this is for all telecom engineers,

1. INTRODUCTION TO GSM

2. INTRODUCTION TO GSM
INTRODUCTION
The Global System for Mobile Communications (GSM) is a set of
recommendations and specifications for a digital cellular telephone
network (known as a Public Land Mobile Network, or PLMN).
These recommendations ensure the compatibility of equipment from
different GSM manufacturers, and interconnectivity between different
administrations, including operation across international boundaries.
GSM networks are digital and can cater for high system capacities.
They are consistent with the world-wide digitization of the telephone
network, and are an extension of the Integrated Services Digital
Network (ISDN), using a digital radio interface between the cellular
network and the mobile subscriber equipment.

3. CELLULAR TELEPHONY
A cellular telephone system links mobile subscribers into the public
telephone system or to another cellular subscriber.
Information between the mobile unit and the cellular network uses radio
communication. Hence the subscriber is able to move around and
become fully mobile.
The service area in which mobile communication is to be provided is
divided into regions called cells.
Each cell has the equipment to transmit and receive calls from any
subscriber located within the borders of its radio coverage area.
Radio
Mobile subscriber
Cell
INTRODUCTION TO GSM

4. INTRODUCTION TO GSM
GSM FREQUENCIES
GSM systems use radio frequencies between 890-915 MHz for receive
and between 935-960 MHz for transmit.
RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for
use.
An RF carrier is a pair of radio frequencies, one used in each direction.
Transmit and receive frequencies are always separated by 45 MHz.
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
890 915 935 960
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ

5. INTRODUCTION TO GSM
Extended GSM (EGSM)
EGSM has 10MHz of bandwidth on both transmit and receive.
Receive bandwidth is from 880 MHz to 890 MHz.
Transmit bandwidth is from 925 MHz to 935 MHz.
Total RF carriers in EGSM is 50.
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
880 890 915 925 935 960
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ

6. INTRODUCTION TO GSM
DCS1800 FREQUENCIES
DCS1800 systems use radio frequencies between 1710-1785 MHz for
receive and between 1805-1880 MHz for transmit.
RF carriers are spaced every 200 kHz, allowing a total of 373 carriers.
There is a 100 kHz guard band between 1710.0 MHz and 1710.1 MHz
and between 1784.9 MHz and 1785.0 MHz for receive, and between
1805.0 MHz and 1805.1 MHz and between 1879.9 MHz and 1880.0
MHz for transmit.
Transmit and receive frequencies are always separated by 95 MHz.
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
1710 MHz 1785 MHz 1805 MHz 1880 MHz
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 95MHZ

7. FEATURES OF GSM

8. FEATURES OF GSM
INCREASED CAPACITY
The GSM system provides a greater subscriber capacity than analogue
systems.
GSM allows 25 kHz per user, that is, eight conversations per 200 kHz
channel pair (a pair comprising one transmit channel and one receive
channel).
Digital channel coding and the modulation used makes the signal resistant to
interference from cells where the same frequencies are re-used (co-channel
interference); a Carrier to Interference Ratio (C/I) level of 12 dB
is achieved, as opposed to the 18 dB typical with analogue cellular.
This allows increased geographic reuse by permitting a reduction in the
number of cells in the reuse pattern.

9. FEATURES OF GSM
AUDIO QUALITY
Digital transmission of speech and high performance digital signal
processors provide good quality speech transmission.
Since GSM is a digital technology, the signals passed over a digital air
interface can be protected against errors by using better error
detection and correction techniques.
In regions of interference or noise-limited operation the speech quality is
noticeably better than analogue.
USE OF STANDARDISED OPEN INTERFACES
Standard interfaces such as C7 and X25 are used throughout the system.
Hence different manufacturers can be selected for different parts of the
PLMN.
There is a high flexibilty in where the Network components are situated.

10. FEATURES OF GSM
IMPROVED SECURITY AND CONFIDENTIALITY
GSM offers high speech and data confidentiality.
Subscriber authentication can be performed by the system to check if a
subscriber is a valid subscriber or not.
The GSM system provides for high degree of confidentiality for the
subscriber. Calls are encoded and ciphered when sent over air.
The mobile equipment can be identified independently from the mobile
subscriber. The mobile has a identity number hard coded into it when it
is manufactured. This number is stored in a standard database and
whenever a call is made the equipment can be checked to see if it has
been reported stolen.

