A

Seminar Report

On

SECURITY IN MOBILE DATABASE SYSTEMS

Submitted By :-

Pankaj Menaria

Yash Vyas Kamlesh Jain

A

Seminar Report

On

SECURITY IN MOBILE DATABASE SYSTEMS

In partial fulfillment of requirements for the degree of

Bachelor of Engineering

In

Computer Engineering

SUBMITTED BY:

Pankaj Menaria

Yash Vyas

Kamlesh Jain

Under the Guidance of

Mr. Ajay Prasad

DEPARTMENT OF COMPUTER SCIENCE ENGINEERING

PAGE INDEX

SN Topic

1. INTRODUCTION

1.1 SECURITY IN MOBILE DATABASE

1.2 MOBILE DATABASE

1.3 MOBILE SECURITY

1.4 DATABASE SECURITY

1.5 NEED FOR MOBILE DATABASE

2. MOBILE DATABASE SYSTEMS

2.1 Fully Connected Information Space

2.2 Personal Communication System (PCS)

2.3 Mobile Database Systems (MDS)

2.4 Transaction Management

2.5 Query Processing

2.6 Location and Handoff Management 2.7 Wireless Information Broadcast

3. MOBILE DATABASE SECURITY

3.1 MOBILE CONDITIONS

3.2 PROTECTION OBJECTS AND ACTION

4. CONCLUSION

5. REFERENCES

1. INTRODUCTION

The importance of databases in modern

businesses and governmental institutions is

huge and still growing. Many mission-

critical applications and business processes

rely on databases. These databases contain

data of different degree of importance and

confidentiality, and are accessed by a wide

variety of users. Integrity violations for a

database can have serious impact on business

processes; disclosure of confidential data in

some cases has the same effect. Traditional

database security provides techniques and

strategies to handle such problems with

respect to database servers in a non-mobile

context.

1.1 SECURITY IN MOBILE DATABASE

With the rise in popularity of smartphones

has come an increasing need to secure them.

Since their introduction mobile phones have

becoming increasingly smaller, more

powerful with increasing storage capacity

and have remained expensive items. With the

rise of their popularity so has the need to

secure the devices from theft, as well as

traditional threats that effect computers such

as malware and the need to back and protect

the data on the devices.

Database security is also a specialty within

the broader discipline of computer security.

For many businesses applications are going

mobile that means using enterprise data in a

mobile context, thus using a mobile DBMS.

With these new developments the business

data of an enterprise can be made available

to an even larger number of users and a

wider range of applications than before.

To work on business data anytime and

anywhere is the major goal pursued by

developing mobility support in database

context. The confidentiality of mission-

critical data must be ensured, even though

most mobile devices do not provide a secure

environment for storage of such data.

Security requirements that apply to a central

company database should apply similarly and

in an appropriate manner to the parts of the

database replicated on mobile devices in the

field. A mobile database security

infrastructure is needed to accomplish this

goal. When developing such an infrastructure

we can benefit from the results of traditional

database security work. But we also need to

adapt the existing techniques and strategies

to the mobile context, and we need to

develop new ones that attack certain issues

specific to use of database systems in a

mobile environment.

1.2 MOBILE DATABASE

A mobile database is a database that can be

connected to by a mobile computing device

over a mobile network. The client and server

have wireless connections. A cache is

maintained to hold frequent data and

transactions so that they are not lost due to

connection failure. A database is a structured

way to organize information. This could be a

list of contacts, price information or distance

travelled.

The use of laptops, mobiles and PDAs is

increasing and likely to increase in the

future[citation needed]

with more and more

applications residing in the mobile systems.

While those same analysts can’t tell us

exactly which applications will be the most

popular, it is clear that a large percentage

will require the use of a database of some

sort. Many applications such as databases

would require the ability to download

information from an information repository

and operate on this information even when

out of range or disconnected.

An example of this is a mobile workforce. In

this scenario user would require to access

and update information from files in the

home directories on a server or customer

records from a database. This type of access

and work load generated by such users is

different from the traditional workloads seen

in client–server systems of today. With the

advent of mobile databases, now users can

load up their smart phones or PDAs with

mobile databases to exchange mission-

critical data remotely without worrying about

time or distance. Mobile databases let

employees enter data on the fly. Information

can be synchronized with a server database at

a later time.

1.3 MOBILE SECURITY

With the rise in popularity of smartphones

has come an increasing need to secure them.

Since their introduction mobile phones have

becoming increasingly smaller, more

powerful with increasing storage capacity

and have remained expensive items. With the

rise of their popularity so has the need to

secure the devices from theft, as well as

traditional threats that effect computers such

as malware and the need to back and protect

the data on the devices.

A recent report from McAfee titled" 2011

Threats Predictions", outlines the company’s

concerns about the changing ―threats

landscape‖ thanks in part to increases in

malware sophistication and targeting and

how they relate to seven areas — including

social media, mobile Apple-related products

and applications.

Although viruses are a key concern, the

actual number of viruses targeting mobile

phones in the wild has not been widespread.

1.4 DATABASE SECURITY

Database security is the system, processes,

and procedures that protect a database from

unintended activity. Unintended activity can

be categorized as authenticated misuse,

malicious attacks or inadvertent mistakes

made by authorized individuals or processes.

Traditionally databases have been protected

from external connections by firewalls or

routers on the network perimeter with the

database environment existing on the internal

network opposed to being located within a

demilitarized zone. Additional network

security devices that detect and alert on

malicious database protocol traffic include

network intrusion detection systems along

with host-based intrusion detection systems.

Database security is more critical as

networks have become more open.

Databases provide many layers and types of

information security, typically specified in

the data dictionary, including:

Access control

Auditing

Authentication

Encryption

Integrity controls

1.5 NEED FOR MOBILE DATABASE

Mobile users must be able to work

without a wireless connection due to

poor or even non-existent connections.

Applications must provide significant

interactivity.

Applications must be able to access

local device/vehicle hardware, such as

printers, bar code scanners, or GPS

units (for mapping or Automatic

Vehicle Location systems).

Bandwidth must be conserved (a

common requirement on wireless

networks that charge per megabyte or

data transferred).

Users don't require access to truly live

data, only recently modified data.

Limited life of power supply(battery)

The changing topology of network

If your application meets any of those

requirements, the chances are good that you

will be required to build a mobile database

application with synchronization.

Mobile database system architecture

For any mobile architecture, things to be

considered are:

Users are not attached to a fixed

geographical location

Mobile computing devices: low-power,

low-cost, portable

Wireless networks

Mobile computing constraints

1) Three parties

Mobile databases typically involve three

parties: fixed hosts, mobile units, and base

stations. Fixed hosts perform the transaction

and data management functions with the help

of database servers. Mobile units are portable

computers that move around a geographical

region that includes the cellular network (or

"cells") that these units use to communicate

to base stations. (Note that these networks

need not be cellular telephone networks.)

Base stations are two-way radios,

installations in fixed locations, that pass

communications with the mobile units to and

from the fixed hosts. They are typically low-

power devices such as mobile phones,

portable phones, or wireless routers.

When a mobile unit leaves a cell serviced by

a particular base station, that station

transparently transfers the responsibility for

the mobile unit's transaction and data support

to whichever base station covers the mobile

unit's new location.

2) Products

Sybase Inc.’s SQL Anywhere dominates the

mobile-database field, with about 68 percent

of the mobile database market. IBM’s DB2

Everyplace is a relational database and

enterprise synchronization server that

extends enterprise applications to mobile

devices. Microsoft SQL Server Compact and

Oracle9i Lite are similar mobile databases.

Products from lesser-known vendors, such as

SQLBase from Gupta Technologies LLC of

Redwood Shores, Calif., HanDBase from

DDH Software Inc. of Lake Worth, Fla.and

Database Viewer Plus from Cellica

Corporation NY, might serve your needs

equally well.

3) Sybase's SQL Anywhere

SQL Anywhere offers enterprise-caliber

databases that scale from 64-bit servers with

thousands of users down to small handheld

devices. SQL Anywhere’s data exchange

technologies extend information in corporate

applications and enterprise systems to

databases running in mission-critical

frontline environments. Design and

management tools within SQL Anywhere

enable developers to implement and deploy

frontline applications and equip

administrators to easily manage and support

them.

4) SQL Anywhere Technologies

SQL Anywhere Server is a high performing

and embeddable relational database-

management system (RDBMS) that scales

from thousands of users in server

environments down to desktop and mobile

applications used in widely deployed, zero-

administration environments.

Ultralite: UltraLite is a database-

management system designed for small-

footprint mobile devices such as PDAs and

smart phones.

Mobilink: MobiLink is a highly-scalable,

session-based synchronization technology for

exchanging data among relational databases

and other non-relational data sources.

QAnywhere: QAnywhere facilitates the

development of robust and secure store-and-

forward mobile messaging applications.

SQL Remote: SQL Remote technology is

based on a store and forward architecture that

allows occasionally connected users to

synchronize data between SQL Anywhere

databases using a file or message transfer

mechanism.

5) IBM DB2 Everyplace (DB2e)

DB2e stores, retrieves, organizes and

manages data on a handheld device. The data

on the handheld device is synchronized to a

server-based relational database management

system (RDMS). DB2e is currently available

for Palm OS, EPOC, Neutrino, Windows CE

and embedded Linux DB2e on the handheld

device includes:

IBM DB2 Database Engine

IBM Sync

Query By Example (QBE)

DB2e includes a component called

Synchronization Server, which:

Allows synchronization between DB2e

and server database

Mobile Device Administration Center

(MDAC)

Table encryption for version 8.1.1

Java ME Sync Client for cell phones

and pagers

6) Microsoft SQL Server Compact

(formerly SQL Server 2005 Mobile

Edition)

Microsoft SQL Server Compact (SSC) is a

small footprint embedded database designed

for developers who target Microsoft

Windows mobile-based devices or desktops.

