gsm fundamentals
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IAIK - Institute for Applied Information Processing and Communication
ACN
GSMGlobal System for Mobile communication
Rainer Bernhard
Rainer Bernhard
Graz, 14.06.2007
GSM1
IAIK - Institute for Applied Information Processing and Communication
Content History GSM Architecture Radio Interface GSM Security GSM Services GPRS EDGE Possible Questions References
Rainer Bernhard
Graz, 14.06.2007
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IAIK - Institute for Applied Information Processing and Communication
History of GSM1982: Groupe Spcial Mobile created by CEPT 1987: GSM MoU (Memorandum of Understanding) 1989: Groupe Spcial Mobile becomes part of ETSI (European Telecommunications Standards Institute) 1990: GSM-900 Standard 1991: DCS-1800 Standard 1992: Launch of commercial GSM-900 providers 2000: Standardization activities transferred to 3GPP (3rd Generation Partnership Project)
Rainer Bernhard
Graz, 14.06.2007
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GSM Architecture Overview
Rainer Bernhard
Graz, 14.06.2007
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GSM ArchitectureBase Station Subsystem (BSS)The BSS is responsible for handling traffic and signaling between a mobile station (MS) and the Network Switching Subsystem (NSS).
Base Transceiver Station (BTS)- Equipment for transmitting and receiving radio signals - Antennas - Encrypting and decrypting communications with the BSC.
Base Station Controller (BSC)- Allocation of radio channels - Receives measurement from the mobile phones - Controls handovers from BTS to BTS - Transcoding (compressing/decompressing)
Packet Control Unit (PCU)- Processing tasks for packet data.
Rainer Bernhard
Graz, 14.06.2007
GSM5
IAIK - Institute for Applied Information Processing and Communication
GSM Architecture (2)Network Switching Subsystem (NSS)The NSS carries out switching functions and manages the communications between mobile phones and the Publich Switched Telephone Network (PSTN).
Mobile Switching Center (MSC)- Provides circuit switched calling - mobility management (roaming) - (traditional) GSM services
Home Location Register (HLR)- central database containing details of each mobile phone subscriber
Authentication Center (AUC)- function to authenticate each SIM card that attempts to connect to the GSM core network.
Visitor Location Register (VLR)- temporary database of the subscribers who have roamed into the area it serves.
Equipment Identity Register (EIR)
Rainer Bernhard
Graz, 14.06.2007
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IAIK - Institute for Applied Information Processing and Communication
GSM Architecture (3)GPRS Core NetworkThe GPRS Core Network is the centralised part of the GPRS system and provides mobility managment, session management and transport for Internet Protocol packet services.
Serving GPRS Support Node (SGSN)- packet routing and transfer - mobility management (roaming) - logical link management - authentication and charging functions
Gateway GPRS Support Node (GGSN)- interface to external packet data networks - packet conversion - IP address assignment - authentication and charging functions
Rainer Bernhard
Graz, 14.06.2007
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IAIK - Institute for Applied Information Processing and Communication
GSM Architecture (4)Operation and Maintenance Center (OMC)The OMC is used to secure the operation of the GSM network. In case of big (regional) networks many OMCs are administrated by a Network Management Center (NMC).
Mobile Station (MS)The MS is the mobile equipment with antenna, power supply, speaker, microphone used for communication.
