
Introduction

!What is telephony?

3


Introduction

!What is telephony?

4


Introduction

!What is telephony?

5


Introduction

!What is telephony

• Make the illusion to users that they are in the same room and that they can talk together

!Technically, it involves

• To set up a network

• To locate users

• To advertise users about incoming calls - signalling

• Voice encoding- Convert the voice signal to a digital signal

• Transmission and routing

• Management and supervision (administration)

!Global interoperability

• Need for standardization

!Quality of service

• Call set up failure

• Time to establish a communication

• Quality of the sound

• Interactivity

6


Main principles…

!Passband for the voice transmission is [300; 3400Hz]

• where the voice is actually between [300; 7000Hz]!Circuit switched network

• Communication circuit reservation

• Need for a call setup and clear-down

!Digital transmission of the signal

• Pulse Code Modulation (PCM)

• Voice rate is 64 kbps

!Signaling network is independent from the voice transmission network

7


History of telephony

!French invention

• 1854 : Charles Bourseul was the first to invent a system for the electric transmission of the voice

!First patent in 1876

• Alexander Graham Bell

• <tele> far away and <phone> sound

!Manual switch

• The connexion between two peers was made manually in telephony offices- Operators manually plugged in cords to provide the necessary circuit

connections

!Nowadays…

• The main concepts remain the same

• The technologie is totally different- Digital, automatic and computer programs

8


The PSTN network Public Switched Telephone Network

!Allow to set up a call

• Find a path between a caller and a receiver

• Temporary connection between two subscribers- Allocate the resources for the duration of the call

• Clear down the resources after the call ends

!Main concepts

• Connection-oriented service

• Circuit switched

• Multiplexing

9


Base elements of the PSTN

……

TandemSwitch

TandemSwitch

Trunks

Local loop on battery

Hundred

meters to

few

kilometers

Central office switch




A hundred or more connections - fiber (used to be 2 pair of wires)

10


Link between switches

!Digital Multiplexing

• Transport of multiple channels on the same physical support

• Multiplexing unit: the sample

• Multiplexing in wavelength for optical fibers

!Required bandwidth

• 8000 bytes / second (1 byte every 125 !s)

• 64 kbps per voice channel

Unique transport system

11


Hierarchical switched Network

12


Routing

!Objective : Find a path in the graph of the switched network

!How does it work

• Static routing: routing tables are defined before deployment at the national level and uploaded in the switches

13


Network property

!Asynchronous : No temporal constraints on packets. Each packet needs to reach the destination as fast as possible

!Synchronous : Temporal constraint on each packet : keep the end-to-end delay below a maximum threshold

! Isochronous : Double temporal constraint for each packet: packets must be transported between a minimum and maximum time

What is the time to cross the network?

14


Impact of the delay

!Defined in the ITU-T G.114 recommandation

" t in ms G.114 Recommandation

0 to 150 ms Acceptable for most applications

150 to 400 ms Acceptable if the effect on applications are known

> 400 ms Not acceptable but in exceptional cases

15


Signaling and signaling network

!This section presents two topics

• Signaling network: network for the transport of messages

• Signaling channel: application level

!Features

• Optimized for digital network

• High level of reliability

• Evolving

• Adapted for channels at 64 kbit/s

• A single signaling channel manages 2000 circuits

16


What is Signaling?

!Set of control information exchanged among switches or between switches and end-terminals that are used to setup, tear down, or manage a communication

!The signaling is used for

• Set up and clear down a voice call

• Billing control

• Supervision and maintenance

17


Introduction to the telephony signaling

!In data network there are 2 signaling modes• In-band signaling

- The signaling is transported inside the data

• out-of-band signaling- The signaling is transported independently from the data

!... in the PSTN• SS5: Channel Associated Signaling (CAS)

- Multiplexing of the voice and signalling within the same channel- DTMF 'Dual-Tone multi-frequency' signaling

• SS6 - SS7:Common Channel Signalling (CCS)- A specific (separated) channel is dedicated to the signaling of several voice channels

- Allow for new services (signaling independent from a call, or during a call)

18


Common Channel Signaling

Control unit Control unit

NNI Signalling

UNI signalling UNI Signalling

Circuit 1

Circuit i

Circuit n

Signaling channelSignal Transfert Point

Signal Transfert Point

19


SS7 Network components

!Service Switching Point (SSP)

• SSPs are the "brains" of the SS7 network and are usually located at phone switches. Because signaling messages will either originate or terminate within them, SSPs are considered "end points" on a network.

