1Antti Siitonen, 2002
GSM & GPRS
Antti Siitonen
Development manager, MSc (EE)
› T-110.300 Telecommunications architectures
› Lectures on 13.11.2002
› Introduction to GSM & GPRS
2Antti Siitonen, 2002
Contents1. Short introduction to mobile telephony / mobile telecommunication
1.1. Radio interface
1.2. Mobility management
1.3. Technology generations
2. GSM
2.1. Architecture overview BSS+NSS
2.2. Mobile handset and SIM
2.3. GSM services
2.4. GSM data enhancements
3. GPRS
3.1. Architecture overview
3.2. GPRS terminals
3.3. GPRS services
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Advantages of wireless access› Speed of deployment and easiness of reconfiguration
› In certain cases cost efficiency
› Independence of wired infrastructure etc..
› BUT THE MAIN ADVANTAGE IS
›MOBILITY
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Frequecy spectrum and spectrum allocation› Who? What band and what bandwidth? What technology?
› Globally CEPT, Europe ERC» World Radio Conference (WRC) every fourth year
› Nationally local regulators (Ficora in Finland)
› Licenced frequencies
› Requires licence, typically for operator use» Co-ordination, frequency planning, interference regulation
» Mobile networks, LMDS, Broadcasting TV and radio, links
» T.ex. 3G spectrum allocation 155 MHz (2*60+35) in 2 GHz band
› Unlicenced frequencies
› Free for all, but within regulated boundaries (maximum power, technology)
» WLANs, cordeless phones, DECT, ..
» 2,4 GHz, 5 GHz, 17 GHz, ..
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Wireless environment
› Path loss
› Radio signals decrease exponentially with distance
› The wide range of path loss associated with different radio links results in the Near-Far problems
› Shadow Fading and Multipath Fading
› Blockage of radio paths by buildings and terrain causes shadow fading. Signals may drop 20 to 30 dB by turning a building corner
› Radio signal received from different paths may destructively combine and result in multipath fading
› In broadband systems the delay spread caused by multipath propagation may result in inter symbol interference
› Traffic loading
› Mobile speed and users density are elusive in nature
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Multiple access methods
› FDMA – Frequency Division Multiple Access (NMT, TACS, AMPS)
› One frequency per user
› Filtering!
› CDMA – Code DivisionMultiple Access (IS-95, UMTS)
› Same frequency, same timeslots,but different codes
› Power Control!
› TDMA – Time Division Multiple Access(GSM, D-AMPS, PDC)
› Same frequency, different timeslots
› Timing advance!
Picture: Ericsson
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Mobility management
› Status of the mobile (on/off) - pageing
› Location of the mobile - Location update
› Moving mobile
› Change the active cell - handover (handoff)» Network optimization
» Movement prediction
› Change the active operator - roaming» Typically when crossing the country border
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Handover
1. Call in progress cell 1
2. Signal cell 2 for handover
3. Switch to cell 2 = handover complete
cell 2
cell 1
› BSC
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Soft handover
› 1. Call in progress cell 1
2. Cell 2 has good signal strength
3. Call in progress cell 1 and cell 2 = soft handover
cell 2 cell 1
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Satellite
GSM + Evolution
- GPRS (2000)(General Packet Radio Service)
- EDGE (2002)(Enhanced Development for GSM
Evolution)
Universal
Mobile
Telecommunication
Service
= UMTS
(> 2002)
Wireless systems in generalkBit/s
Coverage areaRoom House Campus City Country Continent
10
100
1000
10 000
Wireless Local
Area Networks
= WLANs
(Available)
Broadband Fixed Wireless Access
(Available)
100 000 FUTURE
SYSTEMS( >2003)
BLUETOOTH
SCOPE
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1G, 2G, 3G…….
