Transcript Mobile Database Systems

Mobile Database Systems
Vijay Kumar
Computer Sc. Telecommunications
University of Missouri-Kansas City
5100 Rockhill Road
Kansas City, MO 64110, USA
[email protected]
Mobile Database Systems
Outline

Fully Connected Information Space

Personal Communication System (PCS)
Mobile Database Systems (MDS)
Transaction Management
Data Caching
Query Processing
Data Classification
Conclusion






Mobile Database Systems
Fully connected information space
Mobile Database Systems
Fully connected information space
 Each node of the information space has some
communication capability.
 Some node can process information.
 Some node
channel.
can communicate through
 Some node can do both
voice
Mobile Database Systems
Fully connected information space
Can be created and maintained by integrating
legacy database systems, and wired and wireless
systems (PCS, Cellular system, and GSM)
Mobile Database Systems
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
Mobile Database Systems
What is a mobile connectivity?
A mode in which a client or a server can establish
communication with each other whenever needed.
Intermittent connectivity is a special case of mobile
connectivity.
Mobile Database Systems
What is intermittent connectivity?
A node in which only the client can establish
communication whenever needed with the server but the
server cannot do so.
Personal Communication System (PCS)
Part 1




Architecture
Wireless communication
Bandwidth limitations
Frequency reuse
Personal Communication System
(PCS)
A system where wired and wireless networks are integrated
for establishing communication.
PSTN
AC
HLR
VLR
MSC (MTSO)
MSC (MTSO)
EIR
MS
BS
MS
Wireless component
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.
Personal Communication System
(PCS)
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
Personal Communication System
(PCS)
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
Personal Communication System
(PCS)
Cellular telephony overview
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.
frequency
division
multiple
access
It is based on
(FDMA),
AMP
was
designed as a high capacity system based on a frequency
reuse scheme. A total of 50 MHz in the 824-849 MHz and 869894 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.
Personal Communication System
(PCS)
Cellular telephony overview
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.
Personal Communication System
(PCS)
Cellular telephony overview
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.
Personal Communication System
(PCS)
Cellular telephony overview
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.
Personal Communication System
(PCS)
Cordless telephony technologies
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 handsetto-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.
Personal Communication System
(PCS)
Cordless telephony technologies
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.
Personal Communication System
(PCS)
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.
operates in the 1895-1918.1 MHz band.
PHS
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 Communication System
(PCS)
Low-tier PCS telephony overview
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.
Personal Communication System
(PCS)
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)
Low ( 30 mph)
Coverage area
Large/Continuous
macrocell
High
Medium ( 60
mph)
Medium. Micro
and picocell
Low
High (100-800 mW)
Low (5-10 mW)
Low (5-10 mW)
Low (8-13 Kbps)
High (32 Kpbs)
High (32 Kpbs)
High ( 600 ms)
Low (10 ms)
Low ( 20 ms)
Handset
complexity
H-set power use
Speech coding
rate
Delay or latency
Small/Zonal,
picocell
Low
Personal Communication System
(PCS)
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.
Personal Communication System
(PCS)
Wireless Components
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.
Personal Communication System
(PCS)
Wireless Components
MSC (MTSO)
BS
MS
MS
Cell
Wireless
component
Personal Communication System
(PCS)
Wireless channels are limited
Item
Mobile
Phones
Europe (MHz)
NMT: 453-457, 463-467
GSM: 890-915, 935-960,
1710-1785, 1805-1880
Cordless CT1+: 885-887, 930-932
Phones
CT2: 864-868
DECT: 1880-1900
US (MHz)
Japan (MHz)
AMPS, TDMA, CDMA
824-849, 869-894
GSM, TDMA, CDMA
PDC: 810-826
940-956,
1429-1465,
1850-1910, 1930-1990
1477-1513.
PACS
1850-1910,1930-1990;
PHS
1895-1918;
PACS-UB: 1910-1930