It provides synchronization with Microsoft

SQL Server, programming APIs, integrated

development experience through Visual

Studio and a Management Studio.

7) Oracle9i Lite

This is a complete solution for mobile or

wireless applications that require the use of a

relational database on the mobile client. It

includes support for Win32, Windows CE,

PalmOS, and EPOC database clients,

integration with Oracle's Advanced Queuing

(AQ) mechanism, and data and application

synchronization software (to enterprise

Oracle databases. The Oracle9i Lite

relational database is surprisingly[citation needed]

powerful. The database supports 100% Java

development (through JDBC drivers and the

database's native support for embedded SQLJ

and Java stored procedures) as well as

programming from any development tool

that supports ODBC (Visual Basic, C++,

Delphi, and so on).

8) Others

Borland's JDataStore

Borland JDataStore 6 is a fast, versatile Java

database for truly portable embedded,

mobile, and Web server applications.

Compliant with Java and SQL92 standards,

the JDataStore database features a very small

footprint, requires practically zero

maintenance, and delivers the performance,

scalability, and synchronization capabilities

of a full-power database.

MobiSnap

MobiSnap, a research project that aims to

support the development of SQL based

applications for mobile environments,

providing conquerable support for data

divergence control and connectivity

abstractions. MobiSnap aims at developing a

middle-ware infrastructure that allows access

to relational database systems from mobile

computers with a clear semantics in all

operational scenarios (from high to

unavailable connectivity). This platform will

isolate programmers from the problems

related to mobility and disconnection,

allowing them to easily develop new

applications for mobile environments,

focusing only on application specific

problems. MobiSnap will be based on SQL,

thereby also providing close integration to

legacy information systems.

2. MOBILE DATABASE

SYSTEMS

2.1 Fully Connected Information Space

Each node of the information space has

some communication capability.

Some node can process information.

Some node can communicate through

voice channel.

Some node can do both

Can be created and maintained by integrating

legacy database systems, and wired and

wireless systems (PCS, Cellular system, and

GSM)

2.2 Personal Communication System (PCS)

A system where wired and wireless networks are integrated for establishing communication.

PCS refers to variety of wireless access

(communication) and personal mobility

services provided through a small terminal at

any place, and in any form. Business

opportunities (E-commerce) for such

services are tremendous, since every person,

every organization, etc., could be equipped.

Several PCS systems have been developed to

meet rapid growth prompted by market

demand. Most of them are connected to

Public Switched Telephone Network (PSTN)

to integrate with the wired service.

Two of the most popular PCS systems

are:

Cellular telephony

Cordless and low-tier PCS telephony

Cellular telephony overview

Four popular cellular telephony networks

are:

Advanced Mobile Phone Service (AMPS)

Global System for Mobile

Communication (GSM)

EIA/TIA IS-136 Digital Cellular System

EIA/TIA IS-95 Digital Cellular System

Advanced Mobile Phone Service (AMPS)

AMPS was the first cellular system, which

was developed during the 1970s by Bell Lab.

From 1974 to 1978, a large scale AMPS trial

was conducted in Chicago. Commercial

AMPS service has been available since 1983.

It is based on frequency division multiple

access (FDMA), AMP was designed as a

high capacity system based on a frequency

PSTN: Public Switched Network.

MSC: Mobile Switching Center. Also called MTSO

(Mobile Telephone Switching Office).

BS: Base Station.

MS: Mobile Station. Also called MU (Mobile Unit)

or Mobile Host (MH).

HLR: Home Location Register.

VLR: Visitor Location Register.

EIR: Equipment Identify Register.

AC: Access Chanel.

PSTN

BS

VLR

HLR

EIR

AC

MSC (MTSO)MSC (MTSO)

MSMS Wireless component

reuse scheme. A total of 50 MHz in the 824-

849 MHz and 869-894 MHz bands is

allocated for AMPS.This spectrum is divided

into 832 full-duplex channels using 1664

discrete frequencies, that is, 832 downlinks

and 832 uplinks. In AMPS, the typical

frequency reuse plan employs either a 12-

group frequency cluster using

omnidirectional antennas or a 7-group cluster

using three sectors per base stations. Thus,

there are about 50 channels per cell.

Global System for Mobile

Communication (GSM)

GSM is a digital cellular system

developed by Groupe Special Mobile of

Conference Europeenne des Postes et

Telecommunications (CEPT) and its

successor European Telecommunications

Standard Institute (ETSI). GSM combines

time divisioin multiple access (TDMA) and

FDMA. With TDMA, the radio hardware in

the base station can be shared among

multiple users. In GSM the frequency carrier

is divided into eight time slots where the

speech coding rate is 13 Kbps. In a GSM

base station, every pair of radio transceiver-

receiver supports eight voice channels,

whereas an AMPS base station needs one

such pair for every voice channel. The GSM

development process was similar to that of

AMPS, except that no large scale trial was

conducted.

EIA/TIA IS-136 Digital Cellular

System

This system is also referred to as

digital AMPS (DAMPS), American Digital

Cellular (ADC), or North American TDMA

(NA-TDMA), IS-136, the successor to IS-54,

supports a TDMA air interface similar to that

of GSM. IS-54 was renamed IS-136 when it

reached revision C. It supports three voice

channels, where the speech coding rate is

7.95 Kbps. IS-136 capacity is around three

times that of AMPS. An existing AMPS

system can be easily upgraded to IS-136 0n a

circuit-by-circuit basis.

EIA/TIA IS-95 Digital Cellular

System

This digital cellular system was

developed by Qualcomm, and has been

operating in USA since 1996. IS-95 is based

on Code Division Multiple Access (CDMA)

technology. It allows many users to share a

common frequency/time channel for

transmission. The channel bandwidth used

by IS-95 is 1.25 MHz, which has been

extended to 5 MHz in the third generation

wideband CDMA proposal. The speech

coding rate for IS-95 is 13 Kbps or 8 Kbps.

IS-95’s capacity is estimated to be 10 times

that of AMPS.

Cordless Telephone, Second

Generation (CT2)

Developed in Europe, and has been

available since 1989. CT2 is allocated 40

FDMA channels with a 32-Kbps speech

coding rate. For a user, both baseptop

handset signals and handset-to-base signals

are transmitted in the same frequency. The

maximum transmit power of a CT2 handset

is 10 mW. In the call setup procedure, CT2

moves a call path from one radio channel to

another after three seconds of handshake

failure. CT2 also supports data transmission

rates of up to 2.4 Kbps through the speech

code and up to 4.8 Kbps with an increased

rate. CT2 does not support handoff and in a

public CT2 system, call delivery is not

supported.

Digital European Cordless Telephone

(DECT)

The Digital European Cordless

Telephone has been replaced by Digital

Enhanced Cordless Telephone to denote

global acceptance of DECT. DECT supports

high user density with a picocell design.

There are 12 voice channels per frequency

carrier. Sleep mode is employed to converse

handset power. DECT also supports

seamless handoff. DECT is typically

implemented as a wireless-PBX (Private

Brach Exchange) connected to PSTN.

DECT can interwork with GSM to allow user

mobility.

Low-tier PCS telephony overview

Personal Handy Phone System

(PHS)

PHS is a standard developed by the

Research and Development Center for Radio

Systems (RCR), a private standardization

organization in Japan. PHS is a low-tier

digital PCS system that offers

telecommunication services for homes,

offices, and outdoor environment, using

radio access to the public telephone network

or other digital networks. PHS uses TDMA.

Sleep mode enables PHS to support five

hours of talk time, or 150 hours of standby

time. PHS operates in the 1895-1918.1 MHz

band. The bandwidth is partitioned into 77

channels, each with 300 KHz bandwidth.

The band 1906.1-1918.1 MHz (40 channels)

is designed for public systems, and the band

1895-1906.1 MHz (37 channels) is used for

home/office applications.

Personal Access Communications

Systems (PACS)

PACS is a low-power PCS system

developed at Telcordia (formerly Bellcore).

TDMA is used in PACS with eight voice

channels per frequency carrier. In FDD

mode, the PACS uplink and downlink

utilizes different RF carriers, similar to

cellular systems.

Cordless and low-tier PCS telephony overview

System High-tier Cellular Low-tier PCS Cordless

Cell size Large (0.4-22 mile) Medium (30-300’) Small (30-60’)

User speed High ( 160 mph) Medium ( 60

mph)

Low ( 30 mph)

Coverage

area

Large/Continuous

macrocell

Medium. Micro

and picocell

Small/Zonal, picocell

Handset

complexity

High Low Low

H-set

power use

High (100-800 mW) Low (5-10 mW) Low (5-10 mW)

Speech

coding

rate

Low (8-13 Kbps) High (32 Kpbs) High (32 Kpbs)

Delay or

latency High ( 600 ms) Low (10 ms) Low ( 20 ms)

Wireless Components

Base Station (BS): A network element that

interconnects the mobile station (or Mobile

unit (MU)) to the network via the air

interface. Each cell in the network has a BS

associated with it. The primary function of a

BS is to maintain the air interface, or

medium, for communication to any mobile

unit within its cell. Other functions of BS

are call processing, signaling, maintenance,

and diagnostics. The BS communicates to its

mobile unit via the air interface, and to

MTSO by dedicated communication link

such as T1 trunks. Communication links on

the BS to the MTSO interface are also

classified into voice links and signaling link.