Subscriber Identity Module (SIM)- GSM network (provider) specific data
Transmission Power- 2 watts for GSM-900 - 1 watt for DSC-1800
Rainer Bernhard
Graz, 14.06.2007
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IAIK - Institute for Applied Information Processing and Communication
GSM Radio InterfaceGSM uses two multiplexing methods: FDMA-frequency multiplexing and TDMAtime multiplexing. Frequency Division Multiple Access Time Division Multiple AccessDuplex distance 45 MHz
uplink890 915
downlink935 960
880
900
920
940
960
980
MHz
TDMA Frame frame duration 4.615 ms 8 time slots
GSM-900: 124 carrier frequency channels 200kHz
Duplex distance 95 MHz
uplink1710 1785 1805
downlink1880
1700
1750
1800
1850
1900
980
MHz
DCS-1800: 374 carrier frequency channels 200kHz
Rainer Bernhard
Graz, 14.06.2007
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IAIK - Institute for Applied Information Processing and Communication
GSM Radio Interface (2)Channel CodecsFull Rate (FR)- 13 kbit/s
Half Rate (HR)- 6 kbit/s
Enhanced Full Rate (GSM-EFR)- 12.2 kbit/s
Adaptive Multi-rate (AMR-NB)- 8 codecs with 4.75 to 12.2 kbit/s - uses optimized link adaptation (selects one codec based on link conditions)Rainer Bernhard Graz, 14.06.2007 GSM10
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GSM Securitydesigned with a moderate level of security several cryptographic algorithms- A5/1 (stronger) and A5/2 (weaker) stream ciphers
Authentication using shared-secret cryptography- Key stored on SIM card - Key never sent over air interface
Serious weaknesses in both algorithms- Possible to break A5/2 in real-time
Rainer Bernhard
Graz, 14.06.2007
GSM11
IAIK - Institute for Applied Information Processing and Communication
GSM ServicesStandard collection of applications and features available to mobile phone subscribers all over the world.
Voice callsoutgoing callshandled by the Visited MSC (Mobile Switching Center)
incoming callshandled by the Gateway MSC
Rainer Bernhard
Graz, 14.06.2007
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GSM Services (2)Data transmissionCircuit-switched data protocolsCircuit Switched Data (CSD)uses single radio time slot 9.6 kbit/s 14.4 kbit/s (single time slot) by using different error correction can use multiple time slots
High-Speed Circuit Switched Data (HSCD)
General Packet Radio Service (GPRS)packet-switched data transmission protocol incorporated into GSM standard in 1997
Short Message Service (SMS)means of sending messages of up to 160 characters
Rainer Bernhard
Graz, 14.06.2007
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IAIK - Institute for Applied Information Processing and Communication
GSM Services (3)GSM supports a comprehensive set of supplemenatry services that complement and support the telephony and data services shown before.
Supplementary Services- Call Forwarding - Barring of Outgoing/Incoming Calls - Call Hold - Call Waiting - Mulitparty Service (Conference) - Calling Line Identification
Rainer Bernhard
Graz, 14.06.2007
GSM14
IAIK - Institute for Applied Information Processing and Communication
General Packet Radio Service (GPRS)Enhancement to GSM standard introduced in 1997 GPRS is packet-switchedSupports Point-to-Point service (IP and X.25 networks)
Multiple users share same transmission channeltheoretical limit is 160 kbit/s (using 8 time slots 20 kbit/s) practical bit rates are 32-80 kbit/s (max. 4 time slots depending on channel coding)
Rainer Bernhard
Graz, 14.06.2007
GSM15
IAIK - Institute for Applied Information Processing and Communication
General Packet Radio Service (GPRS) (2)GPRS data servicesGPRS upgrades GSM data services providing: Multimedia Messaging Service (MMS) Push to Talk (PTT) Instant Messaging Wireless Application Protocol (WAP) Point-to-Point (PTP) service
Rainer Bernhard
Graz, 14.06.2007
GSM16
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EDGEEnhanced Datarate for GSM Evolution (also EGPRS)Technology that allows to increase data transmission and improve data transmission quality.
bolt-on enhancement to GSM/GPRS networks introduced in 2003requires no HW or SW changes in the GSM core networks
uses 8 phase shift keying (8PSK)produces a 3-bit word for every change in carrier phase
data rates up to 236.8 kbit/s for 4 timeslots (theoretical max. 473.6 kbit/s for 8 timeslots) accepted as part of the IMT-2000 family of 3G standards
Rainer Bernhard
Graz, 14.06.2007
GSM17
IAIK - Institute for Applied Information Processing and Communication
Possible QuestionsWhat are the components of a GSM network? Describe the GSM architecture. What GSM services do you know? Name some GSM services. What is the main advantage of GPRS?
Rainer Bernhard
Graz, 14.06.2007
GSM18
IAIK - Institute for Applied Information Processing and Communication
ReferencesUMTSlink.at Das Mobilefunkportalhttp://umtslink.at
GSM Worldhttp://www.gmsworld.com
Wikipediahttp://en.wikipedia.org/wiki/GSM http://de.wikipedia.org/wiki/Global_System_for_Mobile_Communications
Rainer Bernhard
Graz, 14.06.2007
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