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Chapter 4: Wireless Telecommunication Systems, GSM

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Title: Mobile Communications Subject: Chapter 4 - Wireless Telecommunication Systems Author: Jochen H. Schiller Keywords: GSM, DECT, TETRA, UMTS, IMT-2000 – PowerPoint PPT presentation

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Title: Chapter 4: Wireless Telecommunication Systems, GSM


1
Chapter 4 Wireless Telecommunication Systems,
GSM
(Book Mobile Communications, Schiller)
2
GSM Overview
  • GSM
  • formerly Groupe Spéciale Mobile (founded 1982)
  • now Global System for Mobile Communication
  • Pan-European standard (ETSI, European
    Telecommunications Standardisation Institute)
  • today many providers all over the world use GSM
    (more than 200 countries in Asia, Africa, Europe,
    Australia, America)

3
GSM status (end 2006)
2.18 billion connections in 212 countries 82
market share globally An incredible industry
success!
4
GSM The idea of a common European mobile
communications system
  • 1982 A Nordic group is considering the next
    generation of mobile telephone. NMT (Nordisk
    Mobil Telefon), the analogue first generation
    system has only just been started
  • These ideas are presented to CEPT (European
    Conference of Postal and Telecommunications
    Administrations) in June 1982
  • September 1982 The first meeting in CEPT GSM
    Groupe Spécial Mobile
  • In 1988 ETSI (European Telecommunications
    Standards Institute) is established and the work
    is continued under a new name SMG Special
    Mobile Group

5
GSM - Specifications
  • Original specifications for the GSM system
  • Good subjective voice quality
  • Low terminal and service cost
  • Support for international roaming
  • Support for handheld terminals
  • Support for new services
  • Spectrum efficient
  • Compatible with ISDN

6
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7
GSM - Growth
  • 1991 First operational GSM network in Finland
    Radiolinja
  • 1993 Tele-mobil (later Telenor Mobil) and
    NetCom GSM open their networks in Norway
  • 1998 GSM 1800 is deployed to increase capacity
    in cities and other densely populated areas

8
Performance characteristics of GSM (wrt. analog
sys.)
  • Communication
  • mobile, wireless communication support for voice
    and data services
  • Total mobility
  • international access, chip-card enables use of
    access points of different providers
  • Worldwide connectivity
  • one number, the network handles localization
  • High capacity
  • better frequency efficiency, smaller cells, more
    customers per cell
  • High transmission quality
  • high audio quality and reliability for wireless,
    uninterrupted phone calls at higher speeds (e.g.,
    from cars, trains)
  • Security functions
  • access control, authentication via chip-card and
    PIN

9
Disadvantages of GSM
  • There is no perfect system!!
  • no end-to-end encryption of user data
  • no full ISDN bandwidth of 64 kbit/s to the user
  • reduced concentration while driving
  • electromagnetic radiation
  • abuse of private data possible
  • roaming profiles accessible
  • high complexity of the system
  • several incompatibilities within the GSM
    standards

10
Architecture of the GSM system
  • GSM is a PLMN (Public Land Mobile Network)
  • several providers setup mobile networks following
    the GSM standard within each country
  • subsystems
  • RSS (radio subsystem) covers all radio aspects
  • NSS (network and switching subsystem) call
    forwarding, handover, switching
  • OSS (operation subsystem) management of the
    network

11
Ingredients 1 Mobile Phones, PDAs Co.
The visible but smallest part of the network!
12
Some GSM terminals
Development..
Sony Ericsson W950i the Walkman phone
HTC P4350 Pocket computer running Windows
13
Some more GSM terminals
Nokia N95 with everything, e.g. GPS built in
iPhone Apples Mobile phone initiative
Samsung Blackjack
14
Ingredients 2 Antennas
Still visible cause many discussions
15
Ingredients 3 Infrastructure 1
Base Stations
Cabling
Microwave links
16
Ingredients 3 Infrastructure 2
Not visible, but comprise the major part of the
network (also from an investment point of view)
Management
Data bases
Switching units
Monitoring
17
GSM System Architecture
  • Mobile Station (MS)
  • Mobile Equipment (ME)
  • Subscriber Identity Module (SIM)
  • Base Station Subsystem (BSS)
  • Base Transceiver Station (BTS)
  • Base Station Controller (BSC)
  • Network Switching Subsystem(NSS)
  • Mobile Switching Center (MSC)
  • Home Location Register (HLR)
  • Visitor Location Register (VLR)
  • Authentication Center (AUC)
  • Equipment Identity Register (EIR)

