45+45+

1. GSM
Global System
for Mobiles
1

2. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
2

3. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
3

4. 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
4

5. Background to GSM
• 1G : Advanced Mobile Phone Service (AMPS)
• Analog, Circuit Switched, FDMA, FDD
• 2G : Digital Advanced Mobile Phone Service (D-AMPS)
• Digital, Circuit Switched, FDMA, FDD
• 2G : Global System for Mobile (GSM)
• Digital, Circuit Switched, FDMA and TDMA, FDD
• 2G : Code Division Multiple Access (CDMA)
• Digital, Circuit Switched, FDMA, SS, FDD
5

6. GSM History
6

7. Development of the GSM Standard
1982: Groupe Spécial Mobile (GSM) 1992: Official commercial launch of
created GSM service in Europe. First
Launch in Finland
1984: Description of GSM features
1993: The GSM-MoU has 62
signatories in 39 countries
1985: List of recommendations settled worldwide.
1987: Initial MoU (Memorandum of 1995: Specifications of GSM phase 2
Understanding) aside the drafting are frozen.
of technical specifications was
signed by network operators of 13 1999: GSM MoU joins 3GPP (UMTS)
countries: GPRS Trials begins
1988: Validation and trials, of the radio
2000: 480M GSM subscribers
interface.
Worldwide
First GPRS Networks roll out
1991: First system trials are
demonstrated at the Telecom 91 End 2002: 792M GSM subscribers
exhibition. Worldwide
7

8. GSM Specifications
01 SERIES
12 SERIES GENERAL 02 SERIES
OPERATION AND
MAINTENANCE SERVICE ASPECTS
11 SERIES 03 SERIES
EQUIPMENT AND TYPE NETWORK ASPECTS
APPROVAL SPECIFICATIONS
10 SERIES 04 SERIES
SERVICE INTERWORKING MS-BSS INTERFACE AND
PROTOCOLS
09 SERIES 05 SERIES
NETWORK PHYSICAL LAYER ON THE
INTERWORKING RADIO PATH.
08 SERIES 06 SERIES
BSS TO MSC INTERFACES 07 SERIES SPEECH CODING
TERMINAL ADAPTERS SPECIFICATIONS
FOR MOBILE STATIONS

9. Increasing GSM Data Rates
video
UMTS photo report clip
video
E/GPRS web photo report clip
video
ISDN e-mail web photo report clip
video
PSTN e-mail web photo report clip
video
GSM e-mail web photo report clip
0 10 sec 1 min 10 min 1 hour
GPRS = General Packet Radio Service
Transmission HSCSD = High Speed Circuit Switched Data
EDGE = Enhanced Data rate for GSM Evolution
Time UMTS = Universal Mobile Telecommunication System

10. Wireless Data Technology Options
2M
1M
ket
throughput kbps
p ac
it
rcu
100 k EDGE
64 k ci HSCSD
UMTS
14.4
10 k GPRS
9.6
Time frame
1k
1998 1999 2000 2001 2002
GPRS = General Packet Radio Service
HSCSD = High Speed Circuit Switched Data
EDGE = Enhanced Data rate for GSM Evolution
UMTS = Universal Mobile Telecommunication System
10

11. Circuit-Switched or Packet-Switched
Circuit mode
Packet mode A
→F
A
F
B →F
A
C →H
→G
D
A
CF
→G
C
D
AH
F
→G
C →G
→H
C
D
AF →G
C
G
D →H
D →H
D
H
E
11

12. 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) 12

13. 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 )
13

14. GSM Concepts -
Cellular Structure
2
2 7 Cellular
7 3 1 Networking technology
1 6 that breaks geographic
6 4 5 area into cells shaped
5 like honey comb
Cell
is the radio coverage
area of one base
transceiver station
14

15. What are the types in
GSM Network?
• GSM-900 (Channels 125 operating band 900Mhz
carrier spacing 200khz spacing 45Mhz)
• GSM -1800 (Channels 374 spacing 95Mhz)
• GSM -1900(Used in USA)
15

16. GSM Band Allocations (MHz)
Duplex Duplex
GSM systems Uplink Downlink Band
Spacing channels
GSM 450 450.4-457.6 460.4-467.6 2x7.2 10 35
GSM 480 478.8-486 488.8-496 2x7.2 10 35
GSM 850 824-849 869-894 2x25 45 124
GSM 900 890-915 935-960 2x25 45 124
E-GSM (900) 880-915 925-960 2x35 45 174
R-GSM (900) 876-880 921-925 2x04 41 40
GSM 1800 1710-1785 1805-1880 2x75 95 374
GSM 1900 1850-1910 1930-1990 2x60 80 299
Frequencies are in MHz
Carrier frequency = ARFCN = Absolute Radio Frequency Channel Number

17. GSM Family Radio Band Spectrum
Uplink 450.4 457.6 478.8 486 824 849
GSM 450 GSM 480 GSM 850
Downlink 460.4 467.6 488.8 496 869 894 MHz
915
Uplink
915
876 880 890 915 1710 1785 1850 1910
P-GSM
E-GSM GSM 1800 GSM 1900
R-GSM
921 925 935 960 1805 1880 1930 1990
960 MHz
Downlink
960

18. Traffic/Signaling
Traffic
«bla bla bla...»
Signaling « RING ! »
riiiiing
Network

19. MS
GSM - Network Structure
Um
BTS VLR HLR
BSC
Abis MSC
A B H
MS C AuC
BTS GMSC
E F
Abis
EIR
A E
MSC
BSC PSTN
Um
BTS X.25
VLR
X.25
OMC Server
19

