it802 d mobilecommunicationspart3
DESCRIPTION
Details of GSM system architecture and subsystemsTRANSCRIPT
IT 802DMobile Communications
Part 3Debasis Das
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GSMGSM 900
890-915 uplink, 935-960 downlinkGSM 1800 (DCS 1800)
1700-1785 uplink, 1805-1880 downlinkGSM 1900 (PCS 1900)
1850-1910 uplink, 1930-1990 downlink
GSM 400450.4-457.6/478.8-486 uplink, 460.4-
467.6/488.8-496 for downlinkGSM Rail
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Mobile ServicesBearer Services
Tele services
Supplementary Services
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Services
TE
MT
GSMPLM
N
Transit networ
k
Source/Destination Network
TE
R,S UmU,S,R
Bearer Services
Tele Services
MS
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Services Stacks
Application
Presentation
Session
Transport
Network
DLC
Physical
Bearer ServicesAll services that EnableTransparent Transmission ofData(connection Oriented, circuit Switched.
Tele servicesEnd to end
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Bearer ServicesTransparent
Uses functions of the physical layer only. Data transmission has constant delay and throughput if no errors occur. FEC is possible. Depending on FEC 2.4, 4.8 or 9.6 kbps speeds are supported, no lost data recovery due to shadowing or handover
Non-transparentUses protocols of layer 2 & 3 to implement error
correction & flow control, A radio link protocol or RLP(similar to HDLC) is used, error rates 10^-7 is possible, but delays could be variable
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Bear ServicesSeveral bearer services are specified that use
transparent and non transparent services
PSTN, ISDN and PSPDN (X.25) are used for
internetworking
Data transmission can be full duplex 1.2, 2.4, 4.8 and
9.6 kbps and asynchronous full duplex 300 to 9.6 kbps
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Tele ServicesMainly voice oriented
Encrypted voice, message services, Emergency number, highest priority, to nearest
emergency centerSMS, up to 160 characters, uses unused
capacity of the signaling channels, all kinds of content, updating of software
EMS(760 characters) and MMS(video clips, images)
Group 3 Fax
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Supplementary Services
May vary with provider
User id, call redirection, call forwarding
Closed user group, multi party
communication
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System Architecture
Radio subsystem(RSS)
Network and switching subsystem(NSS)
Operation subsystem(OSS)
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System ArchitectureOMCAUC
BTS
MSC
BSC
MSC
GMSC
BSC IWF
BTS
EIR
VLR
HLR
VLR
MSBSS
ISDNPSTN
Signaling
PDN
OSS
NSS
RSS
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Radio Subsystem(RSS)Radio specific entities
Mobile stationBase station subsystem(BSS)“A” interface connects the RSS to NSS“O” interface for connection to OSSA interface is circuit switched, PCM 30 systems30x 64 kbps connectionsO interface is SS7, management data to/fro
RSS
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Base Station SubsystemA base station controller controls(BSC)
multiple base station subsystems(BSS)BSS contains several base transceiver
stations(BTS)All functions required to maintain radio
communication to MS is carried out by BSSCoding/decoding of voice, rate adaptation
to/fro wireless network part, etc.
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Base Transceiver StationsBTS contains all radio equipmentAntenna, signal processing, amplifiersConnects to MS through a Um interface.
The ISDN U interface for mobile useConnects to BSC through Abis interfaceUm contains all the mechanisms for
wireless transmission such as TDMA, FDMA etc.
The Abis interface contains 16 or 64 kbps connections
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BTS & BSC FunctionsFunction BTS BSC
Management of radio channels yes
Frequency hopping Yes yes
Management terrestrial channels yes
Mapping of terrestrial onto radio channels yes
Channel coding & decoding yes
Rate adaptation yes
Encryption and decryption yes yes
Paging yes yes
Uplink signal management yes
Traffic management yes
Authentication yes
Location registry, location update yes
Handover management yes
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Mobile Station(MS)All user equipment and software needed for communicationHardware, software , subscriber identity module(SIM), stores
user specific data relevant to GSMSIM contains an International mobile equipment
identity(IMEI)Usually contains card type, serial number, ,subscribed
services, PIN, PIN unblocking key, authentication key ki, international mobile subscriber identity(IMSI)
Dynamic information when logged into GSM system, such as cipher key Kc and TMSI or temporary mobile subscriber identity(TMSI) and location area identification(LAI) are stored
The MS can have many other interfaces and vendor specific features.
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Network & Switching Subsystem(NSS)Connects RSS with standard public networksPerforms handovers between different BSSsHas functions for localization of usersSupports charging, accounting, and roaming
of users between different providers in different countries
Subsystems includeMobile services switching center(MSC)Home location register(HLR)Visitor location register(VLR)
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MSCThe fixed backbone network nodes. Connections to other MSCs and BSCs are set
up through theseManages several BSC in a particular
geographic locationA gateway MSC(GMSC) has connections to
other public networks such as PSTN, ISDNCan also connect to public data
networks(PDN) through inter working functions (IWF)
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More on MSCUses the standard signaling system 7 or the
SS7 for all aspects of control signaling for digital networks that includesReliable routing and delivery of control messages
for establishing and monitoring of callsSS7 provides
Number portability, free phone, tool/collect calls, credit calls, call forwarding, 3-way calling etc.
MSC also provides functionality for supplementary services like call forwarding, multi-party calls, reverse charging etc.
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Home Location register(HLR)Database for all user relevant data
Static information like mobile subscriber ISDN number(MSISDN), services subscribed and IMSI
Dynamic information like current location area(LA), mobile subscriber roaming number(MSRN), current VLR and MSC, when a MS leaves LA, the info is updated
Only one set of user home information is maintained in for any user for any user worldwide
Some information may need to meet real time criteria
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Visitor Location Register(VLR)Dynamic database for relevant information
for the MS user in LA associated with the
MSC
Typically, MSISDN, IMSI, HLR address etc.
VLR copies the information from the HLR
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Operation Subsystem(OSS)Consists of the following subsystems
Operation and maintenance center(OMC)
Authentication center (AuC)
Equipment identity center(EIR)
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OMCMonitors and controls all other entities via O
interface (SS7 & X.25). Typical functions include
Traffic monitoring, status reports, subscriber and
security management, accounting and billing
Uses “telecommunication management network”
as standardized by ITU-T
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Authentication center(AuC)Contains algorithms for authentication, as
well as keys for encryption and generates the
values needed for user authentication in HLR
AuC may actually be located in a special
protected part of HLR