1980 1990 2000 2010 2020
1 G• Analog• Voice services• ARP, NMT, AMPS,TACS 3 G
• Advanced digital• Voice, mediumspeed data, multi-media messaging• Convergence ofwireless and internet• IMT 2000 = UMTS, CDMA2000
Beyond 3 G (4G)
• Voice over IP• High speed data, real-timemultimedia services
2 G
• Digital• Voice, messaging and low speed dataservices• GSM (TDMA), cdma one (IS-41), D-AMPS (TDMA), PDC (TDMA)
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GSM
› 1982 Group Special Mobile was established by CEPT
› 1987 Air interface TDMA was chosen as access method and InitialMemorandum of Understanding was signed by telecom operators (from 12 countries)
› 1989 GSM specification responsibility is passed to ETSI
› 1990 GSM First Phase specification
› 1991 First commercial GSM service (Global System for Mobile Communications)
› 1992 More operators signed the MoU
› 1995 GSM Second Phase specification
› check http://www.gsmworld.com/
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GSM radio technology basics› Frequency bands
› GSM400» 450.4 - 457.6 MHz paired with 460.4 - 467.6 MHz or 478.8 - 486 MHz paired with 488.8 - 496 MHz
› GSM900
» 880 - 915 MHz paired with 925 - 960 MHz
› GSM1800
» 1710 - 1785 MHz paired with 1805 - 1880 MHz
› GSM1900
» 1850 - 1910 MHz paired with 1930 - 1990 MHz
› Multiple access method
› TDMA
› Modulation
› GMSK
› Radio transmitted power (Mobile Station)
› 1 W Handset on GSM1800, 2 W Handset on GSM900, 8W Fixed installation (Car)
› Channels per carrier
› 8 timeslots
› Channel bit rate
› 22,8 kbit/s
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PLMN Architecture overview
BSCBTS
BTS
MS +SIM
TRAU
MSC
HLR
EIR
BSS
BSS
BSS
MSC area
BTS
MSC area
MSC area
MSC areaHLR
HLR
VLR
Customer care & Billing system
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Base station subsystem
› BTS = Base Transceiver Station
› Radio-related tasks, Air interface
› Standard configuration (cell size 300 m - 35 km)
› Umbrella configuration
› Sectorized configuration
› BSC = Base Station Controller
› Controls several BTSs and takes care of all central functions of BSS
› TRAU = Transcoding Rate and Adaptation unit
› Bitrate adaptation and voice coding/decoding
› OSS = Operation and support subsystem (also for NSS)
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Network switching subsystem
› MSC = Mobile-Services Switching Center
› Basically ISDN telephone exchange + mobility modifications» Modifications: BSS channel assignments and inter-MSC handover
› Gateway MSCs interface other networks
› HLR = Home Location Register / Authentication Center (AuC)
› Database for subscriber identity - Home
› AuC provides triplets for authentication and ciphering
› VLR = Visitor Location Register
› Database for temporary subscriber identity - Visited
› Integrated into each MSC
› EIR = Equipment Identity Register
› GSM phone IMEI register (Lists: White, Black, Gray)
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Mobile Station
› Voice encoding Voice decoding
› Channel encoding Channel decoding
› Interleaving De-interleaving
› Burst generation Re-formatting
› Ciphering Deciphering
› Modulation Demodulation
› Amplifier Receiver
filter + Antenna
› Burned in IMEI = Individual Moblie Station Equipment Identity
› Central processor, clock and tone, internal bus system, keyboard
› SIM interface
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SIM
› Subscriber Identity Module
› Data storage and algorithm executions
› Memory 8 kB / 16kB / 32 kB /64 kB
› Administrative data: PIN/PUK, SIM service table..
› Security related data: Algorithms A3 and A8, Ki, Kc, CKSN
› Subscriber data: IMSI (International mobile subscriber identity = code for VLR and HLR), MSISDN, Access control classes
› Roaming data: TMSI (Temporary MSI), NCCs (Network Color Codes)
› PLMN data: Network identifier and home network frequencies
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GSM authentication and ciphering- Algorithms A3, A5/X ja A8 . Algorithms are secret.