JCT: 254-380
NMT:
Nordic Mobile Telephone
PDC:
Pacific Digital Cellular
PACS:
Personal Access Communications System
PHS:
Personal Handyphone System
PACS-UB: PACS Unlicensed Band
JCT:
Japanese Cordless Telephone
(Taken from Mobile Communications by Jochen Schiller)
Personal Communication System (PCS)
Limited channels must be utilized efficiently. It is done
so by (a) Frequency reuse and (b) Mobile cell
Frequency reuse
The goal of every mobile service provider is to manage as
many simultaneous calls as possible.
In USA each
cellular provider is allocated 25 MHz of spectrum, 12.5
MHz for transmitting (downstream) and 12.5 MHz for
receiving (upstream). Cellular system is duplex because
transmitting and receiving are allocated their own
frequencies. A person on a mobile call only needs the
allocated frequency of the cell, thus there is no reason
somebody else on the other end of the town cannot be
using the same frequency in a different cell. The concept
of multiple users using the same frequency at the same
time for communication is called frequency reuse.
Personal Communication System (PCS)
Frequency reuse (continued)
For frequency reuse to work correctly it is imperative that
each base station has just sufficient power to reach its
cell boundary. If it puts out too much power, then it will
not only reach the intended cell site, it will reach
unintended cell sites, which others may be using at the
same frequency for a totally different conversation. This
limitation on transmitted power, however, is also an
advantage because the cellular phone’s battery will last
longer.
Personal Communication System (PCS)
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.
Personal Communication System
(PCS)
Mobile cells
Metropolitan area
Metropolitan area
BS
Base Station
Coverage area in one cell
BS
BS
Coverage area in three cells
Large cells.
Low density
Small cells.
High density
Smaller cells.
Higher density
Personal Communication System
(PCS)
Mobile cells
The entire coverage area is a group of a number of
cells. The size of cell depends upon the power of
the base stations.
MSC
PSTN
Personal Communication System
(PCS)
Frequency reuse
A
2
7
3
7
4
6
1
6
5
A
2
2
3
1
4
5
D7
3
1
6
A
A
A
4
5
A
A
D
 3N
R
D = distance between cells using the same frequency
R = cell radius
N = reuse pattern (the cluster size, which is 7).
Thus, for a 7-cell group with cell radius R = 3 miles, the frequency reuse
distance D is 13.74 miles.
Personal Communication System (PCS)
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
Personal Communication System
(PCS)
Handoff
A process, which allows users to remain in touch, even
while breaking the connection with one BS and
establishing connection with another BS.
MSC
MSC
New BS
Old BS
Old BS
MSC
MSC
Old BS
New BS
New BS
Old BS
New BS
Personal Communication System
(PCS)
Handoff
To keep the conversation going, the Handoff
procedure should be completed while the MS (the
bus) is in the overlap region.
Cell overlap region
G
Old BS
New BS
Personal Communication System
(PCS)
Handoff issues

Handoff detection

Channel assignment

Radio link transfer
Personal Communication System
(PCS)
Handoff detection strategies

Mobile-Controlled handoff (MCHO)

Network-Controlled handoff (NCHO)

Mobile-Assisted handoff (MAHO)
Personal Communication System
(PCS)
Mobile-Controlled Handoff (MCHO)
In this strategy, the MS continuously monitors the
radio signal strength and quality of the surrounding
BSs. When predefined criteria are met, then the MS
checks for the best candidate BS for an available
traffic channel and requests the handoff to occur.
MACHO is used in DECT and PACS.
Personal Communication System
(PCS)
Network-Controlled Handoff (NCHO)
In this strategy, the surrounding BSs, the MSC or
both monitor the radio signal. When the signal’s
strength and quality deteriorate below a predefined
threshold, the network arranges for a handoff to
another channel. NCHO is used in CT-2 Plus and
AMPS.
Personal Communication System
(PCS)
Mobile-Assisted Handoff (MAHO)
It is a variant of NCHO strategy. In this strategy,
the network directs the MS to measure the signal
from the surrounding BSs and to report those
measurements back to the network. The network
then uses these measurements to determine
where a handoff is required and to which channel.
MACHO is used in GSM and IS-95 CDMA.
Personal Communication System
(PCS)
Handoff types with reference to the network