11. FEATURES OF GSM
CLEANER HANDOVERS
GSM uses Mobile assisted handover techique.
The mobile itself carries out the signal strength and quality
measurement of its server and signal strength measurement of its
neighbors.
This data is passed on the Network which then uses sophisticated
algorithms to determine the need of handover.
SUBSCRIBER IDENTIFICATION
In a GSM system the mobile station and the subscriber are identified
separately.
The subscriber is identified by means of a smart card known as a SIM.
This enables the subscriber to use different mobile equipment while
retaining the same subscriber number.

12. FEATURES OF GSM
ENHANCED RANGE OF SERVICES
Speech services for normal telephony.
Short Message Service for point ot point transmission of text
message.
Cell broadcast for transmission of text message from the cell to all
MS in its coverage area. Message like traffic information or
advertising can be transmitted.
Fax and data services are provided. Data rates available are 2.4
Kb/s, 4.8 Kb/s and 9.6 Kb/s.
Supplementary services like number identification , call barring,
call forwarding, charging display etc can be provided.

13. FREQUENCY REUSE
There are total 124 carriers in GSM ( additional 50 carriers are available if
EGSM band is used).
Each carrier has 8 timeslots and if 7 can be used for traffic then a
maximum of 868 ( 124 X 7 ) calls can be made. This is not enough
and hence frequencies have to be reused.
The same RF carrier can be used for many conversations in several
different cells at the same time.
4
6
3
7
2
The radio carriers available are allocated according to a
regular pattern which repeats over the whole coverage
area.
The pattern to be used depends on traffic requirement and
spectrum availability.
Some typical repeat patterns are 4/12, 7/21 etc.
1
5
2
1
FEATURES OF GSM

14. NETWORK COMPONENTS

15. NETWORK COMPONENTS

16. NETWORK COMPONENTS
Mobile Switching Centre (MSC)
The Mobile services Switching Centre (MSC) co-ordinates the setting up of
calls to and from GSM users.
It is the telephone switching office for MS originated or terminated traffic and
provides the appropriate bearer services, teleservices and
supplementary services.
It controls a number of Base Station Sites (BSSs) within a specified
geographical coverage area and gives the radio subsystem access to
the subscriber and equipment databases.
The MSC carries out several different functions depending on its position in
the network.
When the MSC provides the interface between PSTN and the BSS in the
GSM network it is called the Gateway MSC.
Some important functions carried out by MSC are Call processing including
control of data/voice call setup, inter BSS & inter MSC handovers,
control of mobility management, Operation & maintenance support
including database management, traffic metering and man machine
interface & managing the interface between GSM & PSTN N/W.

17. NETWORK COMPONENTS
Mobile Switching Centre (MSC)

18. NETWORK COMPONENTS
Mobile Station (MS)
The Mobile Station consists of the Mobile Equipment (ME) and the
Subscriber Identity Module (SIM).
Mobile Equipment
The Mobile Equipment is the hardware used by the subscriber to
access the network.
The mobile equipment can be Vehicle mounted, with the antenna
physically mounted on the outside of the vehicle or portable mobile
unit, which can be handheld.
Mobiles are classified into five classes according to their power rating.
CLASS POWER OUTPUT
1 20W
2 8W
3 5W
4 2W
5 0.8W

19. NETWORK COMPONENTS
SIM
The SIM is a removable card that plugs into the ME.
It identifies the mobile subscriber and provides information about the service
that the subscriber should receive.
The SIM contains several pieces of information
– International Mobile Subscribers Identity ( IMSI ) - This number
identifies the mobile subscriber. It is only transmitted over the air during
initialising.
– Temporary Mobile Subscriber Identity ( TMSI ) - This number also
identifies the subscriber. It can be alternatively used by the system. It is
periodically changed by the system to protect the subscriber from being
identified by someone attempting to monitor the radio interface.
– Location Area Identity ( LAI ) - Identifies the current location of the
subscriber.
– Subscribers Authentication Key ( Ki ) - This is used to authenticate the
SIM card.
– Mobile Station International Standard Data Number ( MSISDN ) - This
is the telephone number of the mobile.

20. SIM
Most of the data contained within the SIM is protected against reading (eg
Ki ) or alterations after the SIM is issued.
Some of the parameters ( eg. LAI ) will be continously updated to reflect the
current location of the subscriber.
The SIM card can be protected by use of Personal Identity Number ( PIN )
password.
The SIM is capable of storing additional information such as accumulated
call charges.
FULL SIZE SIM CARD MINI SIM CARD
G S M
NETWORK COMPONENTS

21. NETWORK COMPONENTS
Mobile Station International Subscribers Dialling Number ( MSISDN ) :
Human identity used to call a MS
The Mobile Subscriber ISDN (MSISDN) number is the telephone number
CC NDC SN
98 XXX 12345
CC
NDC
SN
= Country code
= National Destination Code
= Subscriber Number
of the MS.
This is the number a calling party dials to reach the subscriber.
It is used by the land network to route calls toward the MSC.

