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Wireless Sylabus Overview

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    Cellular Wireless NetworksCellular Wireless Networks

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    Martin cooperMartin cooper

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    Example of a Cellular WirelessExample of a Cellular WirelessNetworkNetwork

    Picture: http://www.scom.hud.ac.ukPicture: http://www.scom.hud.ac.uk

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    1G Cellular Networks1G Cellular Networks

    11ststgeneration cellular networks are purelygeneration cellular networks are purelyanalog cellular systems.analog cellular systems.

    The transmission of data is sent via aThe transmission of data is sent via acontinuously variable signalcontinuously variable signal

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    2G Cellular Networks2G Cellular Networks

    22ndnd generation cellular networks refergeneration cellular networks refer totodigital cellulardigital cellular and PCand PC wireless systems.wireless systems.

    voice and low speed data servicesvoice and low speed data services..

    They consist of digital traffic channels,They consist of digital traffic channels,perform encryption, error detection &perform encryption, error detection &correctioncorrection

    Users share channels dynamicallyUsers share channels dynamically

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    3G Cellular Networks3G Cellular Networks

    33rdrd generation refersgeneration refers to the next generation ofto the next generation ofwireless systems.wireless systems.

    This is digital with high speed data transferThis is digital with high speed data transfer

    It is voice quality comparable with a switchedIt is voice quality comparable with a switchedtelephone network.telephone network.

    Data transmission rates can be asymmetric orData transmission rates can be asymmetric orsymmetrical.symmetrical.

    It provides support for circuit switched andIt provides support for circuit switched andpacket switched data services.packet switched data services.

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    Cellular OperationCellular Operation

    Three basic devicesThree basic devices

    yy Amobile stationAmobile station

    yy Abase transceiver

    Abase transceiver

    yy AMobile Telecommunications Switching OfficeAMobile Telecommunications Switching Office(MTSO)(MTSO)

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    Cellular OperationCellular Operation

    Picture: www.Xanthippi.ceid.upatras.gr

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    Cellular Network OrganizationCellular Network Organization

    Base Station (BS)Base Station (BS) includes an antenna, a controller, and a number of receiversincludes an antenna, a controller, and a number of receivers

    Mobile Telecommunications Switching Office (MTSO)Mobile Telecommunications Switching Office (MTSO) connects calls between mobile unitsconnects calls between mobile units

    Two types of channels available between mobile unit andTwo types of channels available between mobile unit andBSBS

    Control channelsControl channels used to exchange information having to do with setting up andused to exchange information having to do with setting up and

    maintaining calls (outmaintaining calls (out--band or inband or in--band through stealing bits)band through stealing bits)

    Traffic channelsTraffic channels carry voice or data connection between userscarry voice or data connection between users

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    Cellular OperationCellular Operation

    Public Land Mobile Network (PLMN) refers to aPublic Land Mobile Network (PLMN) refers to acellular network that has land and radio basedcellular network that has land and radio basedsections.sections.

    This network consists of:This network consists of:

    Mobile station (MS): Adevice used for communicationMobile station (MS): Adevice used for communicationover the network.over the network.

    Base station transceiver (BST): A transmitter/receiverBase station transceiver (BST): A transmitter/receiverused to transmit/receive signals over the network.used to transmit/receive signals over the network.

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    Cellular OperationCellular Operation

    Mobile switching center (MSC): Sets up andMobile switching center (MSC): Sets up andmaintains calls made over the network.maintains calls made over the network.

