Test your knowledge of GSM architecture for Electrical & Communication Engineering
12 questions covering key concepts, components, and functionalities
Questions
12
Estimated Time
15-20 minutes
Level
Undergraduate
1
Which component in the GSM architecture is responsible for managing radio resources and handling handovers between Base Transceiver Stations (BTS)?
Think about which component controls multiple BTSs in the Base Station Subsystem.
A
Mobile Switching Center (MSC)
B
Base Station Controller (BSC)
C
Home Location Register (HLR)
D
Visitor Location Register (VLR)
Explanation
The Base Station Controller (BSC) is responsible for managing radio resources for one or more BTSs. It handles handovers between BTSs under its control, manages radio channel allocation, and controls frequency hopping and power control. The MSC handles call switching, while HLR and VLR are databases for subscriber information.
2
What is the primary function of the Authentication Center (AUC) in GSM architecture?
This component deals with security and verification of subscribers.
A
To store subscriber location information
B
To switch calls between mobile users
C
To provide authentication and encryption parameters
D
To manage radio resources in a cell
Explanation
The Authentication Center (AUC) is a protected database that stores the authentication key (Ki) for each subscriber. It generates authentication triplets (RAND, SRES, Kc) used to verify the identity of mobile stations and to provide encryption parameters for secure communication. This protects against fraud and ensures privacy of calls and data.
3
Which GSM logical channel is used by the mobile station to request access to the network?
This is an uplink channel used for initial network access.
A
Paging Channel (PCH)
B
Broadcast Control Channel (BCCH)
C
Access Grant Channel (AGCH)
D
Random Access Channel (RACH)
Explanation
The Random Access Channel (RACH) is an uplink common control channel used by the mobile station to request a dedicated channel when it wants to initiate a call, respond to a page, or perform location update. It's called "random" because multiple mobiles may attempt to access it simultaneously, requiring collision resolution mechanisms.
4
What does the SIM card in a GSM mobile station contain?
The SIM card stores subscriber-specific information, not equipment information.
A
International Mobile Subscriber Identity (IMSI)
B
International Mobile Equipment Identity (IMEI)
C
Base Station Identity Code (BSIC)
D
Temporary Mobile Subscriber Identity (TMSI)
Explanation
The SIM card contains the International Mobile Subscriber Identity (IMSI), which uniquely identifies the subscriber. It also stores the authentication key (Ki), subscriber phone number (MSISDN), and other subscriber-specific information. The IMEI identifies the mobile equipment (phone), BSIC identifies the base station, and TMSI is a temporary identity assigned by the network for privacy.
5
Which interface connects the BTS to the BSC in GSM architecture?
This is a standardized interface within the Base Station Subsystem.
A
Um interface
B
Abis interface
C
A interface
D
SS7 interface
Explanation
The Abis interface connects the Base Transceiver Station (BTS) to the Base Station Controller (BSC). It carries traffic and signaling information and is typically implemented over T1/E1 lines. The Um interface is the air interface between MS and BTS, the A interface connects BSC to MSC, and SS7 is the signaling system used between network components.
6
What is the main purpose of the Visitor Location Register (VLR) in GSM?
This component stores information about subscribers who are currently in a specific geographical area.
A
To store permanent subscriber information
B
To authenticate subscribers
C
To store temporary information about subscribers currently in its area
D
To manage handovers between cells
Explanation
The Visitor Location Register (VLR) is a temporary database that stores information about subscribers currently located in the geographical area controlled by the associated MSC. When a subscriber enters a new location area, the VLR retrieves necessary information from the HLR to service the subscriber. This reduces signaling traffic to the HLR and speeds up call setup.
7
Which GSM subsystem is responsible for operation and maintenance of the network?
This subsystem monitors and controls the entire GSM network.
A
Operation Subsystem (OSS)
B
Network Switching Subsystem (NSS)
C
Base Station Subsystem (BSS)
D
Mobile Station (MS)
Explanation
The Operation Subsystem (OSS) is responsible for the operation and maintenance of the GSM network. It includes the Operation and Maintenance Center (OMC) which monitors and controls all other network elements. The OSS handles functions like network monitoring, traffic management, security management, and subscriber billing.
8
What is the function of the Equipment Identity Register (EIR) in GSM?
This component tracks mobile equipment, not subscribers.
A
To store subscriber authentication data
B
To manage frequency allocation
C
To handle call switching
D
To prevent calls from stolen or unauthorized mobile equipment
Explanation
The Equipment Identity Register (EIR) is a database that contains information about mobile equipment using the International Mobile Equipment Identity (IMEI). It maintains three lists: white list (authorized equipment), gray list (equipment to be monitored), and black list (stolen or unauthorized equipment). This helps prevent calls from stolen or faulty mobile devices.
9
Which channel is used in GSM for broadcasting general system information to all mobile stations in a cell?
This is a downlink-only channel that provides cell-specific information.
A
Paging Channel (PCH)
B
Broadcast Control Channel (BCCH)
C
Random Access Channel (RACH)
D
Standalone Dedicated Control Channel (SDCCH)
Explanation
The Broadcast Control Channel (BCCH) is a downlink channel that broadcasts general system information to all mobile stations in a cell. This information includes cell identity, frequency allocations, neighboring cell information, and access parameters. Mobile stations monitor this channel to select the best serving cell and to obtain necessary parameters for network access.
10
What is the primary role of the Mobile Switching Center (MSC) in GSM architecture?
This component is often called the "heart" of the GSM network.
A
To manage radio resources
B
To store subscriber information
C
To perform telephony switching functions and mobility management
D
To authenticate subscribers
Explanation
The Mobile Switching Center (MSC) is the central component of the Network Switching Subsystem (NSS). Its primary functions include call switching between mobile users and between mobile and fixed network users, mobility management (registration, location updating, handovers), and collecting charging information. It also provides connections to other networks like PSTN and ISDN.
11
Which component in GSM performs rate adaptation and speech transcoding between the 13 kbps GSM codec and the 64 kbps PCM used in terrestrial networks?
This component converts between different speech coding formats.
A
Base Transceiver Station (BTS)
B
Base Station Controller (BSC)
C
Mobile Switching Center (MSC)
D
Transcoding and Rate Adaptation Unit (TRAU)
Explanation
The Transcoding and Rate Adaptation Unit (TRAU) performs conversion between the 13 kbps speech coding used over the radio interface and the 64 kbps PCM used in the terrestrial network. This allows efficient use of transmission resources on the Abis and A interfaces. The TRAU can be located at the BTS, BSC, or MSC, depending on the network design.
12
What is the main purpose of the Home Location Register (HLR) in GSM?
This is the primary database for subscriber information.
A
To store permanent subscriber information and current location
B
To manage handovers between cells
C
To perform speech coding conversion
D
To broadcast system information
Explanation
The Home Location Register (HLR) is the central database that stores permanent subscriber information including IMSI, MSISDN (phone number), subscribed services, and the current location (VLR address) of each subscriber. Every subscriber is assigned to one HLR, which is queried during call setup to determine the subscriber's current location for call routing.