This presentation is all about GSM (Global System for mobile Communication). All components, entities ,architecture ,advantages of GSM, future of GSM was the main focus. Call routing for incoming and outgoing call is also included in the presentation.

1. GSM
(GLOBAL SYSTEM FOR MOBILE COMMUNICATION)
By Ankur Kumar
GSM DEC/2014 1

2. Contents
• GSM-Introduction
• Business Objectives of GSM
• Technical Aspects
• History of GSM
• GSM in India
• GSM Services
• Architecture
• GSM Entities
• Mobile Station
• Base Station Subsystem
• Network Switching Subsystem
• Operation Support Subsystem
•
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• Call Routing
• Incoming call
• Outgoing call
• Handover
• Mobile Management
• Security
• Authentication
• Key Generation and encryption
• Characteristics and features
• Advantages
• Applications
• Future in GSM

3. GSM DEC/2014 3
GSM-INTRODUCTION
• Global System for Mobile (GSM) is a second
generation cellular standard developed to
cater voice services and data delivery using
digital modulation

4. GSM DEC/2014 4
GSM: Business Objectives
• Support for international roaming
• Good speech quality
• Ability to support handheld terminals
• Low terminal and service cost
• Spectral efficiency
• Support for a range of new services and facilities
• ISDN compatibility

5. GSM: Technical aspects
• GSM uses combination of FDMA, TDMA & SDMA
• GSM has an allocation of 50 MHz (890-915 MHz & 935-950 MHz)
bandwidth in 900 MHz frequency band
• using FDMA this band is divided into 124 channels (125, 1 not used) each
with 200 KHz bandwidth
• Using TDMA, each of these channels divided into 8 time slots, realizing
992 channels
• To serve hundreds of thousands users, frequency must be reused using
SDMA (cells)
• regular repetition of frequencies in cells results in clustering of cells.
• Number of cells (k) in each cluster defines the size of that cluster
• A cluster consumes whole frequency band
• GSM operates in GSM 900 MHz, GSM 1800 MHz and GSM 1900 MHz
frequency ranges
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6. GSM: History
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Year Event
1982 Conference of European Post and Telecommunication
(CEPT) formed a study group called Group Special Mobile
to study and develop Global System for Mobile
Communication(GSM)
1987 Essential elements of wireless transmission specified
1989 Responsibility of GSM transferred to European
Telecommunication Standard Institute (ETSI)
1991 First GSM network launched (phase 1)
1993 First roaming agreement came into effect
1994 Data transmission capability launched
1995 Fax & SMS roaming services offered (phase 2)
2002 SMS volume crosses 24 billion/year, 750 million subscribers

7. GSM in India
Figures: March 2005
Bharti
27%
BSNL
22%
Spice
4%
Aircel
4%
IDEA
13%
Hutch
19%
BPL
6%
Reliance
3%
MTNL
2%
Bharti
BSNL
Hutch
IDEA
BPL
Aircel
Spice
Reliance
MTNL
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8. GSM SERVICES
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GSM provides integrated services for voice and data. It delivers following three
kind of services:
Tele-services: These services enables voice communication via mobile
phones. Offered services are Mobile telephony, Emergency calling etc.
 Supplementary services: GSM also offers following call related
supplementary services:
• Call Waiting- Notification of an incoming call while on the handset
• Call Hold- Put a caller on hold to take another call
• Call Barring- All calls, outgoing calls, or incoming calls
• Call Forwarding- Calls can be sent to various numbers defined by the user
• Multi Party Call Conferencing - Link multiple calls together
Bearer or Data Services: Include various data services for information
transfer between GSM and other networks like PSTN, ISDN etc. these
are short Message Service (SMS) , Unified Messaging Services(UMS),
Voice mailbox, Electronic mail etc.

9. GSM DEC/2014 9
GSM Architecture
• It consists minimum one administrative region (PLMN:
public land mobile network) assigned to one Mobile
Switching Center (MSC)
• Each administrative region is divided into one or many
Location Area (LA)
• One LA consists of many cell groups
• Each cell group is assigned to one Base Switching Center
(BSC)
• Cells are formed by radio areas covered by Base
Transceiver Station (BTS)
• Several BTSs are controlled by one BSC
• Traffic from Mobile Station (MS) is routed through MSC,
Gateway MSC, ISDN/ Public Switched Telephone Network
(PSTN)/ Packet Data Network (PDN), internet.