18
GSM overview
OMC, EIR, AUC
fixed network
HLR
GMSC
NSS with OSS
VLR
MSC
MSC
VLR
BSC
BSC
RSS
19
A RADIO CELL
20
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21
Location Areas and Base Station SubSystems
22
MSC Areas and Location Areas
23
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24
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25
  • Mobile Station
  • The mobile station (MS) is the starting point of
    a mobile wireless network. The MS can contain the
    following components
  • Mobile terminal (MT)GSM cellular handset
  • Terminal equipment (TE)PC or personal digital
    assistant (PDA)
  • The MS can be two interconnected physical
    devices (MT and TE) with a point-to-point
    interface or a single device with both functions
    integrated.

26
GSM cellular handset
  • GSM cellular handset
  • Mobile equipment (ME) SIM card
  • Subscriber Identity Module (SIM) contains
    encryption key and personal data
  • The user is uniquely identified through
    International Mobile Subscriber Identity (IMSI)
  • The mobile equipment is uniquely identified
    through International Mobile Equipment Identity
    (IMEI)
  • Both equipment and user uniquely identified

GSM cellular handset
27
International Mobile Subscriber Identification
number (IMSI)
It identifies a unique international universal
number of a mobile subscriber, which consists of
MCCMNCMSIN. 1) MCC country code, 460 2)MNC
network code, 00 or 01 3)MSIN subscriber
identification, H1H2H3H4 9XXXXXX, H1H2H3H4
subscriber registering place H1H2 assigned
by the PT Administrative Bureau (operator )to
different provinces, to each province H3H4
assigned by each province/city the IMSI of user
will be written into the SIM card by specific
device and software and be stored into the HLR
with other user information.
28
  • EXAMPLE
  • IMSI 310150123456789
  • MCC 310 USA
  • MNC 150 ATT Mobility
  • MSIN 123456789
  • IMSI 381 01 1234567890 MCC 381 -
    Serbia MNC 01 - Telecom Serbia MSIN
    1234567890 IMSI 310 150 123456789 MCC 310 -
    USA MNC 150 - America Telecom MSIN 123456789

29
  • When registering for service with a mobile
    network operator, each subscriber receives a
    unique identifier, the International Mobile
    Subscriber Identity (IMSI). This IMSI is stored
    in the SIM. A mobile station can only be operated
    if a SIM with a valid IMSI is inserted into
    equipment with a valid IMEI, since this is the
    only way to correctly bill the associated
    subscriber. The IMSI uses a maximum of 15 decimal
    digits and consists of three parts
  • Mobile Country Code (MCC), three digits,
    internationally standardized
  • Mobile Network Code (MNC), two digits, for
    unique identification of mobile networks within a
    country
  • Mobile Subscriber Identification Number (MSIN),
    maximum of 10 digits, identification number of
    the subscriber in their mobile home network.

30
The IMSI is a GSM-specific addressing concept and
is different from the ISDN numbering plan. A
three-digit MCC has been assigned to each of the
GSM countries, and two-digit MNCs have been
assigned within countries (e.g., 262 as MCC for
Germany and MNC 01, 02 and 07 for the networks
of T-Mobile, Vodafone, and O2, respectively).Where
as the MCC is defined internationally, the
National Mobile Subscriber Identity (NMSI MNC
MSIN) is assigned by the operator of the home
network.
31
Mobile subscriber ISDN number
  • The real telephone number of a mobile user is
    called the Mobile Subscriber ISDN Number
    (MSISDN). It is assigned to the subscriber (their
    SIM), such that a mobile station can have several
    MSISDNs depending on the SIM. With this concept,
    GSM was the first mobile system to distinguish
    between subscriber identity and the number to
    call.
  • The separation of call number (MSISDN) and
    subscriber identity (IMSI) primarily serves to
    protect the confidentiality of the IMSI. In
    contrast to the MSISDN, the IMSI need not be made
    public.
  • With this separation, one cannot derive the
    subscriber identity from the MSISDN, unless the
    association of IMSI and MSISDN as stored in the
    HLR has been made public. It is the rule that the
    IMSI used for subscriber identification is not
    known, and thus the faking of a false identity is
    significantly more difficult.