Mobile Units (MU):

Also called Mobile Systems (MS) or Mobile

Hosts (MH). It consists of three components:

(a) transceiver, (b) antenna, and (c) user

interface. The user interface exists only at

MU, which consists of a display, a keypad

for entering information, and an audio

interface for speaking and hearing voice

conversation. This can be a laptop, a

palmtop, or a cell phone, or any other mobile

device. A MU also stores (a) Mobile

Identification Number (MIN), (b) Electronic

Serial Number (EIN), and (C) Station Class

Mark (SCM). These are transmitted upon

power on, cell initiated sampling, and cell

origination.

Mobile cell

Within the cellular allocation the USA

is divided into Metropolitan Statistical

Areas (MSAs) and Rural Statistical

Areas (RSAs). There are six PCS

service providers authorized to provide

mobile service in each of these areas.

Within their geographical region, each

service provider divides their area into

smaller segments called cells. Each of

this cell has a Base Station. Ideally,

the system has a large number of very

small hexagons (cell). The greater the

number of hexagons, the more

simultaneous calls the system can

handle. However, larger number of

hexagons increases the cost of

implementation. Thus, cell coverage

is a dynamic activity, which is

constantly changing in response to

increases in demand.

BS

MSC (MTSO)

MS Wireless

componentMS

Cell

The entire coverage area is a group of a number of cells. The size of cell depends upon the

power of the base stations.

Metropolitan area Metropolitan area

Coverage area in one cell Coverage area in three cells

BS

BS

BSBase Station

Large cells.

Low density

Small cells.

High density

Smaller cells.

Higher density

PSTNMSC

Problems with cellular structure

How to maintain continuous

communication between two parties in the

presence of mobility?

Solution: Handoff

How to maintain continuous

communication between two parties in the

presence of mobility?

Solution: Roaming

How to locate of a mobile unit in the

entire coverage area?

Solution: Location management

Roaming

Roaming is a facility, which allows a

subscriber to enjoy uninterrupted

communication from anywhere in the entire

coverage space.

A mobile network coverage space may

be managed by a number of different service

providers. They must cooperate with each

other to provide roaming facility.

Roaming can be provided only if some

administrative and technical constraints are

met.

Administrative constraints

Billing.

Subscription agreement.

Call transfer charges.

User profile and database sharing.

Any other policy constraints.

Technical constraints

Bandwidth mismatch. For example,

European 900MHz band may not be

available in other parts of the world. This

may preclude some mobile equipment for

roaming.

Service providers must be able to

communicate with each other. Needs

some standard.

Mobile station constraints.

Integration of a new service provider

into the network. A roaming

subscriber must be able to detect this

new provider.

Service providers must be able to

communicate with each other. Needs

some standard.

Quick MU response to a service

provider’s availability.

Limited battery life.

Two basic operations in roaming

management are

Registration (Location update): The

process of informing the presence or arrival

of a MU to a cell.

Location tracking: the process of

locating the desired MU.

Registration (Location update): There are six

different types of registration.

Power-down registration. Done by the

MU when it intends to switch itself

off.

Power-up registration. Opposite to

power-down registration. When an

MU is switched on, it registers.

Deregistration. A MU decides to

acquire control channel service on a

different type of network (public,

private, or residential).

Registration (Location update): There are six

different types of registration.

New system/Location area

registration: when the location area of

the MU changes, it sends a registration

message.

Periodic registration: A MU may be

instructed to periodically register with

the network.

Forced registration: A network may,

under certain circumstances, force all

MUs to register.

2.3 Mobile Database Systems (MDS)

What is a Mobile Database System

(MDS)?

A system with the following structural

and functional properties

Distributed system with mobile

connectivity

Full database system capability

Complete spatial mobility

Built on PCS/GSM platform

Wireless and wired communication

capability

MDS Applications

Insurance companies

Emergencies services (Police, medical,

etc.)

Traffic control

Taxi dispatch

E-commerce

Etc.

MDS Limitations

Limited wireless bandwidth

Wireless communication speed

Limited energy source (battery power)

Less secured

Vulnerable to physical activities

Hard to make theft proof.

MDS capabilities

Can physically move around without

affecting data availability Can reach to

the place data is stored

Can process special types of data

efficiently

Not subjected to connection restrictions

Very high reachability

Highly portable

To build a truly ubiquitous information

processing system by overcoming the

inherent limitations of wireless architecture

MDS Issues

Data Management

Data Caching

Data Broadcast (Broadcast disk)

Data Classification

Transaction Management

Query processing

Transaction processing

Concurrency control

Database recovery

A Reference Architecture (Client-Server model)

MDS Data Management Issues

How to improve data availability to user

queries using limited bandwidth?

Possible schemes

Semantic data caching: The cache

contents is decided by the results of

earlier transactions or by semantic

data set.

Data Broadcast on wireless channels

Semantic caching

Client maintains a semantic

description of the data in its cache

instead of maintaining a list of pages

or tuples.

The server processes simple predicates

on the database and the results are

cached at the client.

Data Broadcast (Broadcast disk)

A set of most frequently accessed data is

made available by continuously

broadcasting it on some fixed radio

frequency. Mobile Units can tune to this

frequency and download the desired data

from the broadcast to their local cache. A

broadcast (file on the air) is similar to a

disk file but located on the air. The

contents of the broadcast reflects the data

demands of mobile units. This can be

achieved through data access history,

which can be fed to the data broadcasting

system. For efficient access the broadcast

file use index or some other method.

How MDS looks at the database data?

Data classification

Location Dependent Data (LDD)

Location Independent Data (LID)

Location Dependent Data (LDD)

The class of data whose value is functionally

dependent on location. Thus, the value of

the location determines the correct value of

the data.

Location Data value

Examples: City tax, City area, etc.

MSC MSC

DB DB HLR VLR

BSC BSC

DBS DBS

MU BS

MU

MU

BS

MU

BS

MU

Fixed host

Fixed host

PSTN

Location Independent Data (LID)

The class of data whose value is functionally

independent of location. Thus, the value of

the location does not determine the value of

the data.

Example: Person name, account

number, etc. The person name remains the

same irrespective of place the person is

residing at the time of enquiry.

Location Dependent Data (LDD)

Example: Hotel Taj has many

branches in India. However, the room

rent of this hotel will depend upon the

place it is located. Any change in the

room rate of one branch would not

affect any other branch.

Schema: It remains the same

only multiple correct values exists in

the database.

LDD must be processed under the

location constraints. Thus, the tax data

of Pune can be processed correctly

only under Pune’s finance rule.

Needs location binding or

location mapping function.

Location binding or location mapping

can be achieved through database

schema or through a location mapping

table.

Location Dependent Data (LDD)

Distribution

MDS could be a federated or a multidatabase

system. The database distribution

(replication, partition, etc.) must take into

consideration LDD.

One approach is to represent a city in

terms of a number of mobile cells, which is

referred to as ―Data region‖. Thus, Pune can

be represented in terms of N cells and the

LDD of Pune can be replicated at these

individual cells.

Concept Hierarchy in LDD

In a data region the entire LDD of that location can be represented in a hierarchical

fashion.

County 1 data County 2 data County n data

City data

Subdivision 1 data Subdivision data Subdivision m data

2.4 Transaction Management

Transaction fragments for distribution

Transaction fragments for distributed

execution

Execution scenario: User issues transactions

from his/her MU and the final results comes

back to the same MU. The user transaction

may not be completely executed at the MU

so it is fragmented and distributed among

database servers for execution. This creates

a Distributed mobile execution.

A mobile transaction (MT) can be defined as

Ti is a triple <F, L, FLM>; where

F = {e1, e2, …, en} is a set of execution

fragments,

L = {l1, l2, …, ln} is a set of locations, and

FLM = {flm1, flm2, …, flmn} is a set of

fragment location mapping where j, flmi (ei)

= li

An execution fragment eij is a partial

order eij = {j, j} where

i = OSj {Ni} where OSj =

kOjk, Ojk {read, write},

and Nj {AbortL, CommitL}.

For any Ojk and Ojl where Ojk = R(x) and

Ojl = W(x) for data object x, then either

Ojk j Ojl or Ojl j Ojk.

Mobile Transaction Models

Kangaroo Transaction:

It is requested at a MU but processed

at DBMS on the fixed network. The

management of the transaction moves

with MU. Each transaction is divided

into subtransactions. Two types of

processing modes are allowed, one

ensuring overall atomicity by requiring

compensating transactions at the

subtransaction level.

MSC MSC

DB DB HLR VLR

BSC BSC

DBS DBS

MUBS

MU

MU

BS

MU

BS

MU

Fixed host

Fixed host

PSTN

Reporting and Co-Transactions:

The parent transaction (workflow) is

represented in terms of reporting and co-

transactions which can execute anywhere. A

reporting transaction can share its partial

results with the parent transaction anytime

and can commit independently. A co-

transaction is a special class of reporting

transaction, which can be forced to wait by

other transaction.

Clustering:

A mobile transaction isdecomposed into a set

of weak and strict transactions. The

decomposition is done based on the

consistency requirement. The read and write

operations are also classified as weak and

strict.

Semantics Based:

The model assumes a mobile transaction to

be a long lived task and splits large and

complex objects into smaller manageable

fragments. These fragments are put together

again by the merge operation at the server. If

the fragments can be recombined in any

order then the objects are termed reorderable

objects.

