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?
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
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
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
GSM in INDIA
Bharti
BSNL
Reliance infocom
Hutch
Idea
Reliance GSM
Tata indicom
Others
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%
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
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
Performance characteristics of GSM
Communication
Total mobility
Worldwide connectivity
High capacity
High transmission quality
Security functions
Greater QOS
The Cell
Cellular Radio involves dividing a large service area
into regions called “cells.”
BTS
BTS
BTS
BTS
BTS
BTS
BTS
Cell Size:
LARGE CELL(35 Km)
SMALL CELL(1 Km)
Frequency & ARFCNu
l= 8
90 t
o 9
15 M
Hz
dl=
935
to
960
MH
z
Ful(n) = 890.0 + (0.2) *n MHz
Fdl(n) = Ful + 45 MHz
where n =ARFCN ; 1 n 124
Tele Services
Telecommunication services that enable voice communication via mobile phones
Offered services
- Mobile telephony
- Emergency calling
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
Supplementary Services
Call related services :
o Call Waiting- Notification of an incoming call while on the handset
oCall Hold- Put a caller on hold to take another call
oCall Barring- All calls, outgoing calls, or incoming calls
oCall Forwarding- Calls can be sent to various numbers defined by the user
oMulti Party Call Conferencing - Link multiple calls together
oCLIP – Caller line identification presentation
oCLIR – Caller line identification restriction
oCUG – Closed user group
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)
Mobile Station
Mobile Station consist of two units
1)Mobile handset
2) SIM(Subscriber Identity Module)
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
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/ SP
TAC = 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)
SIM stands for "Subscriber Identification Module"
SIM cards are small ‘smart’ cards that fit inside phones based on GSM technology.
SIM
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)
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)
IMSI
The 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)
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 IMSI
reduces 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
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
BSC
TCBTS
BTS
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
A BTS in general has the following units:
Transceiver (TRX)
Power unit
Combiner
Duplexer
Antenna
Alarm extension system
Transmission unit
Baseband receiver unit (BBxx)
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
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
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
Transcoder and Sub multiplexer
TC
64 kbps
16 (13+3) kbps
13 kbps16 kbps (90 Channels)
16 kbps
TCSM
MSC
BTS
BSC
SMUX
TC
TC
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)
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)
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.
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)
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:
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
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.
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
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
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
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
0 1 2 3 4 5 6 7
3
Tail
bit
s
57
Coded
data
1
Steal
ing
bit
26
midambl
e
1
Steal
ing
bit
57
Code
d
data
3
Tail
bits
8.25
Guar
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
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
GSM Channel
Physical Logical
Common Dedicated
SCHFCCH BCCH SDCCH
BroadcastCommon control
Dedicated control
Traffic
SACCH FACCH
RACHPCH AGCH TCH/HTCH/FTCH/EFR
PSTNcallingstation
GMSC
HLR VLR
BSSBSSBSS
MSC
MS
1 2
3
4
5
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
PSTN GMSC
VLR
BSS
MSC
MS1
2
6 5
3 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
Handover
What is the purpose of HO?
What is the purpose of HO?
Call continuityCall quality
Others...
Call continuityCall quality
Others...
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
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