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    GSM Architecture

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    34Shreya Chauhan
    The document describes the architecture of a GSM network. It is composed of mobile stations, base station systems connected to base transceiver stations (BTS) and base station controllers (BSC), and a network and switching subsystem connected to mobile switching centers (MSC). The network uses various registers like the home location register (HLR), visitor location register (VLR), and equipment identity register (EIR) to manage subscriber data and authentication.

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    GSM Architecture

    Uploaded by

    34Shreya Chauhan
    24 views18 pages
    The document describes the architecture of a GSM network. It is composed of mobile stations, base station systems connected to base transceiver stations (BTS) and base station controllers (BSC), and a network and switching subsystem connected to mobile switching centers (MSC). The network uses various registers like the home location register (HLR), visitor location register (VLR), and equipment identity register (EIR) to manage subscriber data and authentication.

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    GSM architecture

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    The document describes the architecture of a GSM network. It is composed of mobile stations, base station systems connected to base transceiver stations (BTS) and base station controllers (BSC), and a network and switching subsystem connected to mobile switching centers (MSC). The network uses various registers like the home location register (HLR), visitor location register (VLR), and equipment identity register (EIR) to manage subscriber data and authentication.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    24 views18 pages

    GSM Architecture

    Uploaded by

    34Shreya Chauhan
    The document describes the architecture of a GSM network. It is composed of mobile stations, base station systems connected to base transceiver stations (BTS) and base station controllers (BSC), and a network and switching subsystem connected to mobile switching centers (MSC). The network uses various registers like the home location register (HLR), visitor location register (VLR), and equipment identity register (EIR) to manage subscriber data and authentication.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    of 18

    GSM architecture

    Dr Usha Raghavan
    Network Structure

    • Cell A cell is the basic unit of a cellular system and is defined as the radio coverage given by one
    BTS.

    • Location area A LA is defined as a group of cells. Within the network, a subscriber’s location is
    known by the LA which they are in. The identity of the LA in which an MS is currently located is
    stored in the VLR. (LAI)
    • MSC Service Area An MSC Service Area is made up of LAs and represents the geographical
    part of the network controlled by one MSC.
    • PLMN service area A PLMN service area is the entire set of cells served by one network operator
    and is defined as the area in which an operator offers radio coverage and access to its network.

    2
    GSM SERVICE AREA
    The GSM service area is the entire geographical area in which a
    subscriber can gain access to a GSM network.

    Location
    CellArea
    Location Area
    MSC Service Area
    PLMN Service Area
    GSM Service Area
    3
    GSM Architecture

    In this architecture , a mobile station (MS) communicates with a base station system (BSS) through the
    radio interface.
    The BSS is connected to the Network and Switching Subsystem(NSS) by communicating with a Mobile
    Switching Centre(MSC) using A interface
    Interfaces used for GSM network

    • Um – Used to communicate between BTS and MS


    • A bis – Used to communicate between BSC to BTS
    • A interface- Used to communicate between BSC and MSC
    • SS7 Signalling Protocol- Useed to communicate between MSC and
    other network
    Mobile Station
    GSM MSs consist of:
    • Mobile Equipment (ME)
    • Subscriber Identity Module(SIM)
    A SIM is a smart card protected by a
    Functions of MS personal Identity number(PIN) between
    1. For Voice and Data transmission and Reception 4-8 digits in length
    The Sim consists of Subscriber related
    2. Frequency and Time synchronization
    information
    3. Monitoring Power and Signal quality of
    surrounding cells The Mobile equipment(ME) contains the
    4. Providing location updates even during inactive non- customer related hardware and
    state. software information specific to radio
    interface. When the SIM is removed, the
    5. Can receive, store and send SMS upto 160
    ME cannot be used for reaching the
    characters
    service , except for emergency calls
    6
    Network Identities

    • International Mobile Equipment Identity :The IMEI is an unique code allocated to


    each mobile equipment. It is checked in the EIR.
    IMEI check List
    • White List
    • Grey List
    • Black List
    • Mobile Station ISDN Number : The MSISDN is registered in the telephone directory
    and used by the calling party for dialing. MSISDN shall not exceed 15 digits.CC-
    Country code(1 -3 digits) NDC--National Destination Code SN--Subscriber Number

    7
    International mobile subscriber Identity
    The IMSI is an unique identity which is used internationally and used within the network
    to identify the mobile subscribers. The IMSI is stored in the subscriber identity module
    (SIM), the HLR, VLR database.

    Temporary Mobile subscriber Identity


    TMSI is a temporary IMSI no. made known to an MS at registration.
    The VLR assigns a TMSI to each mobile subscribers entering the VLR area.Assigned
    only after successful authentication.