Serialization of concurrent execution.

Two-phase locking based (commonly

used)

Timestamping

Optimistic

Mobile Transaction execution

DBS4

DBS1

DBS3

DBS2

T2(e

4, e

5)

MU2

MU1 T1(e

1, e

2, e

3) MU3

Reasons these methods may not work

satisfactorily

Wired and wireless message overhead.

Hard to efficiently support disconnected

operations.

Hard to manage locking and unlocking

operations.

Serialization of concurrent execution.

New schemes based on timeout,

multiversion, etc., may work. A scheme,

which uses minimum number of messages,

especially wireless messages is required.

Database update to maintain global

consistency.

Database update problem arises when

mobile units are also allowed to modify the

database. To maintain global consistency an

efficient database update scheme is

necessary.

Transaction commit.

In MDS a transaction may be fragmented and

may run at more than one nodes (MU and

DBSs). An efficient commit protocol is

necessary. 2-phase commit (2PC) or 3-phase

commit (3PC) is no good because of their

generous messaging requirement. A scheme

which uses very few messages, especially

wireless, is desirable.

One possible scheme is ―timeout‖ based

protocol.

Concept: MU and DBSs guarantee to

complete the execution of their fragments of

a mobile transaction within their predefined

timeouts. Thus, during processing no

communication is required. At the end of

timeout, each node commit their fragment

independently.

Protocol: TCOT-Transaction Commit

On Timeout

Requirements

Coordinator: Coordinates transaction

commit

Home MU: Mobile Transaction (MT)

originates here

Commit set: Nodes that process MT

(MU + DBSs)

Timeout: Time period for executing a

fragment

Protocol:

TCOT-Transaction Commit On

Timeout

MT arrives at Home MU.

MU extract its fragment, estimates

timeout, and send rest of MT to the

coordinator.

Coordinator further fragments the

MT and distributes them to

members of commit set.

MU processes and commits its

fragment and sends the updates to

the coordinator for DBS.

DBSs process their fragments and

inform the coordinator.

Coordinators commits or aborts

MT.

Transaction and database recovery

Complex for the following reasons

Some of the processing nodes are

mobile

Less resilient to physical use/abuse

Limited wireless channels

Limited power supply

Disconnected processing capability

Desirable recovery features

Independent recovery capability

Efficient logging and

checkpointing facility

Log duplication facility

Independent recovery capability

reduces communication overhead.

Thus, MUs can recover without any

help from DBS

Efficient logging and

checkpointing facility conserve

battery power

Log duplication facility improves

reliability of recovery scheme

Possible approaches

Partial recovery capability

Use of mobile agent technology

Possible MU logging approaches

Logging at the processing node

(e.g., MU)

Logging at a centralized location

(e.g., at a designated DBS)

Logging at the place of registration

(e.g., BS)

Saving log on Zip drive or floppies.

Mobile Agent Technology

A mobile agent is an independent software

module capable of

Migrating to any node on the network

Capable of spawning and eliminating

itself

Capable of recording its own history

A mobile agent can be used for the following

activities, which are essential for recovery.

Centralized and distributed logging

Log carrier. A Mobile unit may need to

carry its log with it for independent

recovery

Log processing for database recovery

Transaction commit or abort

Possible approaches

Agent broadcast on a dedicated wireless

channel

Pool of agents at every processing node

Agent migration to a required node.

Mobile E-commerce

What is E-commerce?

Mapping of business activity on the network.

The network may be mobile of ad-hoc in

which case the scope of business activities

significantly increases.

Why mobile E-commerce?

To make business activity free from spatial

constraints. This allows tremendous

flexibility to customers as well as to vendors.

Important gain: Making information

available at the right time, at the right

location, and in a right format.

Requirements for a mobile E-system

Security

Reliability

Efficient

Customer trust

Quality of service

These requirements are difficulty and

complex to achieve

Security

Conventional key approaches needs revision.

Reliability

Hard to provide mainly because of the

unreliability and limitations of resources.

Efficient

This capability can be easily improved

mainly because of the elimination of spatial

constraints.

Customer trust

A time consuming activity. Customer do not

easily trust electronic communication and

always wants to see a reliable backup

service.

Quality of service

Mobility and web provides ample scope for

improving the quality of service. An

integration of mobility, web, data

warehousing and workflow offers

tremendous growth potential and a very

controlled way of managing business

activities

2.5 Query Processing

MDS Query processing

Query types

Location dependent query

Location aware query

Location independent query

Location dependent query

A query whose result depends on the

geographical location of the origin of the

query.

Example

What is the distance of Pune railway

station from here?

The result of this query is correct only

for ―here‖.

Location dependent query

Situation: Person traveling in the car desires

to know his progress and continuously asks

the same question. However, every time the

answer is different but correct.

Requirements: Continuous monitoring of the

longitude and latitude of the origin of the

query. GPS can do this.

2.6 Location and Handoff Management

The handoff process is provided and the

topic of location management is introduced.

It first explains how these processes work

and then discusses their relevance to

transaction management in mobile database

systems. Quite a few location management

schemes have been proposed recently, but

none of them have been implemented in any

commercial system, so they are not

discussed. The working of existing handoff

and location mechanisms given in IS-41 is

explained.

Location Management

In cellular systems a mobile unit is free to

move around within the entire area of

coverage. Its movement is random and

therefore its geographical location is

unpredictable. This situation makes it

necessary to locate the mobile unit and

ecord its location to HLR and VLR when a

call has to be delivered to it.

Thus, the entire process of the mobility

management component of the cellular

system is responsible for two tasks:

(a) location management- that is,

identification of the current geographical

location or current point of attachment of a

mobile unit which is required by the MSC

(Mobile Switching Center) to route the call-

and

(b) handoff- that is, transferring (handing off)

the current (active) communication session to

the next base station, which seamlessly

resumes the session using its own set of

channels. The entire process of location

management is a kind of directory

management problem where locations are

current locations are maintained

continuously.

One of the main objectives of efficient

location management schemes is to minimize

the communication overhead due to database

updates (mainly HLR) [6,9, 151.

The other related issue is the distribution of

HLR to shorten the access path, which is

similar to data distribution problem in

distributed database systems. Motivated by

these issues, recently a number of innovative

location management schemes have appeared

in the research world [ 141. The current point

of attachment or location of a subscriber

(mobile unit) is expressed in terms of the cell

or the base station to which it is presently

connected. The mobile units (called and

calling subscribers) can continue to talk and

move around in their respective cells; but as

soon as both or any one of the units moves to

a different cell, the location management

procedure is invoked to identify the new

location.

The unrestricted mobility of mobile units

presents a complex dynamic environment,

and the location management component

must be able to identify the correct location

of a unit without any noticeable delay. The

location management performs three

fundamental tasks: (a) location update, (b)

location lookup, and (c) paging. In location

update, which is initiated by the mobile unit,

the current location of the unit is recorded in

HLR and VLR databases. Location lookup is

basically a database search to obtain the

current location of the mobile unit and

through paging the system informs the caller

the location of the called unit in terms of its

current base station.

These two tasks are initiated by the MSC.

The cost of update and paging increases as

cell size decreases, which becomes quite

significant for finer granularity cells such as

micro- or picocell clusters. The presence of

frequent cell crossing, which is a common

scenario in highly commuting zones, further

adds to the cost. The system creates location

areas and paging areas to minimize the cost.

A number of neighboring cells are grouped

together to form a location area, and the

paging area is constructed in a similar way.

In some situations, remote cells may be

included in these areas. It is useful to keep

the same set of cells for creating location and

paging areas, and in most commercial

systems they are usually identical. This

arrangement reduces location update

frequency because location updates are not

necessary when a mobile unit moves in the

cells of a location area. A large number of

schemes to achieve low cost and infrequent

update have been proposed, and new

schemes continue to emerge as cellular

technology advances.

A mobile unit can freely move around in

(a) active mode,

(b) doze mode, or

(c) power down mode.

In active mode the mobile actively

communicates with other subscriber, and it

may continue to move within the cell or may

encounter a handoff which may interrupt the

communication. It is the task of the location

manager to find the new location and resume

the communication. In doze mode a mobile

unit does not actively communicate with

other subscribers but continues to listen to

the base station and monitors the signal

levels around it, and in power down mode

the unit is not functional at all. When it

moves to a different cell in doze or power

down modes, then it is neither possible nor

necessary for the location manager to find

the location. The location management

module uses a two-tier scheme for location-

related tasks.

The first tier provides a quick location

lookup, and the second tier 4earch is initiated

only when the first tier search fails.

Handoff Management

This section discuses how a handoff is

managed to provide continuous connectivity.

Figure illustratesthe presence of an overlap

region between Cell 1 and Cell 2. A mobile

unit may spends some time in this overlap

area and the value of this duration depends

upon the movement speed of the mobile unit.

The duration a mobile unit stays in this area

is called the degradation interval . The

objective is to complete a handoff process

while the mobile unit is still in the overlap

area. This implies that the handoff must not

take more than the degradation interval to

complete he process. If for some reason the

process fails to complete in this area or

within degradation interval, then the call is

dropped.

Fig. Cell overlap region.

A handoff may happen within or outside a

registration area. If it happens within a

registration area, then it is referred to as

intra-system handoff where the same MSC

manages the entire process. An intersystem

handoff occurs between two separate

registration areas where two MSCs are

involved in handoff processing. In each of

these cases the handoff processing is

completed in three steps:

Handoff detection: The system detects

when a handoff process needs to be

initiated.

