2. TOPICS
TELECOM BASIS
GSM HISTORY
GSM CONCEPT AND STRUCTURE
IDENTITIES USED IN GSM
MOBILITY MANAGEMENT
CALL MANAGEMENT
2
3. TELECOM BASICS
Communication
Voice and Data
Analog and Digital
Circuit Switched and Packet Switched
Media - Copper Wire, Co-axial cable, Air, Optical
Fibre
Networks -PSTN, ISDN, PDN and Mobile
Networks
3
4. BACKGROUND TO GSM
1G : Advanced Mobile Phone Service (AMPS)
Analog, Circuit Switched, FDMA
2G : Digital Advanced Mobile Phone Service (D-AMPS)
Digital, Circuit Switched, FDMA
2G : Global System for Mobile (GSM)
Digital, Circuit Switched, FDMA and TDMA
2G : Code Division Multiple Access (CDMA)
Digital, Circuit Switched, CDMA
4
5. DEVELOPMENT OF THE GSM
STANDARD
5
1982: Groupe Spécial Mobile
(GSM)
created
1984: Description of GSM features
1985: List of recommendations
settled
1987: Initial MoU (Memorandum of
Understanding) aside the
drafting of technical
specifications was signed by
network operators of 13
countries:
1988: Validation and trials, of the
radio interface.
1991: First system trials are
demonstrated at the
Telecom 91 exhibition.
1992: Official commercial launch
of GSM service in Europe.
First Launch in Finland
1993: The GSM-MoU has 62
signatories in 39 countries
worldwide.
1995: Specifications of GSM
phase 2 are frozen.
1999: GSM MoU joins 3GPP
(UMTS) GPRS Trials
begins
2000: 480M GSM Network
operators Worldwide
First GPRS Networks roll
out
End 2002: 792M GSM Net work
Operators
Worldwide
6. INCREASING GSM DATA RATES
Transmission
Time
GPRS = General Packet Radio Service
HSCSD = High Speed Circuit Switched Data
EDGE = Enhanced Data rate for GSM Evolution
UMTS = Universal Mobile Telecommunication System
10 sec 1 min 10 min 1 hour0
UMTS
E/GPRS
ISDN
PSTN
GSM
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7. WIRELESS DATA TECHNOLOGY OPTIONS
7
throughputkbps
10 k
100 k
64 k
1 M
2 M
1 k
1998 1999 2000 2001 2002
Time frame
UMTS
GPRS
HSCSD
9.6
14.4
GPRS = General Packet Radio Service
HSCSD = High Speed Circuit Switched Data
EDGE = Enhanced Data rate for GSM Evolution
UMTS = Universal Mobile Telecommunication System
EDGE
9. GSM CONCEPTS -
CELLULAR STRUCTURE
9
Cellular
Networking technology
that breaks geographic
area into cells shaped
like honey comb
Cell
is the radio coverage
area of one base
transceiver station
1
2
3
4
5
6
7
6
7
2
1
5
10. MULTIPLE ACCESS TECHNIQUE
Multiple Access – Achieved by dividing the available radio
frequency spectrum, so that multiple users can be given
access at the same time.
FDMA - Frequency Division Multiple Access
( eg: GSM each Frequency channel is 200KHz)
TDMA - Time Division Multiple Access
( eg: GSM each frequency channel is divided into 8
timeslots)
CDMA - Code Division Multiple Access
(eg: IS95- Each User data is coded with a unique
code)
10
11. DUPLEX TECHNIQUE
Duplex - How the up link and Down link of a user is
separated
FDD - Frequency Division Duplex
(eg:In GSM the up link and down link of a user is separated by
45MHz )
TDD - Time Division Duplex
(the up link and down link of a user will be at the same
frequency but at different Time )
11
12. 12
GSM IN COMPARISON WITH OTHER
STANDARDS
GSM gives mobility without any loss in Audio quality
Encryption techniques used gives high security in the air
Interface and also use of SIM.
Bit Interleaving for high efficiency in Transmission.
Variable Power (Power budgeting- extend battery life)
Minimum Interference.
Features-CCS7 Signaling
SMS (Short Message Services)
Emergency Calls
CELL Broadcast
13. 13
Time Division Multiple Access
Each carrier frequency subdivided in time domain
into 8 time slots
Each mobile transmits data in a frequency, in its
particular time slot - Burst period = 0.577 milli secs.
8 time slots called a TDMA frame. Period is .577 * 8
= 4.616 milli secs
0 1 2 3 4 5 6 7
4.616 ms
0.577 ms
ACCESS TECHNIQUES ...
16. FROM SPEECH TO RADIO TRANSMISSION
Blah… Blah… Blah...Blah... Blah... Blah...