20. GSM System specifications
Frequency band
Uplink 890 - 915 MHz
Downlink 935 - 960MHz
Duplex Frequency Spacing 45MHz
Carrier separation 200KHz
Frequency Channels 124
Time Slots /Frame(Full Rate) 8
Voice Coder Bit Rate 13Kbps
Modulation GMSK
Air transmission rate 270.833333 Kbps
Access method FDMA/TDMA
Speech Coder RPE-LTP-LPC
20

21. Paired Radio Channels in GSM
Case of GSM 900
Uplink Downlink BTS
890 MHz Frequency 915 MHz 935 MHz Frequency 960 MHz
0 channel # 124 0 channel # 124
Example:
Channel 48
Duplex spacing = 45 MHz
Frequency band spectrum = 2 x 25 MHz
Channel spacing = 200 kHz
21

22. GSM Time Division Multiplex
Frame and Physical Channels
Time-slot TDMA frame TDMA frame
TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
(frames repeat continuously)
Time
0 4.615 ms 9.23 ms
Physical channel # 2 = recurrence of time-slot # 2

23. Physical Channel
BTS
BTS time Without FH
With FH
n+1
TDMAs
7
n TS
0
n-1 MS1
MS2
MS3
1 //
FDMA 2 124 ARFCN

24. Radio Link Aspects
• From Speech to RF Signal
Blah... Blah... Blah... Blah… Blah… Blah...
Digitizing and
Source Decoding
Source Coding
Channel Coding Channel Decoding
Interleaving De-interleaving
Ciphering Deciphering
Burst Formatting Burst De-formatting
Modulating Demodulating

25. Functions of the Radio Interface
• Speech and user's data Communication
Idle mode • Signaling mode
BTS
BTS-1 BTS-2

26. Access Techniques
Uplink 890 MHz to 915 MHz
Down Link 935 MHz to 960 MHz
25 MHz divided into 125 channels of 200 KHz
bandwidth
UP 890.0 890.2 890.4 914.8 915.0
DOWN 935.0 935.2 935.4 959.8 960.0
26

27. Access Techniques ...
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
0.577 ms
0 1 2 3 4 5 6 7
4.616 ms 27

28. 28

29. Fundamentals
960 MHz
959.8MHz 124 TS: Time slot
123
DOWNLINK ……. GSM utilizes two bands(TDMAMHz. 890-915
Downlink of 25 frame) = 8 TS
…… MHz band is used for uplink while the 935-
2 960 MHz is used for downlink.
200KHz
935.2 Mhz 1 0 1 2 3 4 5 6 7
The frequency bands are divided into 200
935 MHz KHz wide channels called ARFCNs (Absolute
Radio Frequency Channel Numbers) i.e.
Data burst = 156.25 bit periods = 576.9μs
there are 125 ARFCNs out of which only 124
915 MHz
are used.
914.8 MHz 124
Each ARFCN supports 8 users with each user
45 MHz 123
200KHz …….
slot (TS).
0 1 2 3 4 5 6 7
transmitting / receiving on a particular time
Delay
UPLINK ……
2
Uplink (TDMA frame)
890.2 MHz 1
890 MHz
Therefore 1 TDMA frame = 156.25 x 8 = 1250 bits
The technology and has a duration of 576.92μs x 8 = 4.615 ms 29

30. GSM Delays Uplink TDMA Frames
BTS side The start of the uplink TDMA TDMA Frame (4.615 ms)
is delayed of three time-slots
0 1 2 3 4 5 6 7
R R R R R R R R
Downlink TDMA
BTS
T T T T T T T T
Down Up
MSs side link link
MS1 R T
MS2 R T
Fixed transmit
delay of three
time-slots

31. Timing Advance
1 - Propagation Delay
M2 d2 d1>>d2 M1
BTS Frame reference TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7
Propagation Delay τp
Bits Overlapping
MSs transmit

32. Timing Advance
2 - Without Timing Advance: Collision
TX BTS CAN W HAT GSM HOW W HEN WHAT
RX BTS yes the ms-isdn
TA
RX MS1 CAN
TX MS1 +3TS yes
RX MS2 W HAT
TX MS2 the
RX MS3 GSM
D
TX MS3
D ms-isdn
RX MS4 HOW
TX MS4
RX MS5
TX MS5 Propagation Delay W HEN
RX MS6 WHAT
TX MS6
RX MS7
TX MS7
RX MS8
TX MS8
32

33. Timing Advance
3 - With Timing Advance: No Collision
TX BTS CAN WHAT GSM HOW WHEN WHAT
RX BTS yes the ms-isdn
RX MS1 CAN
TX MS1 +3TS - TA yes
RX MS2 WHAT
TX MS2 D the
RX MS3 GSM
TX MS3 D ms-isdn
RX MS4 HOW
TX MS4
RX MS5 WHEN
TX MS5
Propagation Delay
RX MS6 WHAT
TX MS6
RX MS7
TX MS7
Timing Advance = 2 * Propagation Delay
RX MS8
TX MS8
33

34. 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
34

35. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT 35

36. MS
GSM - Network Structure
Um
BTS VLR HLR
BSC
Abis MSC
A B H
MS C AuC
BTS GMSC
E F
Abis
EIR
A E
MSC
BSC PSTN
Um
BTS X.25
VLR
X.25
OMC Server
36

37. GSM Network
SS
Switching
AUC System
External
PSTN & VLR HLR EIR
PDN N/W OMC
MSC
MS Mobile Station
BTS Base transceiver System
BSC Base Station Controller
MSC Mobile Switching Center BSS BSC Base Station
HLR Home Location Register
VLR Visitor Location Register BTS
System
EIR Equipment Identity Register
AUC Authentication Center MS 37
OMC Operation And Maintenance Center