10. GSM DEC/2014 10
GSM System Architecture
BSC
BSC
MSC
MS
MS BTS
MS
BTS
BTS
PSTN
ISDN
PDN
GMSC
EIR
AUC
HLR
VLR

11. GSM DEC/2014 11
GSM Entities
GSM network can be divided into five main groups:
• The Mobile Station (MS): it includes Mobile Equipment (ME) &
Subscriber
Identity Module (SIM)
• The Base Station Subsystem (BSS): It includes BTS & BSC
• The Network and Switching Subsystem (NSS): It includes
– Mobile Switching Center (MSC)
– Home Location Register (HLR)
– Visitor Location Register (VLR)
– Equipment Identity Register (EIR)
– Authentication Center (AUC)
•The Operation Support Subsystem (OSS): it includes Operation and
Maintenance Center (OMC)
•The data infrastructure that includes Public Switched Telephone
Network (PSTN), Integrated System Digital Network(ISDN), Public Data
Network (PDN)

12. GSM Entities
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13. GSM DEC/2014 13
Mobile Station (MS): Mobile
Equipment
Mobile Equipment (ME) or the mobile device or a phone without
SIM
• Portable, vehicle mounted, hand held device
• Uniquely identified by an IMEI (International Mobile Equipment Identity)
• Voice and data transmission
• Monitoring power and signal quality of surrounding cells for optimum
handover
• Power level : 0.8W – 20 W
• Other features are weight, volume, battery life etc.

14. Mobile Station (MS): Subscriber Identity Module (SIM)
• Smart processor with small memory
• Smart card contains the International Mobile Subscriber Identity (IMSI)
• Allows user to send and receive calls and receive other subscribed
services
• SIM Application Toolkit (SAT) is used to develop and store the
applications into the SIM
• Protected by a password or PIN
• Can be moved from phone to phone – contains key information to
activate the phone
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15. GSM DEC/2014 15
Base Station Subsystem (BSS)
Base Transceiver Station (BTS):
• Encodes, encrypts, multiplexes, modulates and feeds the RF signals
to the antenna.
• Communicates with Mobile station and BSC
Base Station Controller (BSC)
• Manages Radio resources for BTS
• Assigns Frequency and time slots for all MS’s in its area
• Handles call set up
• Handover for each MS
• Radio Power control
• It communicates with MSC and BTS

16. Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
• Heart of the network equivalent of an exchange in a fixed network
• Manages communication between GSM and other networks
• Call setup function and basic switching
• Call routing by using HLR/VLR.
• Billing information and collection
• Mobility management
- Registration
- Location Updating
- Inter BSC and inter MSC call handoff
• MSC does gateway function while its customer roams to other
network by using HLR/VLR.
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17. GSM DEC/2014 17
Network Switching Subsystem(NSS)
• Home Location Registers (HLR)
• permanent database that stores all mobile subscribers in a large
service area (generally one per GSM network operator)
• database contains
• International Mobile Subscriber Identity (IMSI),
• Mobile Subscriber ISDN number (MSISDN),
• Subscribed services ( Call forwarding, call routing, prepaid /
postpaid, roaming restrictions, GPRS, supplementary services
etc)
• Visitor Location Registers (VLR)
• Temporary database which updates whenever new MS enters in its
area, by HLR database
• Controls those mobiles roaming in its area
• Reduces number of queries to HLR
• Some VLR are capable to manage upto one million customers

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Network Switching Subsystem(NSS)
• Equipment Identity Register (EIR)
- Database of handsets using the IMEI (International Mobile Equipment
Identity) registered for this network
- Made up of three sub-classes:
- The White List (list of valid device IMEIs),
- The Black List (list of locked/stolen device IMEIs) and
- the Gray List (list of malfunctioning device IMEIs)
• Authentication Center (AUC)
- Protects against intruders in air interface
- Maintains authentication keys and algorithms and provides security
- Generally associated with HLR

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Operation Support Subsystem (OSS)
• Connected to different components of the NSS & BSS
• Operation & Maintenance Center (OMC) controls and
monitors other network entities.
• OMC functions are traffic monitoring, status report of network
entities, subscriber’s security management and billing.
• Uses Equipment Identity Register (EIR) to identify valid, invalid
and malfunctioning subscribers.
• Uses Authentication Center (AuC) for authentications of a
subscriber. It helps to verify user’s identity.