    Base station controller (BSC): CommunicationBase station controller (BSC): Communicationbetween a group of BSTs and a single MSC isbetween a group of BSTs and a single MSC iscontrolled by the BSCcontrolled by the BSC

    Public switched telephone network (PSTN): SectionPublic switched telephone network (PSTN): Sectionof the network that is land basedof the network that is land based

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    Cellular OperationCellular Operation

    Outgoing from mobileOutgoing from mobile

    input phone number and press sendinput phone number and press send

    mobile links to base transceiver via controlmobile links to base transceiver via controlchannelchannel

    base to MTSO to PSTNbase to MTSO to PSTN

    MTSO routes connection back to mobile viaMTSO routes connection back to mobile via

    voice channelvoice channelmobile shifts from control to voicemobile shifts from control to voice

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    Cellular OperationCellular Operation

    Incoming to mobileIncoming to mobile

    call goes from PSTN to MTSOcall goes from PSTN to MTSO

    on control channel,M

    TSO searches for mobileon control channel,M

    TSO searches for mobileby PAGING every active mobileby PAGING every active mobile

    If found, MTSO rings it and establishes voiceIf found, MTSO rings it and establishes voicechannel connectionchannel connection

    uses transceiver with strongest signal fromuses transceiver with strongest signal frommobilemobile

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    Cellular Network Organization (Cells)Cellular Network Organization (Cells)

    Cells use low powered transmitters.Cells use low powered transmitters.

    Each cell is allocated a band of frequencies, andEach cell is allocated a band of frequencies, andis served by its own antenna as well as a baseis served by its own antenna as well as a base

    station consisting of a transmitter, receiver andstation consisting of a transmitter, receiver andcontrol unit.control unit.

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    Hexagon Reuse ClustersHexagon Reuse Clusters

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    Cellular Coverage RepresentationCellular Coverage Representation

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    Frequency ReuseFrequency Reuse

    EachEachcolour/lettercolour/letteruses the sameuses the samefrequency bandfrequency band

    Picture: netlab.cis.temple.edu/~jmulik/teaching/8550s03-slides/ 8550-Cellular-14.sxi.pdf

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    33--cell reuse patterncell reuse pattern (i=1,j=1)(i=1,j=1)

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    44--cell reuse patterncell reuse pattern (i=2,j=0)(i=2,j=0)

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    77--cell reuse patterncell reuse pattern (i=2,j=1)(i=2,j=1)

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    1212--cellcell reuse patternreuse pattern (i=2,j=2)(i=2,j=2)

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    1919--cell reuse pattern (i=3,j=2)cell reuse pattern (i=3,j=2)

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    Relationship betweenRelationship between QQ andand NN

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    Factors limiting frequency reuseFactors limiting frequency reuse

    CoCo--channel interferencechannel interference

    Adjacent channel interferenceAdjacent channel interference

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    Adjacent Channel InterferenceAdjacent Channel Interference

    Adjacent channel interference can be controlled with transmit andAdjacent channel interference can be controlled with transmit andreceive filtersreceive filters

    Picture: xanthippi.ceid.upatras.gr/courses/ mobi_net/Lecture1.ppt

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    Coping with increasing capacityCoping with increasing capacity

    yy Adding new channelsAdding new channels

    yy Frequency borrowingFrequency borrowing

    yy frequencies are taken from adjacent cells byfrequencies are taken from adjacent cells by

    congested cellscongested cells

    Picture: www.its.bth.se/courses/etc019/handouts/ ch10_Cellular_wireless_netw.pdf

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    Coping with increasing capacityCoping with increasing capacity

    yy Cell splittingCell splittingyy cells in areas of high usage can be split intocells in areas of high usage can be split into

    smaller cellssmaller cells

    yy Cell sectoringCell sectoringyy cells are divided into a number of wedgecells are divided into a number of wedge--

    shaped sectors, each with their own set ofshaped sectors, each with their own set ofchannelschannels

    MicrocellsMicrocells antennas move to buildings, hills, and lampantennas move to buildings, hills, and lamp

    postsposts

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    Cell SplittingCell Splitting

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    Site ConfigurationsSite Configurations

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    HandoffsHandoffs

    Network protocols must refresh and renewNetwork protocols must refresh and renewpaths as a mobile station host movespaths as a mobile station host movesbetween cells.between cells.

    Handoffs are the function of one cellHandoffs are the function of one cellhanding over the communication linkhanding over the communication linkbetween itself and a mobile station as thebetween itself and a mobile station as themobile station moves out of the boundarymobile station moves out of the boundaryof its region into the boundary of anof its region into the boundary of anadjacent cell.adjacent cell.

