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Wireless Telecommunication Systems   Hanna Kalosha [email_address]
Outline <ul><li>Market </li></ul><ul><li>GSM </li></ul><ul><ul><li>Overview </li></ul></ul><ul><ul><li>Services </li></ul>...
How does it work? <ul><li>How can the system locate a user? </li></ul><ul><li>Why don’t all phones ring at the same time? ...
GSM: Overview <ul><li>GSM </li></ul><ul><ul><li>formerly: Groupe Spéciale Mobile (founded 1982) </li></ul></ul><ul><ul><li...
Performance characteristics of GSM <ul><li>Communication  </li></ul><ul><ul><li>mobile, wireless communication; support fo...
Disadvantages of GSM <ul><li>no end-to-end encryption of user data </li></ul><ul><li>reduced concentration while driving <...
GSM: Mobile Services <ul><li>GSM offers </li></ul><ul><ul><li>several types of connections ( voice connections, data conne...
Bearer Services <ul><li>Telecommunication services to transfer data between access points, i.e. all services that enable t...
Tele Services <ul><li>Offered services </li></ul><ul><ul><li>mobile telephony </li></ul></ul><ul><ul><li>Emergency number ...
Supplementary services <ul><li>Services in addition to the basic services, cannot be offered stand-alone </li></ul><ul><li...
Architecture of the GSM system <ul><li>GSM is a PLMN (Public Land Mobile Network) </li></ul><ul><ul><li>several providers ...
Ingredients Mobile phones PDAs Antennas Infrastructure Monitoring
GSM: overview fixed network BSC BSC MSC MSC GMSC OMC, EIR,  AUC VLR HLR NSS with OSS RSS VLR
GSM: elements and interfaces NSS  MS MS BTS BSC GMSC IWF OMC BTS BSC MSC MSC A bis U m EIR HLR VLR VLR A BSS PDN ISDN, PST...
GSM: system architecture PSPDN CSPDN U m A bis A BSS radio subsystem MS MS BTS BSC BTS BTS BSC BTS network and switching s...
Radio subsystem <ul><li>The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers </li><...
GSM: cellular network <ul><ul><li>use of several carrier frequencies </li></ul></ul><ul><ul><li>not the same frequency in ...
Network and switching subsystem <ul><li>NSS is the main component of the public mobile network GSM </li></ul><ul><ul><li>s...
Operation subsystem <ul><li>The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of al...
GSM - TDMA/FDMA 1 2 3 4 5 6 7 8 higher GSM frame structures 935-960 MHz 124 channels (200 kHz) downlink 890-915 MHz 124 ch...
Mobile Terminated Call <ul><li>calling a GSM subscriber </li></ul><ul><li>2: forwarding call to GMSC </li></ul><ul><li>3: ...
Mobile Originated Call <ul><li>1, 2: connection request </li></ul><ul><li>3, 4: security check </li></ul><ul><li>5-8: chec...
Security in GSM <ul><li>Security services </li></ul><ul><ul><li>access control/authentication </li></ul></ul><ul><ul><ul><...
GSM – subscriber authentication A3 RAND K i 128 bit 128 bit SRES*  32 bit A3 RAND K i 128 bit 128 bit SRES  32 bit SRES* =...
GSM - key generation and encryption A8 RAND K i 128 bit 128 bit K c 64 bit A8 RAND K i 128 bit 128 bit SRES RAND encrypted...
Data services in GSM I <ul><li>Data transmission standardized with only 9.6 kbit/s </li></ul><ul><ul><li>advanced coding a...
Data services in GSM II <ul><li>GPRS (General Packet Radio Service) </li></ul><ul><ul><li>packet switching </li></ul></ul>...
GPRS architecture and interfaces MS BSS GGSN SGSN MSC U m EIR HLR/ GR VLR PDN G b G n G i SGSN G n
DECT <ul><li>DECT (Digital European Cordless Telephone) standardized by ETSI (ETS 300.175-x) for cordless telephones </li>...
UMTS and IMT-2000: 3G <ul><li>Proposals for IMT-2000 (International Mobile Telecommunications) </li></ul><ul><ul><li>UWC-1...
Frequencies for IMT-2000 IMT-2000 1850 1900 1950 2000 2050 2100 2150 2200 MHz MSS  ITU allocation (WRC 1992) IMT-2000 MSS...
IMT-2000 family IMT-DS (Direct Spread) UTRA FDD (W-CDMA) 3GPP IMT-TC (Time Code) UTRA TDD (TD-CDMA); TD-SCDMA 3GPP IMT-MC ...
Questions and answers  <ul><li>Question 1 :  </li></ul><ul><li>Which types of different services does GSM offer? </li></ul...
Sources <ul><li>Chapter 4. Telecommunication Systems. Mobile Communications by J. Shiller, 2003 </li></ul><ul><li>Technolo...
