security during roaming.

Base Station Subsystem

Base Transceiver Station (BTS): Responsible for radio frequency (RF) signal transmission and reception, including channel encoding, ciphering, and modulation.
- International Cell Global Identity (CGI): A unique identifier for the cell.
- Base Station Identity Code (BSIC): Identifies the BTS within a particular cell.
Elements of RBS or BTS:
- DXU: Distribution Switch Unit.
- TRU: Transceiver Unit.
- CDU: Combining and Distribution Unit.
- ECU: Energy Control Unit, including PSU (Power Supply Unit) and BFU (Battery Fuse Unit).
Link Configuration:
- Cascade: BTSs connected in a chain.
- Loop: BTSs connected in a loop.
- Star: BTSs connected to a central BSC.

Base Station Controller

Responsible for managing and controlling multiple BTSs, including paging, channel allocation, dynamic power control, handover management, and frequency hopping.

GSM Call Scenarios

The GSM system uses a combination of digital and analog technologies for voice and data transmission.
The GSM standard defines specific protocols and procedures for call setup, handover, and other network functions.
The network uses various signal strength measurements, time synchronization, and location tracking to ensure smooth and efficient communication.