Assignment of channels: During handoff

processing the system

identifies new channels to be assigned

for continuous connectivity.

Transfer of radio link: The identified

channels are allocated to the mobile

unit.

Handoff Detection

Handoff processing is expensive, so the

detection process must correctly detect a

genuine and False Handoff which also

occurs because of signal fading. There are

three approaches for detecting handoff

effectively and accurately.

A brief description of these approaches,

which are applied on GSM system but also

used in PCS, is presented here and further

details can be found in Ref. [lo]. They are

called:

Mobile-Assisted Handoff (MAHO)

Mobile-Controlled Handoff (MCHO)

Network-Controlled Handoff (NCHO)

Mobile-Assisted Handoff (MAHO):

This scheme is implemented in second-

generation systems where TDMA technology

is used. In this approach, every mobile unit

continuously measures the signal strength

from surrounding base stations and notifies

the strength data to the serving base station.

The strength of these signals are analyzed,

and a handoff is initiated when the strength

of a neighboring base station exceeds the

strength of the serving base station. The

handoff decision is made jointly by base

station and Mobile Switching Center (MSC)

or base station controller (BSC). In case the

Mobile Unit (MU) moves to a different

registration area, an intersystem handoff is

initiated.

Mobile-Controlled Handoff (MCHO):

In this scheme the Mobile Unit (MU) is

responsible for detecting a handoff. The MU

continuously monitors the signal strength

from neighboring base stations and identifies

if a handoff is necessary. If it finds the

situation for more than one handoff, then it

selects the base station with strongest signal

for initiating a handoff.

Network-Controlled Handoff (NCHO):

In this scheme, Mobile Unit (MU) does not

play any role in handoff detection. The BS

monitors the signal strength used by MUs

and if it falls below a threshold value, the BS

initiates a handoff. In this scheme also BS

and MSC are involved in handoff detection.

In fact the MSC instructs BSs to monitor the

signal strength occasionally, and in

collaboration with BSs the handoff situation

is detected. The MAHO scheme shares some

detection steps of NCHO. Necessary

resources for setting up a call or to process a

handoff request may not always be available.

For example, during a handoff the

destination BS may not have any free

channel, the MU is highly mobile and has

requested too many handoffs, the system is

taking too long to process a handoff, the link

transfer suffered some problem, and so on. In

any of these cases the handoff is terminated

and the mobile unit loses the connection.

Radio Link Transfer

The last phase of handoff is the transfer of

the radio link. The hierarchical structure of

cellular system (PCS and GSM) presents the

following five-link transfer cases for which

handoff has to be processed.

Intracell handoff Link or channel

transfer occurs for only one BS. In this

handoff a MU only switches channel.

Figure 3.10 illustrates the scenario.

Intercell or Inter-BS handoff The link

transfer takes place between two BSs

which are connected to the same BSC.

Figure 3.1 1 illustrates the scenario.

Inter-BSC handoff: The link transfer

takes place between two BSs which are

connected to two different BSCs and the

BSC is connected to one MSC. Figure

3.12 illustrates the scenario.

Intersystem or Inter-MSC handoff The

link transfer takes place between two BSs

which are connected to two different

BSCs. These two BSCs are connected to

two different MSCs. Figure 3.13

illustrates the situation.

As discussed in Ref. [ 101, typical call

holding time is around 60 seconds. Some

real-life data indicates that there could be

around 0.5 inter-BS handoff, 0.1 inter-BSC

Fig. 3.10 Channel transfer in intracell handoff.

Fig. 3.11 Channel transfer between two BSs with one BSC.

handoff, and 0.05 inter-MSC handoff. The

data also indicate that the failure rate of

inter-MSC handoff is about five times more

than inter-BS handoff. It is quite obvious that

efficient processing of handoff is quite

important for minimizing the call waiting

time. There are two ways to achieve link

transfer. One way is referred to as Hard

Handofland the other as Soft Handoff.

Fig. 3.72 Channel transfer between two BSs connected to two BSCs.

Hard Handoff:

In this handoff process the user experiences a

brief silence or discontinuity in

communication which occurs because at any

time the MU is attached to only one BS and

when the link is transfer the connection is

broken temporarily resulting in a silence. The

steps of the handoff for MCHO link transfer

is described below.

1. MS sends a ―link suspend‖ message to the

old BS which temporarily suspends the

conversation (occurrence of silence).

2. The MS sends a ―handoff request

message― to the network through the new

BS. The new BS then sends a ―handoff

acknowledgement― message and marks the

slot busy. This message indicates the

initiation of the handoff process.

3. This acknowledgment message indicates

to MU that the handoff process has started,

and so MU returns to the old channel it was

using and resumes voice communication

while network process the handoff.

4. When the new BS receives the handoff

request message, then two cases arise:

(a) It is an intra-BS handoff or

(b) it is an inter-BS handoff. In the former

case the BS sends a handoff

acknowledgment message and proceeds with

handoff.

In the later case, since it is between two

different BSCs, the BS must complete some

security check. It gets the cypher key from

the old BS and associates it with the new

channel.

6. The MSC bridges the conversation path

and the new BS.

Fig. 3.13 Channel transfer between two BSs with two BSCs connected to two MSCs.

6. On the command of the network, the MS

processes the handoff where it releases the

old channel by sending an ―access release‖

message to the old BS. In this rocess the

voice communication is briefly interrupted

again. The MU sends a ―handoff complete‖

message through the new channel and

resumes the voice communication. A

detailed discussion on hard handoff for other

kinds of link transfer.

2.6 Wireless Information Broadcast

The data dissemination discipline gives an

illusion that the space is an infinite size

persistent data storage from where a user can

download desired information. For example,

information about airline schedule, weather,

stock quotes, etc., can be downloaded from

the broadcast. Initially, data dissemination

system appeared as an information

dissemination tool similar to radio broadcast,

but with advances in wireless and satellite

communication, it is becoming an

information management system as well.

This chapter discusses data dissemination

technology and development of schemes

such as indexing, push and pull, data staging,

surrogates, and so on, for incorporating

transactional facility. The discussion in this

chapter is based mostly on research reports

because a truly data broadcast system has not

been developed and deployed for commercial

use. It also discusses in detail the architecture

and working of a reference data

dissemination and processing system called

DAYS (DAta in your Space).

The discipline of data dissemination

through wireless channel, that is, data

broadcast, has added another dimension in

the area of mobile computing. The mobile

database systems, discussed in preceding

chapters, provided terminal and personal

mobility in information management, and the

wireless data dissemination took mobile

systems one step further and allowed the user

to tune and access and process desired

information from anywhere in the world.

Accessing data from wireless channel is a

very useful facility because it allows users

to get desired data through many

computationally enabled devices such as

cellular phones, PDAs, other new devices.

Manufacturers continue to develop

increasingly powerful mobile devices while

decreasing their size and cost. If it is

assumed that there is an abundance of

wireless channels, then servers can continue

to push all data users can ever need on these

channels and users can pull whatever they

require. This is an ideal scenario. In reality,

wireless channels are always less than the

number required to satisfy users’ demands.

Thus, the task of data dissemination

technology is to develop ways for satisfying

users’ data demand with limited wireless

resources.

Data broadcast is predominately user-

independent. The users are passive in that

they can only read what is contained in a

broadcast. While this model fits well into

some types of data dissemination (such as

local traffic information), it is not general

enough for many different types of

applications. Some examples can help to

identify its usefulness and limitations.

Data Broadcast Mode

The mode of data transfer is essentially

asymmetric, that is, the capacity of the

transfer of data from the server to the mobile

client downstream communication is

significantly larger than the client or mobile

user to the server upstream communication.

The effectiveness of a data

dissemination system is evaluated by its

ability to provide a user his required data

ubiquitously. There are two basic modes of

data dissemination. These modes are

motivated mainly by limited power

consideration. The lifetime of a battery is

expected to increase only 20% over the next

10 years 1221. A typical AA cell is rated to

give 800 mA/hour at I .2 V (0.96 Whour).

The constant power dissipation in a CD-

ROM (for disk spinning itself) is about 1 W,

and the power dissipation for display is

around 2.5 W. The available power source is

likely to last for 2.7 hours and to preserve

battery power; these activities must be

disabled whenever possible. The Hobbit chip

from AT&T allows the operation in two

modes:

(a) active mode – the full operational

mode where CPU and all other components

are in running state and

(b) doze mode - the power conserving

mode where the CPU is inactive.

The power consumption in the active

mode is 250 mW, and the power

consumption in doze mode is 50 pW. The

ratio of power consumption in the active

mode to doze mode is 5000.

When the mobile unit (palmtop) is

listening to the channel, the CPU must be in

the active mode for examining data buckets

in the broadcast. The CPU consumes more

power than some receivers, especially if it

has to be active to examine all incoming

buckets. Therefore, it will be beneficial if the

CPU can be switched to the doze mode

whenever it is not being used and switched

back to active mode when the data of interest

arrives on the broadcast channel. This facility

is called selective tuning.

Transmitting and accessing data also

consumes power. A number of factors like

the terrain, landscape, the height and kind of

trees, foliage, season, rain, etc., play an

important role in determining the power

required in data dissemination. With distance

the power requirement increases significantly

1261. For large cells the energy required for

transmission could reach tens of watts.

