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Presentation on: . GSM BASICS. Presented by: Sandip Thakkar Saurabh Gandhi. Fixed line telephones. What are the drawbacks ?. No mobility Delay in new connections Security Hazards Prone to failures (line disconnection, etc) Very less value added services . What is GSM?. - PowerPoint PPT PresentationTRANSCRIPT
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Presentation on:
GSM BASICS
Presented by:Sandip ThakkarSaurabh Gandhi
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Fixed line telephonesWhat are the drawbacks ?
• No mobility
• Delay in new connections
• Security Hazards
• Prone to failures (line disconnection, etc)
• Very less value added services
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What is GSM?
Global system for Mobile communication
Standard defined by ETSI (European Telecommunications Standards Institute)
Global System for Mobile (GSM) is a second generation cellular standard developed to cater voice services and data delivery using digital modulation
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GSM: History
1982 CEPT initiated a new cellular system (GSM) in the 900 Mhz band.
1986 CEPT tested 8 experimental systems in Paris.
1987 MoU of allocations of frequencies.(uplink and downlink)
1991 First official call in the world with GSM on 1st July.
1992 New freq. allocation for GSM 1800.
1995 There were 117 GSM networks operating around the world.
2006 >1300 miilion subscribers in the world & >45 millions subscribers in india.
Aim : to replace the incompatible analog system
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Evolution
1G 3G2G+
2G
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GSM in world Arab world
Asia pacific
Africa
East central asia
Europe
Russia
India
North amer-ica
South amer-ica
43%
37%
4%
3%
3%
3%4% 3%3%
1%
INDIA
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GSM in INDIA
BhartiBSNLReliance infocomHutchIdeaReliance GSMTata indicomOthers
21.91%BHARTI
19.2%BSNL
17.24%Relianceinfocom
18.04%Others
5.43%Tata
10.11%HUTCH
Reliance GSM
5.973%Idea
2.075%
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GSM Specifications-1
RF Spectrum
GSM 900 Mobile to BTS (uplink): 890-915 Mhz BTS to Mobile(downlink):935-960 Mhz Bandwidth : 2* 25 Mhz
GSM 1800 Mobile to BTS (uplink): 1710-1785 Mhz BTS to Mobile(downlink): 1805-1880 Mhz Bandwidth : 2* 75 Mhz
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GSM-900 System Specifications
Frequency Range : 890 MHz to 915 MHz for Uplink 935 MHz to 960 MHz for Downlink. Uses TDMA technology for Downlink / Uplink. 124 Reusable Spot frequencies of 200 kHz bandwidth each. Each Spot Frequency carries 8 Time slots for Traffic/Signalling. Compatible to ISDN & PSPDN. Modulation Method : GMSK
Modulation data rate : 270.833 Kbps
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Performance characteristics of GSM Communication
Total mobility
Worldwide connectivity
High capacity
High transmission quality
Security functions
Greater QOS
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CONSIDERATIONS
FREQUENCY
CAPACITY
COVERAGE
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The CellCellular Radio involves dividing a large service area into regions called “cells.”