Digitizing and
Source Coding
Channel Coding
Interleaving
Ciphering
Burst Formatting
Modulating Demodulating
Burst De-formatting
Deciphering
De-interleaving
Channel Decoding
Source Decoding
17. 17
GSM NETWORK
OMC
AUC
HLR
MSC
EIRVLR
BSC
BTS
MS
External
PSTN &
PDN N/W
SS
BSS
Switching
System
Base Station
System
MS Mobile Station
BTS Base transceiver System
BSC Base Station Controller
MSC Mobile Switching Center
HLR Home Location Register
VLR Visitor Location Register
EIR Equipment Identity Register
AUC Authentication Center
OMC Operation And Maintenance Center
18. 18
MOBILE STATION (MS)
Hand portable unit
Contains Mobile Equipment(ME) and
Subscriber Identity Module (SIM)
19. 19
MOBILE EQUIPMENT(ME)
Frequency and Time Synchronization
Voice encoding and transmission
Voice encryption/decryption functions
Power measurements of adjacent cells
Display of short messages
International Mobile Equipment Identifier (IMEI)
20. 20
SIM
Portable Smart Card with memory (ROM-6KB to 16KB-
A3/A8 algorithm, RAM- 128KB TO 256KB, EEPROM- 3KB
to 8KB )
Static Information
International Mobile Subscriber Identity(IMSI)
Personal Identification Number (PIN)
Authentication Key (Ki)
Dynamic Information
Temporary Mobile Subscriber Identity(TMSI)
Location Area Identity (LAI)
Phone memories, billing information
Ability to store Short Messages received
21. 21
BASE STATION CONTROLLER (BSC)
Provides all the control functions and physical links
between the MSC and BTS
External Interfaces
‘Abis’ interface towards the BTS
‘A’ interface towards the MSC
Monitors and controls several BTSs
Management of channels on the radio interface
Alarm Handling from the external interfaces
Performs inter-cell Handover
Switching from ‘Abis’ link to the ‘A’ link
Interface to OMC for BSS Management
22. 22
MOBILE SWITCHING CENTER (MSC)
Performs call switching
Interface of the cellular network to PSTN
Routes calls between PLMN and PSTN
Queries HLR when calls come from PSTN to mobile user
Inter-BSC Handover
Paging
Billing
23. 23
HOME LOCATION REGISTER (HLR)
Stores user data of all Subscribers related to the GMSC
International Mobile Subscriber Identity(IMSI)
Users telephone number (MS ISDN)
Subscription information and services
VLR address
Reference to Authentication center for key (Ki)
Referred when call comes from public land network
24. 24
VISITOR LOCATION REGISTER (VLR)
Database that contains Subscriber
parameters and location information for all
mobile subscribers currently located in the
geographical area controlled by that VLR
Identity of Mobile Subscriber
Copy of subscriber data from HLR
Generates and allocates a Temporary
Mobile Subscriber Identity(TMSI)
Location Area Code
Provides necessary data when mobile
originates call
25. 25
AUTHENTICATION CENTER (AUC)
Stores Subscriber authentication data called Ki, a copy of
which is also stored in in the SIM card
Generates security related parameters to authorize a
subscriber (SRES-Signed RESponse)
Generates unique data pattern called Cipher key (Kc) for
user data encryption
Provides triplets - RAND, SRES & Kc, to the HLR on
request.
26. 26
EIR (EQUIPMENT IDENTITY REGISTER)
EIR is a database that contains a list of all valid
mobile station equipment within the network,
where each mobile station is identified by its
International Mobile Equipment Identity(IMEI).
EIR has three databases.,
White list - For all known,good IMEI’s
Black list - For all bad or stolen handsets
Grey list - For handsets/IMEI’s that are
on observation
27. 28
GSM PROTOCOLS
CM - Connection Management
MM - Mobility Management
RR - Radio resource
LAPDm - LAPD for mobile
LAPD - Link Access Procedure for D channel
BTSM - BTS Management Part
BSSAP - BSS Application Part (BSC - MSC)
DTAP - Direct Transfer Application Part (MS - MSC)
MAP - Mobile Application Part
MTP - Message Transfer part of SS7
SCCP - Signalling Connection Control Part of SS7
TCAP - Transaction Capabilities Application Part
ISUP- ISDN User Part
28. 29
Functional Plane of GSM
MS BTS BSC MSC/ HLR GMSC
VLR
MS BTS BSC MSC/VLR HLR GMSC
CM
MM
RR
Trans
29. 30
SUBSCRIBER IDENTITY -MSISDN
The MSISDN is a GSM directory number which
uniquely identifies a mobile subscription in the Public
Switched Telephone Network (PSTN).
Calls will be routed from the PSTN and other
networks based on the Mobile Subscribers’ MSISDN
number.
MSISDN= CC + NDC + SN
CC= Country Code (91)
NDC= National Destination Code(98370)
SN= Subscriber Number (12345)
30. 31
INTERNATIONAL MOBILE SUBSCRIBER
IDENTITY [IMSI]
Subscriber always identified within the GSM network by the
IMSI
This is used for all signaling in the PLMN stored in SIM and
HLR/VLR
The IMSI consists of three different parts
MCC = Mobile Country Code(3 Digits)
MNC = Mobile Network Code(2 Digits)
MSIN = Mobile Station Identification Number(Upto 10 digits)
31. 32
TEMPORARY MOBILE SUBSCRIBER
IDENTITY [TMSI]
The TMSI is used for the subscriber’s confidentiality.