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    HandoffsHandoffs

    This practice must preserve endThis practice must preserve end--toto--endendconnectivity in a dynamically reconfiguredconnectivity in a dynamically reconfigurednetwork topology.network topology.

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    Handoff Types (contd)Handoff Types (contd)

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    Avoiding handoff: Umbrella cellsAvoiding handoff: Umbrella cells

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    Encoding:Encoding:Modulation(1)Modulation(1)

    Amplitude ModulationAmplitude ModulationFrequency ModulationFrequency Modulation

    Phase ModulationPhase Modulation

    are the three different methods of encodingare the three different methods of encodingbinary information on a regular wave.binary information on a regular wave.

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    Encoding:Encoding:Modulation(2)Modulation(2)

    When using digital signals the methods areWhen using digital signals the methods are

    known as Amplitude Shift Keying (ASK),known as Amplitude Shift Keying (ASK),Frequency Shift Keying (FSK), and PhaseFrequency Shift Keying (FSK), and PhaseShift Keying (PSK).Shift Keying (PSK).

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    Encoding:Encoding:

    Multiplexing(1)Multiplexing(1)

    Multiplexing allows many mobile users to useMultiplexing allows many mobile users to use

    cellular radio transmission schemes at thecellular radio transmission schemes at thesame time. The different schemes are:same time. The different schemes are:

    Frequency Division MultiplexingFrequency Division Multiplexing

    Time Division MultiplexingTime Division Multiplexing Code Division MultiplexingCode Division Multiplexing

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    Encoding:Encoding:

    Multiplexing(2)Multiplexing(2)Frequency Division MultiplexingFrequency Division Multiplexing involves a differentinvolves a differentfrequency channel given to each userfrequency channel given to each user

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    Encoding:Encoding:Multiplexing(3)Multiplexing(3)

    Time Division MultiplexingTime Division Multiplexing involves a channelinvolves a channelwith a given number of time slots (perwith a given number of time slots (permillisecond) where each user is assigned certainmillisecond) where each user is assigned certain

    time interval.time interval.Code Division MultiplexingCode Division Multiplexing gives each user agives each user acode for differentiation purposes. The receivercode for differentiation purposes. The receiverpicks out each channel from the noise usingpicks out each channel from the noise usingthe code. Wide frequency band is used. Doesthe code. Wide frequency band is used. Doesnot contain single frequencies or time slots.not contain single frequencies or time slots.

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    Differences between FDMA, TDMA,and CDMA.

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    Advantages ofAdvantages ofCode Division MultiplexingCode Division Multiplexing

    better protection against interferencebetter protection against interference

    good securitygood security

    signal difficult to jamsignal difficult to jam

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    Disadvantages ofDisadvantages ofCode Division MultiplexingCode Division Multiplexing

    pseudopseudo--random code sequencesrandom code sequencesgenerated by the transmitters andgenerated by the transmitters and

    receivers are not always randomreceivers are not always random

    fast power control system needed so thatfast power control system needed so thatstrong signals dont overpower weakerstrong signals dont overpower weaker

    signals.signals.

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    AnalogyAnalogy::

    MultiplexingMultiplexingLectures at a learning institute:Lectures at a learning institute:

    Frequency Division:Frequency Division: takes place intakes place in

    different roomsdifferent rooms Time Division:Time Division: taking turns in a singletaking turns in a single

    roomroom

    Code Division:Code Division: lectures on differentlectures on differentsubjects.subjects.

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    Wired vs. WirelessWired vs. Wireless

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    Wired vs. WirelessWired vs. Wireless (1)(1)

    Aproblem with wireless networks is thatAproblem with wireless networks is that

    anyone with a wireless network card is ableanyone with a wireless network card is ableto access this network and is potentiallyto access this network and is potentiallyharmful since they are able to corrupt andharmful since they are able to corrupt andsteal important files.steal important files.

    These networks transmit data over an areaThese networks transmit data over an areasuch that the network signals may penetratesuch that the network signals may penetratephysical areas such as walls.physical areas such as walls.