For example, a Wavelan card consumes 1.7

W with the receiver powered on and 3.4 W

with the transmitter powered on. The

effective bandwidth of wireless network is

only a fraction of the bandwidth that is

available in wired networks. The current

ATM (Asynchronous Transfer Mode)

standards are designed to yield a bandwidth

of up to 622 Mbps. This bandwidth is

projected to go up to gigabits [20]. The

wireless bandwidth varies from 1.2 kbps for

slow paging channels to about 2 Mbps of the

wireless LAN.

Data broadcast can be managed with

three different modes to satisfy user needs.

These modes are further elaborated later in

this chapter as Push and Pull technology.

Broadcast Mode: In this mode the broadcast

server periodically broadcast most popular

data on some wireless channels from which

users can listen and, if necessary, download

the required data. There is no uplink channel

involved in this mode. Simple filtering of

broadcast data stream according to a user

specified filter [6] is applied to access data.

On-Demand Mode: This mode allows

a client to request specific data which is not

available in the current broadcast or may

never appear in the broadcast. The client

sends the query for the required data through

an uplink channel.

Hybrid Mode: In this mode, broadcast

and on-demand modes are combined. The

server allows individual data requests from

clients through uplink channel and allows

data broadcast through downlink channel. It

also, if necessary, broadcasts on-demand data

if its popularity matches the popularity of

broadcast data.

Pull Process

Pull process is user (client)-oriented. A

user assumes that the desired information is

available in the wireless space, and he pulls it

by tuning the channel. For example, a user

keys in a URL on the web browser and pulls

the desired information. The server is not

concern with the individual user’s access. It

is also immaterial whether the user finds the

desired data or encounters an error or delay

occurs in downloading the data. In day-to-

day activities, pull process is frequently

applied: borrowing a book from a library,

renting a movie or music CD, buying an

airline ticket, and so on. It is clear from these

examples that in pull the user initiates a

conditional information flow where the

condition is defined by the user with an

understanding that the condition is likely to

be satisfied-for example, renting a movie

with a particular title, purchasing a ticket for

a particular destination, and so on. Using an

e-mail facility may appear to follow pull

process, but actually it is not so. A recipient

of an e-mail does not select the e-mails he

receives; rather they are dropped in the user’s

space without his knowledge and they just

appear on his e-mail directory, some as spam

but some quite useful. It is also clear that

what a user intends to pull may or may not

be present in the pulled information. For

example, pulling information from Google

with some condition brings quite a lot of

trash along with the desired information. An

intelligent pull technique such as a semantic

web has yet to be fully developed.

Advantages of Pull: It is user-friendly

and provides interactive capability to users

for accessing the information through query.

The user does not need to search in the

wireless information space by tuning several

channels.

Disadvantages of Pull: In wireless

data dissemination platform, the pull

approach is resource-intensive. A user

requires a separate channel to send the

request as a SQL query or in some other

form to the server for the desired

information. The server, after receiving the

request, composes the result and must send it

to the user on a back channel (downstream)

known to the user. Thus every pull needs two

channels for completing the process

successfully. If there are a large number of

users and they need identical information,

then each user will occupy two channels with

identical data on all back channels. This

cannot be easily afforded because of narrow

bandwidth available for wireless

communication. It appears from these

limitations that pull is good for special cases

of data retrieval.

Push Process

In the push process, the server

broadcasts data (pushes data) on one or

multiple channels. For example, it can push

weather information on one channel, traffic

information on another channel, and so on.

Clients, depending upon their data

requirements, tune the appropriate channel.

In a push system a client cannot send a

specific query to the server, nor is the server

broadcast client-specific. The push

technology was introduced somewhere

around April 1996 by an internet company

called PointCast Inc. The company started

push scheme by broadcasting selected news

and stock quotes to a client’s machine at

predefined intervals [ 141. The client tuned

and downloaded information at these

intervals. This was the beginning of an

effective way of reaching a larger number of

customers. Developers and researchers found

the push scheme quite useful; since then, it

was deployed on the internet in many ways

such as webcasting or netcasting. Sometimes

it is also called PointCusting to honor the

company which invented it.

The main objective of push technology

was to handle the problem of information

overload due to low bandwidth which

restricted users to receive multimedia

contents. The push scheme provided an

effective means to pre-deliver much larger

packages of audio, large graphics, or short

video clips. The push technology can be

augmented with a number of mechanisms to

increase its scope and effectiveness. For

example, message indexing can be

implemented to speed up broadcast search,

caching can be used to reduce data miss, data

staging can be augmented to enhance data

availability, personalization of channel

contents can help to satisfy specific user, the

smart-pull approach can assist users to get

specific information, and so on. These topics

are discussed in detail in subsequent sections.

Push Application

The push technology has been

deployed for sometime in many real-world

activities such as in the financial world to

broadcast stock quotes, mutual funds costs,

real state costs and inflation status, news,

cable television broadcast, etc. Nearly all

software manufacturers use push to broadcast

application and system updates and fixes to

clients’ machines. Many companies use this

technology for advertisement. In fact, most

of the commercials on broadcast media such

as television, radio, etc., are pushbased.

Companies are at a great advantage for

making use of the push technology which

allows them to make instant changes in the

broadcast or refresh it entirely based on

users’ feedback to increase their effect on

consumers. It is not now necessary for them

to rely on a human operator to search a site

for outdated material. The push technology

applies to entertainment and leisure equally

effectively.

The push technology is especially

useful in the intranet market. Companies can

push on their intranet corporate information

to employees using a predefined schedule. It

guarantees identical message delivery, which

is highly desirable, to all employees.

Accessing Information from Broadcast

Clients can access and download

required information in a variety of ways,

which depends upon how the broadcast was

composed and pushed on the channel by the

server. In a channel the push is strictly

sequential. Data are dropped in the channel,

one at a time. This can be viewed as a string

of different categories of data. For example,

if the broadcast is composed of weather

information, traffic information, and dining

places information, then they will appear on

the broadcast sequentially in the order they

were dropped in the channel. The client will

receive the broadcast in the order sent by the

server.

At the client’s end the Fimplest way to

access the information is sequentially. In

most cases this access is time consuming. A

client, if interested only i n dining

information, has to tune and wait until the

dining information appears in the broadcast.

In a wireless platform, any waiting-let alone

waiting for information to appear-is quite

resource-expensive, especially from a

bandwidth viewpoint. An ideal scheme is to

tune when the desired information appears

(e.g., selective tuning) and download the

data; that is, the waiting time for information

access is zero. It is impossible to implement

the ideal scheme, but the access time can be

significantly minimized through efficient

indexing and carefully composing the

broadcast. Such arrangements actually create

a notion of smart-pull where client can pull

exactly the information he wanted with

minimum redundancy. However, even

though push applications are not really push,

there is a difference in them. The difference

is the automation of the process both for the

server and the client. There are a couple of

true push technology applications-for

example, products like AirMedia Live and

Wayfarer (INCISA).

Push Advantages and Disadvantages

Push technology has been a favorite

choice of data dissemination because of its

several advantages. It has, however, several

disadvantages which makes it unsuitable,

especially for providing transactional facility.

Advantages

In a large information flow it minimizes

the burden of acquiring data. The server

can keep the information up to date by

broadcasting it on a regular interval;

consequently, the user always has the

latest information. A user is aware of the

broadcast channel carrying the

information and the exact location of the

data in the broadcast. This setup

significantly reduces the search time.

Sends the user the time-critical data for

immediate attention.

Helps organizations (academic, business,

or commercial) to identify, focus, and

reach those users with precision who are

more likely to benefit from their products

or services.

Automatically delivers directly to clients’

machines software upgrades and fixes

faster and, at the same time, reduce or

eliminate the shipping cost. This facility

requires a mechanism to check clients’

machines for software and configuration

and then modify these configurations.

Uses incremental updates where only new

and changed information has to be sent to

the computer which significantly reduces

access and download time.

Helps server to reserve more processing

time for data production by avoiding to

handle numerous client requests

individually.

Shortens response time.

Easily protects user privacy because push

applications run mostly at the client

machine and client’s profile and the log

information about the client’s behavior

are stored on the client’s computer.

Enables intelligent information filtering

based on personalized user profiles

describing required information needs.

Satisfies a large client base using few

resources.

Disadvantages

The push technology, while it is useful

in a number of situations and does conserve

resources and energy, has a number of

limitations and disadvantages [ 141. Some

important ones are given below.

Push applications are complex, and the

development cost (time and resource) are

generally high compared to creating static

pages. Static pages can be viewed by any

browser on any operating system, but the

push system requires specific tools and

applications.

It requires more powerful hardware and

specialized software to provide push

service.

Identifying the location of the desired

information in the broadcast and

downloading the multimedia contents

require a huge amount of disk storage.

It suffers a number of unresolved

bandwidth problems. Problems arise due

to the enormous bandwidth that push

technologies can require when feeding

data to thousands of end users. Caching

proxy servers, for example, as well as

multicast solutions, will likely solve many

of the bandwidth problems of push and

allow it to scale. Some providers allow

users to choose when the information is

downloaded, so users can schedule it for

times that they will be away from their

computer.

The push scheme is still not that useful

for individual users; however, the

emergence of music P2P systems has

made it quite popular. Its usefulness is

still confined to organizations that have a

good customer base.

In multiple push a user can get frequent

interruption. For example, during a song

broadcast, some urgent message can

appear to notify user of some serious

event. Although users get the information,

they may have to live with constant

interruption. Such interruptions cannot be

preplanned because they may occur

randomly.

Push system software may suffer with

incompatibility problem. Many vendors-

Air Media, Alpha Microsystems,

Berkeley Systems, IntraExpress,

Marimba, Pointcast, to name a few,

develop application software with

minimum portability and scalability.