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Wireless Telecommunication Systems

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  • Roaming – changing VLRs with uninterrupted availability of all services
  • no full ISDN bandwidth of 64 kbit/s to the user, no transparent B-channel
  • MS – mobile station MT – mobile termination – performs all network specific tasks (TDMA,FDMA, coding, etc.) TE – terminal GSM-PLMN – GSM public land mobile network (the infrastructure needed for the GAM network) PSTN – public switched telephone network ISDN – integrated services digital network Interfaces: Um interface – radio interface, consists of all mechanisms necessary for wireless transmissions (TDMA, FDMA): media access, multiplexing,… U,S,R – interfaces for the transparent transmission of data. Not defined for all networks. Which one is used - depends on the specific network Bearer services - All services that enable the transparent transmission of data between the interfaces to the network. Eg. From interface S for mobile station – to the network Tele services – application specific. They are specified end-to-end, ie from one terminal to the other
  • Dataservices use full-duplex channels . Such channels allow for simultaneous access to the medium by base station and and mobile station, ie allow simultaneous transmission in both directions FDD – frequency division duplex
  • Telecommunication services that enable voice communication via mobile phones All these basic services have to obey cellular functions, security measurements etc. Offered services mobile telephony primary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 kHz Emergency number common number throughout Europe (112); mandatory for all service providers; free of charge; connection with the highest priority (preemption of other connections possible) Multinumbering several ISDN phone numbers per user possible Additional services Non-Voice-Teleservices group 3 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 (160 characters) using the signaling channel, thus allowing simultaneous use of basic services and SMS (almost ignored in the beginning now the most successful add-on!)
  • Offer varoius enchancements to the standard telephony services =&gt; can’t be offered stand-alone
  • Mobile phones – The visible but smallest part of the network! Antennas – Still visible and cause many discussions… Switching units , Management, Data bases, Monitoring – Not „visible“, but comprise the major part of the network (also from an investment point of view…)
  • Radio subsystem MS – mobile station – all user equipment + software needed for communication with GSM network. It consists of the phone and SIM (subscriber identity module). All user-specific mechanizms (charging, authentication) are based on SIM. SIM contains, PIN, PUK (PIN unblocking key), authentication key Ki, and international mobile subscriber identity. BSS – base station subsystem – each is controlled by base station controller BSC. It performs all functions necessary to maintain radio connections to an MS, coding/decoding of voice. BTS – base tranciever station – all radio equipment: antennas, signal processing BSC – base station controller – manages the BTSs. It reserves radio frequencies, handles handover from one BTS to another and performs paging of MS. Network and Switching Subsystem: MSC – mobile services switching centre – hight performance digital ISDN switches. They form a fixed backbone network for a GSM system. An MSC manages several BSCs in a geogr. region. Handles all signalling needed for connection setup and all functions needed for supplementary services GMSC – gateway MSC has additional connections to other fixed networks HLR – home location register – most important database in GSM system – it stores all user-relevant information. This comprises static info, such as mobile subscriber IDSN number, subscribed services, international mobile subscriber identity. Dynamic info comprises of current location area (LA) of the ms, mobile subscriber roaming number, the current VLR and MSC. This info is updated every time the MS leaves its current LA. It also supports charging and accounting. Each user has exactly one record in HLR. Capacity is several million customers. Tight time-bounds for request answering. VLR – visitor location register – one VLR is associated with each MC, it is a dynamic database which stores all important info needed for the MS users currently in the LA associated withthis MSC. When a new user comes into this LA, the VLR copies all relevant info for this user from HLR. This hierarchy helps to avoid long distance signalling of user info and also frequent HLR updates.Manages up to 1 million customers Operation subsystem : OMC – operation and maintanance center – typical functions are traffic monitoring, status reports of network entities, subscriber and security management, accounting and billing AuC – authentication centre – since radio interface is particularly vulnerable =&gt; needed to to protect user identity and data transmision. Contains the algorithms for authentication and keys for encryption. It also generates values needed for user authentication in the HLR EIR – equipment identity register – database, stores the all device identifications registered for this network. Eg. Has a blacklist of stolen or locked mobile devices (phones). Disadvantage – blacklists of different providers are not usually synchronized. Also contains white list (valid devices) and gray list (mulfunctioning devices).