BTSBTS
BTS
BTS
BTSBTS
BTS
Cell Size:
LARGE CELL(35 Km)
SMALL CELL(1 Km)
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Frequency & ARFCNul
= 8 9
0 to
915
MH
z
dl=
9 35
to 9
60 M
Hz
Ful(n) = 890.0 + (0.2) *n MHz
Fdl(n) = Ful + 45 MHz
where n =ARFCN ; 1 n 124
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GSM Services
Tele-services Bearer or Data Services Supplementary services
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Tele Services
Telecommunication services that enable voice communication via mobile phones
Offered services - Mobile telephony - Emergency calling
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Bearer Services
Include various data services for information transfer between GSM and other networks like PSTN, ISDN etc at rates from 300 to 9600 bps
Short Message Service (SMS) up to 160 character alphanumeric data transmission to/from the mobile terminal
Unified Messaging Services(UMS)
Voice mailbox
Electronic mail
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Supplementary ServicesCall related services :
o Call Waiting- Notification of an incoming call while on the handsetoCall Hold- Put a caller on hold to take another calloCall Barring- All calls, outgoing calls, or incoming callsoCall Forwarding- Calls can be sent to various numbers defined by the useroMulti Party Call Conferencing - Link multiple calls togetheroCLIP – Caller line identification presentationoCLIR – Caller line identification restrictionoCUG – Closed user group
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GSM System Architecture
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BSC
BSC
MSC
MS
MS
MS BTS
BTS
BTS
GMSC
PSTNISDNPDN
EIRAUC
HLR
VLR
OMC
SMSC
VMSC
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GSM System Architecture-I
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)
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Mobile Station Mobile Station consist of two units
1)Mobile handset
2) SIM(Subscriber Identity Module)
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Mobile Station (MS)
A Typical Handset Consists of the following parts:
• A microscopic microphone, A speaker, An LCD or plasma display, A mini keyboard, An Antenna, A battery, A Circuit board, SIM
MS is the radio mobile terminal carried by the subscriber
MS consists of User independent HW and SWSIM (Subscriber Identity Module)
MS can be identified by IMEI (Intl Mobile Equipment Identity)
MSs have transmit power of 2W and 1W
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IMEI
The Mobile Equipment is identified inside any GSM network by the International Mobile Equipment Identity (IMEI)
The IMEI is a 15-digit number
IMEI = TAC/ FAC/ SNR/ SPTAC = Type Approval Code, determined by the main body of the GSM (6 digits)FAC = Final Assembly Code, identifies the maker (2 digits)SNR = Serial Number (6 digits)SP = A spare supplementary number (1digit)
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SIM stands for "Subscriber Identification Module"
SIM cards are small ‘smart’ cards that fit inside phones based on GSM technology.
SIM
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SIM Uniquely associated to a user
Not to an equipment, as in first generation cellular networks Stores user addresses
IMSI MSISDN Temporary addresses for location, roaming, etc
Authentication and encryption featuresAll security features of GSM are stored in the SIM for max. protection
subscriber’s secret authentication key (Ki) Authentication algorithm (“secret” algorithm - A3 – not unique) Cipher key generation algorithm (A8)
Personalization SIM stores user profile (subscribed services) RAM available for SMS, short numbers, user’s directory, etc
Protection codes PIN (Personal Identification Number, 4-8 digits) PUK (PIN Unblocking Key, 8 digits)
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MSISDN (Mobile Subscriber ISDN Number)
MSISDN: the “usual” telephone numberStructure:
CC/NDC/SN
CC : Country Code(up to 3 digits)NDC : National Destination Code (3 digits ,for PLMN)SN : Subscriber Number (max 10 digits)
IMSIThe IMSI has the following:
MCC / MNC / MSIN where MCC: Mobile Country Code (2 or 3 digits, 404 for INDIA) MNC: Mobile Network Code (2 digits) MSIN: Mobile Station Identification Number (max 13 digits)
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Temporary addresses
TMSI – Temporary Mobile Subscriber
Identity
32 bits assigned by VLR within an administrative area
has significance only in this area
transmitted on the radio interface instead of IMSIreduces problem of“eavesdropping”
MSRN –Mobile Station Roaming
Number
An MSISDN number• CC, NDC of the visited
network• SN assigned by VLR
Used to route calls to a roaming MSSubscriber Number (SN)assigned to provide routinginformation towards actuallyresponsible
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Base Station Subsystem (BSS)
Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing operation between components made by different suppliers
1. Base Transceiver Station (BTS)2. Base Station Controller (BSC)
BTS
TCBSC
BSCTC
BTS
BTS
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Base Transceiver Station (BTS):SHELTER +Transmission Medium +TOWER
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BTS has a set of Transceivers to talk to MS.
One BTS covers one or more than one cell.
Capacity of BTS depends on no of Transceivers. BTS is connected to BSC via A’bis interface.
Transmission rate on A’bis is 2 Mbps (G.703).
Interface between MS & BTS is called Air I/f.
Transmission rate on Air interface is 13 Kbps.
BTS controls RF parameters of MS.
Each TRx has 8 TDMA channels to carry Voice & signalling
BTS
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A BTS in general has the following units:Transceiver (TRX)
Power unit
Combiner
Duplexer
Antenna
Alarm extension system
Transmission unit
Baseband receiver unit (BBxx)
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Nokia BTS’s
Nokia ultrasite
Nokia metrosite
Nokia flexisite
1-12 1-4 1-24 TRx capacity
Max Tx power(dBm
) 43
30
49.5
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Base Station Controller (BSC)
• BSC controls several BTSs.