38. GSM Architecture
GSM VMSC SMSC
Air interface
B
S
C A AUC
interface HLR
Abis
interface
TRAU MSC PSTN
B VLR
BTS S
BTS C
BTS EIR
OMCS
BTS BTS
BTS
Network and switching
subsystem
Mobile A interface SS7 / speech
Station X.25
OMCR SS7
Base Station System 38

39. 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)
39

40. 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
40

41. SIM-Card and GSM Mobile
Equipment
Global GSM Mobility
Card
= +
The Smart Card to use
GSM
Contains:
- IMSI
SIM-Card

42. The SIM-Card Functions
Credit Card Size
µ SIM-Card
Global GSM Mobility
Card
15 mm The Smart Card to use
25 mm
GSM
Permanent data:
- Unique mobile subscriber identity Microchip with stored
through IMSI number and PIMSI user information
for Packet Mode
- Authentication parameter Ki,
- Authentication algorithm A3, Removable data:
- Generating encryption key Kc - Temporary Mobile Subscriber Number,
algorithm A8, - Location Area Identification
- Routing Area Identification (Packet mode)
- PIN code.

43. Subscriber Identification
IMSI MS - ISDN
Mobile Station -
International Mobile Subscriber Identity
Nature Integrated Services Digital Network Nb
Similar to ISDN,
Conformity with E212
Conformity with E164/E213
Identify a PLMN Identify the subscriber
National Significant Mobile Number
worldwide of a PLMN
MCC MNC MSIN CC NDC SN
Format H1 H2 x x x ......... x x x M1 M2 xx xx xx xx
Country
Mobile Mobile Mobile Subscriber National Mobile Subscriber
Code
Meaning Country Network Ident. Nb
(where Destination (national definition)
Code Code H1 H2 = Identity of HLR
subscription Code * M1 M2 = nbr of logical HLR
within the home PLMN
has been made)
Nb. digits 3 2 max 10 1 to 3 2 to 4 total max 15
*This code does not identify a geographical area
but an operator

44. Description Stored in SIM Card
Global GSM Mobility
Card
MCC MNC The Smart Card to use
= =
208 (France) 71(APBSNL)
234 (G-B) 72(TNBSNL)
262 (Germany) 20 (Bytel) IMSI = 15 digits max GSM
404,405(India)
Mobile Mobile Mobile Subscriber Identification Number (MSIN)
Country Network
Code Code
H1 H2 X X X X X X
3 digits 2 digits 10 digits max
NMSI Temporary Mobile
Subscriber Identity
LAI
4 octets
Mobile Mobile
Country Network Location Area Code Routing Area Code
Code Code
LAC RAC
3 digits 2 digits
RAI

45. Description Stored in the Network
MS-ISDN (15 digits max)
Country National Subscriber Number (SN) Must be dialed to
Code Destination make a call to
Code M1 M2 X X X X X X X X X X X X X mobile
3 digits max 2 or 3 digits 10 digits max subscriber
MSRN
Roaming Number (RN) Is a PSTN-like
National number used to
Country reach a roaming
Destination
Code MS
Code
Is a PSTN-like
number to track the
National
Country MS that hands over
Code
Destination HO-number to another MSC
Code during call-in-state
NDC = 9448(BSNL-karnataka)
CC = 33 (France)
9845,9880(Airtel)
091(India)
9886(Hutch)
001(US)
45
= 660, 661, 618 (Bytel)

46. Descriptor Embodied in the Mobile
Equipment
IMEI enables the operator to check
the Mobile Equipment Identity
at call setup and make sure
that no stolen or unauthorized MS
is used in the GSM network
E D
YP VE
T O
R
APP
TAC FAC SNR SP
Type Approval Serial NumbeR (SPare)
Code Final Assembly
Code

47. International Mobile Equipment Identity (IMEI)
E D
T YP OVE
R
APP
TAC FAC SNR SP
Type Approval Serial number (SPare)
Code Final Assembly
Code
IMEI: #06#
351475 60 926514 4
*

48. MS Classmark
Power classes
Classmark For GMSK modulation
Revision level GSM GSM GSM
Class
400/850/900 1800 1900
RF power
1 1 W** 1 W**
Encryption algorithm 8 W*
2 0.25 W 0.25 W
Frequency 3 5W 4W 2W
Short message 4 2 W**
LoCation Services 5 0.8 W
MS Positioning Method
For 8-PSK modulation
8-PSK modulation GSM GSM GSM
Class
Multi-slot class 400/850/900 1800 1900
E1 2W 1W 1W
Multi-band
E2 0.5 W 0.4 W 0.4 W
* Typical value for car mounted E3 0.2 W 0.16 W 0.16 W
** Typical value for handheld

49. Base Transceiver Station
(BTS)
• Handles the radio interface to the mobile station.
• Consists of one or more radio terminals for
transmission and reception
• Each Radio terminal represents an RF Channel
• TRX and MS communicates over Um interface
• Received data transcoding
• Voice encryption/decryption
• Signal processing functions of the radio interface
• Uplink Radio channel power measurements
49

50. 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
50

51. 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
51

52. 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
52

53. 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
53

54. 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.
54

55. 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
55

56. Location Area Identity
• LAI identifies a location area which is a group of
cells..
• It is transmitted in the BCCH.
• When the MS moves into another LA (detected by
monitoring LAI transmitted on the BCCH) it must
perform a LU.
• LAI = MCC + MNC + LAC
– MCC= Mobile Country Code(3 digits), identifies the country
– MNC= Mobile Network Code(1-2 digits), identifies the GSM-
PLMN
– LAC= Location Area Code, identifies a location area within a
GSM PLMN network. The maximum length of LAC is 16
bits,enabling 65536 different location areas to be defined in
56
one GSM PLMN.

