IT6601 MOBILE COMPUTING

UNIT – III

Dr.A.Kathirvel, Professor and Head, Dept of IT

Mrs. D. Anbarasi, Asst. Professor/IT

Anand Institute of Higher Technology, Chennai

Unit - III

MOBILE TELECOMMUNICATION SYSTEM

Global System for Mobile Communication (GSM) –

General Packet Radio Service (GPRS) – Universal Mobile

Telecommunication System (UMTS).

*Prasant Kumar Pattnaik, Rajib Mall, “Fundamentals of Mobile Computing”, PHI Learning Pvt. Ltd, New Delhi

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Synopsis

Global System for Mobile Communication (GSM)

GSM Services

System Architecture of GSM

GSM Security

General Packet Radio Service (GPRS)

GPRS Services

GPRS Architecture

Universal Mobile Telecommunication System (UMTS)

UMTS Network Architecture

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What is GSM?

GSM (Global System for Mobile communication)

is a digital mobile telephony system that is widely

used in Europe and other parts of the world.

GSM is a second generation cellular standard

developed to cater voice services and data delivery

using digital modulation.

GSM uses a variation of time division multiple

access (TDMA) and is the most widely used of the

three digital wireless telephony technologies

(TDMA, GSM, and CDMA).

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What is GSM?

GSM digitizes and compresses data,

then sends it down a channel with two

other streams of user data, each in its

own time slot.

It operates at either the 900 MHz or

1800 MHz frequency band

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GSM Services

TELE SERVICES : Includes mobile

phones, emergency calling etc.

DATA SERVICES : Includes SMS

(Short message service), fax, voicemail,

electronic mail.

SUPPLYMENTARY SERVICES : I/C

& O/G calls, call forwarding, call hold,

call waiting, conference, etc.

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GSM Subscriber Services

Dual-Tone MultiFrequency (DTMF)—DTMF is a tone

signaling scheme often used for various control purposes via

the telephone network, such as remote control of an answering

machine. GSM supports full-originating DTMF.

facsimile group III—GSM supports CCITT Group 3

facsimile. As standard fax machines are designed to be

connected to a telephone using analog signals, a special fax

converter connected to the exchange is used in the GSM

system.

short message services—A convenient facility of the GSM

network is the short message service. A message consisting of

a maximum of 160 alphanumeric characters can be sent to or

from a mobile station.

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GSM Subscriber Services cell broadcast—A variation of the short message service is the

cell broadcast facility. A message of a maximum of 93

characters can be broadcast to all mobile subscribers in a certain

geographic area. Typical applications include traffic congestion

warnings and reports on accidents.

voice mail—This service is actually an answering machine

within the network, which is controlled by the subscriber. Calls

can be forwarded to the subscriber's voice-mail box and the

subscriber checks for messages via a personal security code.

fax mail—With this service, the subscriber can receive fax

messages at any fax machine. The messages are stored in a

service center from which they can be retrieved by the

subscriber via a personal security code to the desired fax

number.

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GSM Supplementary Services

call forwarding—This service gives the subscriber the ability

to forward incoming calls to another number if the called

mobile unit is not reachable, if it is busy, if there is no reply, or

if call forwarding is allowed unconditionally.

barring of incoming calls—This function allows the subscriber

to prevent incoming calls. The following two conditions for

incoming call barring exist: baring of all incoming calls and

barring of incoming calls when roaming outside the home

PLMN.

advice of charge (AoC)—The AoC service provides the mobile

subscriber with an estimate of the call charges. There are two

types of AoC information: one that provides the subscriber with

an estimate of the bill and one that can be used for immediate

charging purposes.

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GSM Supplementary Services

call hold—This service enables the subscriber to interrupt an

ongoing call and then subsequently reestablish the call. The

call hold service is only applicable to normal telephony.

call waiting—This service enables the mobile subscriber to

be notified of an incoming call during a conversation. The

subscriber can answer, reject, or ignore the incoming call.

Call waiting is applicable to all GSM telecommunications

services using a circuit-switched connection.

multiparty service—The multiparty service enables a

mobile subscriber to establish a multiparty conversation—

that is, a simultaneous conversation between three and six

subscribers. This service is only applicable to normal

telephony.

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GSM Supplementary Services

Calling line identification presentation/restriction—

These services supply the called party with the integrated

services digital network (ISDN) number of the calling

party. The restriction service enables the calling party to

restrict the presentation. The restriction overrides the

presentation.

Closed user groups (CUGs)—CUGs are generally

comparable to a PBX. They are a group of subscribers

who are capable of only calling themselves and certain

numbers.

