Basic Concepts
1. What does GSM stand for?
Global System for Mobile Communications
2. In what year was GSM first deployed?
1991 (in Finland)
3. What is the original frequency band for GSM networks in Europe?
900 MHz (later expanded to 1800 MHz for DCS networks)
4. What multiple access technique does GSM use?
TDMA/FDMA combination (Time Division Multiple Access and Frequency Division Multiple Access)
5. What is the channel bandwidth in GSM?
200 kHz
6. How many time slots are there in one GSM frame?
8 time slots (each lasting 0.577 ms)
7. What is the duration of one GSM TDMA frame?
4.615 ms (8 time slots × 0.577 ms)
8. What modulation scheme is used in GSM?
Gaussian Minimum Shift Keying (GMSK)
9. What is the theoretical maximum data rate for basic GSM (without GPRS/EDGE)?
9.6 kbps per time slot
10. What is the purpose of the SIM card in GSM?
Stores subscriber information, authentication data, and enables portability between devices
Network Architecture
11. What are the three main subsystems in GSM architecture?
Base Station Subsystem (BSS), Network Switching Subsystem (NSS), and Operation Support Subsystem (OSS)
12. What is the function of the BTS in GSM?
Base Transceiver Station - handles radio transmission/reception with mobile stations
13. What is the role of the BSC in GSM networks?
Base Station Controller - manages radio resources and handovers for multiple BTSs
14. What is the central component of the NSS?
Mobile Switching Center (MSC)
15. What are the two main databases in the NSS?
Home Location Register (HLR) and Visitor Location Register (VLR)
16. What information is stored in the HLR?
Permanent subscriber data and current location information
17. What is the function of the AUC in GSM?
Authentication Center - provides authentication and encryption parameters
18. What is the purpose of the EIR in GSM networks?
Equipment Identity Register - tracks stolen or unauthorized mobile equipment
Channels and Protocols
19. What are the three types of logical channels in GSM?
Traffic channels (TCH), Control channels (CCH), and Broadcast channels (BCCH)
20. What is the purpose of the Broadcast Control Channel (BCCH)?
Broadcasts general information about the network and cell identity
21. What is the difference between SDCCH and TCH?
SDCCH (Standalone Dedicated Control Channel) is for signaling, TCH (Traffic Channel) carries voice/data
22. What protocol is used between MS and BTS?
Um interface (air interface) using LAPDm protocol
23. What is the purpose of the GSM MAP protocol?
Mobile Application Part - enables communication between different MSCs and network elements
24. What is the function of the RACH in GSM?
Random Access Channel - used by mobile to request a dedicated channel
25. What are the two types of handovers in GSM?
Intra-cell handover (between channels in same cell) and inter-cell handover (between different cells)
26. What is the purpose of the Timing Advance parameter in GSM?
Compensates for propagation delay by adjusting mobile station transmission timing
Advanced Concepts
27. How does GSM provide security for communications?
Through authentication, encryption (A5 algorithm), and temporary identity (TMSI)
28. What is the difference between GSM and GPRS?
GPRS (General Packet Radio Service) adds packet-switched data capability to GSM's circuit-switched network
29. What enhancement did EDGE provide over basic GSM?
Higher data rates (up to 384 kbps) using 8-PSK modulation instead of GMSK
30. What is the main reason GSM became the dominant 2G standard globally?
Open standard with international roaming capabilities and better voice quality than analog systems