57. Interfaces and Protocols
Digital
Networks
ISUP
Abis A E
LAPD BSSAP TUP
MAP
Um LAPDm F MAP B POTS
MAP
C
D G
57

58. GSM Entities and Signaling
Architecture
58

59. 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
59

60. Functional Plane of GSM
MS BTS BSC MSC/VLR HLR GMSC
CC
MM
RR
Trans
MS BTS BSC MSC/ HLR GMSC
VLR
60

61. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTIFIERS USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
61

62. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
62

63. Channels : differentiating
between Physical and Logical
channels
Physical channels : The combination of an ARFCN
and a time slot defines a physical channel.
Logical channels : These are channels specified by
GSM which are mapped on physical channels.
63

64. Channel concept
Physical channel:
One timeslot of a TDMA-frame on one carrier
is referred to as a physical channel.
There are 8 physical channels per carrier in
GSM,channel 0-7(timeslot 0-7)
Logical channel:
A great variety of information must be
transmitted between BTS and the MS,for e.g.
user data and control signaling.Depending
on the kind of information transmitted we
refer to different logical channels.These logical
channels are mapped on physical 64
channel.

65. Logical Channels on Air interface
LOGICAL
CHANNELS
COMMON DEDICATED
CHANNELS CHANNELS
BROADCAST COMMON DEDICATED TRAFFIC
CHANNELS CONTROL CONTROL CHANNELS
CHANNELS CHANNELS
FCCH SCH BCCH SDCCH SACCH FACCH
PCH RACH AGCH TCH/F TCH/H TCH/EFR
65

66. Logical channels
Logical channels
Control channels Traffic channels
Half Full
CCCH DCCH
BCH rate rate
FCCHSCH BCCH CBCH PCH AGCH RACH SDCCH SACCH FACCH
66

67. Broadcast channels BCH
• Broadcast Channel-BCH
– Alloted one ARFCN & is ON all the time in every cell.
Present in TS0 and other 7 TS used by TCH.
• Frequency correction channel-FCCH
– To make sure this is the BCCH carrier.
– Allow the MS to synchronize to the frequency.
– Carries a 142 bit zero sequence and repeats once in every
10 frames on the BCH.
• Synchronization Channel-SCH
– This is used by the MS to synchronize to the TDMA frame
structure within the particular cell.
– Listening to the SCH the MS receives the TDMA frame
number and also the BSIC ( in the coded part- 39 bits).
67
– Repeats once in every 10 frames.

68. Broadcast channels BCH ...
• BCCH
– The last information the MS must receive in order to receive
calls or make calls is some information concerning the cell.
This is BCCH.
– This include the information of Max power allowed in the cell.
– List of channels in use in the cell.
– BCCH carriers for the neighboring cells,Location Area
Identity etc.
– BCCH occupies 4 frames (normal bursts) on BCH and
repeats once every Multiframe.
– This is transmitted Downlink point to multipoint.
• Cell Broadcast Channel - CBCH
– Used for the Transmission of generally accessible
information like Short Message Services(SMS) 68

69. Common Control Channels
CCCH
• CCCH-
– Shares TS-0 with BCH on a Multiframe.
• Random access channel-RACH:
– Used by Mobile Station for requesting for a channel. When
the mobile realizes it is paged it answers by requesting a
signaling channel (SDCCH) on RACH. RACH is also used
by the MS if it wants to originate a call.
– Initially MS doesn’t know the path delay (timing advance),
hence uses a short burst (with a large guard period = 68.25
bits).
– MS sends normal burst only after getting the timing advance
info on the SACCH.
– It is transmitted in Uplink point to point.
69

70. Common Control Channels
CCCH ..
• Access Grant Channel-AGCH
– On request for a signaling channel by MS the network
assigns a signaling channel(SDCCH) through AGCH. AGCH
is transmitted on the downlink point to point.
• Paging Channel-PCH
– The information on this channel is a paging message
including the MS’s identity(IMSI/TMSI).This is transmitted on
Downlink, point-to-multipoint.
70

71. Dedicated Control Channels-
DCCH
• Stand alone dedicated control channel(SDCCH)
• AGCH assigns SDCCH as signaling channel on
request by MS.The MS is informed about which
frequency(ARFCN) & timeslot to use for traffic.
• Used for location update, subscriber authentication,
ciphering information, equipment validation and
assignment of TCH.
• This is used both sides, up and Downlink point-point.
71

72. Dedicated Control Channels-
DCCH
• Slow associated control channel-SACCH
– Transmission of radio link signal measurement, power
control etc.
– Average signal strengths(RXLev) and quality of service
(RXQual) of the serving base station and of the neighboring
cells is sent on SACCH (on uplink).
– Mobile receives information like what TX power it has to
transmit and the timing advance. It is associated with TCH
or SDCCH
• Fast associated control channel-FACCH
– Used for Hand over commands and during call setup and
release. FACCH data is sent over TCH with stealing flag set
72

73. 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.
73

74. GSM Channels
GSM Channels
Traffic Channels Control Channels
(TCHs)
Broadcast Common Control Dedicated Control
Channels Channels Channels
(BCHs) (CCCHs) (DCCHs)
(down uplink)
Full Half
Downlink Downlink Uplink
rate rate
Fast Slow
TCH /F TCH /H FCCH SCH BCCH PCH AGCH CBCH RACH SDCCH FACCH SACCH
Traffic Multiframing Signaling Multiframing Traffic Multiframing
74

