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Introduction To GSM

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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

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GSM Logical Channels

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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

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GSM Architecture Overview

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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

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—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

ادامه مطلب و دانلود مقاله

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.

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