!Signaling Transfer Point (STP)

• STPs relay signaling messages. An STP is a packet switch that acts as a hub to transfer messages to other STPs, SCP databases, or SSPs.

!Service Control Point (SCP)

• An SCP is a database that holds information required to provide services that are more complex than basic call control (e.g., providing a business with an 800 number).

Voice circuits

SS7 link

SS7 link

20


SS7 protocols architecture

OSI model SS7 protocols

21


MTP - Message Transfer Part

! Switched network for data transmission

• First 3 levels of the stack

! The goal of MTP is to route signaling packets and ensure reliability

! MTP1

• Called Signaling Data Link Functional Level (Data Link Level)

• Equivalent to the physical layer of OSI

! MTP2

• Called Signaling Link Functional Level (Link Level)

• Equivalent to the data link of OSI (HDLC-like)

• Provides error detection and sequence checking, and retransmits unacknowledged messages

! MTP3

• Signaling Network Functional Level (Network Level)

• Equivalent to the network layer of OSI

• Addresses are only valid on the local (national) network

22


Message Signaling Unit

INFORMATIONCIC

INFORMATIONSLSOPCDPCSIO FIN

INFORMATIONSLSOPCDPCSIO

Header

SLS : Route between the Signaling PointOPC / DPC : Src and dst SP

SIO: SAP

MTP2

MTP3

ISUP

Routing label

23


User protocols

!Generate the signaling

!Several types

• ISDN User Part (see next)

• SCCP (signaling Connection Control Part)- Add functionalities to MTP3 - offer connection and non-oriented connection mode- Allow exchange of data independently from any telephony communication

• TCAP (Transactions Capabilities Application Part)- Also called Transaction Manager- Between the application and SCCP to facilitate dialog independently from any applications- Communication support for applications- Examples:

– Location of users– Call with a credit card (need further verification)– Network administration

24


ISDN User Part (ISUP)

!Signalling protocol

• Use the MTP3 services (may also use SCCP)

!User sub-system

• Call setup

• Call clear-down

• Supervision of the call channel ((un)blocking, check, restart)

• Additional services

!Usage

• Analogic networks

• Mix networks

• Digital networks

25


Protocols stack of ISUP

MTP 1

MTP 2

MTP 3

ISUPSCCP

MTP 1

MTP 2

MTP 3

ISUPSCCP

SS7

Signalisation NNI

Source Destination

26


Overview of the user protocol

A B

User hangs up

Phone is ringing

User picks up

Communication

Call

Signaling User Part

27


Call scenario

A B

REL

ACM

ANM

Communication

IAM

RLC

28


Call scenario

SSP

STP

CAA CTPCTS

CAA

STP

STP

SSP SSP SSP

Ring

IAM

IAMIAM

pick up

Tone

Dial

Commutateur

d’origine

Commutateur

destination

29


SSP

STP

CAA CTP CAA

STP

STP

SSP SSP SSP

ACM

ACMACM

Commutateur

d’origine

Commutateur

destination

CTS

30

Call scenario


SSP

STP

CAA CTP CAA

STP

STP

SSP SSP SSP

ANM

ANMANM

Commutateur

d’origine

Commutateur

destination

Décroché

CTS

31

Call scenario


Call scenario

SSP

STP

CAA CTP CAA

STP

STP

SSP SSP SSP

Commutateur

d’origine

Commutateur

destination

Communication

CTS

32


ISDN

Integrated Services Digital Network

!First and last hop digital

!Why digital

• Allow the transmission of various type of communication on the same line (voice, image, video, text)

• May be seen as the evolution of the telephony network

• Tolerate more errors than an analogic signal

• Increase the power of computation (multiplexing, switch)

!ISDN

• Digital continuity from end to end

• Extend the concept of Common Channel Signaling to the interface between the user and the switch

33


Goals and implementation

!The ISDN signaling extends the information exchanged between the user and the network

• Dedicated signaling channel

!Setup of a single network

• Simultaneous and heterogeneous services (e.g., voice + data)

!Service support

• Voice

• Audio 3,1KHz

• Digital Information without restriction

!Téléservice

• Télécopie

• Videotex

• Téléconférences

• Additional services : id of the caller, portability, call presentation, etc

34


Signaling

ISUPISUP

Q.931 Q.931

UNI NNI UNI

35


How does it work?