75. The Logical Channels on Radio Interface
TS 0123456 7
BTS MS
FCCH TCH
Frequency correction Traffic (speech-data)
SCH FACCH
Synchronization Associated Signaling
BCCH
Broadcast control
RACH Radio Measurement + SMS
SACCH
Access request SDCCH
Dedicated Signaling
PCH
Subscriber paging CBCH
Broadcast info
AGCH
Answer to Access request
FCCH
CBCH
Broadcast info SCH
M.S. Pre-synchronization
SDCCH
Dedicated Signaling BCCH
SACCH
Sys InFo 5, 6 + SMS RACH
Access request
PCH
Traffic (speech data) Subscriber paging
TCH
AGCH
Associated Signaling Answer to Access request
FACCH
75

76. Logical Channel Description
(1/2)
SACCH MESSAGES
TCH MESSAGES
Measures:
- power level of the communication • Speech
- quality level of the communication • Data
- level on the beacon frequency of • Handover Access message (uplink)
the neighboring cells
• Timing Advance
• Power Control
• SMS
FACCH MESSAGES
• Connection establishment from
SDCCH to TCH
SDCCH MESSAGES • End validation of a SDCCH-TCH
commutation
• Request for a SDCCH assignment
• Characteristics of the future used BS
• Request for the end of channel after handover
assignment
• Connection establishment to BS after
• Order of commutation from SDCCH to handover
TCH
• Validation of an handover
• SMS
76

77. Logical Channel Description
FCCH MESSAGES AGCH MESSAGES
(2/2)
• no message is sent (all bits 0) • For dedicated channel assignment:
- frequency number
- slot number
- frequency hopping description
SCH MESSAGES - Timing Advance (1st estimation)
• Frame Number - MS identification
• Base Station Identity Code (BSIC)
CBCH MESSAGES
BCCH MESSAGES • Specific information
(weather, road information
• System Information type 1, 2, 2bis,
2ter, 3, 4, 7, 8
(idle mode) RACH MESSAGES
• Service request:
- emergency call
PCH MESSAGES - answer to an incoming call
- outgoing call
• messages containing a mobile - short message
identity for a call, a short message - call re-establishment
or an authentication - inscription
77

78. GPRS Channels
DL
PDTCH
PBCCH
PACCH
PPCH BSC
PTCCH GPRS
PAGCH PCUSN
PNCH CORE
NETWORK
PDTCH
PRACH Packet
PACCH Common
PTCCH Control
UL CHannels
Packet
PDCH = Packet Data Traffic
CHannel CHannels
PBCCH
78

79. Traffic and Control Multiframing
Traffic channel Control channel
Frame
4.615 ms
TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
26 traffic frames = 120 ms
0 1 2 3 4 21 22 23 24 25 0 1 2 3 4 46 47 48 49 50
1326
frames
0 1 2 3 4 51 x 26 traffic frames = 6.12 s 46 47 48 49 50
0 1 2 3 26 x 51 control frames = 6.12 s 22 23 24 25
0 1 2 3 4 5 2042 2043 2044 2045 2046 2047
1 Hyperframe = 2,715,648 frames= 3h 28 min. 53 s 760 ms
79

80. 80

81. 81

82. Logical Channel Mapping
1 - Traffic Channel Combination
T
Full Rate - Downlink & Uplink
26 frames = 120 ms
T T T T T T T T T T T T A T T T T T T T T T T T T time
Half Rate - Downlink & Uplink
26 frames = 120 ms
T0 T1 T0 T1 T0 T1 T0 T1 T0 T1 T0 T1 A0 T1 T0 T1 T0 T1 T0 T1 T0 T1 T0 T1 T0 A1 time
T : TCH Ti : TCH A : SACCH Ai : SACCH : IDLE
sub-channel no. i sub-channel no. i
82

83. Logical Channel Mapping
2 - Dedicated Signaling Channel Combination
A A A A
Downlink
51 frames = 235 ms
D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3
D0 D1 D2 D3 D4 D5 D6 D7 A4 A5 A6 A7
time
Uplink
51 frames = 235 ms
A5 A6 A7 D0 D1 D2 D3 D4 D5 D6 D7 A0
A1 A2 A3 D0 D1 D2 D3 D4 D5 D6 D7 A4
time
A : SACCH D : SDCCH : IDLE
83

84. Logical Channel Mapping
3 - Common Channel Combination
Downlink Multiframe m
Multiframe Multiframe
m-1 51 frames = 235.38 ms m+1
C FS B C FS C C FS C C FS C C FS C C FS B
Frames repeat continuously time
PCH/AGCH
Physical Channel
BTS ARFCN (n) TS (s) MS
SCH BCCH
FCCH
Uplink
51 frames = 235.38 ms
R R R RR R R RR R R RR R R RR R R RR R R RR R R RRR R R R R RR R R RR R R RR RR RR R R R
time
: PCH /
F : FCCH S : SCH B : BCCH C AGCH R : RACH : IDLE
84

85. Logical Channel Mapping
4 - Common Channel Combination
Downlink
51 frames = 235 ms
FS B C FS C C FS D0 D1 FS D2 D3 FS A0 A1
FS B C FS C C FS D0 D1 FS D2 D3 FS A2 A3
time
Uplink
51 frames = 235 ms
D3 RR A2 A3 RRRRRRRRRRRRRRRRRRRRRRR D0 D1 RR D2
D3 RR A0 A1 RRRRRRRRRRRRRRRRRRRRRRR D0 D1 RR D2
time
: AGCH
F : FCCH S : SCH B : BCCH C /PCH R : RACH A : SACCH D : SDCCH : IDLE
85