It should be combined with the LAI to uniquely identify a MS.
Since the TMSI has only local significance (that is, within the
MSC/VLR area), the structure may be chosen by each
administration.
The TMSI should not consist of more than four octets.
32. 33
INTERNATIONAL MOBILE EQUIPMENT
IDENTITY [IMEI]
The IMEI is used for equipment identification. An
IMEI
uniquely identifies a mobile station as a piece or
assembly of equipment.
IMEI = TAC + FAC + SNR + sp
TAC= Type Approval Code (6 digits),determined by GSM
body
FAC= Final Assembly Code (2 digits), identifies
themanufacturer
SNR= Serial Number (6 digits), uniquely identifying all
equipment within each TAC and FAC
sp = Spare for future use (1 digit)
33. 34
TRAFFIC CHANNELS-TCH
TCH carries the voice data.
Two blocks of 57 bits contain voice data in the normal burst.
One TCH is allocated for every active call.
Full rate traffic channel occupies one physical channel(one
TS on a carrier) and carries voice data at 13kbps
Two half rate (6.5kbps) TCHs can share one physical
channel.
34. 35
FRAMES TYPES ON UM INTERFACE
TDMA Frame
8 Time slots (Burst Period)
Length is 4.62 ms(8 * 0.577ms)
26-TDMA Multiframe
26 TDMA Frames (24 TCH, SACCH, Idle)
120 ms (26 * 4.62ms)
51-TDMA Multiframe
26 TDMA Frames (FCCH, SCH, BCCH, SDCCH, CCCH)
235.6 ms (51 * 4.62ms)
35. 36
BTS commands MS at different
distances to use different power levels
so that the power arriving at the BTS’s Rx is
approximately the same for each TS
- Reduce interference
- Longer battery life
POWER CONTROL
36. 37
HANDOVER
Means to continue a call even a mobile crosses
the border of one cell to another
Procedure which made the mobile station really
roam
Handover causes
RxLev (Signal strength , uplink or downlink)
RxQual (BER on data)
O & M intervention
Timing Advance
Traffic or Load balancing
37. 38
HANDOVER TYPES
Internal Handover (Intra-BSS)
Within same base station - intra cell
Between different base stations - inter cell
External Handover (Inter-BSS)
Within same MSC -intra MSC
Between different MSCs - inter-MSC
39. 40
Periodic Measurement
Reports (SACCH)
Periodic Measurement
Reports
HO required
Activate TCH(facch)
with HoRef#
if
1. Check for HO passed
2. Channel avail in new BTS
Acknowledges and
alloctes TCH (facch)
HO cmd with HoRef#
Receives new BTS data(FACCH)
MS tunes into new frequency
and TS and sends HO message to
new BTS (facch)
Periodic Measurement
Reports (SACCH)
HO performed
Release TCH
Cell 1
Cell 2
BSC
BTS 1
BTS 2
Intra BSC handover
40. 41
WIRELESS DATA
98 99 2000 2001
GSM
DATA
HSCSD
GPRS
EDGE
UMTS
SIM
Toolkit
WAP
Data Application
Time
Circuit Switched technology
Packet Switched technology
Technology for Applications
SMS Data: 160 -numeric characters
User Data Rate : 9.6kbps
One time slot over the air interface
High Speed Circuit Switched Data
User Data Rate:14.5kbps
Use multiple timeslots (max=8),
hence max rate = 115.2kbps.
Needs a duplexor in MS for
simultaneous Tx and Rx
Add-on to GSM network :
PCU; Packet Segmentation/re-assembly and scheduling
• Radio channel access control and management
• Transmission error detection and retransmission.
• Power control
SGSN: GPRS mobility
• Encryption
• Charging
GGSN : Interface to the PDN, Internet
Max user data rate : 21.4 kbps
Dynamic rate adaptation to suit the radio conditions at
that time ( 9.05 kbps, 13.4 kbps, 15.6 kbps 21.4 kbps)
W@P Gateway W@P Service
W
@
P
F
o
n
e
Internet
Mobile Network
Surf the Internet while on the move
W@P Gateway :
• Adaptation of the information to the mo
• Compression of the data
• Buffering of the information
Enhanced Data rate for GSM Evolution
• EDGE is an enhancement of GPRS and CSD
technologies.
• Based on the current GSM technology - same TDMA
frame structure, same bandwidth (200 kHz).
• Uses 8-PSK modulation instead of GMSK.
• Requires good propagation conditions.
• Allows upto 48 kbps (EGPRS) and upto 28.8 kbps
(ECSD) on every radio channel
• EDGE helps GSM-Only operators to compete with
UMTS.
Universal Mobile Telecommunication Standards
• Innovative Service Architecture : VHE Concept - providing
the us
the same look and feel of its personalized services
independent of network and terminal.
• Global Convergence : Fixed/Mobile, Telecom/Datacom,
public/private
• Mobile Multimedia driven market.
• Wideband bearers - 2GHz band ( 5 MHz per carrier), -
max. 2Mbps