TNR

TE TE TE

Terminal equipment

RTC

ISDN bus : 144 kbits/sEach of the B channel: 64 kbpsD channel : 16 kbps

Digital termination of the network

36


Q.931 signaling - main messages

! SETUP

• indicating the establishment of a connection! CALL PROCEEDING

• indicating that the call is being processed by the destination terminal! ALERTING

• tells the calling party that the destination terminal is ringing! CONNECT

• sent back to the calling party indicating that the intended destination has answered the call! DISCONNECT

• sent to indicate a request to terminate the connection, by the end that seeks to terminate! RELEASE

• sent in response to the disconnect request indicating that the call is to be terminated! RELEASE COMPLETE

• sent by the receiver of the release to complete the handshake

37


Classical call flow

B

User hangs up

Phone is ringing

User picks up

Communication

Call

A B

Disconnect

Call Proceeding

Communication

Set Up

A

Alerting

Connect

Release

Release Complete

38


Conclusion

!Global network for a dedicated application

• Everything is defined

!High level of QoS

!Main concepts

• PCM coding

- Passband [300, 3400Hz]

- Sampling at 8 kHz

- 64 kbps

• Separate two planes

- Data plane

- Control plane

!High cost of maintenance and evolution

39

On overview of GSM networks Global System for Mobile communication


Terrestrial Mobile Service

!The terrestrial mobile service designates the telecommunication system that allows mobile stations to communicate, while being subject to movement within the border of a country or a continent

• This definition does not include satellite systems

• We consider bi-directional services

• We consider services including voice communications

• We focus on cell phone networks

41


From the fixed networkto the mobile network

!During the 1900’s, a fixed network for telephony has been set up

• PSTN - Public Switched Telephony Network

• A network dedicated for telephony

!GSM aims at extending the PSTN to mobile user

• Use a radio interface between the user and the network

- Cut the cable which link a phone, computer, fax

• Support user mobility

• Main principals are maintained

- Separation of control and data plans

- Application protocol to establish / realize voice calls

- Digital communication

- Circuit switched network

42


Main challenges for GSM

!Interconnection with the PSTN and potentially other networks

!Radio interface

• is shared among large amount of users

• is a broadcast channel

• is less reliable

• is rare and expensive

• Security

!Support the users mobility

• Roaming (movement without communication)

• Handover (movement while being in communication)

43


Principles

!Re-use of radio resources

!Several identities for users

!Authentication and confidentiality

!Location managers

!Gateways between different kinds of networks

!Integration of services

• Voice and data

• Security

• Teleservices

44


Cellular concept

!The goal of the GSM technology is to provide mobile communication for an entire country

!Communication between Base Station and Mobile Station

• The coverage is provided by a set of Base Stations

- Base Stations are distributed within an area in a way to provide full coverage

• Mobile Stations attach to those Base Stations which allow voice calls and other services

!The link between fixed telephony network and mobile system is provided through a fixed network called PLMN (Public Land Mobile Network)

!Frequency bands are 450MHz, 900MHz and 1800MHz

45


Concept of a cell

! A service is made available if the radio link with a mobile station is good enough

! Control the power of the Base Station which are distributed on a region

• The area within which a Mobile Station is able to establish a link with a Base Station is called a Cell

•

! The problem is to set up a system with continuous services, which means that cells must be continuous

MobileStation

BaseStation

Cell

?

46


Deployment example

Which frequency to use ?

Where is a user?

47


Roaming and handover

!A mobile station must be able to call and to be called wherever it is located in the network

!During a communication, a Mobile Station may exit the coverage area of its serving Base Station

• The mobile Station needs to switch Base Station

48


Overview of the location management for an incoming call

Cell 1 Cell 2

Home RegisteryMobile 1 is in Cell 1

1. Initiate a communication with Mobile

2. Call Mobile

3. Call Mobile

Visited registery

4. Voice conversation

49


Overview of the Location Management

Cell 1 Cell 2

Home NetworkMobile 1 is in Cell 1

1. Mobile moves to Cell 2

3. Redirection of voice traffic

2. Information exchange between old and new

location

Active voice communication

50


Radio resource management

!Number of frequencies is limited

!Number of Base Stations is large to cover a region

=> Re-use of the frequencies in non-adjacent cells

R - Radius of the cellD - Re-use distance

R

D

R

51


Cellular deployment

!Pave the area with regular hexagon

!Optimize the number of simultaneous communication in an area

52


Multiplexing

!Objectives

• Provide channel access to several users

• Provide a downlink and an uplink

!Uplink and downlink

• Frequency division

• Half of the frequency band is used for downlink and half is used for uplink

!Share the medium among several users

• TDMA - Time Division Multiple Access

• 8 time slots are used per channel

53


Terminal and SIM card

! Subscriber = person who obtains a service from an operator and who is responsible of the payment