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Call Routing: Incoming Call
1. Calling a GSM subscribers
2. Forwarding call to GSMC
3. Signal Setup to HLR
4. 5. Request MSRN from VLR
6. Forward responsible MSC to
GMSC
7. Forward Call to current MSC
8. 9. Get current status of MS
10.11. Paging of MS
12.13. MS answers
14.15. Security checks
16.17. Set up connection

21. GSM DEC/2014 21
Call Routing: Outgoing Call
1. MS sends dialed number to BSS
2. BSS sends dialed number to MSC
3,4 MSC checks VLR if MS is allowed
the requested service.
5 MSC routes the call to GMSC
6 GMSC routes the call to local
exchange of called user
7, 8,
9,10 Answer back (Ring back) tone is
routed from called user to MS via
GMSC,MSC,BSS

22. GSM DEC/2014 22
Handovers
Four different types of handover in the GSM
• Channels (time Slots) in the same
cell.
• Between 1 and 2 – Inter BTS /
Intra BSC
• Between 1 and 3 – Inter BSC/
Intra MSC
• Between 1 and 4 – Inter MSC
Internal Handovers - Involved only one base station controller.
External Handovers - These are handled by MSC.

23. GSM DEC/2014 23
Mobility Management : Location Management
• A powered on mobile is informed of an incoming call by a paging message
sent over the paging channel of the cells within the current location area.
• The location updating ,and subsequent call routing ,use the MSC and both
HLR and VLR.
• Information send to HLR is normally the SS7 address of the new VLR.
• If the subscriber is entitled to service ,the HLR sends a subset of the
subscriber information needed for call control to the new MSC / VLR ,and
sends the message to the old MSC/VLR to cancel the old registration.
• An incoming mobile terminating call is directed to the gateway MSC(GMSC)
function.
• The GSMC is basically a switch. which is able to interrogate the subscriber’s
HLR , though the GMSC function is distinct from the MSC function ,it is
usually implemented within the MSC.
• The routing information that is returned to the GMSC is the MSRN( Mobile
station roaming Number) it is defined by the E.164 numbering plan .MSRNs
are related to the geographical numbering plan ,and not assigned to
subscribes.

24. GSM DEC/2014 24
• Routing procedure begin with the GMSC querying the
called subscriber’s HLR for an MSRN. The HLR typically
stores only the SS7 address of the subscriber current
VLR.
• The VLR temporarily allocates an MSRN from its pool for
the call.
• This MSRN is returned to the HLR and back to the
GMSC, which can then route the call to the new MSC.
• At the new MSC, the IMSI corresponding to the MSRN is
looked up , and the mobile is paged in its current location
area.
• HLR is referred for incoming call , VLR is referred for
outgoing call.

25. GSM DEC/2014 25
Security in GSM
• On air interface, GSM uses encryption and TMSI
Temporary Mobile Subscriber Identity instead of IMSI.
• SIM is provided 4-8 digit PIN to validate the ownership of
SIM
• 3 algorithms are specified :
- A3 algorithm for authentication
- A5 algorithm for encryption
- A8 algorithm for key generation

26. GSM DEC/2014 26
Authentication in GSM

27. GSM DEC/2014 27
Key generation and Encryption

28. GSM DEC/2014 28
Characteristics of GSM Standard
• Fully digital system using 900,1800 MHz frequency
band.
• TDMA over radio carriers(200 KHz carrier spacing.
• 8 full rate or 16 half rate TDMA channels per carrier.
• User/terminal authentication for fraud control.
• Encryption of speech and data transmission over the
radio path.
• Full international roaming capability.
• Low speed data services (upto 9.6 Kb/s).
• Compatibility with ISDN.
• Support of Short Message Service (SMS).

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Advantages of GSM over Analog system
• Capacity increases
• Reduced RF transmission power and longer battery life.
• International roaming capability.
• Better security against fraud (through terminal validation
and user authentication).
• Encryption capability for information security and privacy.
• Compatibility with ISDN, leading to wider range of
services

30. GSM DEC/2014 30
GSM Applications
• Mobile telephony
• GSM-R
• Telemetry System
- Fleet management
- Automatic meter reading
- Toll Collection
- Remote control and fault reporting of DG sets
• Value Added Services

31. Future Of GSM
2nd Generation
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GSM -9.6 Kbps (data rate)
2.5 Generation ( Future of GSM)
HSCSD (High Speed ckt Switched data)
Data rate : 76.8 Kbps (9.6 x 8 kbps)
GPRS (General Packet Radio service)
Data rate: 14.4 - 115.2 Kbps
EDGE (Enhanced data rate for GSM Evolution)
Data rate: 547.2 Kbps (max)
 3 Generation
WCDMA (Wide band CDMA)
Data rate : 0.348 – 2.0 Mbps

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