  • MS – mobile station MT – mobile termination – performs all network specific tasks (TDMA,FDMA, coding, etc.) TE – terminal GSM-PLMN – GSM public land mobile network (the infrastructure needed for the GAM network) PSTN – public switched telephone network ISDN – integrated services digital network Interfaces: Um interface – radio interface, consists of all mechanisms necessary for wireless transmissions (TDMA, FDMA): media access, multiplexing,… U,S,R – interfaces for the transparent transmission of data. Not defined for all networks. Which one is used - depends on the specific network Bearer services - All services that enable the transparent transmission of data between the interfaces to the network. Eg. From interface S for mobile station – to the network Tele services – application specific. They are specified end-to-end, ie from one terminal to the other
  • Components MS (Mobile Station) BSS (Base Station Subsystem): consisting of BTS (Base Transceiver Station): sender and receiver BSC (Base Station Controller): controlling several transceivers Interfaces Um : radio interface Abis : standardized, open interface with 16 kbit/s user channels A : standardized, open interface with 64 kbit/s user channels Components MSC (Mobile Services Switching Center): IWF (Interworking Functions) ISDN (Integrated Services Digital Network) PSTN (Public Switched Telephone Network) PSPDN (Packet Switched Public Data Net.) CSPDN (Circuit Switched Public Data Net.) Databases HLR (Home Location R egister) VLR (Visitor Location R egister) EIR (Equipment Identity Register
  • The MSC (mobile switching center) plays a central role in GSM switching functions additional functions for mobility support management of network resources interworking functions via Gateway MSC (GMSC) integration of several databases Functions of a MSC specific functions for paging and call forwarding termination of SS7 (signaling system no. 7) mobility specific signaling location registration and forwarding of location information provision of new services (fax, data calls) support of short message service (SMS) generation and forwarding of accounting and billing information
  • Radio interface: -- Um! – comprises mechanizms fo rmultiplexing and media access GSM implements SDMA using cells and assigning MS to BTS FDD (frequency division duplex) is used to separate uplink and downlink Media access combines TDMA and FDMA GSM 900 – 124 channels in each direction (32 channels are reserved, 90 are used for user data) GSM 1800 – 374 channels in each direction On the picture time division is shown, professor already shown frequency division earlier in his lectures. Tail – is set to 0 and is used to enchance receiver performance Training sequence in the middle – is used to adapt the parameters of receiver to the current path propagation characteristics and to select the strongest signel in case of multipath propagation Flag S indicates whether the data field containsuser or network control data Mju – micro M – mili
  • A couple of localization an calling scenarios: To locate an MS and to adress an MS several numbers are needed: Mobile station international IDSN number – this is the actual phone number, that consists on country code, national destination code (or address of the network provider) and the subscriber number. International Mobile subscriber identity – internal unique identification of subscriber. Consists of mobile contry cose and mobile network code. Temporary Mobile subscriber identity – this number is used to hide IMSI, which would give away the exact identity of the user. It is selected by current VLR and is only valid temporary. VLR may also change his number periodically Mobile station roaming number – temporaty adress that also hides identity and location of the user. It is generated by VLR by request of MSC, the adress id then stored in HLR. Consists of visitor country code, visitor national destination code, the identifiction of current MSC + the subscriber number. This number helps HLR to find subscriber for an incoming call. The first example is mobile terminated call – when a station (which is outside of GSM network) calls mobile station. This fugure shows the steps necessary to to connect to the calling station PSTN - public switched telephone network GMSC – gateway MSC
  • Mobile originated call – mobile sataion calls a number
  • [AuC – authentication centre – since radio interface is particularly vulnerable =&gt; needed to to protect user identity and data transmision. Contains the algorithms for authentication and keys for encryption. It also generates values needed for user authentication in the HLR] GSM offers security services using information stored in SIM and AuC. Eg. SIM stores secret key Ki used for authentication and encryption procedures. Confidentiality: NO end-to-end encryption!!! All user-related data is encrypted between MS and BTS only!
  • Challenge-response method: AC – access controll – generates RAND(random number), MS answers with SRES(signed response) A3 – algorithm used for authentication – is stored in SIM and in AuC RAND is generated by AuC, Result is compared in VLR!!!
  • Cipher key Kc is thus NOT (!) sent over the air!
  • Data transmission standardized with only 9.6 kbit/s advanced coding allows 14,4 kbit/s not enough for Internet and multimedia applications HSCSD (High-Speed Circuit Switched Data) mainly software update bundling of several time-slots to get higher AIUR (Air Interface User Rate) (e.g., 57.6 kbit/s using 4 slots, 14.4 each) advantage: ready to use, constant quality, simple disadvantage: channels blocked for voice transmission GPRS (General Packet Radio Service) packet switching using free slots only if data packets ready to send (e.g., 50 kbit/s using 4 slots temporarily) standardization 1998, introduction 2001 advantage: one step towards UMTS, more flexible disadvantage: more investment needed (new hardware) GPRS network elements GSN (GPRS Support Nodes): GGSN and SGSN GGSN (Gateway GSN) interworking unit between GPRS and PDN (Packet Data Network) SGSN (Serving GSN) supports the MS (location, billing, security) GR (GPRS Register) user addresses
  • GSN – GPRS Support Nodes – are in fact routers. All of them are integrated into standard GSM architecture and many new interfaces have been defined GGSN - Gateway GPRS Support Nodes – interworking unit between the GPRS network and external packet data networks ( PDN ). This node contains routing information for GPRS users, performs address conversion, and tunnels data to a user. It is connected to external networks and transfers packets to the SGSN via IP-based GPRS network. SGSN – Servicing GPRS support node. It requests user adresses from GPRS register ( GR ), keeps track of individual MSs’ locations, collects billing info (eg. Counting bytes) and performs several security functions such as access control. GR – GPRS register – is typically a part of the HLR, stores all GPRS-relevant data.