Intra-system handoff or Inter-BS handoff
The new and the old BSs are connected to
the same MSC.
MSC
Old BS
New BS
Personal Communication System
(PCS)
Intra-system handoff or Inter-BS handoff
Steps
1.
The
MU
(MS)
momentarily
suspends
conversation and initiates the handoff
procedure by signaling on an idle (currently
free) channel in the new BS. Then it resumes
the conversation on the old BS.
MSC
Old BS
New BS
Personal Communication System
(PCS)
Intra-system handoff or Inter-BS handoff
2.
Upon receipt of the signal, the MSC transfers the encryption
information to the selected idle channel of the new BS and
sets up the new conversation path to the MS through that
channel. The switch bridges the new path with the old path
and informs the MS to transfer from the old channel to the
new channel.
MSC
Old BS
New BS
Personal Communication System
(PCS)
Intra-system handoff or Inter-BS handoff
3.
After the MS has been transferred to the new BS, it signals
the network and resumes conversation using the new
channel.
MSC
Old BS
New BS
Personal Communication System
(PCS)
Intra-system handoff or Inter-BS handoff
4.
Upon the receipt of the handoff completion signal, the
network removes the bridge from the path and releases
resources associated with the old channel.
MSC
Old BS
New BS
Personal Communication System
(PCS)
Handoff types with reference to the network

Intersystem handoff or Inter-MSC handoff
The new and the old BSs are connected to
different MSCs.
PSTN
BS1
MSC A
Trunk
BS2
MSC B
BS1
MSC A
Trunk
BS2
MSC B
Personal Communication System
(PCS)
Handoff types with reference to link transfer

Hard handoff
The MS connects with only one BS at a time,
and there is usually some interruption in the
conversation during the link transition.

Soft handoff
The two BSs are briefly simultaneously
connected to the MU while crossing the cell
boundary. As soon as the mobile's link with
the new BS is acceptable, the initial BS
disengages from the MU.
Personal Communication System
(PCS)
Handoff types with reference to link transfer
Hard handoff
1.
MU temporarily suspends the voice conversation
by sending a link suspend message to the old BS.
2.
MU sends a handoff request message through an
idle time slot of the new BS to the network.
3.
The new BS sends a handoff ack message and
marks the slot busy.
4.
The MU returns the old assigned channel by
sending a link resume message to the old BS.
Personal Communication System
(PCS)
Handoff types with reference to link transfer
Hard handoff
5.
MU continues voice communication while the
network prepares for the handoff.
6.
Upon receipt of a handoff request message, the
new BS sends a handoff ack message and
reconfigures itself to effect the handoff.
7.
The MSC inserts a bridge into the conversation
path and bridges the new BS.
8.
Finally, the network informs the MU to execute the
handoff via both the new and old BSs by sending
the handoff execute message.
Personal Communication System
(PCS)
Handoff types with reference to link transfer
Hard handoff
9.
MU releases the old channel by sending an
access release message to the old BS.
10. Once the MU has made the transfer to the new BS,
it sends the network a handoff complete message
through the new channel, and resumes the voice
communication. The network removes the bridge
from the path and frees up the resources
associated with the old channel.
Personal Communication System
(PCS)
Handoff types with reference to link transfer
Soft handoff
1.
MU sends a pilot strength measurement message
to the old BS, indicating the new BS to be added.
2.
The old BS sends a handoff request message to
the MSC. If the MSC accepts the handoff request,
it sends a handoff request message to the new
BS.
3.
The BS sends a null traffic message to the MU to
prepare the establishment of the communication
link.
Personal Communication System
(PCS)
Handoff types with reference to link transfer
Soft handoff
4.
The new BS sends a join request message to the
MSC. The MSC bridges the connection for the
two BSs, so that the handoff can be processed
without breaking the connection.
5.
The new BS sends a handoff ack message to the
old BS via the MSC. The old BS instructs the MU
to add a link to the new BS by exchanging the
handoff command and handoff complete
messages.
Personal Communication System
(PCS)
Handoff types with reference to link transfer
Soft handoff
6.
The old BS and the MSC conclude this procedure
by exchanging the required handoff information.
The quality of the new link is guaranteed by the
exchange of the pilot measurement request and
the pilot strength measurement message pair
between the MU and the new BS.
Personal Communication System
(PCS)
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.
Personal Communication System
(PCS)
Roaming
Administrative constraints