! SIM = Subscriber Identity Module

• Smart card

• Store the user data

- Identity- Last location area- Authorized services- Personal passwords

54

Mobile phone - device

Subscriber


Phone numbers and identities

!MSISDN

• Mobile Station ISDN Number

• Phone number at which a subscriber can be called

! IMSI

• International Mobile Subscriber ID

• Uniquely identifies a user in the network

! IMEI

• International Mobile Equipment ID

• Unique identifier of equipment (cell phone)

!Other numbers

• MSRN - Mobile Station Roaming Number

• TMSI - TEmporary Mobile Station ID

55


Why having multiple identities?

!More practical to manage subscribers

!It is possible to associate several numbers to a single user

!Protect the user from identity stealing

• Avoid sending the IMSI over the radio interface

!Manage mobility

56

GSM Architecture


Three sets

!BSS - Base Station Subsystem

• Radio interface management

!NSS - Network Subsystem

• Communication management (switch and data base)

!OSS - Operation Support System

• Network management by the operator

58


Why these sets?

!NSS vs BSS

• Communication management VS radio management

• NSS manages roaming- Memorize location and route calls

• BSS manages the specifics of the radio- channel allocation, radio transmission, handover

59


Global overview

Um

60


Components

! BSS: radio subsystem

• BTS Base Transceiver Station

- Antenna with a minimum of intelligence

• BSC - Base Station Controller

- Control a set of BTS

61

• NSS: Fixed subsystem

• MSC - Mobile Service Switching center

• Switch for mobile

• VLR - Visitor Location Register

• Data base for visiting mobiles

• HLR - Home Location Register

• Data base for subscribers


Power of the BTS

!It is possible to dynamically control the power of the BTS

Class Power in Watts for GSM 900 Power in Watts for DCS 1800

1 from 320 to 640 from 20 to 40

2 from 160 to 320 from 10 to 20

3 from 80 to 160 from 5 to 10

4 from 40 to 80 from 2.5 to 5

5 from 20 to 40

6 from 10 to 20

7 from 5 to 10

8 from 2.5 to 5

M1 from 0.08 to 0.25 from 0.5 to 1.6

M2 from 0.03 to 0.08 from 0.16 to 0.5

M3 from 0.01 to 0.03 from 0.05 to 0.16

Normal BTS

Micro-BTS

62


BTS-BSC configuration

63


BSC functionalities

!Smart part of the BSS

!Manage the radio interface

• Channels Allocation

• Use of the measures made by the MS and the BTS

• Control the power of the MS

• Decision for handovers

!Manage interfaces with the architecture

• With BTS

• With MSC

• With OSS

64


HLR - Home Location Register

!Manage data base for subscribers

• Information on a user

- IMSI - International Mobile Station Identity

- MSISDN - Mobile Station ISDN Number

- Profile: restriction, additional services, etc

• Location information

- Identity of the VLR where the subscriber is

65


MSC - Mobile-Services Switching Centre

! Manages communication between the mobile stations and the PSTN

! Executes some handover

! Link with the PSTN network

! GMSC function

• Gateway for the incoming calls

! SM-GMSC function

• Gateway for short messages

! Scale

• several hundred of thousands subscribers

66


VLR - Visitor Location Register

! Data base of mobile users that are currently connected to

the MSC

• IMSI - International Mobile Station Identity

• MSISDN - Mobile Station ISDN Number

• TMSI - Temporary Mobile Station Identity

• User profile (restriction, additional services)

• Location area

! Manage the roaming number MSRN

• Mobile Station Roaming Number

• Used for incoming calls between the GMSC and the MSC

! Deployment

• It is possible to have n VLR for 1 MSC or 1 VLR for n MSC

• Usually 1 VLR is coupled with 1 MSC

• Several hundred of thousands subscribers are managed by

a VLR

67


Administration subsystem

! Role

• Monitor network performance

• Commercial administration

• Monitor security

• Equipment maintenance

! EIR - Equipment Identity Register

• Optional - may not be used

• Data base of IMEI (International Mobile Equipment Identity)

! Network management is split in 2 parts

• OMC - Operation and Maintenance system

- Supervise a set of local equipment

- Ex: an OMC-radio may manage some BTS and BSC

• NMC - Network Management Centre

- General administration of the whole network

68


Terminal equipment

! Car phone

• Equipment which is mounted inside a vehicle with an outdoor antenna

! Portable

• Equipment that we can carry, but the antenna is not physically attached to the set keyboard/screen.