  • EIR – equipment identity register – database, stores the all device identifications registered for this network. Eg. Has a blacklist of stolen or locked mobile devices (phones). Disadvantage – blacklists of different providers are not usually synchronized. Also contains white list (valid devices) and gray list (mulfunctioning devices).
  • Reasons to use instead of GSM: Dect can offer service to some 10,000 people within 1 km^2 Base station costs ~100 Euro vs 10,000 Euro for GSM base station DECT base stations can be used by individuals to create private natworks, whereas GSM cannot, since all GSM frequences must be licensed to network operators
  • ETSI – European telecommunication standards institute UMTS (Universal Mobile Telecommunications System)
  • Prorposal: allocate 1885-2025 and 2110-2200 MHz as the frequency bands that should be available worldwide for the new IMT-2000 systems. MSS – mobile satellite services However this figure shows the problem of such a world wide availability of the proposed frequency bands.
  • Thus due to frequency band unavailability and also because of patenting issues the idea of a common global system was dropped and so called family of 3G standars was adopted The figure here gives an overview ITU – international telecommunications union (geneva) – responsible for worldwide coordination of telecommunication activities ITU-R – international telecommunications union radiocommunications sector – handles standartization in the wireless sector IMT – international mobile telecommunications IMT-DS: Europe and Japan W-CDMA – wideband cdma UTRA FDD – this name is used by ETSI to avoid confusion Standartization takes place in 3GPP (3 rd generation partnership project) IMT-TC: still not introduced, proposal only Time-division CDMA, plus Time-division synchronous CDMA proposed by China Standartization will be handled by 3GPP (3 rd generation partnership project) IMT-MC IMT-SC: Initially promoted by UWCC – universal wireless communications consortium IMT-FT: For applications that do not require high mobility ETSI is responsible for standartization of DECT
  • Transcript of "Wireless Telecommunication Systems"

    1. 1. Wireless Telecommunication Systems Hanna Kalosha [email_address]
    2. 2. Outline <ul><li>Market </li></ul><ul><li>GSM </li></ul><ul><ul><li>Overview </li></ul></ul><ul><ul><li>Services </li></ul></ul><ul><ul><li>Sub-systems </li></ul></ul><ul><ul><li>Components </li></ul></ul><ul><li>DECT </li></ul><ul><li>UMTS/IMT-2000 </li></ul>Examlpe Coverage of GSM Networks T-Mobile (GSM-900/1800) Germany AT&T (GSM-850/1900) USA
    3. 3. How does it work? <ul><li>How can the system locate a user? </li></ul><ul><li>Why don’t all phones ring at the same time? </li></ul><ul><li>What happens if two users talk simultaneously? </li></ul><ul><li>Why don’t I get the bill from my neighbor? </li></ul><ul><li>Why can an Australian use her phone in Ottawa? </li></ul><ul><li>Why can’t I simply overhear the neighbor’s communication? </li></ul><ul><li>What are the key components of the mobile phone network? </li></ul>
    4. 4. GSM: Overview <ul><li>GSM </li></ul><ul><ul><li>formerly: Groupe Spéciale Mobile (founded 1982) </li></ul></ul><ul><ul><li>now: Global System for Mobile Communication </li></ul></ul><ul><ul><li>Pan-European standard (ETSI, European Telecommunications Standardisation Institute) </li></ul></ul><ul><ul><li>simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication administrations. Seamless roaming within Europe possible </li></ul></ul><ul><ul><li>today many providers all over the world use GSM (more than 200 countries in Asia, Africa, Europe, Australia, America) </li></ul></ul><ul><ul><li>more than 1.2 billion subscribers in more than 630 networks </li></ul></ul><ul><ul><li>more than 75% of all digital mobile phones use GSM (74% total) </li></ul></ul><ul><ul><li>over 200 million SMS per month in Germany, > 550 billion/year worldwide (> 10% of the revenues for many operators) </li></ul></ul>