22. NETWORK COMPONENTS
International Mobile Subscribers Identity ( IMSI ) :
Network Identity Unique to a MS
The International Mobile Subscriber Identity (IMSI) is the primary
identity of the subscriber within the mobile network and is
permanently assigned to that subscriber.
The IMSI can be maximum of 15 digits.
MCC MNC MSIN
404 XX 12345..10
MCC
MNC
MSIN
= Mobile Country Code ( 3 Digits )
= Mobile Network Code ( 2 Digits )
= Mobile Subscriber Identity Number

23. NETWORK COMPONENTS
Temporary Mobile Subscribers Identity ( TMSI ) :
 The GSM system can also assign a Temporary Mobile
Subscriber Identity (TMSI).
 After the subscriber's IMSI has been initialized on the
system, the TMSI can be used for sending messages
backwards and forwards across the network to identify
the subscriber.
 The system automatically changes the TMSI at regular
intervals, thus protecting the subscriber from being
identified by someone attempting to monitor the radio
channels.
 The TMSI is a local number and is always allocated by
the VLR.
 The TMSI is maximum of 4 octets.

24. NETWORK COMPONENTS
Equipment Identity Register ( EIR )
 The Equipment Identity Register (EIR) contains a centralized
database for validating the international mobile station equipment
identity, the IMEI.
 The database contains three lists:
 The white list contains the number series of equipment identities
that have been allocated in the different participating countries.
This list does not contain individual numbers but a range of
numbers by identifying the beginning and end of the series.
 The grey list contains IMEIs of equipment to be monitored and
observed for location and correct function.
 The black list contains IMEIs of MSs which have been reported
stolen or are to be denied service.
 The EIR database is remotely accessed by the MSC’s in the
Network and can also be accessed by an MSC in a different PLMN.
.

25. NETWORK COMPONENTS
Equipment Identity Register ( EIR )
White List
All Valid
assigned ID’s
Range 1
Range 2
Range n
Black List
Service denied
MS IMEI 1
MS IMEI 2
MS IMEI n
EIR
Grey List
Service allowed
but noted
MS IMEI 1
MS IMEI 2
MS IMEI n

26. International Mobile Equipment Identity ( IMEI ) :
IMEI is a serial number unique to each mobile
Each MS is identified by an International Mobile station Equipment Identity
(IMEI) number which is permanently stored in the Mobile Equipment.
On request, the MS sends this number over the signalling channel to the
TAC FAC SNR
6 2 6 1
TAC
FAC
SNR
SP
SP
= Type Approval Code
= Final Assembly Code
= Serial Number
= Spare
MSC.
The IMEI can be used to identify MSs that are reported stolen or operating
incorrectly.
NETWORK COMPONENTS

27. NETWORK COMPONENTS
HOME LOCATION REGISTER( HLR )
 The HLR contains the master database of all subscribers in the PLMN.
 This data is remotely accessed by the MSC´´s and VLRs in the network.
The data can also be accessed by an MSC or a VLR in a different
PLMN to allow inter-system and inter-country roaming.
 A PLMN may contain more than one HLR, in which case each HLR
contains a portion of the total subscriber database. There is only one
database record per subscriber.
 The subscribers data may be accessed by the IMSI or the MSISDN.
 The parameters stored in HLR are
– Subscribers ID (IMSI and MSISDN )
– Current subscriber VLR.
– Supplementary services subscribed to.
– Supplementary services information (eg. Current forwarding
address ).
– Authentication key and AUC functionality.
– TMSI and MSRN

28. NETWORK COMPONENTS
VISITOR LOCATION REGISTER ( VLR )
 The Visitor Location Register (VLR) is a local subscriber database,
holding details on those subscribers who enter the area of the network
that it covers.
 The details are held in the VLR until the subscriber moves into the
area serviced by another VLR.
 The data includes most of the information stored at the HLR, as well
as more precise location and status information.
 The additional data stored in VLR are
– Mobile status ( Busy / Free / No answer etc. )
– Location Area Identity ( LAI )
– Temporary Mobile Subscribers Identity ( TMSI )
– Mobile Station Roaming Number ( MSRN )
 The VLR provides the system elements local to the subscriber, with
basic information on that subscriber, thus removing the need to
access the HLR every time subscriber information is required.