! Hand-held station

• Cell phone where the antenna, the keyboard and the screen are on the same device

GSM 900 Power Type

Class 2 8W Vehicule/Portable

Class 3 5W hand-held

Class 4 2W hand-held

Class 5 0.8W hand-held

69

Protocols suite


Role of each interface

Name Location Usage

Um MS - BTS Radio interface

Abis BTS - BSC Various

A BSC - MSC Various (interface BSS - NSS)

C GMSC - HLR Request HLR for incoming calls

C SM-GMSC - HLR Request HLR for incoming short msg

D VLR - HLR Location and subscription management

D VLR - HLR Additional services

E MSC - SM-GMSC Short messages transport

E MSC - MSC Handover execution

F VLR - VLR Subscriber information management

G MSC - EIR Check the terminal ID

H HLR - AUC Authentication

SS7

71


SS7 usage in GSM networks

72

! SS7 is the signalling system in telephony network

! SS7 is used on

• A interface, between the BSC and MSC/VLR

• Within NSS

! Organization

• Each operator defines its own semaphore network

• MSC/VLR and HLR are Semaphore Point

• a MSC/VLR from a country must be able to call an HLR in another country

! Use of MAP (Mobile Application Part) for mobility management in NSS

! Re-use ISUP protocol for call establishment


Inter-connection with PSTN

73


International connection

!Each PLMN is connected

• To the international SS7 network

• To the international telephony circuit switched network

74


Level 3 of the radio interface

! CM - Connection Management

• Re-use of the layer 3 of ISDN between the MS and the MSC (Q.931)

• 3 components

- CC - Call control

- SS - Supplementary services

- SMS - Short Messages

! MM - Mobility Management

• Between the MS and the MSC

• Location update, authentication, MM connection management

! RR - Radio Resource management

• Between the MS and the BSC

• Allocate channel, handover decision, etc

75


The protocol stack

CM = Connection ManagementMM = Mobility ManagementRR = Radio RessourceLAPD = Link Access Protocol-D ChannelMTP = Message Transfer PartSCCP = Signaling Connection Control PartBSSAP = Base Station System Application Part

(SS7)

76


Message identification

Wired case

!Each subscriber line is connected to a port on the switch

• Physical identification of the link

77


Message identification

GSM case

!MS sends messages over the radio interface

!MSC receives the messages from a SCCP connection with the BSC

• Does not see the radio specificities

!Usage of an association table in the BSC

BTS + physical channel SCCP connection

15 (slot 3, Freq 41) Connection 27

... ...

Physical channel SCCP connection

78


Layered architecture in NSS

!Principles• Use SS7

• Re-use at maximum classic protocols (ISUP, SSUTR2)

• Additional protocol MAP to manage roaming

79

CO

Roaming and security


Problem Statement

!Roaming

• Location of each mobile station

• Active mobile, even if is is in stand-by mode

!Radio channel

• User authentication

• Temporary identity

• Encryption

81


Numbers

! IMSI - International Mobile Station Identity

• Permanent identification of a user within the GSM network

!TMSI - Temporary Mobile Station Identity

• Temporary identity of a mobile station used between the mobile station and its BTS

!MSISDN - Mobile Station ISDN Number

• Phone number (can be used by other network, e.g., from the PSTN)

!MSRN - Mobile Station Roaming Number

• Number which is allocated for a call

! IMEI - International Mobile Equipment Identity

• Uniquely identify a device (phone terminal)

82


Call example

7. MSC finally calls the MS by using the TMSI

1. The MSISDN is dialed and routed by the fixed network to the closest MSC

2. GMSC requests the HLR to identify the current MSC

3. HLR translates the MSISDN and request the current VLR

4. VLR allocates a MSRN and send it to the HLR

5. HLR forwards the MSRN to GMSC

6. GSMC establishes the call toward the current MSC, just as a classic call

83


Authentication and encryption

!Radio communication

• Confidentiality threads

- Communication may be listened

• Security threads

- Pirate mobile phone

!GSM solution

• IMSI confidentiality

• User authentication

• User data confidentiality

• Signaling confidentiality

84


User identity confidentiality

!GSM avoids to send IMSI over the radio interface

• Maintain the confidentiality of users identity

• Usage of the TMSI

!Implementation

• VLR generates TMSI for MS

- At least each time the MS changes VLR, and maybe more often

• VLR maintains the correspondence between IMSI and TMSI

• Only at bootstrap or upon failure, the IMSI needs to be sent over the radio interface