Billing.

Subscription agreement.

Call transfer charges.

User profile and database sharing.

Any other policy constraints.
Personal Communication System
(PCS)
Roaming
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.
Personal Communication System
(PCS)
Roaming
Technical 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.
Personal Communication System
(PCS)
Roaming
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.
Personal Communication System
(PCS)
Roaming
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).
Personal Communication System
(PCS)
Roaming
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.
Personal Communication System
(PCS)
Registration
Two-Tier Scheme
HLR: Home Location Register
A HLR stores user
geographical location.
profile
and
the
VLR: Visitor Location Register
A VLR stores user profile and the current
location who is a visitor to a different cell that
its home cell.
Personal Communication System
(PCS)
Registration
Two-Tier Scheme steps. MU1 moves to cell 2.
Cell 1
Cell 2
MU1
MU1
Personal Communication System
(PCS)
Registration
Steps
1.
MU1 moves to cell 2. The MSC of cell 2 launches a
registration query to its VLR 2.
2.
VLR2 sends a registration message containing MU’s
identity (MIN), which can be translated to HLR address.
3.
After registration, HLR sends an acknowledgment
back to VLR2.
4.
HLR sends a deregistration message to VLR1 (of cell
1) to delete the record of MU1 (obsolete). VLR1
acknowledges the cancellation.
Personal Communication System
(PCS)
Location tracking
Steps
1.
VLR of cell 2 is searched for MU1’s profile.
2.
If it is not found, then HLR is searched.
3.
Once the location of MU1 is found, then the
information is sent to the base station of cell 1.
4.
Cell 1 establishes the communication.
Personal Communication System
(PCS)
Location tracking
Two-Tier Scheme steps location search
5
Dest
HLS
Id
HLS
Dest Dest-HLS
3
Id
LS
Dest Dest-ls
-
6
4
Source
ls
9
Id
MSS
Dest Dest-mss
-
8
Dest
ls
10
2
Source-mss
1
Src
Dest
7
Personal Communication System
(PCS)
Location tracking
Two-Tier Scheme steps location update
5
Id
LS
MU New-ls
Id
MSS
MU New-mss
-
HLS
6
10
4
9
New-ls
Old-ls
3
Id HLS
MU HLS
-
2
8
New-mss
1
MU
7
Mobile Database Systems (MDS)
Part 2

Architecture

Data categorization

Data management

Transaction management

Recovery
Mobile Database Systems (MDS)
A Reference Architecture (Client-Server model)
PSTN
DB
DB
HLR
VLR
DBS
DBS
MSC
MSC
BSC
BSC
Fixed host
Fixed host
BS
MU
MU
MU
BS
BS
MU
MU
Mobile Database Systems (MDS)
MDS Applications

Insurance companies

Emergencies services (Police, medical, etc.)