29. NETWORK COMPONENTS
Authentication Centre ( AUC )
 The AUC is a processor system that perform
authentication function.
 It is normally co-located with the HLR.
 The authentication process usually takes place each
time the subscriber initialises on the system.
 Each subscriber is assigned an authentication key (Ki)
which is stored in the SIM and at the AUC.

30. NETWORK COMPONENTS
Base Station Sub-System ( BSS ) :
 The BSS is the fixed end of the radio interface that provides
control and radio coverage functions for one or more cells and
their associated MSs.
 It is the interface between the MS and the MSC.
 The BSS comprises one or more Base Transceiver Stations
(BTSs), each containing the radio components that
communicate with MSs in a given area, and a Base Site
Controller (BSC) which supports call processing functions and
the interfaces to the MSC.
 Digital radio techniques are used for the radio communications
link, known as the Air Interface, between the BSS and the MS.
 The BSS consists of two basic Network Elements (NEs). .
 Base Station Controller (BSC).
 Base Transceiver Stations (BTSs) assigned to the BSC. .

31. NETWORK COMPONENTS
Base Station Controller (BSC)
 The BSC network element provides the control for the BSS.
 It controls and manages the associated BTSs, and interfaces
with the Operations and Maintenance Centre (OMC).
 The purpose of the BSC is to perform a variety of functions.
The following comprise the functions provided by the BSC:
– Controls the BTS components.-
– Performs Call Processing.
– Performs Operations and Maintenance (O & M).
– Provides the O & M link (OML) between the BSS and the
OMC.
– Provides the A Interface between the BSS and the MSC.
– Manages the radio channels.
– Transfers signalling information to and from MSs.

32. NETWORK COMPONENTS
Base Station Controller (BSC) – Huawei BSC
Power
distribution
box
Air
defence
subrack
subrack
插插框框
Air inlet and
Fan subrack

33. NETWORK COMPONENTS
Base Transceiver Station (BTS)
 The BTS network element consists of the hardware
components, such as radios, interface modules and
antenna systems that provide the Air Interface between
the BSS and the MSs.
 The BTS provides radio channels (RF carriers) for a
specific RF coverage area.
 The radio channel is the communication link between
the MSs within an RF coverage area and the BSS.
 The BTS also has a limited amount of control
functionality which reduces the amount of traffic
between the BTS and BSC.

34. NETWORK COMPONENTS
Base Transceiver Station (BTS)

35. BTS Connectivity
MSC BSC BTS12
BTS1
BTS2
BTS4
BTS11 BTS3
BTS13 BTS14
BTS5
BTS6
BTS7
BTS8
BTS9
BTS11
Open ended Daisy Chain
Daisy Chain with a
fork. Fork has a
return loop back to
the chain
Star
Daisy Chain with a
fork. Fork has a
return loop back to
the chain
NETWORK COMPONENTS

36. Operation And Maintenance Centre For Radio (OMC-R)
 The OMC controls and monitors the Network elements within a region.
 The OMC also monitors the quality of service being provided by the
Network.
The following are the main functions performed by the OMC-R
– The OMC allows network devices to be manually removed for or
restored to service. The status of network devices can be checked
from the OMC and tests and diagnostics invoked.
– The alarms generated by the Network elements are reported and
logged at the OMC. The OMC-R Engineer can monitor and analyse
these alarms and take appropriate action like informing the
maintenance personal.
– The OMC keeps on collecting and accumulating traffic statistics from
the network elements for analysis.
– Software loads can be downloaded to network elements or uploaded
to the OMC.
NETWORK COMPONENTS

37. NETWORK COMPONENTS
Operation And Maintenance Centre For Radio (OMC-R)

38. TERRESTERIAL INTERFACE
 The terrestrial interfaces comprises all the connections
between the GSM system entities ,apart from the Um
or air interface.
 The terrestrial interfaces transport the traffic across the
system and allows the passage of thousands of data
messages to make the system function.

39. INTERFACE NAMES
Each interface specified in GSM has a name associated with it.
NAME INTERFACE
Um MS ----- BTS
Abis BTS ----- BSC
A MSC ------ BSC
B MSC ------ VLR
C MSC ------ HLR
D VLR ----- HLR
E MSC ------ MSC
F MSC ------ EIR
G VLR ------ VLR
H HLR ------ AUC