- SIM parameters:
Parameter Need:
Algorithms A3 ja A8 (mandatory, fixed) Authentication, Key Kc calculation
Key Ki (individual) (mandatory, fixed) Unique key, stored in SIM+HLR
Key Kc (cipher) (mandatory, changeable) Result of A8 algorithm, calculated from Ki and RAND
CKSN (mandatory, changeable) Ciphering key sequence number, referred to Kc
- Ciphering:MS has at least A5/1 and A5/2 (There are seven different ciphering algorithms, MS informs the network of it´s capabilities). Cipher is only for air interface.
- Note! Ciphering is optional!
- Network parameters:
› Every subscription has unique Ki stored in HLR
› AuC provides authentication triples. For one user five triplets may be generated at one time. HLR forwards triplets to VLR. VLR negotiates authentication and ciphering with MS
› Triplet:» Signed Response (SRES), Random Number (RAND) and Kc
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GSM authentication processNetwork challenges the user. User must prove to have correct identity.
BSCBTS
VLR
MSCAuC/HLR
2. Terminal (SIM)- Receives RAND- A3(Ki&RAND) = SRES- Returns SRES to VLR
3. VLR compares SRES
1. Triplet to VLR- Key Kc- RAND- A3(Ki&RAND) = SRES
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GSM ciphering process
BSCBTS
VLR
MSCAuC/HLR
2. Cipher key A8(Ki&RAND)=Kc
3. VLR provides BTS information of chosenA5/x algorithm and key Kc4. BTS transfers the information to MS5. Traffic is ciphered and decipheredin 114 bit sequences
1. Cipher key A8(Ki&RAND) =Kc
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GSM Services › Bearer services: Bit transmission, 3,1 kHz voice, sync./async.data
› Voice
› Full Rate codec 13 kbit/s (+ 9,8 kbit/s for error correction)
› Enhanced Full Rate codec 13 kbit/s (+ 9,8 kbit/s for error correction)
› Half Rate codec 6,5 kbit/s (+ 4,9 kbit/s for error correction)
› Emergency call
› Suplementary services: Call forwarding, Calling line identity..
› Fax
› 9,6 kbit/s Fax
› Data
› 9,6 kbit/s transparent data (no error correction)
› 9,6 kbit/s non-transparent data (with error correction)
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GSM Services (cont.)
› Voice mail
› Answering machine type of service. Colocated with MSC
› SMS
› The initial SMS Center may be simply a voice mail platform module or alternatively a standalone SMS Center. It is not possible to make the Short Message Service available without an SMS Center since all short messages pass through the SMS Center.
› SMS Mobile terminate
› Often SMS Mobile Terminate Services are offered along with voice mail notifications.
› SMS Mobile originate
› True two-way SMS capability.
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Value added services (examples)
› Mainly SMS based services
› Edited content for SMS
› Ringtones
› Logos and picture messages
› CHAT
› Payment methods
› Menu driven SMS applications
› Sim Application Toolkit (STK) - set of tools possible to implement applications and menus executed on the SIM card
› Wireless Application Protocol WAP
› Attemp to standardize mobile applications
› Optimized for wireless networks (not only for GSM)
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Operator service offering
› Operators
› Typically Network and Service operators are same corporation
› Pure service operators have entered during last years
› Subscriptions for different needs
› Business use, Private use, Pure data
› Basic services without extra subscription
› Call waiting, hold, group call, SMS, Calling line identity, Roaming, data
› Premium services
› Voice mail, SMS-service packets, Billing limits, Mobile E-mail, MMS ..
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Data in GSM-network
Internet
ISP(accessserver)
GSM-network
PSTN
BSMSC
Connection time5-30 s
Data rate9.6 kbit/s
Poor user interface fordata applications
Time basedbilling
Circuitswitchedconnection
- features and restrictions
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GSM data development
› Basic GSM data:
› Connections to any modem service
› 9,6 Kbit/s data rate
› Enhancements:
› ISDN type connection - faster connection time
› V.42bis compression - 4:1 basic text compression (limited)
› HSCSD - High Speed Circuit Switched Data» Non transparent: 1-4 time slot per MS - up to 38,4 kbit/s - dynamic
allocation of channels
» Transparent: Up to 8 time slots per MS - static allocation of channels
› 14,4 kbit/s channel coding» Less bits for error correction if signal is good enough
» Can be combined to HSCSD and/or V.42bis
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New service requirements
› Location Related Services
› Can be implemented to the current architecture» Still no established way to implement (Oct. 2001)
› Different methods give different accuracy
› Need for packet based mobile data?