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    Wired vs. WirelessWired vs. Wireless (1)(1)

    Although this problem is relevant to a wiredAlthough this problem is relevant to a wirednetwork also, it exists to a greater degreenetwork also, it exists to a greater degree

    in a wireless network.in a wireless network.With regard to wired networks, theWith regard to wired networks, the

    electromagnetic waves that are given offelectromagnetic waves that are given off

    from the current traveling through thefrom the current traveling through thenetwork cables.network cables.

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    Advantages of wirelessAdvantages of wirelessnetworksnetworks

    FlexibleFlexible

    Cost is less (long term)Cost is less (long term)

    Mobile user choiceMobile user choice

    Accesses areas that wired networksAccesses areas that wired networkscannot reachcannot reach

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    Disadvantages of wirelessDisadvantages of wirelessnetworksnetworks

    Compared to wired networks the dataCompared to wired networks the datarates are slowerrates are slower

    User location determines performanceUser location determines performance Devices such as microwaves, cordlessDevices such as microwaves, cordless

    phones, etc may cause interferencephones, etc may cause interference

    Can be accessed by hackers from theCan be accessed by hackers from theoutsideoutside

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    Wired Equivalent PrivacyWired Equivalent PrivacyAlgorithm (WEP) (1)Algorithm (WEP) (1)

    Wireless networks may include additionalWireless networks may include additionalsecurity elements, which are notsecurity elements, which are notsupported in wired networks.supported in wired networks.

    For eg. The use of security algorithms suchFor eg. The use of security algorithms suchas WEP (Wired Equivalent Privacyas WEP (Wired Equivalent PrivacyAlgorithm), that uses an encryptionAlgorithm), that uses an encryption

    algorithm which deals with unauthorizedalgorithm which deals with unauthorizedaccess to the network (eavesdropping).access to the network (eavesdropping).

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    WEP (2)WEP (2)

    WEP is a implemented such that a block ofWEP is a implemented such that a block ofplaintext (input text) is bitwise XORed with anplaintext (input text) is bitwise XORed with anequal length random key sequence. Aequal length random key sequence. Arandom number generator is used on therandom number generator is used on the

    initialization vector and the secret key andinitialization vector and the secret key andoutputs a key sequence of random of octets.outputs a key sequence of random of octets.

    An integrity check value is produced to protectAn integrity check value is produced to protectagainst data modification.against data modification.

    The key sequence combined with plaintextThe key sequence combined with plaintextcombined with the integrity check value givescombined with the integrity check value givesthe enciphered message. The integrity checkthe enciphered message. The integrity checkvalue and the ciphertext is the combination ofvalue and the ciphertext is the combination ofthe output.the output.

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    Block CiphersBlock Ciphers

    Another security algorithm is Block Ciphers whichAnother security algorithm is Block Ciphers whichis the most common of the encryptionis the most common of the encryption

    techniques. The Block Cipher consists of:techniques. The Block Cipher consists of:

    Data Encryption Standard (DES)Data Encryption Standard (DES)

    Triple Data Encryption (TDEA)Triple Data Encryption (TDEA)

    Advanced Encryption Standard (AES).Advanced Encryption Standard (AES).

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    The GSM NetworkThe GSM Network

    TheThe GGloballobal SSystem forystem for MMobileobilecommunications.communications.--most widely used digitalmost widely used digitalcellular communications systemcellular communications system

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    The GSM NetworkThe GSM Network

    Picture: http://www.alphaorg.com/cellular/Picture: http://www.alphaorg.com/cellular/

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    Mobile StationMobile Station

    Mobile equipment or terminalMobile equipment or terminal

    3 types: fixed, portable, handheld3 types: fixed, portable, handheld

    Subscriber Identity ModuleSubscriber Identity Module (SIM).(SIM).