    5. 5. Performance characteristics of GSM <ul><li>Communication </li></ul><ul><ul><li>mobile, wireless communication; support for voice and data services </li></ul></ul><ul><li>Total mobility </li></ul><ul><ul><li>international access, chip-card enables use of access points of different providers </li></ul></ul><ul><li>Worldwide connectivity </li></ul><ul><ul><li>one number, the network handles localization </li></ul></ul><ul><li>High capacity </li></ul><ul><ul><li>better frequency efficiency, smaller cells, more customers per cell </li></ul></ul><ul><li>High transmission quality </li></ul><ul><ul><li>high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains) </li></ul></ul><ul><li>Security functions </li></ul><ul><ul><li>access control, authentication via chip-card and PIN </li></ul></ul>
    6. 6. Disadvantages of GSM <ul><li>no end-to-end encryption of user data </li></ul><ul><li>reduced concentration while driving </li></ul><ul><li>electromagnetic radiation </li></ul><ul><li>abuse of private data possible </li></ul><ul><li>roaming profiles accessible </li></ul><ul><li>high complexity of the system </li></ul><ul><li>several incompatibilities within the GSM standards </li></ul>
    7. 7. GSM: Mobile Services <ul><li>GSM offers </li></ul><ul><ul><li>several types of connections ( voice connections, data connections, short message service) </li></ul></ul><ul><ul><li>multi-service options (combination of basic services) </li></ul></ul><ul><li>Three service domains </li></ul><ul><ul><li>Bearer Services </li></ul></ul><ul><ul><li>Tele Services </li></ul></ul><ul><ul><li>Supplementary Services </li></ul></ul>GSM-PLMN transit network (PSTN, ISDN) source/ destination network TE TE bearer services tele services R, S (U, S, R) U m MT MS
    8. 8. Bearer Services <ul><li>Telecommunication services to transfer data between access points, i.e. all services that enable the transparent transmission of data between the interfaces to the network </li></ul><ul><li>Specification of services up to the terminal interface </li></ul><ul><li>Different data rates for voice and data (original standard) </li></ul><ul><ul><li>data service (circuit switched) </li></ul></ul><ul><ul><ul><li>synchronous: 2.4, 4.8 or 9.6 kbit/s </li></ul></ul></ul><ul><ul><ul><li>asynchronous: 300 - 1200 bit/s </li></ul></ul></ul><ul><ul><li>data service (packet switched) </li></ul></ul><ul><ul><ul><li>synchronous: 2.4, 4.8 or 9.6 kbit/s </li></ul></ul></ul><ul><ul><ul><li>asynchronous: 300 - 9600 bit/s </li></ul></ul></ul><ul><li>Today: data rates of approx. 50 kbit/s possible </li></ul>
    9. 9. Tele Services <ul><li>Offered services </li></ul><ul><ul><li>mobile telephony </li></ul></ul><ul><ul><li>Emergency number (112) </li></ul></ul><ul><ul><li>Multinumbering </li></ul></ul><ul><li>Additional services (non-voice teleservices) </li></ul><ul><ul><li>group 3 fax </li></ul></ul><ul><ul><li>voice mailbox </li></ul></ul><ul><ul><li>electronic mail </li></ul></ul><ul><ul><li>... </li></ul></ul><ul><ul><li>Short Message Service (SMS) </li></ul></ul>
    10. 10. Supplementary services <ul><li>Services in addition to the basic services, cannot be offered stand-alone </li></ul><ul><li>Similar to ISDN services besides lower bandwidth due to the radio link </li></ul><ul><li>May differ between different service providers, countries and protocol versions </li></ul><ul><li>Important services </li></ul><ul><ul><li>identification: forwarding of caller number </li></ul></ul><ul><ul><li>suppression of number forwarding </li></ul></ul><ul><ul><li>automatic call-back </li></ul></ul><ul><ul><li>conferencing with up to 7 participants </li></ul></ul><ul><ul><li>locking of the mobile terminal (incoming or outgoing calls) </li></ul></ul><ul><ul><li>... </li></ul></ul>
    11. 11. Architecture of the GSM system <ul><li>GSM is a PLMN (Public Land Mobile Network) </li></ul><ul><ul><li>several providers setup mobile networks following the GSM standard within each country </li></ul></ul><ul><ul><li>components </li></ul></ul><ul><ul><ul><li>MS (mobile station) </li></ul></ul></ul><ul><ul><ul><li>BS (base station) </li></ul></ul></ul><ul><ul><ul><li>MSC (mobile switching center) </li></ul></ul></ul><ul><ul><ul><li>LR (location register) </li></ul></ul></ul><ul><ul><li>subsystems </li></ul></ul><ul><ul><ul><li>RSS (radio subsystem): covers all radio aspects </li></ul></ul></ul><ul><ul><ul><li>NSS (network and switching subsystem): call forwarding, handover, switching </li></ul></ul></ul><ul><ul><ul><li>OSS (operation subsystem): management of the network </li></ul></ul></ul>