Barring of outgoing calls—This service makes it

possible for a mobile subscriber to prevent all outgoing

calls.

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GSM Architecture

Network sub-system

Radio sub-system

Operation and maintenance sub-system

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GSM Architecture

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Mobile Station(MS)

The Mobile Station is made up of two entities:

Mobile Equipment (ME)

Subscriber Identity Module (SIM)

Mobile Equipment (ME)

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

160 character long SMS.

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Mobile Station(MS)

Subscriber Identity Module(SIM)

Smart card contains the International Mobile Subscriber Identity (IMSI)

Allows user to send and receive calls and receive other subscribed services

Protected by a password or PIN

Can be moved from phone to phone – contains key information to activate the phone

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Network sub-system/Switching System

Home location register (HLR) —The HLR is a

database used for storage and management of

subscriptions. The HLR is considered the most

important database, as it stores permanent data about

subscribers, including a subscriber's service profile,

location information, and activity status.

Mobile services switching center (MSC) —The

MSC performs the telephony switching functions of

the system. It controls calls to and from other

telephone and data systems. It also performs such

functions as toll ticketing, network interfacing,

common channel signaling, and others.

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Network sub-system/Switching System

Visitor location register (VLR) —The VLR is a

database that contains temporary information about

subscribers that is needed by the MSC in order to

service visiting subscribers. The VLR is always

integrated with the MSC.

Authentication center (AUC) —A unit called the

AUC provides authentication and encryption

parameters that verify the user's identity and ensure

the confidentiality of each call. The AUC protects

network operators from different types of fraud found

in today's cellular world.

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Network sub-system/Switching System

Equipment identity register (EIR) —The

EIR is a database that contains information

about the identity of mobile equipment that

prevents calls from stolen, unauthorized, or

defective mobile stations. The AUC and

EIR are implemented as stand-alone nodes

or as a combined AUC/EIR node.

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Base Station System/Radio Sub-System

BSC —The BSC provides all the control functions

and physical links between the MSC and BTS. It is a

high-capacity switch that provides functions such as

handover, cell configuration data, and control of

radio frequency (RF) power levels in base

transceiver stations. A number of BSCs are served by

an MSC.

BTS —The BTS handles the radio interface to the

mobile station. The BTS is the radio equipment

(transceivers and antennas) needed to service each

cell in the network. A group of BTSs are controlled

by a BSC.

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Base Station System/Radio Sub-System

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OPERATION AND

MAINTENANCE SUBSYSTEM

Dynamic monitoring and controlling of

network.

Operation and maintenance data function.

Configuration management.

Fault report and alarm handling.

Performance supervision.

Storage of software and data.

Stores data for minimum one year.

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Security in GSM

On air interface, GSM uses encryption and

TMSI 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

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GSM Security Design Requirements

Add significant overhead on call set up

Increase bandwidth of the channel

Increase error rate

Add expensive complexity to the system

Cost effective scheme

Define security procedures

Generation and distribution of keys

Exchange information between operators

Confidentiality of algorithms

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GSM Security Features

Key management is independent of equipment Subscribers can change handsets without compromising security

Subscriber identity protection not easy to identify the user of the system intercepting a user data

Detection of compromised equipment - Detection mechanism whether a mobile device was compromised or not

Subscriber authentication - The operator knows for billing purposes who is using the system

Signaling and user data protection- Signaling and data channels are protected over the radio path

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Authentication and Encryption Scheme

A3

Mobile Station Radio Link GSM Operator

A8

A5

A3

A8

A5

Ki Ki

Challenge RAND

Kc Kc

mi Encrypted Data mi

SIM

Signed response (SRES) SRES SRES

Authentication: are SRES

values equal?

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A3 – MS Authentication Algorithm

Goal

Generation of SRES response to MSC’s random

challenge RAND

A3

RAND (128 bit)

Ki (128 bit)

SRES (32 bit)

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A8 – Voice Privacy Key Generation

Algorithm

Goal

Generation of session key Kc

A8 specification was never made public

A8

RAND (128 bit)

Ki (128 bit)

KC (64 bit)

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Logical Implementation of A3 and A8

Both A3 and A8 algorithms are implemented

on the SIM

Operator can decide, which algorithm to use.

Algorithms implementation is independent of

hardware manufacturers and network operators.

COMP128 is used for both A3 and A8 in most

GSM networks.