32
International Mobile Equipment Identification
code (IMEI)
It will uniquely identify a mobile station. It is
a decimal number of 15 digits. Its structure
is TACSNA TACtype allocation code, 8
digits SNserial no, 6 digits ACheck Digit, 1
digit
33
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34
Other Addresses
  • Mobile station roaming number
  • The Mobile Station Roaming Number (MSRN) is a
    temporary location-dependent ISDN number. It is
    assigned by the locally responsible VLR to each
    MS in its area. Calls are routed to theMS by
    using the MSRN.
  • Temporary mobile subscriber identity
  • The VLR responsible for the current location of
    a subscriber can assign a TemporaryMobile
    Subscriber Identity (TMSI), which has only local
    significance in the area handled by the VLR. It
    is used in place of the IMSI for the definite
    identification and addressing of the MS.
  • In this way nobody can determine the identity
    of the subscriber by listening to the radio
    channel, since this TMSI is only assigned during
    the presence of the MS in the area of one VLR,

35
  • Base Transceiver Station
  • When a subscriber uses the MS to make a call in
    the network, the MS transmits the call request to
    the base transceiver station (BTS). The BTS
    includes all the radio equipment (i.e., antennas,
    signal processing devices, and amplifiers)
    necessary for radio transmission within a
    geographical area called a cell. The BTS is
    responsible for establishing the link to the MS
    and for modulating and demodulating radio signals
    between the MS and the BTS.

36
Base Station Controller
  • Base Station Controller
  • A Base Station Controller (BSC) is a
    high-capacity switch with radio communication and
    mobility control capabilities. The functions of a
    BSC include radio channel allocation, location
    update, handover, timing advance, power control
    and paging.

37
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38
  • Base Station Subsystem
  • A GSM network is comprised of many base station
    subsystems (BSSs), each controlled by a BSC. The
    BSS performs the necessary functions for
    monitoring radio connections to the MS, coding
    and decoding voice, and rate adaptation to and
    from the wireless network. A BSS can contain
    several BTSs.

39
  • Mobile Switching Center
  • The mobile switching center (MSC) is a digital
    ISDN switch that sets up connections to other
    MSCs and to the BSCs. The MSCs form the wired
    (fixed) backbone of a GSM network and can switch
    calls to the public switched telecommunications
    network (PSTN). An MSC can connect to a large
    number of BSCs.

40
  • The mobile switching center (MSC) performs the
    telephony switching function. A mobile station
    must be attached to a single MSC at a time
    (either homed or visitor), if it is currently
    active (not switched off). The visitor location
    register (VLR) is a database attached to an MSC
    to contain information about its currently
    associated mobile stations.

41
  • Information of currently attached mobile
    stations
  • IMSI/TMSI numbers
  • MSISDN/MSRN numbers
  • Security triple (authentication and encryption
    information)
  • Location Area Identity (where the mobile
    station is currently located)
  • List of base stations that belong to this
    MSC/VLR (by their BSIC or Base Station Identity
    Code)
  • List of location areas that belong to this
    MSC/VLR (by their LAI or Location Area Identity
    code)

42
  • Equipment Identity Register
  • The equipment identity register (EIR) is a
    database that stores the international mobile
    equipment identities (IMEIs) of all the mobile
    stations in the network. The IMEI is an equipment
    identifier assigned
  • by the manufacturer of the mobile station.
    The EIR provides security features such as
    blocking calls from handsets that have been
    stolen.

43
  • Home Location Register
  • The home location register (HLR) is the central
    database for all users to register to the GSM
    network. It stores static information about the
    subscribers such as the international mobile
    subscriber identity
  • (IMSI), subscribed services, and a key for
    authenticating the subscriber. The HLR also
    stores dynamic subscriber information (i.e., the
    current location of the mobile subscriber).

44
  • The home location register (HLR) is a database
    used for storing and managing subscriptions. When
    an individual buys a subscription from one of the
    GSM operators, he or she is registered in the HLR
    of that operator.

