GSM: The European Standard
for Mobile Telephony
Presented by
Rattan Muradia
Requirement for course CSI 5171
Presentation Objective

No discussion of mobile network concepts
already covered (MSC, BSC, HLR, VLR,
registration, call setup, roaming, handover,
OSS etc..)
 GSM Architecture
 Focus on features specific to GSM
 Provide basic information required for
presentations on CAMEL, GPRS and UMTS
Evolution of Digital Mobile
Systems
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1st Generation, Analogue Cellular AMPS, ETACS, NMT, C-NET...
2nd Generation, Digital Cellular GSM, PDC, DAMPS, CDMA...
2nd Generation Cordless - DECT, PHS...
2nd Generation Satellite - Iridium, Globalstar..
2.5 Generation GPRS...
3rd Generation Universal - IMT-2000, UMTS
Digital Mobile Systems
Americas CTAC
Operating Manual
Issue: 2.3
Standard
PDC
D- AMPS
GSM 900
Frequency band
Uplink
940-956 MHz
1429-1441 MHz
1453-1465 MHz
824-849 MHz
890-915 MHz
Frequency band
Downlink
810-826 MHz
1477-1489 MHz
1501-1513 MHz
869-894 MHz
935-960 MHz
Channel separation
25 kHz
30 kHz
200 kHz
Multiplexing
Bearer
Bits/ frequency
channel
3 (6) channel TDMA
42 kbit/ s
46.6 kbit/ s
8 (16) ch TDMA
270 kbit/ s
GSM Overview
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Developed in Europe
One of first ‘intelligent’ networks with
distributed processing
International roaming
174 countries, 647 million subscribers
67% of world wireless market share
GSM Network

Mobile Station (MS)
 Base Station Subsystem (BSS)
 Network and Switching Subsystem (NSS)
 Operation and Support Subsystem (OSS)
GSM Network Architecture
CELL TRANSMITTER
& RECEIVER
INTERFACE TO LAND
TELEPHONE
NETWORKS
HIERARCHY
OF CELLS
PHONE
STOLEN, BROKEN
CELLPHONE LIST
ENCRYPTION,
AUTHENTICATION
SIM:
IDENTIFIES A
SUBSCRIBER
LIST OF
ROAMING
VISITORS
LIST OF SUBSCRIBERS
IN THIS AREA
SOURCE: UWC
GSM Reference Model
GSM Protocol Stack
GSM Address and Identifiers

International Mobile Subscriber Identity (IMSI)
– 3 digit Mobile Country Code + 2 digit Mobile Network Code
+ 10 digit Mobile Subscriber Identification Number
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International Mobile Equipment Identity (IMEI)
– 19 digit unique ID, used by air interface, stored in EIR
Mobile Subscriber ISDN Number (MSISDN)
– upto 3 digit Country Code + 2-3 digit national Destination
Code + max 10 digit Subscriber Number
– mapped to MSRN by HLR
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Mobile Station Roaming Number (MSRN)
– temporary ISDN number assigned by VLR
GSM Mobile Station

Each MS identified by IMEI
 In addition to the physical equipment common
to most MS, GSM equipment includes a SIM.
 Subscriber Identity Module (SIM) provides
true mobility. Access to subscribed services:
– regardless of location of the terminal
– regardless of use of specific terminal
 SIM contains IMSI, secret key for
authentication + more information
GSM Databases

Equipment Identity Register (EIR)
– contains list of valid mobile equipment (IMEI)
– an IMEI can be marked invalid if MS is stolen,
unauthorized or defective
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Authentication Center (AuC)
– protected database that stores authentication and
encryption parameters
– used to verify user identity and ensure
confidentiality of each call
GSM Call Delivery
GSM Services
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Patterned after ISDN
 Bearer Services
– sync, async data transport, represent layers 1-3
– also used by higher layers to offer teleservices
 Teleservices
– voice, SMS, FAX, Teletext etc..
 Supplementary Services
– modify or supplement teleservices
GSM Services - Phase 1
Offered by all operators in 1991.
GSM Services - Phase 2
Introduced in 1996. Major rework of standards. Backward compatible.
More supplementary services.
GSM Phase 2+
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Increased globalization using SIM, multiband
systems and terminals
 Phase 2+
– increase network capacity via spectral efficiency
– improve voice quality
– group call (party line)
– integration of packet services (on air interface) and
higher data speeds (GPRS)
– expand supplementary services (SMS Forwarding,
Multiple Subscriber profile, Call Xfer etc..)
(see GPRS presentation by Miao Lu and Nancy Samaan on April 5th).
GSM Phase 2+
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No complete revision of standards in Phase 2+
Each subject area treated separate, allowed to
implement and introduce independently
Standardize mechanisms for service
introduction, not complete services
Reduce time-to-market, allow differentiation
GSM already has similarities with IN
(MSC=SSP, HLR=SCP, SS7 signaling)
Convergence of GSM and IN - CAMEL
(see CAMEL presentation by Tina Deng and Yinyan Zhou on April 2th).
Beyond GSM - 3G
Road to UMTS/IMT2000
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New generation of mobile systems based on IP
Must support large number of subscribers
Wide range of voice and data services
Build on existing GSM infrastructure as much
as possible.
Higher bandwidth for multimedia applications
– new radio interface
– better use of spectrum
(see IMT2000 presentation by Mingdi Zhao and Wei Lin on April 9th).
Questions?
GSM/GPRS/UMTS
Backup slide 1
GSM Network Architecture
backup slide
Backup slide 2
SOURCE: UWC
Backup slide 3
GSM Protocol Stack