Introduction To GSM
< استفاده از مطالب سایت فراکنش با ذکر منبع مجاز است.>
GSM
– GSM: Global System for Mobile Communication
– Pan-European standard (ETSI, European Telecommunications Standardisation Institute)
– simultaneous introduction of essential digital cellular services in 3 phases (1991, 1994, 1996) by the European
GSM: PHYSICAL & LOGICAL CHANNELS
GSM Logical Channels
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
- several providers setup mobile networks following the GSM standard within each country
- components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
- subsystems
BSS (Base Station Subsystem ) or RSS (Radio SubSystem): covers all radio aspects
NSS (Network and Switching Subsystem): call forwarding, handover, switching
OSS (Operation SubSystem): management of the network
GSM Architecture Overview
Mobile Station (MS)
– MS is the user’s handset and has two parts:
1.Mobile Equipment (ME)
Radio equipment
User interface
Processing capability and memory required for various tasks
– Call signalling
– Encryption
– SMS
Equipment IMEI number
2.Subscriber Identity Module (SIM)
Subscriber Identity Module (SIM)
– A small smart card
– Main task: data storage
– Includes:
Encryption codes needed to identify the subscriber (Ki, Kc, …)
IMSI: International Mobile Subscriber Identify
For identification
Subscriber’s own information (telephone directory)
Third party applications (banking etc.)
– Advantage: independence from the ME
– Can also be used in other systems besides GSM,
e.g., some WLAN access points accept SIM based user authentication
Base Station Subsystem (BSS)
– The Base Station Subsystem (BSS) performs :
All functions necessary to maintain Radio connection to the MS
Coding/Decoding of Voice
Rate Adaptation to/from the Wireless Network part
GSM is a Cellular Network
segmentation of the area into cells
use of several carrier frequencies
not the same frequency in adjoining cells
cell sizes vary from some 100 m up to 35 km depending on user density, geography, transceiver power etc.
hexagonal shape of cells is idealized (cells overlap, shapes depend on geography)
if a mobile user changes cells
– handover of the connection to the neighbor cell
References
– General Packet Radio Service (GPRS) For Engineers, Aircom International.
– Patrick Traynor, CS 8803 – Cellular and Mobile Network Security, Georgia Tech Information Security Center, 2012.
– ICS 243E – Ch4. Wireless Telecomm. Sys.