86. 86

87. Why 26 and 51 per Multiframe?
Frames
0 1 10 20 30 40 50 0 1
FS B C FS C C FS C C FS C C FS C C FS
TTTTTTTTTTTTATTTTTTTTTTTT TTTTTTTTTTTTATTTTTTTTTTTT
01 12 25 0 1 12 25
Downlink
message
Uplink
message
Mobile Rx Rx Tx Rx Rx Tx Rx Rx Tx
activity (n) (n) (n)
Neighboring BTS
(downlink)
Measurement Windows
87

88. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
88

89. From Speech to Radio Transmission
Speech
Digitizing and Source
Step 1 source coding decoding
Channel Channel
Step 2 coding decoding
Interleaving De-interleaving
Step 3
Burst deformatting
Burst formatting
Deciphering
Step 4 Ciphering
Demodulation
Step 5 Modulation equalization
Step 6 Diversity
Transmission
89

90. GSM Radio Link
• Speech Coding -Done at Transcoder of BSC and MS
– The Linear Predictive Coder uses RPE-LTP(Regular Pulse
Excitation- Long Term Prediction)
– Converts 64kbps voice to 13kbps(260 bits every 20ms)
• Channel Coding - Done at BTS and MS
– Uses Convolution Coding and CRC (Cyclic Redundancy
Check)
– Converts 13 kbps to 22.8 kbps (456 bits per 20ms)
90

91. GSM Radio Link
• Bit Interleaving - Done at BTS and MS
• Encryption - Done at BTS and MS
– EX OR data with cipher block, which is generated by
applying A5 Algorithm to the Ciphering Key(Kc)
• Multiplexing - Done at BTS
• Modulation - Done at BTS and MS
– GMSK(Gaussian filtered Minimum Shift Keying)
– Phase change of +90 for 0 and -90 for 1
91

92. Why Digitizing and Coding the
Speech?
SPEECH
TRANSMISSION
BETWEEN MOBILE
AND NETWORK BSS
MS
SPEECH MUST BE
DIGITIZED AND CODED
Better Quality Lower Rate
64 kbit/s

93. Speech Quality – Source Coding
Codec Type Mean Opinion Score Rate (kb/s)
(MOS)
PCM A law 4.25 64
GSM EFR 4.2 12.2
CDMA 13 4.2 13
D-AMPS 4 8
GSM FR 3.8 13
CDMA 8 3.4 8
Quality MOS Listening Effort Required
Excellent 5 Complete relaxation possible, no effort.
Good 4 Attention necessary, no appreciable effort.
Fair 3 Moderate effort.
Poor 2 Considerable effort.
Bad 1 No meaning understood with feasible effort.
93

94. Speech Coding
BP A/D SPEECH
ENCODER
CHANNEL
CODING
To modulator
Every 20ms 160 samples 1A 1B 2
BAND Every 125μ s value is taken
PASS Data rate = 160 * 13/20ms
300 Hz -
sampled from analog 50 132 78
signal and quantised by = 104 kbps
3.4 kHZ
13 bit word 3 crc bits
Data rate = 13/125*10 -6 Four 0 bits for codec
= 104 kbps
50 3 132 4
Conv coding rate = 1/2 delay = 4
Linear Predictive Coding & Regular Long term prediction analysis
Pulse Excitation Analysis 1. Previous sequences stored in memory
378 coded bits 78
1. Generates 160 filter coeff 2. Find out the correlation between the
2. These blocks sorted in 4 sequence present seq. And previous sequences
1,5,9,…37 / 2,6,10----38/ 3. Select the highest correlation sequence 456 bits in 20 ms = 22.8 kbps
3,7,11…39/8,12,16…40 4. Find a value representing the difference 57 x 8 = 456
3. Selects the sequence with most between the two sequences.
1A = Filter Coeff
energy
Reduces data rate = 26 kbps/2 = 13 kbps block ampl, LTP
ie 260 bits in 20ms params
So data rate = 104/4 = 26 kbps
1B = RPE pointers &
pulses
2 = RPE pulse & filter
params
CHANNEL
LP D/A SPEECH
DECODER
DECODING
94

95. Channel Processing in GSM
Overview for Full Rate
20 ms Speech blocks 20 ms 20 ms
A B C
Codec dependent Codec dependent Codec dependent
Source coding
Channel coding
A 456 bits B 456 bits C 456 bits
A A A A B B B B B B B B 8 Sub blocks C C C C
5 6 7 8 Interleaving 1 2 3 4 5 6 7 8 1 2 3 4
of 57 bits
A5 A6 A7 A8 B5 B6 B7 B8
8 Bursts B1 B2 B3 B4 C1 C2 C3 C4
Normal 3 57 bits 1 26 bits 1 57 bits 3
burst
Tail Information CRL Training CRL Information Tail
95

96. 96

97. Channel Processing in GSM
Overview for Half Rate
20 ms Speech blocks 20 ms 20 ms
A B C
Codec dependent Codec dependent Codec dependent
Source coding
Channel coding
A 228 bits B 228 bits C 228 bits
A A A A B B B B 4 Sub blocks C C C C
1 2 3 4 Interleaving 1 2 3 4 1 2 3 4
of 57 bits
A3 A4 B3 B4
4 Bursts B1 B2 C1 C2
Normal
burst 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
97

98. Interleaving: TCH Full Rate
0 1 2 3 4 5 6 7 8 ... ... 452 453 454 455
456
coded bits
Divide 456 bits in 8 sub-blocks
0 1 2 3 4 5 6 7
57 Rows
8 9 10 11 12 13 14 15 reordering
•
• •
• •
• •
• •
• •
• •
• •
•
&
• • • • • • • • partitioning
out
448 449 450 451 452 453 454 455
4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3
diagonal
interleaving
bit
interleaving
burst
b0 b1 b56 b0 b1 b56
98