› Asymmetric traffic» WAP-services
» Internet services: Web browsing
› Multiple Services with Variable Bit Rates
› Multi-Session and “Always On” Features
› Variable QoS Requirements
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time
traffic
Traffic in mobile network
08:00 17:00
› GSMnetwork is planned for
circuit switched voice services
› ”Rush hour” is the capacity
planning key
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WWW browsing traffic
Rate (kbit/s) uplink downlink14.4 4.8% 19.5%28.8 3.9% 20%64 3.0% 11.7%
Rate (kbit/s) uplink downlink14.4 4.8% 19.5%28.8 3.9% 20%64 3.0% 11.7%
- Measured usage rate on a circuit switched* data connection**
* GSM and HSCSD are circuit switched* measurements are made during six days on may 1999 from the Kolumbus ISP’s access server
aika
Typical downlink traffic
Home page... WWW download...Reading...Reading...
GPRS uses channel only when there is traffic» Resources areavailbe for otherusers when there isno traffic
Data traffic
No traffic
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GPRS Data rates - Link layer
9,05 kbps
13,4 kbps
15,6 kbps
21,4 kbps
CS-1
CS-2
CS-3
CS-4
1-8channel
171,2 kbpsin theory
Practical data rate is 10 - 40 kbit/s
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GPRS Reference network architecture
Gf
Gi
Gn
GbGc
D
Gp
Gs
Signalling and Data Transfer InterfaceSignalling Interface
MSC/VLR
MS BSS TEPDN
Um
Gr
HLR
Other GPRS Nw
SGSN
GGSN
GGSN
EIR
A
BSS=Base Station Subsystem, GGSN=Gateway GPRS Support Node, HLR=Home Location Register, MS=Mobile Station,MSC=Mobile Switching Centre, SGSN=Serving GPRS Support Node, PDN=Packet Data Network, VLR=Visitor Location Register
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GPRS Network architecture
BTS
SGSN GGSN
BSC MSC/VLR HLR
IPNetwork
X.25NetworkBackbone
NetworkIP
MS
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GPRS updates to GSM network
Element Software HardwareMS Upgrade required Upgrade requiredBTS Upgrade required No changeBSC Upgrade required PCU Interface
TRAU No change No changeMSC/VLR Upgrade required No change
HLR Upgrade required No changeSGSN New NewGGSN New New
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SGSN = Serving GPRS Support Node
› Authentication, Authorization
› GTP tunneling to GGSN
› Ciphering and compression
› Mobility management
› Session management
› Interaction with HLR, MSC/VLR
› Collects charging and statistics information about data networkusage
› Interfaces towards OSS (Operation and Management)
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GGSN = Gateway GPRS Support Node
› Interfaces external data networks
› Internet, Intranets, Operator ISP network
› Encapsulates end user data in GTP packets
› Routes mobile originated packets to right destination
› Filters end user traffic
› Collects charging and statistics information about data networkusage
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RL service network
WAP GW
Internet
RL ISP ExternalWAP GWor ISP
GPRS- connections
GPRS
GSM
HLR (GSM&GPRS)
GGSN
APN= internet
APN= wap
APN= yritys.fi
SGSN
soittosarja
Corporatenetwork
WAP GWAPN = Access Point Name(Logical Name)
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Connection protocol stack
Relay
NetworkService
GTP
Application
IP / X.25
SNDCP
LLC
RLC
MAC
GSM RF
SNDCP
LLC
BSSGP
L1bis
RLC
MAC
GSM RF
BSSGP
L1bis
Relay
L2
L1
IP
L2
L1
IP
GTP
IP / X.25
Um Gb Gn GiMS BSS SGSN GGSN
NetworkService
UDP /TCP
UDP /TCP
BSSGP=BSS GPRS Protocol, GTP=GPRS Tunneling Protocol, LLC=Logical Link Protocol, MAC=Medium Access Control, GSMRF=GSM Radio Physical Layer, SNDCP=Subnetwork Dependent Convergence, UDP=User Datagram Protocol,TCP=Transmission Control Protocol