    12. 12. Ingredients Mobile phones PDAs Antennas Infrastructure Monitoring
    13. 13. GSM: overview fixed network BSC BSC MSC MSC GMSC OMC, EIR, AUC VLR HLR NSS with OSS RSS VLR
    14. 14. GSM: elements and interfaces NSS MS MS BTS BSC GMSC IWF OMC BTS BSC MSC MSC A bis U m EIR HLR VLR VLR A BSS PDN ISDN, PSTN RSS radio cell radio cell MS AUC OSS signaling O
    15. 15. GSM: system architecture PSPDN CSPDN U m A bis A BSS radio subsystem MS MS BTS BSC BTS BTS BSC BTS network and switching subsystem MSC MSC fixed partner networks IWF ISDN PSTN SS7 EIR HLR VLR ISDN PSTN
    16. 16. Radio subsystem <ul><li>The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers </li></ul><ul><li>Components </li></ul><ul><ul><li>Base Station Subsystem (BSS): </li></ul></ul><ul><ul><ul><li>Base Transceiver Station (BTS): radio components including sender, receiver, antenna – if directed antennas are used one BTS can cover several cells </li></ul></ul></ul><ul><ul><ul><li>Base Station Controller (BSC): switching between BTSs, controlling BTSs, managing of network resources, mapping of radio channels (U m ) onto terrestrial channels (A interface) </li></ul></ul></ul><ul><ul><ul><li>BSS = BSC + sum(BTS) + interconnection </li></ul></ul></ul><ul><ul><li>Mobile Stations (MS) </li></ul></ul>
    17. 17. GSM: cellular network <ul><ul><li>use of several carrier frequencies </li></ul></ul><ul><ul><li>not the same frequency in adjoining cells </li></ul></ul><ul><ul><li>cell sizes vary from some 100 m up to 35 km depending on user density, geography, transceiver power etc. </li></ul></ul><ul><ul><li>hexagonal shape of cells is idealized (cells overlap, shapes depend on geography) </li></ul></ul><ul><ul><li>if a mobile user changes cells – handover of the connection to the neighbor cell </li></ul></ul>possible radio coverage of the cell idealized shape of the cell cell
    18. 18. Network and switching subsystem <ul><li>NSS is the main component of the public mobile network GSM </li></ul><ul><ul><li>switching, mobility management, interconnection to other networks, system control </li></ul></ul><ul><li>Components </li></ul><ul><ul><li>Mobile Services Switching Center (MSC) controls all connections via a separated network to/from a mobile terminal within the domain of the MSC - several BSC can belong to a MSC </li></ul></ul><ul><ul><li>Databases (important: scalability, high capacity, low delay) </li></ul></ul><ul><ul><ul><li>Home Location Register (HLR) central master database containing user data, permanent and semi-permanent data of all subscribers assigned to the HLR (one provider can have several HLRs) </li></ul></ul></ul><ul><ul><ul><li>Visitor Location Register (VLR) local database for a subset of user data, including data about all user currently in the domain of the VLR </li></ul></ul></ul>
    19. 19. Operation subsystem <ul><li>The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems </li></ul><ul><li>Components </li></ul><ul><ul><li>Authentication Center (AUC) </li></ul></ul><ul><ul><ul><li>generates user specific authentication parameters on request of a VLR </li></ul></ul></ul><ul><ul><ul><li>authentication parameters used for authentication of mobile terminals and encryption of user data on the air interface within the GSM system </li></ul></ul></ul><ul><ul><li>Equipment Identity Register (EIR) </li></ul></ul><ul><ul><ul><li>registers GSM mobile stations and user rights </li></ul></ul></ul><ul><ul><ul><li>stolen or malfunctioning mobile stations can be locked and sometimes even localized </li></ul></ul></ul><ul><ul><li>Operation and Maintenance Center (OMC) </li></ul></ul><ul><ul><ul><li>different control capabilities for the radio subsystem and the network subsystem </li></ul></ul></ul>
    20. 20. GSM - TDMA/FDMA 1 2 3 4 5 6 7 8 higher GSM frame structures 935-960 MHz 124 channels (200 kHz) downlink 890-915 MHz 124 channels (200 kHz) uplink frequency time GSM TDMA frame GSM time-slot (normal burst) 4.615 ms 546.5 µs 577 µs tail user data Training S guard space S user data tail guard space 3 bits 57 bits 26 bits 57 bits 1 1 3