99. Burst Formatting
Normal Burst
1 frame:
4.615 ms
0 1 2 3 4 5 6 7
Training Guard
DATA S S DATA
sequence Band
3 57 1 26 1 57 3 8.25
Burst
148 bits Guard
156.25 bits duration
(0.577 ms)
99

100. Burst Formats
Frequency Correction Burst
(FCCH) Guard
Tail Data Tail Period
3 bits 142 fixed bits (0) 3 bits 8.25 bits
156.25 bits duration
(0.577 ms)
Synchronization Burst
(SCH) Guard
Tail Data Extended Training Sequence Data Tail Period
3 bits 39 encrypted bits 64 synchronization bits 39 bits 3 bits 8.25 bits
156.25 bits duration
(0.577 ms)
100

101. Burst Formats
Normal Burst
Tail Data Training Sequence Data Tail Guard
Period
3 bits 57 encrypted bits 1 26 bits 1 57 encrypted bits 3 bits 8.25 bits
156.25 bits (0.577 ms)
Dummy Burst
Guard
Tail Dummy Sequence Training Sequence Dummy Sequence Tail Period
3 bits 58 mixed bits 26 midamble bits 58 mixed bits 3 bits 8.25 bits
156.25 bits (0.577 ms)
Access Burst
Training
Tail Sequence Data Tail Guard Period
8 bits 41 synch bits 36 encrypted bits 3 bits 68.25 bits
156.25 bits (0.577 ms)
101

102. Ciphering
Burst to be
Data S S Data
transmitted
Plain data: 0 1 1 1 0 0 1 0.....
Ciphering sequence: 0 0 0 1 1 0 1 0.....
XOR:
Ciphered data (transmitted): 0 1 1 0 1 0 0 0.....
Ciphered sequence: 0 0 0 1 1 0 1 0.....
XOR:
Recovered data: 0 1 1 1 0 0 1 0.....
Received S
Training
S
Data Data
burst sequence
102

103. Interleaving
Encoded speech blocks - Diagonal Interleaving
57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57
57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 Even bits
57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 Odd bits
Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3
Encoded control channel blocks - Rectangular Interleaving
57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57
57 57 57 57 57 57 57 57 57 57 57 57 Even bits
57 57 57 57 57 57 57 57 57 57 57 57 Odd bits
Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3
Tb Coded Data F Training Sequence F Coded Data Tb Gp
3 57 1 26 1 57 3 8.25
103

104. Burst
• The information format transmitted during one
timeslot in the TDMA frame is called a burst.
• Different Types of Bursts
– Normal Burst
– Random Access Burst
– Frequency Correction Burst
– Synchronization Burst
104

105. Normal Burst
156.25 bits 0.577 ms
T Coded Data S T. Seq. S Coded Data T GP
3 57 1 26 1 57 3 8.25
Tail Bit(T) :Used as Guard Time
Coded Data :It is the Data part associated with the burst
Stealing Flag :This indicates whether the burst is carrying
Signaling data (FACCH) or user info (TCH).
Training Seq. :This is a fixed bit sequence known both to
the BTS & the MS.This takes care of the
signal deterioration.
105

106. 156.25 bits 0.577 ms
T Training Sequence Coded Data T GP
3 41 36 3 68.25
Random Access Burst
156.25 bits 0.577 ms
T Fixed Bit Sequence T GP
3 142 3 8.25
Freq. Correc. Burst
156.25 bits 0.577 ms
T Coded Data Training Sequence Coded T GP
3 39 64 Data 39 3 8.25
Synchronization Burst
106

107. Transmission on the
radio channels
• A timeslot has a duration of .577 m seconds (148 Bits)
• 8 timeslots(8 x 0.577 = 4.62 ms) form a TDMA frame
• If a mobile is assigned one TS it transmits only in this time
slot
• and stays idle for the other 7 with its transmitter off, called
bursting
• The start on the uplink is delayed from downlink by 3 TS
periods
• One TS = duration of 156.25 bits, and its physical contents is
• called a burst
Downlink 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
BTS > MS
Uplink 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
MS > BTS
107
Offset

108. Timing Advance
MS1 0 1 2 3 4 5 6 7 MS1 0 1 2 3 4 5 6 7
near near
MS2 MS2
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
far far
At At
BTS BTS
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
108

109. 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)
109

110. Frames Types On Um
Interface
• Super Frame
– 51* 26 TDMA Frames
– 6.12 S
• Hyper Frame
– 2048 * 51* 26 TDMA Frames
– 3 Hours, 28 Minutes, 53 Secs and 760 ms
110

111. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
111

112. Mobility Management
• Mobility Management (MM)
• Location updating- normal,periodic, IMSI attach
• Paging
• Security Management
– Preventing unauthorized users- authentication
– Maintaining Privacy of users- ciphering
• Providing roaming facility
• MM functionality mainly handled by MS, HLR,
MSC/VLR.
112

113. Network Attachment
• Cell Identification
• MS scans complete GSM frequency band for
highest power
• Tunes to highest powered frequency and looks
for FCCH. Synchronizes in frequency domain
• Get training sequence from SCH which follows
FCCH. Synchronizes in time domain.
• Accesses BCCH for network id, location area and
frequencies of the neighboring cells.
• Stores a list of 30 BCCH channels
113