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    The Base Station Subsystem (BSS)The Base Station Subsystem (BSS)

    The Base Station Subsystem connects theThe Base Station Subsystem connects theMobile Station and the Network andMobile Station and the Network andSwitching Subsystem. It is responsible forSwitching Subsystem. It is responsible for

    transmission and reception and can betransmission and reception and can bedivided into two parts:divided into two parts:

    The Base Transceiver Station (BTS) or BaseThe Base Transceiver Station (BTS) or BaseStation.Station.

    The Base Station Controller (BSC).The Base Station Controller (BSC).

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    The Base Transceiver Station (BTS)The Base Transceiver Station (BTS)

    The BTS corresponds to the transceiversThe BTS corresponds to the transceiversand antennas used in each cell of theand antennas used in each cell of thenetwork. It is usually placed in the centernetwork. It is usually placed in the centerof a cell. The size of a cell defines theof a cell. The size of a cell defines thetransmitting power. ABTS can have up totransmitting power. ABTS can have up to16 transceivers. It all depends on the16 transceivers. It all depends on the

    density of users in the cell.density of users in the cell.

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    The Base Station Controller (BSC)The Base Station Controller (BSC)

    The BSC controls a group of BTS.The BSC controls a group of BTS.

    ABSC is primarily responsible forABSC is primarily responsible forhandovers, frequency hopping, exchangehandovers, frequency hopping, exchangefunctions and control of the frequencyfunctions and control of the frequencypower levels of the BTSs.power levels of the BTSs.

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    The Network and SwitchingThe Network and SwitchingSubsystem (NSS)Subsystem (NSS)

    Its main role is to manage theIts main role is to manage thecommunications between the mobile userscommunications between the mobile usersand other users, such as mobile users,and other users, such as mobile users,

    ISDN users, landline users, etc.ISDN users, landline users, etc. It also has databases that storeIt also has databases that store

    information about the subscribers and toinformation about the subscribers and tomanage their mobility.manage their mobility.

    The different components of the NSS areThe different components of the NSS aredescribed below.described below.

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    The Mobile services Switching CenterThe Mobile services Switching Center(MSC)(MSC)

    Central component of the NSS.Central component of the NSS.

    It performs switching functions and alsoIt performs switching functions and alsoprovides connection to other networks.provides connection to other networks.

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    The Gateway Mobile servicesThe Gateway Mobile servicesSwitching Center (GMSC)Switching Center (GMSC)

    Agateway is a node that interconnectsAgateway is a node that interconnectstwo networks.two networks.

    The GMSC is the interface between theThe GMSC is the interface between themobile cellular network and the Publicmobile cellular network and the PublicSwitched Telephone Network (PSTN).Switched Telephone Network (PSTN).

    It is responsible for routing calls from theIt is responsible for routing calls from the

    fixed network towards a GSM user.fixed network towards a GSM user.

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    Home Location Register (HLR)Home Location Register (HLR)

    The HLR is an important database as it storesThe HLR is an important database as it storesinformation about the subscribers belonging toinformation about the subscribers belonging tothe covering area of a MSC.the covering area of a MSC.

    It stores the current location of theseIt stores the current location of thesesubscribers and the services to which they havesubscribers and the services to which they haveaccess.access.

    The location of the subscriber corresponds toThe location of the subscriber corresponds tothe SS7 address of the Visitor Location Registerthe SS7 address of the Visitor Location Register(VLR) associated to the terminal.(VLR) associated to the terminal.

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    Visitor Location Register (VLR)Visitor Location Register (VLR)

    The VLR contains information from aThe VLR contains information from asubscriber's HLR.subscriber's HLR.

    It is necessary for the provision of subscribedIt is necessary for the provision of subscribedservices to visiting users.services to visiting users.

    When a subscriber enters the covering area of aWhen a subscriber enters the covering area of anew MSC, the VLR associated to this MSC willnew MSC, the VLR associated to this MSC willrequest information about the new subscriber torequest information about the new subscriber toits corresponding HLR.its corresponding HLR.

    The VLR will then have enough information toThe VLR will then have enough information toassure the subscribed services without needingassure the subscribed services without needingto confirm with the HLR each time ato confirm with the HLR each time acommunication is established.communication is established.