Competition to dominate the information

space in this technology is growing fast

and vendors are unable to develop

software compatible to all systems. The

push technology is not good for the

typical knowledge worker who mines

information from a variety of sources and

then draws conclusions by digesting that

information [ 141.

Creating and maintaining user profiles is

time-consuming. This becomes more

expensive with number of users. One of

the main reasons is that users’

information needs are constant to some

degree only.

There is no reliable solution to achieve

secured broadcast. Security safeguards are

highly needed.

Standards are currently lacking in this

area (competing de facto industry

standards are pushed by companies) .

Market for Push Technology

Microsoft Corp. and Netscape

Communications Corp. are the two leading

competitors

in the push technology. Microsoft is pushing

the Extensible Markup Language (XML)-

based Channel Definition Format (CDF) for

defining push updates. Netscape is using the

Meta-Content Format (MCF), which was

invented by Apple Computer. For example,

Marimba Inc. has begun cooperation with

Netscape. Microsoft and Netscape each have

created their own push clients for use in

conjunction with their latest browsers. The

push market can be divided into four basic

categories :

Application Distributor: The products

of this category such as Marimba’s

Castanet provide automatic delivery of

application software to end users.

Content aggregator: The products of this

category-for example, PointCast Business

Network-gather and format the contents

in a consistent wrapper and push it to

users’ workstations.

Platform provider: The products of this

category-for example, BackWeb-are

similar to content aggregators, except

they are actually infrastructure to deploy

content delivery systems.

Real-time data transfer: The products of

this category-for example, TIBCO and

Wayfarer (1NCISA)-offer the advantage

of multicasting. It is expensive to

implement, but they guarantee timely

delivery of information possible.

Push information delivery models can be

categorized at least into three main

categories :

Push Server Model: It is the most

common Push Server Model which

provides a client, a server, and

development tools. A proprietary client is

supplied, and the applications may use a

proprietary protocol. Both users and

content providers have control over the

content. Some examples of this model are

BackWeb and Marimba’s Castanet.

Web Server Extension Model: In this

model, the push vendor directs feedback

and demographic information to an

external server, so that information can be

retained by the push vendor. No

proprietary client is required. These run

within the user’s installed browser, such

as Pointcast or the server delivers content

using e-mail, such as ChannelManager

and InfoBeat.

Client Agent Model: This model uses a

―client agent‖ to retrieve the information

from the web. Each agent is designed to

provide different search results and allows

us to establish an anonymous relationship

between the vendor and the subscriber.

The user is responsible for deployment

and the search type extensibility.

BROADCAST DISK

In this section a novel broadcast scheme

called broadcast disk is discussed. The main

idea of this scheme is to efficiently use the

available bandwidth to push data to a

majority of users. This approach created the

notion of multiple disks spinning at different

speeds on a single broadcast channel to

create an effect of a fine grained storage

hierarchy. The broadcast data on a faster disk

are pushed (repeated) more frequently than

the dataon slower disks channel). Users tune

to these disks (channels) and download their

desired data .

Fig. 9.3 A simple broadcast disk setup.

Figure 9.3 illustrates a simple

broadcast set up using broadcast disk

approach. The broadcast station has a

channel on which it continuously broadcasts

(pushes) data items A, B, C and D in that

order. The oval represents a broadcast disk

(channel) which if accessed (tuned) by a few

mobile devices. If the broadcast station has a

number of channels with different capacity,

then each channel can be used ac a different-

size disk. This arrangement can be compared

with radio broadcast where different

programs are transmitted over different

stations (frequencies).

The relative speed of these disk3 in the

air (airdisks) significantly affects the

broadcast configuration. The speed can be

tweaked to satisfy a variety of information

needs of users. In a similar manner, a set of

different types of information such as

weather, traffic, stock quotes, airline

schedule, news flashes, and so on, can be

transmitted on different speed channels.

Bandwidth Allocation

The way a set of information is arranged and

pushed on to the broadcast channels is called

schedule. In an ideal schedule the latency

time and tuning time are minimum. Latency

Time: Similar to conventional disk access, it

is the total time for (a) a client request to

arrive at the server and (b) the time when the

desired data is available in the broadcast

channel. This time becomes important

especially in interactive applications such as

video games which require fast scan. Tuning

Time: It is the total time required to tune to

the channel which is broadcasting the desired

data. This time becomes important for fast

changing data such as stock quotes. The

client must be able to quickly tune to the

right channel to get the data.

Access Time: Another parameter

which is called access time is the total time

to download the desired data from the

broadcast channel to a client's local storage.

In the push approach, an increase in length of

the broadcast can lead to an unacceptably

long access time for the user.

Figure 9.4 illustrates access and tuning

time. A client submits a request at To and

receives the desired response at time T7. If

the client listens continuously from the time

the query was submitted and until the

response is received, then the access and

tuning times can be expressed as AT = TT =

(T7 ~ To). If, on the other hand, the client

slips into doze mode intermittently, that is,

tunes selectively (selective tuning), then the

actual tuning time will be 7T = (T7 - Ts)+ (Ts

- T4) + (Ts - TL)+ (TI- 2'0). Tn selective

tuning the mobile unit will be in doze mode

(DM) for (TL- TI ) + (T4 ~ Tj) + (TG - T5). If

DM > 7T then the tuning time saves energy

and the saving will be highest only if the

client has accurate information about the

tuning time for accessing data. The task,

therefore, is to find optimal points in the 2D

space of access and tuning times. This is

quite difficult because there is a trade-off

between these two times. The access time

depends on broadcast size, and the tuning

time depends on the identification of exact

data location in the broadcast which is

achieved through selective tuning.

Unfortunately, selective tuning requires extra

information to be appended to the broadcast

data which increases the size of the

broadcast. This increase in size affects access

time. An efficient broadcast scheme,

therefore, must balance this trade-off.

The broadcast program can be

addressed in terms of bandwidth allocation.

An efficient bandwidth allocation scheme is

directly linked with data popularity among

the client population. Client information

requirement is highly random. Different

samples of client populations may have

orthogonal data requirements. In some client

population, geographical information may be

highly important and accessed most

frequently while some population may

frequently access stock quotes, and so on.

Thus, the relationship among data

popularity, client samples, and geographical

domain becomes very complex, which makes

it very hard, if not impossible, to develop an

optimal schedule for all situations. However,

with the help of popularity computation,

broadcast indexing, and broadcast

composition an efficient schedule can be

created.

Figure 9.5 presents three broadcast

samples [4]. Schedule

(a) is a flat schedule where data items set D1,

D2, and D3 continuously appear in the

broadcast. Schedule

(b) is a skewed broadcast where data item D1

appears twice one after another followed

by D2 and D3. Schedule

(c) is a regular broadcast where the inter-

arrival time of each page is the same. The

difference between schedule (a) and (b) is

quite obvious. In (b), data item D1 is treated

as more frequently accessed than other items

on the broadcast.

The benefit of a particular broadcast

schedule can be understood by thcir expected

access delay.

BROADCAST INFRASTRUCTURE

The usefulness of data dissemination

system lies in its ability to broadcast a huge

amount of data on a number of topics such as

weather, stock, entertainment, traffic, and so

on. The future broadcast systems are likely to

be used as a large data warehouse storing

(pushing) a large amount of data on all

topics. It may provide yellow pages services,

encyclopedia, dictionary, etc. This will

require not only efficient broadcast schedules

but also a faster way to reduce the search

space of requested data.

So far a data broadcast has been seen

as a push-based system while a mobile

database has been seen as pull-based, where

users initiate all kinds of transactions. The

trend now is to integrate both facilities into

one infrastructure. A new generation of data

management system is thus capable of

disseminating data for universal access and

at the same time efficiently process all types

of transactions with full database support as

we are used to.

The main components of such a

system are

(a) data access frequency,

(b) broadcast schedules, and

(c) data access from the broadcast.

These components are discussed in detail

below.

Data Access Frequency

The aim of the broadcast server is to achieve

the highest hit rate for every type of data it

pushes. This makes it necessary that the

server must first identify a high demand set

of data, arrange them in a specific order

considering the size of broadcast channel,

and broadcast them. The access frequency

identification can be done in many ways, for

example, by (a) monitoring current access

pattern by some means, (b) reaching active

clients to look at their data access history, (c)

studying the market trends, and so on. All

these approaches essentially identify the

access probability. For achieving the highest

data hit rate and highest channel utilization,

static and dynamic approaches can be used.

In the static approach a user notifies the

broadcast server regarding its present and

future data pull and approximate duration for

their use. The server will continue to

broadcast the static data set for the defined

period.

In the dynamic approach the data

requirements will be identified using (a)

Residence

latency (RL) and Expected Departure Time

(EDT) [8], (b) Popularity Factor (PF) and

Ignore Factor (IF), (c) user movement, and

(d) channel tunability.

RL and EDT: When the server decides

to include an item in its broadcast, it also

needs to decide the length of time the item

will remain in its broadcast set. To identify

the esidency duration of a data item an RL

value is associated with each data set. The

RL value for a specific data set is the average

length of time a mobile user resides in a cell,

and it can be computed a priori based on the

advanced knowledge of user movement

patterns and cell geography. A data item’s

EDT from a broadcast can be computed by

adding the item’s entry into the broadcast

and data’s RL.