45
HLR Data Elements
  • Mobile Stations Identities
  • IMSI (International Mobile Subscriber Identity)
    (the primary Key),
  • Current TMSI (Temporary IMSI)
  • IMEI (International Mobile Equipment Identity)
  • Mobile Stations Telephone number
  • MSISDN (Mobile Stations ISDN number)
  • Current MSRN (Mobile Station Roaming Number),
    if assigned
  • Name and address of the subscriber
  • Current service subscription profile
  • Current location (MSC/VRL address)
  • Authentication and encryption keys
  • Individual Subscriber Authentication Key (KI)
  • Mobile Country Code (MCC) and MNC (Mobile
    Network Code)
  • List of MSC/VLR that belongs to this HLR

46
  • Authentication Center
  • Associated with the HLR is the authentication
    center (AuC) this database contains the
    algorithms for authenticating subscribers and the
    necessary keys for encryption to safeguard the
    user input for authentication.

47
  • Visitor Location Register
  • The visitor location register (VLR) is a
    distributed database that temporarily stores
    information about the mobile stations that are
    active in the geographic area for which the VLR
    is responsible. A VLR is
  • associated with each MSC in the network.
    When a new subscriber roams into a location area,
    the VLR is responsible for copying subscriber
    information from the HLR to its local database.
    This relationship between the VLR and HLR avoids
    frequent HLR database updates and long distance
    signaling of the user information, allowing
    faster access to subscriber information.

48
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49
GSM elements and interfaces
radio cell
BSS
MS
MS
Um
radio cell
MS
RSS
BTS
BTS
Abis
BSC
BSC
A
MSC
MSC
NSS
VLR
VLR
signaling
HLR
ISDN, PSTN
GMSC
PDN
IWF
O
EIR
OSS
OMC
AUC
50
GSM system architecture
radio subsystem
network and switching subsystem
fixed partner networks
MS
MS
ISDN PSTN
Um
MSC
Abis
BTS
BSC
EIR
BTS
SS7
HLR
VLR
BTS
BSC
ISDN PSTN
BTS
MSC
A
IWF
BSS
PSPDN CSPDN
51
System architecture radio subsystem
radio subsystem
network and switching subsystem
MS
MS
  • 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

Um
Abis
BTS
MSC
BSC
BTS
A
BTS
MSC
BSC
BTS
BSS
52
System architecture network and switching
subsystem
network subsystem
fixed partner networks
  • 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 Register)
  • VLR (Visitor Location Register)
  • EIR (Equipment Identity Register)

ISDN PSTN
MSC
EIR
SS7
HLR
VLR
ISDN PSTN
MSC
IWF
PSPDN CSPDN
53
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54
Radio subsystem
  • The Radio Subsystem (RSS) comprises the cellular
    mobile network up to the switching centers
  • Components
  • Base Station Subsystem (BSS)
  • Base Transceiver Station (BTS) radio components
    including sender, receiver, antenna - if directed
    antennas are used one BTS can cover several cells
  • Base Station Controller (BSC) switching between
    BTSs, controlling BTSs, managing of network
    resources, mapping of radio channels (Um) onto
    terrestrial channels (A interface)
  • BSS BSC sum(BTS) interconnection
  • Mobile Stations (MS)

55
Example coverage of GSM networks
(www.gsmworld.com)
T-Mobile (GSM-900/1800) Germany
O2 (GSM-1800) Germany
ATT (GSM-850/1900) USA
Vodacom (GSM-900) South Africa
56
Base Transceiver Station and Base Station
Controller
  • Tasks of a BSS are distributed over BSC and BTS
  • BTS comprises radio specific functions
  • BSC is the switching center for radio channels

57
Network and switching subsystem
  • NSS is the main component of the public mobile
    network GSM
  • switching, mobility management, interconnection
    to other networks, system control
  • Components
  • 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
  • Databases (important scalability, high capacity,
    low delay)
  • 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)
  • Visitor Location Register (VLR) local database
    for a subset of user data, including data about
    all user currently in the domain of the VLR

58
Mobile Services Switching Center
  • 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

59
Operation subsystem
  • The OSS (Operation Subsystem) enables centralized
    operation, management, and maintenance of all GSM
    subsystems
  • Components
  • Authentication Center (AUC)
  • generates user specific authentication parameters
    on request of a VLR
  • authentication parameters used for authentication
    of mobile terminals and encryption of user data
    on the air interface within the GSM system
  • Equipment Identity Register (EIR)
  • registers GSM mobile stations and user rights
  • stolen or malfunctioning mobile stations can be
    locked and sometimes even localized
  • Operation and Maintenance Center (OMC)
  • different control capabilities for the radio
    subsystem and the network subsystem
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