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    The Authentication Center (AuC)The Authentication Center (AuC)

    The AuC register provides the parametersThe AuC register provides the parametersneeded for authentication and encryptionneeded for authentication and encryptionfunctions.functions.

    These parameters help verify the user'sThese parameters help verify the user'sidentity.identity.

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    The Equipment Identity RegisterThe Equipment Identity Register(EIR)(EIR)

    The EIR is also used for security purposes.The EIR is also used for security purposes.It is a register containing informationIt is a register containing informationabout the mobile equipment.about the mobile equipment.

    It particularly contains a list of all validIt particularly contains a list of all validterminals.terminals.

    A terminal is identified by its InternationalA terminal is identified by its International

    Mobile Equipment Identity (IMEI).Mobile Equipment Identity (IMEI).

    The EIR uses this to forbid calls fromThe EIR uses this to forbid calls fromstolen or unauthorized terminals.stolen or unauthorized terminals.

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    The GSM Interworking Unit (GIWU)The GSM Interworking Unit (GIWU)

    The GIWU corresponds to an interface toThe GIWU corresponds to an interface tovarious networks for datavarious networks for datacommunications.communications.

    During these communications, theDuring these communications, thetransmission of speech and data can betransmission of speech and data can bealternated.alternated.

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    The Operation and SupportThe Operation and SupportSubsystem (OSS)Subsystem (OSS)

    The OSS is connected to the differentThe OSS is connected to the differentcomponents of the NSS and BSC in ordercomponents of the NSS and BSC in orderto control and monitor the GSM system.to control and monitor the GSM system.

    It also takes care of controlling the trafficIt also takes care of controlling the trafficload of the BSS.load of the BSS.

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    In GSM, there are five main functions:In GSM, there are five main functions:

    Transmission.Transmission.

    Radio Resources management (RR).Radio Resources management (RR).

    Mobility Management (MM).Mobility Management (MM).

    Communication Management (CM).Communication Management (CM).

    Operation, Administration and MaintenanceOperation, Administration and Maintenance

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    GSMGSM

    GSM uses an intriguing method to sendGSM uses an intriguing method to senddata. By simply sending computer data asdata. By simply sending computer data asit would send voice data, GSM allowsit would send voice data, GSM allowsevery phone to be "data enabled."every phone to be "data enabled."

    Since the GSM network is already a packetSince the GSM network is already a packetnetwork of sorts because of its frequencynetwork of sorts because of its frequencyhopping, it requires no additionalhopping, it requires no additional

    hardware to support data.hardware to support data. GSM allows data rates in multiples of300GSM allows data rates in multiples of300

    bits per second, up to 64 kilobits perbits per second, up to 64 kilobits persecond.second.

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    Advantages of Cellular NetworksAdvantages of Cellular Networks

    Cellular networks use "small" cells with lowCellular networks use "small" cells with lowpowered transceivers instead of one large areapowered transceivers instead of one large areawith a high powered transceiver.with a high powered transceiver.

    Using cellular networks increases overall callUsing cellular networks increases overall callhandling capacity.handling capacity.

    Avoids central point of failure.Avoids central point of failure.

    Allows dynamic distribution of capacity based onAllows dynamic distribution of capacity based ondemand.demand.

    Less interference with other wirelessLess interference with other wirelesscommunicationscommunications

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    Conclusion (1)Conclusion (1)

    Mobile phone contracts provide a useful andMobile phone contracts provide a useful andrelatively cheap service.relatively cheap service.

    Cellular radio network infrastructures areCellular radio network infrastructures aregrowing at a tremendous rate.growing at a tremendous rate.

    Cellular networks are becoming high speedCellular networks are becoming high speeddata networks.data networks.

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    Conclusion (2)Conclusion (2)

    Speeding up the development of mobileSpeeding up the development of mobilecommunication technologies is thecommunication technologies is thefocus of the industry. The idealfocus of the industry. The ideal

    communication system where bothcommunication system where bothvoice and data services can bevoice and data services can bedelivered regardless of location,delivered regardless of location,

    network, or terminal.network, or terminal.


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