PF: Popularity factor of a data set D at

time T identifies the number of clients in the

cell at time T who are interested in D. It can

be denoted as PFS or just PFn. One way to

maintain PF of a data item at the rerver in a

cell is to increment it by 1 when a client

requests D. The server also records the

corresponding time. Let the timestamp of the

ith increment to PFD be denoted by Th. The

popularity of D goes down after its RL value,

and a corresponding decrement of 1 is

performed on the value of PFn at time (Th +

RL). This reflects the anticipated departure of

the client whose request caused the 7th

increment. In reality the client population is

very large, as is the database to support their

requests. Since the increment and decrement

are frequently invoked operations, one way

to implement them is through an abstract

data type-for example, a PF queue with these

operations.

Data Staging with Surrogates

Staging data in a surrogate allows users to

extend their limited caching capacity. This is

done by borrowing storage space from the

surrogate and by joint operation of the client

proxy of the mobile user, the file server in

the base station (broadcast tower), and the

surrogate where data is to be staged. The

surrogate is connected to the file server with

a high-speed wired network. It is only a

single wireless hop away from the mobile

unit and connected by wireless technologies

such as 802.1 1. The client proxy

continuously monitors the data access

operation of the mobile user. It maintains a

log file into which it stores the three types of

control information of each page: BT, PT,

and T . The control information it stores is

for the broadcast and pages which are pulled

by the user. Thus, it is able to store the

information of the user access pattern

without using much cache area. Since it is

working internally and does not need to log

on to the wirelesq channel continuously, the

power consumption of the mobile unit does

not increase. Based on the information stored

in the log file, the proxy generates a periodic

routine which contains the information about

what the mobile user is most likely to access

at any time. The routine contains the control

information about the pushed data which is

requested and the information about a

particular pulled data which has been

frequently accessed by the user. The proxy

continuously maintains and upgrades this

routine.

Fig. 9.27 Data staging in DAYS.

Figure 9.27 shows the data staging

architecture. It consists of a surrogate, which

is connected to the mobile user by wireless

technologies such as 802.1 1 and to the file

server with a high speed wired network. The

client proxy present in the mobile user has a

periodic routine which contain information

about the data the user is most likely to

access at any point of time. Based on the

amount of storage available, the surrogate

allows the user to use a certain amount of

space for staging data. The user sends the

periodic routine to the surrogate. The time of

dispatch of the periodic routine is arbitrary. It

may send it periodically or at the time the

user requests a data. Since the public data is

staged in the machine, we believe that proper

handling of data storage in a surrogate can

significantly increase the efficiency of data

access, and thus the overall latency time can

be reduced. Figure 9.28 shows accesses of

data from the surrogates by a mobile user.

The overall aim of data staging is to allow

the user to access data at a minimum latency.

For this, we calculate a time bound, Tbound,

for the user to access a data.

Let time required for a broadcast = n

minutes. Thus, total number of broadcasts in

a day is 24 x 601n. Let size of the data pages

= M kbytes. The channel bandwidth for

broadcast is B kbps. So, the number of pages

broadcast per second = B / M pages.

Let approximate number of pages in a

broadcast be N ( N may vary, but it is fixed

for

this calculation). Total time taken for a

broadcast is N/(B/M) = ( ( N x M ) / B ) .

Thus, the average wait for any page in the

broadcast is ((N x M)l(2 x B)). Let the size of

an index page be I kbytes where I << M .

There is a time bound for accessing the index

which is interleaved in the broadcast so that

the user does not have to wait for the entire

broadcast to access the index. Let the time

bound for getting the index be Ttndcz = 5,

where n: << ( N x M)IB is total time for each

broadcast. Thus, on an average, the user has

to wait for Tindez/2 units of time to receive

the index. So, the index should be

broadcasted after every (B/M) x:l; number of

pages by the base station.

3. MOBILE DATABASE

SECURITY

Mobile work using mobile devices and

wireless links comprehends a row of

problems concerning security issues like

availability, con dentiality, integrity and

accountability. These requirements occur for

network components as well as database

systems. Mobile work including mobile

database access makes ubiquitous computing,

anywhere and anytime possible. The

mobility requires suitable hardware and

software. Mobile devices like handhelds

connected via wireless networks support

mobile users, especially in connection with

position searching tools. New risks and

challenges for security and privacy occur in

this environment. The goal is the protection

of mobile users and their data.

Security measures must take into

account the distribution of data and their

heterogeneous handling regarding to security

models. Scarce mobile resources make

insecure communication necessary to

replicate used data and increase the risk of

restricting or dismissing security measures.

3.1 MOBILE CONDITIONS

Mobile work is context-sensitive work

with contexts describing environmental

characteristics and the relationships between

them. In Lubinski, 1998], the special

problems of database systems in such a

mobile environment are described more

detailed. In this section, we summarize the

main mobile circumstances causing various

threats. Applications and required data are

location dependent, but their access must be

location transparent. Determined tasks are

applicable on special whereabouts. The

mobile infrastructure restricts the available

volume and type of data and the data transfer.

Context information comprehends further

which people and objects in the environment

stay.

Supporting mobile work involves

providing access to interesting data at the

appropriate location, time and device, i.e.

where and when the data are used based on

user aims, preferences, knowledge and

skills.For this purpose we require di erent

information regarding the current

infrastructure,available mobile resources,

connectivity, costs and duration of

connections, and bandwidths. Mobile work is

characterized by infrequent and temporary

short connections to the fixed network (low

connectivity) and by a variety of access types

(register and query data). The mobile user

accesses data that are also accessed by other

users or itself on different locations and

devices, respectively.

The mobile context includes mobile

work and communication attending metadata

to support users. This meta-information is

covered in four parts of the mobile context:

human factors, their tasks, roles, other

persons

location (and changing location in

time), hard- and software (mobile site

and network characteristics, equipment

and tools)

information, application characteristics

(like type, size)

These mobile circumstances, and

especially their dynamics, and restrictions

like frequent disconnections make a mobile

work with database systems di cult. This is

the reason for various di culties in securing

mobile work and for requiring a new

viewpoint to well known security measures,

or demand new ones.

3.2 PROTECTION OBJECTS AND

ACTIONS

Assuming distributed and/or replicated

databases, we must take into account

protection of the main action types

management, accesses and transfer to

protection objects data and metadata.

Metadata are used on di erent levels.

Database systems manage object types,

keys,and integrity rules. Transfer

components need at least receiver and sender

addresses of messages. Metadata include

necessarily mobile context data and security

relevant information like security policies.

Data and metadata are the items which must

be protected,whereas metadata are

additionally used for their protection.

Combining possible actions with

protection items gets the following table. The

first row and column shows the possible

items and actions to be protected and

characterize them in a short manner. The

body of the table illustrates the special

problems, threats or desired security

characteristics, respectively, for the

particular combinations of actions and items

appearing in the special mobile environments.

E.g., the distribution and heterogeneity leads

to typical distributed security problems

including data exchange between systems

with differing models and aims. Moreover,

mobile systems are characterized by very

mobile hardware.

The thread of lost confidence by loss

of devices is often underrated. Wireless links

are predestinated to be eavesdropped on.

Profiles of communicating users are simply

creatable. Attacks and security for mobile

communication are described in[ Federrath,

1999].

We focus in this paper database related

mobile security issues and ignore

communication security. Our approach

consists in three main tasks to keep mobile

work secure (see also[ Lubinski, 1998]), the

restriction of database transparencies, a

horizontal and vertical separation of

metadata and an adaptation of security.

Restrict transparencies:

Database transparencies like distribution

and replication transparency is soften to

allow user's participation. This requirement

concerns transparent security management

and control, too. However, every

transparency must be remain controlled by

the system to avoid insecure system states.

Separate metadata:

Because of the opportunity to misuse

context information, a useful protection lies

in separation or anonymization of it. The

sensitive aggregation of user identifying data

and other contexts must be avoided. A

powerful access control realize this type of

separation. Separated physical context

management improves the acces control.

We distinguish two kinds of data

separation, vertical and horizontal. The

accessed and as a rule location dependent

data gives information to the whereabout of

users.

Vertical separation supports

confidentiality requirements by protecting

users from tracing their movement. It allows

only a view to a (role dependent) section or a

facet of mobility patterns and behaviour.

Additionally, audit data should be

anonymized or pseudonymized.

Horizontal separation represents a

layered view and constitutes a prevention of

undesired information flow between different

system layers outside the controlled area.

Inner-database-communication

has to be unobservable by intruders

(encrypted) as well as by underlying services.

Adapt security:

There are a few papers which focus

security in heterogeneous database systems

meeting requirements of integration and

access to data of various policies. But the

essential criterion in mobile environments is

their dynamics due to possibly very dynamic

mobile contexts.

A flexible adaptation to the changing

environment characteristics decides about

suitable choice of applicable security

mechanisms. We enforce a resource aware

approach but assure a minimal security.

4. Conclusions

Wireless network is becoming a

commonly used communication platform. It

provides a cheaper way to get connected and

in some cases this is the only way to reach

people. However, it has a number of easy

and difficult problems and they must be

solved before MDS can be built. This

tutorial discussed some of these problems

and identified a number of possible

approaches.

The emerging trend is to make all

service providing disciplines, such as web,

E-commerce, workflow systems, etc., fully

mobile so that any service can be provided

from any place. Customer can surf the

information space from any location at any

time and do their shopping, make flight

reservation, open bank account, attend

lectures, and so on. This is what the wireless

technology driving us to.

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14. L. Loeb, ―Secure Electronic

Transactions‖, Artech House, 1998.

Approved by (Signature):

Guide : Mr Ajay Prasad Mr Arun Kumar

Asst. Pro. (CSE) HOD (CSE Dept.)