    21. 21. Mobile Terminated Call <ul><li>calling a GSM subscriber </li></ul><ul><li>2: forwarding call to GMSC </li></ul><ul><li>3: signal call setup to HLR </li></ul><ul><li>4, 5: request MSRN from VLR </li></ul><ul><li>6: forward responsible MSC to GMSC </li></ul><ul><li>7: forward call to </li></ul><ul><li>current MSC </li></ul><ul><li>8, 9: get current status of MS </li></ul><ul><li>10, 11: paging of MS </li></ul><ul><li>12, 13: MS answers </li></ul><ul><li>14, 15: security checks </li></ul><ul><li>16, 17: set up connection </li></ul>PSTN calling station GMSC HLR VLR BSS BSS BSS MSC MS 1 2 3 4 5 6 7 8 9 10 11 12 13 16 10 10 11 11 11 14 15 17
    22. 22. Mobile Originated Call <ul><li>1, 2: connection request </li></ul><ul><li>3, 4: security check </li></ul><ul><li>5-8: check resources (free circuit) </li></ul><ul><li>9-10: set up call </li></ul>PSTN GMSC VLR BSS MSC MS 1 2 6 5 3 4 9 10 7 8
    23. 23. Security in GSM <ul><li>Security services </li></ul><ul><ul><li>access control/authentication </li></ul></ul><ul><ul><ul><li>user  SIM (Subscriber Identity Module): secret PIN (personal identification number) </li></ul></ul></ul><ul><ul><ul><li>SIM  network: challenge response method </li></ul></ul></ul><ul><ul><li>confidentiality </li></ul></ul><ul><ul><ul><li>voice and signaling encrypted on the wireless link (after successful authentication) </li></ul></ul></ul><ul><ul><li>anonymity </li></ul></ul><ul><ul><ul><li>temporary identity TMSI (Temporary Mobile Subscriber Identity) </li></ul></ul></ul><ul><ul><ul><li>newly assigned at each new location update </li></ul></ul></ul><ul><ul><ul><li>encrypted transmission </li></ul></ul></ul><ul><li>3 algorithms specified in GSM </li></ul><ul><ul><li>A3 for authentication (open interface) </li></ul></ul><ul><ul><li>A5 for encryption (standardized) </li></ul></ul><ul><ul><li>A8 for key generation (open interface) </li></ul></ul><ul><li>“ secret”: </li></ul><ul><li>A3 and A8 available via the Internet </li></ul><ul><li>network providers can use stronger mechanisms </li></ul>
    24. 24. GSM – subscriber authentication A3 RAND K i 128 bit 128 bit SRES* 32 bit A3 RAND K i 128 bit 128 bit SRES 32 bit SRES* =? SRES SRES RAND SRES 32 bit mobile network SIM AC MSC SIM K i : individual subscriber authentication key SRES: signed response
    25. 25. GSM - key generation and encryption A8 RAND K i 128 bit 128 bit K c 64 bit A8 RAND K i 128 bit 128 bit SRES RAND encrypted data mobile network (BTS) MS with SIM AC BSS SIM A5 K c 64 bit A5 MS data data cipher key
    26. 26. Data services in GSM I <ul><li>Data transmission standardized with only 9.6 kbit/s </li></ul><ul><ul><li>advanced coding allows 14,4 kbit/s </li></ul></ul><ul><ul><li>not enough for Internet and multimedia applications </li></ul></ul><ul><li>HSCSD (High-Speed Circuit Switched Data) </li></ul><ul><ul><li>mainly software update </li></ul></ul><ul><ul><li>bundling of several time-slots to get higher AIUR (Air Interface User Rate) (e.g., 57.6 kbit/s using 4 slots, 14.4 each) </li></ul></ul><ul><ul><li>advantage: ready to use, constant quality, simple </li></ul></ul><ul><ul><li>disadvantage: channels blocked for voice transmission </li></ul></ul>
    27. 27. Data services in GSM II <ul><li>GPRS (General Packet Radio Service) </li></ul><ul><ul><li>packet switching </li></ul></ul><ul><ul><li>using free slots only if data packets ready to send (e.g., 50 kbit/s using 4 slots temporarily) </li></ul></ul><ul><ul><li>standardization 1998, introduction 2001 </li></ul></ul><ul><ul><li>advantage: one step towards UMTS, more flexible </li></ul></ul><ul><ul><li>disadvantage: more investment needed (new hardware) </li></ul></ul><ul><li>GPRS network elements </li></ul><ul><ul><li>GSN (GPRS Support Nodes): GGSN and SGSN </li></ul></ul><ul><ul><li>GGSN (Gateway GPRS Support Nodes ) </li></ul></ul><ul><ul><ul><li>interworking unit between GPRS and PDN (Packet Data Network) </li></ul></ul></ul><ul><ul><li>SGSN (Serving GSN) </li></ul></ul><ul><ul><ul><li>supports the MS (location, billing, security) </li></ul></ul></ul><ul><ul><li>GR (GPRS Register) </li></ul></ul><ul><ul><ul><li>user addresses </li></ul></ul></ul>
    28. 28. GPRS architecture and interfaces MS BSS GGSN SGSN MSC U m EIR HLR/ GR VLR PDN G b G n G i SGSN G n