COMP128 is a keyed hash function

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A5 – Encryption Algorithm

A5 is a stream cipher

Implemented very efficiently on hardware

Design was never made public

Leaked to Ross Anderson and Bruce Schneier

Variants

A5/1 – the strong version

A5/2 – the weak version

A5/3

GSM Association Security Group and 3GPP design

Based on Kasumi algorithm used in 3G mobile systems

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A5 Encryption

Mobile Stations Base Station

Subsystem

Exchange

System

Network

Management

Subscriber and terminal

equipment databases

BSC MSC VLR

HLR

EIR

AUC

OMC BTS

BTS

BTS

A5 Encryption

General packet radio service (GPRS)

General packet radio service (GPRS) is a packet

oriented mobile data service on the 2G and 3G cellular

communication system's global system for mobile

communications(GSM). GPRS was originally

standardized by European Telecommunications

Standards Institute (ETSI) in response to the

earlier CDPD and i-mode packet-switched cellular

technologies.

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GPRS Networks based on the Internet Protocol (IP) and X.25

Theoretically maximum rate is just 171. 2 Kbits/sec.

A realistic estimation on transfer is between 5 and 40

kbps.

It applies a packet radio principle to transfer user data

packets in an efficient way.

This principle offers a more user-friendly billing than

that offered by circuit switched services.

User can be "online" over a long period of time but

will be billed based on the transmitted data volume.

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GPRS Architecture

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GPRS Architecture

A serving GPRS support node (SGSN) is responsible for

Delivery of data packets from and to the mobile stations within its service area.

Packet routing and transfer

Mobility management (attach/detach and location management)

Authentication and charging functions. The location register of the SGSN stores location information and user profiles (IMSI, addresses used in the packet data network) of all GPRS users registered with this SGSN.

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GPRS Architecture

A gateway GPRS support node (GGSN) acts as an interface between the GPRS backbone network and the external packet data networks.

It converts the GPRS packets coming from the SGSN into the appropriate packet data protocol (PDP) format (IP or X.25) and sends them out on the corresponding packet data network.

In the other direction, PDP addresses of incoming data packets are converted to the GSM address of the destination user. The readdressed packets are sent to the responsible SGSN. For this purpose, the GGSN stores the current SGSN address of the user and his or her profile in its location register.

Also performs authentication and charging functions.

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GPRS Mobility Management

GPRS Attachment

GPRS Detachment

Location Management

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GPRS Attachment Procedure

Before a mobile station can use GPRS services, it must register with an

SGSN of the GPRS network. This procedure follows as

mobile is authenticated

with the mobile's Home

Location Register

SGSN does an update

of the GPRS location

SGSN sends an "Attach

Accept" message to the

mobile

mobile responds with

an "Attach Complete"

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Attach request which includes IMSI which then processed by the network

to P-TMSI.

GPRS Detachment Procedure The disconnection from the GPRS. It can be initiated

by the mobile station or by the network (SGSN).

In MS initiated one; MS informs that it wants to leave the system, this is MS’s wish. If any contexts are active, network will clear them. Afterwards MS’s location is not tracked anymore.

In Network initiated one; Network wants to “get rid of the MS” because of;

Ill behaving mobile

Congested network

Immediate service termination (IST)(E.g. Bills are not paid)

Load new parameters (Configuration has been changed and they should be taken into use)

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Location Management

Aim is to keep track of the user's current location, so that incoming packets can be routed to his or her MS.

If the MS sends update messages seldom, its location is not known exactly, resulting in a significant delivery delay.

On the other hand, if location updates happen very often, the MS's location is well known to the network, and the data packets can be delivered without any additional delay. But, quite a lot of uplink radio capacity and battery power is consumed for mobility management.

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Location Management

A MS can be in one of three states depending on its current traffic amount; the location update frequency is dependent on the state of the MS.

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Location Management

In IDLE state the MS is not reachable. Performing a GPRS attach, the MS gets into READY state. With a GPRS detach it may disconnect from the network and fall back to IDLE state. All PDP contexts will be deleted.

The STANDBY state will be reached when an MS does not send any packets for a longer period of time, and therefore the READY timer, which was started at GPRS attach, expires.

In IDLE state, no location updating is performed, the current location of the MS is unknown to the network.

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Location Management

An MS in READY state informs its SGSN of every movement to a new cell(in GSM).

In GPRS, for the location management of an MS in STANDBY state, a GSM location area (LA) is divided into several routing areas (RA). In general, an RA consists of several cells. The SGSN will only be informed when an MS moves to a new RA; cell changes will not be disclosed. Whenever an MS moves to a new RA, it sends a "routing area update request" to its assigned SGSN. The message contains the routing area identity (RAI) of its old RA.