• BSC manages channel allocation, & Handover of calls from one BTS to another BTS.
• BSC is connected to MSC via A interface.
• Transmission rate on A I/f is 2 Mbps (G.703).
• Interface between BSC & BTS is called A’bis I/f.
• BSC has database for all of its BTS’s parameters.• BSC provides path from MS to MSC.
1 BSC may control up to 40 BTS
BSC
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BTS & BSC Tasks of a BSS are distributed over BSC and BTS
Functions BTS BSCManagement of radio channels XFrequency hopping (FH) X XManagement of terrestrial channels XMapping of terrestrial onto radio channels XChannel coding and decoding XRate adaptation XEncryption and decryption X XPaging X XUplink signal measurements XTraffic measurement XAuthentication XLocation registry, location update XHandover management X
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Transcoder and Sub multiplexer
TC
64 kbps
16 (13+3) kbps
13 kbps16 kbps (90 Channels)16 kbps
TCSM
MSC
BTSBSC
SMUX
TC
TC
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Taking care of speech transcoding,
For transmission over the air interface, the speech signal is compressed by the mobile station to
13Kbits/s (Full Rate) or 5.6Kbits/s (Half Rate).
TCSM incorporates the transcoder and the sub-multiplexer into one piece of hardware.
Minimum possible PCM line: 4 Maximum (half rate channel): 7
TC enable also (DTx=discontinous transmssion)
In NOKIA =TCSM2E(European version) or TCSM2A(American version)
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Network Switching Sub-System (NSS)
Elements:Mobile Switching Center (MSC) / Gateway MSC (GMSC)Home Location Register (HLR ) / Authentication Center (AuC)Visitor Location Register (VLR)Equipment Identity Register (EIR)
Functions:Call controlUser management
Inter-component communication:Via SS7 signalling networkWith suitable extensions (e.g. MAP – Mobile Application
Part)
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Mobile Switching Center (MSC) Heart of the network Manages communication between GSM and other
networks Call setup function and basic switching Call routing Billing information and collection Mobility management
- Registration- Location Updating- Inter BSS and inter MSC call handoff
MSC does gateway function while its customer roams to other network by using HLR/VLR.
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database per operator (PLMN)
HLR entries: Every user / MSISDN that has subscribed to the operator
Stores: Permanent information associated to the user
• IMSI, MSISDN• Services subscribed• Service restrictions (e.g. roaming
restrictions)• Parameters for additional services• info about user equipment (IMEI)• Authentication data
Temporary information associated to the user
• Link to current location of the user:
• Current VLR address (if avail)• Current MSC address (if avail)• MSRN (if user outside PLMN)
Home location register (HLR)
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Subscriber and subscription data
IMSI, MSISDN Parameters for additional
services info about user equipment
(IMEI) Authentication data
Tracking & routing information
Mobile Station Roaming No(MSRN) Temporary Mobile Station Identity Location Area Identity (LAI) where
MS has registered Used for paging and call setup
Visitor Location Register (VLR)
At most 1 database per MSC
VLR entries:Every user / MSISDN actually staying in the administrative area of
the associated MSC
Entry created when an MS enters the MSC area (registration)
NOTE: may store data for roaming users (subscribed to different operators)
Stores:
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Authentication Centre (AUC)
HLR
MSC
Authentication is a process to verify the subscriber SIM. Secret data & verification algorithm are stored in to the
AUC. AUC & HLR combined to authenticate the subscribers. Subscriber authentication can be done on every call, if required.
AUC
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Equipment Identity Register (EIR)
EIR
MSC
All subscriber's mobile handset data is stored in EIR. MSC asks mobile to send it IMEI & then checks it with data available in EIR. EIR has different classification for mobile handset like, White list, Grey list & Black list. According to category the MS can make calls or can be stopped from making calls.
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VMSC & SMSC
MSC
SMSC VMSC
Voice Mail Service Centre : To provide Voice Mail service. It has database for all the VMS subscribers & also stores voice messages for them. Short Message Service Centre : To provide text message service. To send short messages from mobile to another mobile subscriber.