    Mobile Station Roaming Number


    The MSRN is used in the GMSC to set up a connection to the visited MSC/VLR.MSRN--
    is a temporary identity which is assigned during the establishment of a call to a roaming
    subs.
    Base Station System(BSS)

    • The BSS connects the MS and the NSS. The BSS consists of 2
    parts
    1. Base Transceiver Station (BTS)
    2. Base Station Controller(BSC)
    Base Transceiver Station(BTS)

    • Radio resources: The BTS contains Transmitter, Receiver and signaling


    equipment specific to the radio interface in order to contact the MS
    • Signal Processing: An important part of the BTS is the Transcoder Rate Adapter
    Unit (TRAU) that carries out GSM –Specific encoding/decoding and rate
    adaptation in data transmission
    • Synchronization
    • Local maintenance handling
    • Functional supervision and Testing
    Base Station Controller

    • Radio Resource Management: The BSC is responsible for switching functions in


    BSS.
    • It is connected to an MSC in the NSS
    • BSC supports radio channel allocation / release and handoff management
    • A BSC connects many BTSs and maintains cell configuration data to the BTSs
    • A BSC is engineered at 80 % utilization. When a BSC is overloaded, it first rejects
    location update, next MS originating calls and then handoffs
    Network and Switching Subsystem(NSS)

    • NSS supports the switching functions, Subscriber profiles and mobility management
    • The basic switching function in the NSS is performed by MSC. The interface follows the signaling protocol
    used in telephone network
    • The MSC also communicates with other network elements external to GSM utilizing the same signaling
    protocol. The various components of NSS are
    • Mobile Switching Centre(MSC) The current location of an MS is usually maintained by the HLR and
    • Home Location Register(HLR) VLR.
    • Visitor Location Register(VLR)
    When an MS moves from the home system to a visited system, its
    location is registered in the VLR of the visited system.
    • Authentication Centre(AuC) The VLR then informs the MS’s HLR of its current location.
    • Equipment Identity Register(EIR)The authentication centre is used in the security data management for
    the authentication of subscribers. The AuC may be Co-located with HLR
    MSC Functions
    • Switching and call routing
    • Charging
    • Service provisioning
    • Communication with HLR
    • Communication with VLR
    • Communication with other MSCs
    • Control of connected BSCs

    13
    VISITOR LOCATION REGISTER (VLR)

    • It contains data of all mobiles roaming in its area. Data In VLR


    • IMSI & TMSI
    • One VLR may be in-charge of one or more LA. • MSISDN
    • MSRN.
    • VLR is updated by HLR on entry of MS its area. • Location Area
    • Supplementary service
    parameters
    • VLR assigns TMSI which keeps on changing. • MS category
    • Authentication Key

    14
    Home Location Register(HLR)
    • Reference store for subscriber’s parameters, Permanent data in HLR -Data stored is
    numbers, authentication & Encryption values. changed only by commands.

    • Current subscriber status and associated VLR. • IMSI, MS-ISDN number.

    • Both VLR and HLR can be implemented in the • Category of MS ( whether pay phone or not )
    same equipment in an MSC. • Roaming restriction ( allowed or not ).
    • one PLMN may contain one or several HLR. • Supplementary services like call forwarding
    Temporary data in HLR -The data changes from call to call & is dynamic

    MSRN , RAND /SRES and Kc, VLR address , MSC address, Messages waiting data used for SMS
    15
    EQUIPMENT IDENTITY REGISTER ( EIR )

    • This data base stores IMEI for all registered mobile equipment and is unique to
    every ME.

    • Only one EIR per PLMN.

    • White list : IMEI, assigned to valid ME.


    • Black list : IMEI reported stolen
    • Gray list : IMEI having problems like faulty software, wrong make of equipment etc.
    16
    Authentication Center (AUC)
    • To authenticate the subs. attempting to use a network.
    • AUC is connected to HLR which provides it with authentication parameters and ciphering
    keys used to ensure network security.
    • AuC perform subscriber authentication and to establish ciphering procedures on the radio
    link between the network and MS. Information provided is called a TRIPLET which consists of:

    1.RAND(non predictable random number)

    2.SRES(Signed response)

    3.Kc(ciphering key)

    • 17
    Operations and Maintenance Centre (OMC)
    • The centralized operation of the various units in the system and functions needed to
    maintain the subsystems.

    • Dynamic monitoring and controlling of the network


    Functions of OMC
    O&M data function

    -Configuration management

    --Fault report and alarm handling

    -Performance supervision/management

    -Storage of system software and data


    18

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