In same SGSN routing area update

In different SGSN routing area update

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Session Management

To exchange data packets with external PDNs

after a successful GPRS attach, a mobile

station must apply for one or more addresses

used in the PDN, e.g., for an IP address in case

the PDN is an IP network.

This address is called PDP address (Packet

Data Protocol address).

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Session Management The allocation of the PDP address can be static or

dynamic.

Static : The network operator of the user's home-PLMN permanently assigns a PDP address to the user.

Dynamic : PDP address is assigned to the user upon activation of a PDP context.

The PDP address can be assigned by the operator of the user's home-PLMN (dynamic home-PLMN PDP address)

By the operator of the visited network (dynamic visited-PLMN PDP address).

In case of dynamic PDP address assignment, the GGSN is responsible for the allocation and the activation/ deactivation of the PDP addresses

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Session Management For each session, a PDP context is created, which

describes the characteristics of the session. It contains;

the PDP type (e.g., IPv4),

the PDP address assigned to the mobile station (e.g., 129.187.222.10),

the requested QoS,

the address of a GGSN that serves as the access point to the PDN

This context is stored in the MS, the SGSN, and the GGSN. With an active PDP context, the mobile station is "visible" for the external PDN and is able to send and receive data packets. The mapping between the two addresses, PDP and IMSI, enables the GGSN to transfer data packets between PDN and MS.

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Session Management

PDP context activation procedure

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Quality of Service

GPRS allows defining QoS profiles using the parameters service precedence, reliability, delay, and throughput.

The service precedence is the priority : high, normal, and low.

The reliability indicates the transmission characteristics required by an application. Three reliability classes are defined, which guarantee certain maximum values for the probability of loss, duplication, missequencing, and corruption (an undetected error) of packets.

The delay parameters define maximum values for the mean delay. The delay is defined as the end-to-end transfer time between two communicating mobile stations or between a mobile station and the Gi interface to an external packet data network.

The throughput specifies the maximum bit rate and the mean bit rate.

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GPRS Services

Offers end-to-end packet switched data transfer

Bearer Services

PTP - Point-To-Point service (CLNS mode)

PTM - Point-To-Multipoint service(CONS Mode)

PTM-M Multicast service

PTM-G Group call service

Supplementary Services

SMS-Short Message Service

CFU-Call Forwarding Unconditional

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GPRS Services

CFNRc Call Forwarding on mobile subscriber

not reachable

CUG Closed User Group

Tele action, access to data bases

Quality of Service

GPRS allows defining QoS profiles

Service precedence, reliability, delay,

throughput

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Advantages of GPRS

Improves the utilization of the radio resources

Multiple users can share one physical

channel

Volume-based billing

Higher transfer rates

Max 171.2Kbits/sec

Shorter access times

Simplifies the access to packet data networks

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Applications of GPRS

Textual and Visual Information

Still Images

Web Browsing

Document Sharing

Corporate Email

Internet Email

Vehicle Positioning

File Transfer

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Universal Mobile Telecommunications

System(UMTS)

UMTS is a 3G networking standard used throughout much of

the world as an upgrade to existing GSM mobile networks.

UMTS makes use of WCDMA, a technology that shares

much with CDMA networks used throughout the world,

though it is not compatible with them.

Base level UMTS networks are generally capable of downlink

speeds as fast as 384kbps. Newer HSDPA variants are capable

of rates as high as 3.6Mbps or more.

Originally used only on the 2100MHz frequency band in

Europe, UMTS is now supported on the 850MHz and

1900MHz bands in North America.

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UMTS Architecture

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UMTS Bearer Services

TE

MT

UTRAN

CN Iu

EDGE

NODE

CN

Gateway

TE

End-to-End Service

External Bearer

Service

Radio Access Bearer

Service

Backbone

Network Service

UTRA

FDD/TDD

Service

TE/MT Local

Bearer Sevice UMTS Bearer Service

CN Bearer

Service

Radio Bearer

Service

Iu Bearer

Service

Physical Bearer

Service

UMTS

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UMTS QoS Classes Traffic class Conversational

class

Streaming

class

Interactive

class

Background

Fundamental

characteristics

Preserve time

relation

between

information

entities of the

stream

Conversational

pattern

(stringent and

low delay)

Preserve time

relation

between

information

entities of the

stream

Request

response

pattern

Preserve data

integrity

Destination is

not expecting

the data

within a

certain time

Preserve data

integrity

Example of the

application

Voice,

videotelephony,

video games

Streaming

multimedia

Web browsing,

network games

Background

download of

emails

Questions ?

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