• The allocation of the TMSI is encrypted

85


TMSI allocation

SIM MSC/VLR

Location Updating Request (LAI, TMSIold)

Encryption process

Allocation of TMSInew

TMSI Reallocation Command (TMSInew)

Memorize TMSInew

TMSI Reallocation Complete

Deallocation of TMSIold

86


Authentication and encryption Main principles

!Random Numbers (RAND)

!Authentication key Ki

• Ki is the base secret

• Allocated to a user (never sent over the network)

• Authentication (SRES) and determination of the encryption key Kc

!Kc is an encryption key

!Several algorithms

• SRES = A3(RAND, Ki)

• Kc = A8(RAND, Ki)

• A5 algorithm for encryption from Kc

87


Security principals

RAND Ki

A3 A8

RAND SRES Kc

Authentication A5Encryption

Triplet

88


User ID authentication

89


Encryption

90


Distribution of security data

91

Roaming & Location Management


Why do we need location management?

! The last hop is wireless

• Radio interface

• No wired link between the network and the terminal

! No wire ⇒ mobility

• Users can move around

- While they are in stand-by mode

- While they are in a communication

⇒ We need to locate a user

• In case of an incoming call

• Support its mobility : do not break the communication while the user is moving

• Provide efficient methods

- To scale to a large number of users and coverage

- Because signaling is not paid by users

93


Definition

!Roaming: MS without any active communication which is in motion

!Handover: MS with an active voice call which is moving

!Several types of movement

• Inter / intra BSC

• Inter / intra MSC

!Paging

• Research of a user in the network

94


Location management Different choices

! Only search a MS when you need it

• Cost of location: 0

• Cost of research: high

- The entire network is flooded to find the MS

! Always know the exact position of MS

• Cost of location: high

- Each movement must be advertised to the network

- The network needs to store large amount of information

• Cost of research: 0

- The network knows exactly where is the MS, paging is not needed

! Intermediate mechanism

• Define Location Area

95


Location Area

!Set of cells

!Location of the MS = identifier of the location area

!Allow having a rough location of the MS

Cell Border of the location area

96


When do you update the location?

!Manually

• In some systems (e.g., CT2/CAI) users could manually update their position

• Simplify the terminal and network functions

• Does not scale

!Periodically

• Every Xs, the terminal sends its position to the network

• Easy to implement, but may generate to much traffic

!Update upon a change

• When the terminal detects a change in its location area, it informs the network

• Need the BTS to periodically send a Location Area Identifier

97


Roaming management

! Location trade-off

• Make the precise location of MS known by all entity is costly

- Frequent location updates are needed

• Maintain a rough location of MS

- Cost of location update is low

- Research of the MS is costly

! GSM choice : 2 mechanisms

• Location

- Knowledge of the location area of the mobile station

- Location updates are made by the MS

– At each change in the location area

– Periodically

• Paging

- Find the precise location of a mobile station upon an incoming call

- Only look into the known location area

98


Location Area Identification

!MCC - Country Code

!MNC - PLMN identification

!LAC - Number of the location area, freely allocated by the operator

MCC MNC LAC

99


Who knows what?

LAIk

IMSIa, TMSIa, LAIk

IMSIa => MSCj, LAIk, TMSIa

MSCj

GMSC

MSISDN => VLRi, IMSIa

100

Some call flows


Outgoing calls

102


Incoming call

103


Incoming call

104


Conclusion

!GSM is a very popular system

• By 2005, more than 75% of the worldwide cellular network market

• Over 3 billions of subscribers in 219 countries

!Extend the fixed telephony network with a radio interface

• TArget the same quality of service - a dedicated architecture for a dedicated (single) application

!Strongly evolve over the past 15 years towards data communication

105

2G 3G 4G

GSM 1992

GPRS 1997

EDGE 1998

UMTS 2000

HSPA 2002

HSPA+ 2007

LTE 2008

LTE-Adv

2011

traditional telephony network and...

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