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GPRS phases
›Phase 1
› Point-to-Point packet service
› CS1 and CS2 channel coding
› Internal interfaces
› Flexible radio resource allocation, I.e. Multiple users per timeslot and multiple timeslots per user
› Support for Class B and C Mobiles
› GPRS Charging (packet based billing)
› IP and X.25 packet data networks
› Static and dynamic IP address allocation
› Authentication and Ciphering
›Phase 2
› Enhanced QoS support
› Access to ISP and Intranets
› GPRS prepaid
› Group call
› Point to multipoint services
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GPRS roaming
› International Roaming Experts Group (IREG) Proposal
› Roaming traffic will be carried over central managed hierarchical Roaming Network where commonly agreed policies are followed
› GPRS Roaming Exchange (GRX) at least in every continent; some cases thre could be many GRX’s in one country
› Every Roaming Operator will have connection to GRX using some ofthe following methods
» Layer 1 connection (Leased Line, fibre, etc.)
» Layer 2 logical connection (ATM/Frame Relay, etc)
» Layer 3 IP VPN connection over public IP Network (IPsec tunnel)
› Connection will carry BGP routing (Border Gateway)
› Public addressing in GPRS backbone networks
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Roaming network
BTS
FW
BSC
Home networkHome network
Visited networkVisited network
FW
VisitedNetwork
BB
BG
BTS
SGSN DNS
GGSN
Inter-operatorBB
HomeBB GGSN
DNS
SGSN
Internet
BSC• Border Gateway
• Inter-operator Backbone
BG
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Three categories of terminals›Class A
› simultaneous circuit switched and packet connection
›Class B
› both circuit and packed switched connections possible but not at the same time
›Class C
› only packet switched or circuit switched connection
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Different capabilities
›Terminals are typically asymmetric
› Receiving is more simple than sending
› Full duplex radio
› Tx Rx
› 1 + 1 Ch
› 1 + 2 Ch
› 1 + 4 Ch
› 2 + 2 Ch
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GPRS-terminal types and service usageGPRS-terminal types and service usage
Card phone+Notebook
PDAWAP
Smart phone
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EDGE
› Enhanced Data rates for Global (GSM) Evolution
› Modulation update: from GMSK to 8-PSK
› In theory modulation efficiency will be tripled
› In practice the maximum bit rate increases from GPRS’s 171,2 kbit/s up to 384 kbit/s
› Needs new radio interface & terminals
› Transport network needs to be also upgraded
› Currently EDGE deployments are mainly going on in USA
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GSMcapable systems
IMT-2000capable systems
Functionality& bitrate
Time
Speech
Circuit data
HSCSD
GPRS
WCDMAEDGE
Summary and conclusion
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GSM-based network evolution
GSMGSM
HSCSDHSCSD
GPRSGPRS
EDGEEDGE UMTSUMTS
1997 1998 1999 2000 2001 2002 2003
Non-UMTS
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For those who are interested to know more
Literature beyond course material:
› Yi-Bing Lin, Imric Chlamtac: ”Wireless and Mobile Network Architectures”
› Christoffer Andersson: ”GPRS and 3G Wireless Applications: Professional Developer’s Guide”
› Timo Halonen, Javier Romero, Juan Melero: ” GSM, GPRS and EDGE Performance: Evolution Toward 3G/UMTS”
Internet:
http://www.3gpp.org/
http://www.cs.hut.fi/~hhk/GPRS/gprs_index.html
http://www.google.com/ ☺