114. Network Attachment…..
• PLMN Selection
• Get the operator information from SIM.
• Cell Selection
• Selected cell should be a cell of the selected
PLMN
• Signal strength should be above the threshold.
• Cell should not be barred
• Location Update
• Register with the network by means of location
updation procedures.
114

115. MS Location Update
MS BTS BSC
(registration)
(G)MSC VLR HLR
Action
Channel Request (RACH)
Channel Assignment (AGCH)
TMSI + old LAI
Location Update Request (SDCCH)
Authentication Request (SDCCH)
Authentication Response (SDCCH)
Comparison of Authentication param
Accept LUP and allocTMSI (SDCCH)
Ack of LUP and TMSI (SDCCH)
Entry of new area and identity into
VLR and HLR
Channel Release (SDCCH)
115

116. Security - Authentication
MS
Ki RAND
Authentication center
provides RAND to Mobile
A3 AuC generates SRES using
SRES Ki of subscriber and RAND
Mobile generates SRES
MS BTS AuC using Ki and RAND
Mobile transmits SRES to
BTS
RAND
BTS compares received
SRES
SRES with one generated
SRES by AuC
Auth Result
116

117. Security - Ciphering
MS
Ki RAND
A8
Data sent on air
interface ciphered
for security
Kc
Um interface A5 and A8
MS Network
Kc
algorithms used to
Kc
cipher data
Data Ciphered Data
A5 A5 Ciphering Key is
Data
never transmitted
on air
117

118. TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
118

119. Communication Management
(CM)
• Setup of calls between users on request
• Routing function i.e. Choice of transmission
segments linking users
• Point to Point Short message services
119

120. GSM Actors
NSS
BSS
MSC Public
Switched
BSC Telephone
Network
BTS
VLR HLR
AUC
Fixed subscriber
Mobile subscriber

121. PLMN Selection
Yes Yes
Is there an up to date
found PLMNs list?
No
Creation of a found
PLMN list
manual automatic
mode mode
The user selects a The MS selects the first
PLMN from the PLMN from the preferred
displayed PLMNs PLMNs list (if it is not in
the forbidden PLMNs list)
No (manual)
Cell Selection
succeed?
Yes Selection of the
No (automatic) next preferred
End of PLMN possible PLMN
selection

122. PLMN Selection
• Constitution of the "Found PLMN list"
Listen to all the
frequencies of the GSM
spectrum:
power level measurement (124 channels in GSM
and average on these 900, 374 in GSM 1800
measurements and 299 in GSM 1900
Select the best
frequencies
according to the
power level (30 in GSM 900 and 40 in GSM 1800)
Memorize the
beacon
frequencies in the
precedent
selection
=> Create the
Found PLMN list

123. Initial Cell Selection
List of the
frequencies of the
selected PLMN
Selection of
Eligible cell? another PLMN
No
Yes
C1 Computation for
Suitable cell:
eligible cells
- cell of the selected PLMN
Eligible cell
- cell not barred
- C1 > 0 Suitable cell?
No
Yes
Look for the cell with the best
C1 in the suitable cells list
PLMN set in the
IMSI Attach forbidden
PLMN list
End of Cell Selection
Rejected?
No Yes

124. Cell Selection
Purpose: get synchronization
with the GSM network
prior establishing any communication.
1
1
BTS-5
1 BTS-4 1
H 2
FCC
1 3
BTS-3 5 SCH
4
CH
BC BTS-1
This cell
BTS-2

125. Immediate Assignment
MS BTS BSC MSC
CHANNEL REQUEST
1 CHANNEL REQUIRED
RACH 2
CHANNEL ACTIVATION
3 Immediate
4
CHANNEL ACTIVATION Assignment
ACK.
IMMEDIATE ASSIGNMENT IMMEDIATE ASSIGNMENT
5
5 COMMAND
AGCH
CM SERVICE REQUEST
6
SDCCH or TCH
OR
LOCATION UPDAT. REQU.
6
SDCCH or TCH

126. Registration: the Very First Location
Update
1
BSS
IMSI 2
2 4 MSC
4 BSC TMSI
5
TMSI 6
5 BTS 2
Release
6
4 TMSI
5
LAI HLR VLR
IMSI 3 IMSI
VLR id TMSI
LAI

127. Intra – VLR Location Update
1 BSS
TMSI + old LAI 2
2 MSC
BSC
new TMSI 3
3
BTS 4
4 2
New TMSI
TMSI
3
New LAI VLR
IMSI
TMSI
LAI
IMSI not Required

128. Inter – VLR Location Update
1 BSS
2
TMSI + old LAI
2 BSC 5 MSC
newTMSI
5
BTS 7
7 2
TMSI New TMSI
5
New LAI Old VLR New VLR
IMSI, TMSI 3 IMSI,TMSI
Old LAI LAI
RAND, SRES, 4 RAND, SRES,
Kc Kc
6
IMSI not Required HLR subscriber
6 data
new
VLR id
128

129. IMSI Attach
CHANNEL
1
REQUEST BSS
IMMEDIATE
2
ASSIGNMENT
3 LOCATION UPDATING BSC 3
REQUEST (IMSI Attach)
Authentication BTS 4
Procedure
4 MSC
LOCATION UPDATING
5
5
ACCEPT (LAC, TMSI)
4
VLR
6
129

130. IMSI Detach
CHANNEL
1 BSS
REQUEST
IMMEDIATE
2
ASSIGNMENT
BSC MSC
3 IMSI DETach
IMSI DETach
3 INDication
INDication BTS
CHANNEL
4
RELEASE
VLR
130

131. Outgoing Call
Great Britain France Germany
Telephone
network
BSS
Terminating Gateway
BSC MSC
BTS MSC
VLR HLR
FT
131