    29. 29. DECT <ul><li>DECT (Digital European Cordless Telephone) standardized by ETSI (ETS 300.175-x) for cordless telephones </li></ul><ul><li>standard describes air interface between base-station and mobile phone </li></ul><ul><li>DECT has been renamed for international marketing reasons into „Digital Enhanced Cordless Telecommunication“ </li></ul><ul><li>Characteristics </li></ul><ul><ul><li>frequency: 1880-1990 MHz </li></ul></ul><ul><ul><li>channels: 120 full duplex </li></ul></ul><ul><ul><li>duplex mechanism: TDD (Time Division Duplex) with 10 ms frame length </li></ul></ul><ul><ul><li>multplexing scheme: FDMA with 10 carrier frequencies, TDMA with 2x 12 slots </li></ul></ul><ul><ul><li>modulation: digital, Gaußian Minimum Shift Key (GMSK) </li></ul></ul><ul><ul><li>power: 10 mW average (max. 250 mW) </li></ul></ul><ul><ul><li>range: approx. 50 m in buildings, 300 m open space </li></ul></ul>
    30. 30. UMTS and IMT-2000: 3G <ul><li>Proposals for IMT-2000 (International Mobile Telecommunications) </li></ul><ul><ul><li>UWC-136, cdma2000, WP-CDMA </li></ul></ul><ul><ul><li>UMTS (Universal Mobile Telecommunications System) from ETSI </li></ul></ul><ul><li>UMTS </li></ul><ul><ul><li>UTRA (was: UMTS, now: Universal Terrestrial Radio Access) </li></ul></ul><ul><ul><li>enhancements of GSM </li></ul></ul><ul><ul><ul><li>EDGE (Enhanced Data rates for GSM Evolution): GSM up to 384 kbit/s </li></ul></ul></ul><ul><ul><ul><li>CAMEL (Customized Application for Mobile Enhanced Logic) </li></ul></ul></ul><ul><ul><ul><li>VHE (virtual Home Environment) </li></ul></ul></ul><ul><ul><li>fits into GMM (Global Multimedia Mobility) initiative from ETSI </li></ul></ul><ul><ul><li>basic requirements </li></ul></ul><ul><ul><ul><li>min. 144 kbit/s rural (goal: 384 kbit/s) </li></ul></ul></ul><ul><ul><ul><li>min. 384 kbit/s suburban (goal: 512 kbit/s) </li></ul></ul></ul><ul><ul><ul><li>up to 2 Mbit/s urban </li></ul></ul></ul>
    31. 31. Frequencies for IMT-2000 IMT-2000 1850 1900 1950 2000 2050 2100 2150 2200 MHz MSS  ITU allocation (WRC 1992) IMT-2000 MSS  Europe China Japan North America UTRA FDD  UTRA FDD  T D D T D D MSS  MSS  DE CT GSM 1800 1850 1900 1950 2000 2050 2100 2150 2200 MHz IMT-2000 MSS  IMT-2000 MSS  GSM 1800 cdma2000 W-CDMA MSS  MSS  MSS  MSS  cdma2000 W-CDMA PHS PCS rsv.
    32. 32. IMT-2000 family IMT-DS (Direct Spread) UTRA FDD (W-CDMA) 3GPP IMT-TC (Time Code) UTRA TDD (TD-CDMA); TD-SCDMA 3GPP IMT-MC (Multi Carrier) cdma2000 3GPP2 IMT-SC (Single Carrier) UWC-136 (EDGE) UWCC/3GPP IMT-FT (Freq. Time) DECT ETSI GSM (MAP) ANSI-41 (IS-634) IP-Network IMT-2000 Core Network ITU-T IMT-2000 Radio Access ITU-R Interface for Internetworking Flexible assignment of Core Network and Radio Access Initial UMTS (R99 w/ FDD)
    33. 33. Questions and answers <ul><li>Question 1 : </li></ul><ul><li>Which types of different services does GSM offer? </li></ul><ul><li>Answer : </li></ul><ul><li>Bearer services (telecommunication services to transfer data between access points) </li></ul><ul><li>Tele services (telephony, emergency number, SMS) </li></ul><ul><li>Supplementary services (identification, call redirection, call forwarding, call conferencing) </li></ul><ul><li>Question 2 : </li></ul><ul><li>What is the main problem when transmitting data using wireless systems such as GSM that were made for voice transmission? </li></ul><ul><li>Answer : </li></ul><ul><li>The standard bandwidth available for data transmission is not sufficient for the requirements of today’s computers </li></ul><ul><li>Question 3 : </li></ul><ul><li>How can higher data rates be achieved in standard GSM? </li></ul><ul><li>Answer : </li></ul><ul><li>By bundling several traffic channels – in HSCSD (high speed circuit switched data). </li></ul><ul><li>By providing packet oriented data transmissions – in GPRS (general packet radio service). </li></ul>
    34. 34. Sources <ul><li>Chapter 4. Telecommunication Systems. Mobile Communications by J. Shiller, 2003 </li></ul><ul><li>Technology Trends in Wirless Communications by R. Prasad, M. Ruggieri, 2003 </li></ul><ul><li>http://www.site.uottawa.ca/%7Eivan/csi-5169-org-06.pdf </li></ul>
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