Introduction to GSM:Mobile Phone Subscribers Worldwide
Introduction to GSM: Development of Mobile Telecommunication Systems
GSM Overview
Several first generation analog cellular systems in Europe but incompatible - limited roaming
1987-1989 ETSI standards for pan-European Global System for Mobile Communications (GSM, originally Group Spe’ciale Mobile 1982) at 900 MHz
1992 GSM is launched
1990-1993 Standards for Digital Cellular System at 1800 MHz (DCS 1800, recently renamed GSM 1800; US version is PCS 1900)

GSM: Overview

Simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication administrations  seamless roaming within Europe possible
Today many providers all over the world use GSM (more than 184 countries in Asia, Africa, Europe, Australia, America)
More than 747 million subscribers
More than 70% of all digital mobile phones use GSM
GSM, cont..
Objectives:
Broad offering of speech and data services
Compatible with wireline networks
Automatic roaming and handoff
Highly efficient use of frequency spectrum
Support for different types of mobile terminal equipment (e.g., cars, portable handsets)
Digital signaling and transmission
Low cost infrastructure and terminal equipment


GSM, cont..
13 recommendations
R.00: Preamble
R.01: General structure of recommendations, GSM overview
R.02: Service aspects: types of services
R.03: Network aspects: architecture, call routing, performance objectives
R.04: Mobile/base station interface and protocols

GSM, cont..
R.05: Physical layer on radio path: multiple access, channel coding, modulation, transmission
R.06: Speech coding aspects
R.07: Terminal adaptors for mobile stations
R.08: Base station and mobile switching center (MSC) interface
R.09: Interworking with PSTN and packet data networks
R.10: Service interworking, short message service
R.11: Equipment specification
R.12: Operation and maintenance, tariffs, traffic administration



GSM, cont..
Summary of features

GSM, cont..
Summary of service quality requirements

GSM: Performance Characteristics
Communication
Mobile, wireless communication; support for voice and data services
Total mobility
International access, chip-card enables use of access points for different providers
Worldwide connectivity
One number, the network handles localization
High capacity
Better frequency efficiency, smaller cells, more customers per cell
High transmission quality
High audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains)
Security functions
Access control, authentication via chip-card and PIN
GSM: Mobile Services
GSM offers
Several types of connections
Voice connections, data connections, short message service
Multi-service options (combination of basic services)
Three service domains
Bearer Services
Telematic Services
Supplementary Services
Bearer Services
Telecommunication services to transfer data between access points
Different data rates for voice and data (original standard)
Data service (circuit switched)
synchronous: 2.4, 4.8 or 9.6 kbit/s
asynchronous: 300 - 1200 bit/s
Data service (packet switched)
synchronous: 2.4, 4.8 or 9.6 kbit/s
asynchronous: 300 - 9600 bit/s
Today: data rates of approx. 50 kbit/s possible
Tele Services I
Offered Services
Mobile Telephonyprimary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 kHz
Emergency Numbercommon number throughout Europe (112); mandatory for all service providers; free of charge; connection with the highest priority (preemption of other connections possible)

Tele Services II
Additional services
Non-Voice-Teleservices
Fax
Voice mailbox (implemented in the fixed network supporting the mobile terminals)
Electronic mail (MHS, Message Handling System, implemented in the fixed network)

Short Message Service (SMS)alphanumeric data transmission to/from the mobile terminal using the signaling channel, thus allowing simultaneous use of basic services and SMS
Supplementary Services
May differ between different service providers, countries and protocol versions
Important services
Identification: forwarding of caller number
Suppression of number forwarding
Automatic call-back
Conferencing with up to 7 participants
Locking of the mobile terminal (incoming or outgoing calls)
...
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
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
GSM: Reference Architecture
GSM General Architecture
System Architecture: Radio Subsystem
GSM General Architecture, cont..
Mobile station (MS) communicates to base stations through radio interface Um

Mobile termination (MT) supports physical channel between MS and base station (radio transmission, channel coding, speech coding)
GSM General Architecture, cont..
Terminal equipment (TE), e.g., telephone set.

Contains terminal/user-specific data in form of smart card (subscriber identify module or SIM card), plugs into any GSM terminal like credit card and identifies user to network for personal mobility (in addition to terminal mobility) and security
GSM General Architecture, cont..
Base station Subsystem (BSS) communicates with mobile switching center through network interface A

Base Transceiver Station (BTS) handles channel allocation, signaling, frequency hopping, handover initiation, etc.

BTS communicates with BSC using Abis interface
GSM General Architecture, cont..
Base station controller (BSC) manages radio channels, paging, handoff for several BTSs
BSC communicates with MSC using A interface
Mobile switching center (MSC) is gateway to PSTN and packet data networks
Performs switching, paging functions, MS location updating, handoff control, etc.

GSM General Architecture, cont..
Home location register (HLR) stores subscriber info and part of MS’s location info to route incoming calls to visitor location register (VLR) where mobile is roaming
VLR registers users roaming in its area and assigns roaming numbers
GSM General Architecture, cont..
Authentication center (AUC) is accessed by HLR to authenticate a user for service.
It contains authentication and encryption keys for subscribers
Equipment identity register (EIR) allows stolen or fraudulent mobile stations to be identified

GSM General Architecture, cont..
Operation subsystem (OSS) contains: Operations and Maintenance Center (OMC), Network Management Center (NMC), and Administration Center (ADC).
These network elements work together to monitor, control, maintain, and manage the network
System Architecture: Network and Switching Subsystem
Components
MSC (Mobile Services Switching Center):

ISDN (Integrated Services Digital Network)
PSTN (Public Switched Telephone Network)


Databases
HLR (Home Location Register)
VLR (Visitor Location Register)
EIR (Equipment Identity Register)
Radio Subsystem
The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers
Components
Mobile Stations (MS)
Base Station Subsystem (BSS):
Base Transceiver Station (BTS): radio components including sender, receiver, antenna - if directed antennas are used one BTS can cover several cells
Base Station Controller (BSC): switching between BTSs, controlling BTSs, managing of network resources, mapping of radio channels (Um) onto terrestrial channels (A interface)
BSS = BSC + sum(BTS) + interconnection
Mobile Station
Terminal for the use of GSM services
A mobile station (MS) comprises two elements:
ME (Mobile Equipment):
Peripheral device of the MS, offers services to a user
Speaker, microphone, keypad, and radio modem
Usually subsidized by the service provider to encourage new subscribers
SIM (Subscriber Identity Module):
Smart card issued at subscription time
Personalization of the mobile terminal, stores user parameters such as address and type o

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