Messages can also be sent by Manual Terminal connected to SMSC.0
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OMC All the network elements are connected to OMC.
OMC monitors health of all network elements & carry out maintenance operation, if required.
OMC link to BTSs are via parent BSC.
OMC keeps records of all the faults occurred.
OMC can also do Traffic analysis.
OMC may prepares MIS Report for the network.
OMC
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GSM Terrestrial Interfaces
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Broadly classified into two types of interfaces -
Standard Interfaces
2 Mbps Trunks (E1)
Signalling System No. 7 SS7 ( CCS7)
X.25 (Packet Switched Mode)
GSM Interfaces
Air interface: MS-BTS Abis interface: BTS-
BSC Ater interface: BSC-
TCSM A interface: TCSM-MSC Gb interface: MSC-
SGSN X.25(protocol): MSC-
DCN
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GSM Operation
Speech decoding
Channel decoding
De-interleaving
Burst Formatting
De-ciphering
DemodulationModulation
Ciphering
Burst Formatting
Interleaving
Channel Coding
Speech coding
Radio Interface
Speech Speech
13 Kbps
22.8 Kbps
22.8 Kbps
33.6 Kbps
33.6 Kbps
270.83 Kbps
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GSM Framing
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0 1 2 3 4 5 6 7
3Tail bits
57Coded data
1Stealing bit
26midambl
e
1Stealing bit
57Code
d data
3Tail bits
8.25Guar
d perio
d
120 ms
4.615 ms
6.12 ms
576.92 micro sec
51 Multiframes
26 frames
8 time slots
Superframe
Multiframe
Frame
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Multiple access TechniquesIn
GSM
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FDD / TDMA
In GSM FDD/TDMA is used.
f
c
t
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FDD is used to separate downlink and uplink.
GSM TDMA System:In TDMA one radio freq. channel is devides into consecutive periods of time.
124 traffic channels * 8 slots/Ch = 992 simultaneous conversations
13 kbps coding data rate
Each TDMA frame contain 8 shorter periods of time
known as Time slots.
TDMA time slots are called physical channel
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GSM Channels
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GSM Channel
Physical Logical
Common Dedicated
SCHFCCH BCCH SDCCH
Broadcast Common control
Dedicated control Traffic
SACCH FACCH
RACHPCH AGCH TCH/HTCH/F TCH/EFR
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Incoming Call &
Outgoing Call
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PSTNcallingstation GMSC
HLR VLR
BSSBSSBSS
MSC
MS
1 2
3
45
6
7
8 9
10
11 12
1316
10 10
11 11
11
14 15
17
1: Calling a GSM subscriber2: Forwarding call to GMSC3: Signal call setup to HLR4, 5: Request MSRN from VLR6: Forward responsible MSC to GMSC7: Forward call to current MSC8, 9: Get current status of MS10, 11: Paging of MS12, 13: MS answers14, 15: Security checks16, 17: Set up connection
Incoming Call
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PSTN GMSC
VLR
BSS
MSC
MS1
2
6 53 4
9
10
7 8
1. MS sends dialled number to BSS 2. BSS sends dialled number to MSC3,4 MSC checks VLR if MS is
allowed the requested service.If so,MSC asks BSS to allocate resources for call.
5 MSC routes the call to GMSC6 GMSC routes the call to local
exchange of called user7, 8,9,10 Answer back(ring back) tone is
routed from called user to MS via GMSC,MSC,BSS
Outgoing C all
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Handover
What is the purpose of HO?
Call continuityCall quality
Others...
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Reasons:
Handover due to traffic reasons
Handover due to Signal quality and strength
Four Possible Handover Scenarios:
Intra-cell handover
Inter-cell, intra-BSC handover
Inter-BSC, intra-MSC handover
Inter MSC handover
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HandoversHard Handoff
Analog, TDMA and GSM
Soft HandoffCDMA
Break before Make Make before Break
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GSMData
HSCSD
GPRS
EDGEEGPRS
WCDMA
1998 1999 2003
WCDMAPhase I
Time
Evolution
14.4 kbps
14.4 – 57.6 kbps
64 ~ 170 kbps
384 kbps
144 - 384 kbps
384 - 2048 kbps
2002 2004 2005
Technology UpgradationThe Evolutionary Path
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Thanking You……