Traffic control

Taxi dispatch

E-commerce

Etc.
Mobile Database Systems (MDS)
MDS Limitations

Limited wireless bandwidth

Wireless communication speed

Limited energy source (battery power)

Less secured

Vulnerable to physical activities

Hard to make theft proof.
Mobile Database Systems (MDS)
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
Mobile Database Systems (MDS)
Objective
To build a truly ubiquitous information processing
system by overcoming the inherent limitations of
wireless architecture.
Mobile Database Systems (MDS)
MDS Issues


Data Management

Data Caching

Data Broadcast (Broadcast disk)

Data Classification
Transaction Management

Query processing

Transaction processing

Concurrency control

Database recovery
Mobile Database Systems (MDS)
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
Mobile Database Systems (MDS)
MDS Data Management Issues
How to improve data availability to user queries
using limited bandwidth?
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
Data Broadcast (Broadcast disk)
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
How MDS looks at the database data?
Data classification

Location Dependent Data (LDD)

Location Independent Data (LID)
Mobile Database Systems (MDS)
MDS Data Management Issues
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
Location Dependent Data (LDD)
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
Location Dependent Data (LDD)
Location binding or location mapping can be
achieved through database schema or through
a location mapping table.
Mobile Database Systems (MDS)
MDS Data Management Issues
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.
Mobile Database Systems (MDS)
MDS Data Management Issues
Concept Hierarchy in LDD
In a data region the entire LDD of that location
can be represented in a hierarchical fashion.
City data
County 1 data
Subdivision 1 data
County 2 data
Subdivision data
County n data
Subdivision m data
Mobile Database Systems (MDS)
MDS Query processing
Query types

Location dependent query

Location aware query

Location independent query
Mobile Database Systems (MDS)
MDS Query processing
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”.
Mobile Database Systems (MDS)
MDS Query processing
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.
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction
properties:
ACID
Consistency, Isolation, and Durability).
(Atomicity,
Too rigid for MDS. Flexibility can be introduced
using workflow concept.
Thus, a part of the
transaction can be executed and committed
independent to its other parts.
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction fragments for distribution.
PSTN
DB
DB
HLR
VLR
DBS
DBS
MSC
MSC
BSC
BSC
Fixed host
Fixed host
BS
MU
MU
MU
BS
BS
MU
MU
Mobile Database Systems (MDS)
MDS Transaction Management
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.
Mobile Database Systems (MDS)
MDS Transaction Management
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
Mobile Database Systems (MDS)
MDS Transaction Management
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 Database Systems (MDS)
MDS Transaction Management
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.
Mobile Database Systems (MDS)
MDS Transaction Management
Mobile Transaction Models
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.
Mobile Database Systems (MDS)
MDS Transaction Management
Mobile Transaction Models
Clustering: A mobile transaction is decomposed 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.
Mobile Database Systems (MDS)
MDS Transaction Management
Mobile Transaction Models
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.
Mobile Database Systems (MDS)
MDS Transaction Management
Mobile Transaction execution.
DBS1
DBS2
T2(e4, e 5)
MU1
MU3
T1(e1, e 2, e 3)
MU2
DBS4
DBS3
Mobile Database Systems (MDS)
MDS Transaction Management
Serialization of concurrent execution.

Two-phase locking based (commonly used)

Timestamping

Optimistic
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.
Mobile Database Systems (MDS)
MDS Transaction Management
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.
Mobile Database Systems (MDS)
MDS Transaction Management
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.
Mobile Database Systems (MDS)
MDS Transaction Management
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.
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction commit.
One possible
protocol.
scheme
is
“timeout”
based
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.
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction commit.
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
Mobile Database Systems (MDS)
MDS Transaction Management
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.




Mobile Database Systems (MDS)
MDS Transaction Management
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
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction and database recovery.
Desirable recovery features

Independent recovery capability

Efficient logging and checkpointing facility

Log duplication facility
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction and database recovery.

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
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction and database recovery.
Possible approaches

Partial recovery capability

Use of mobile agent technology
Mobile Database Systems (MDS)
MDS Transaction Management
Transaction and database recovery.
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 Database Systems (MDS)
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
Mobile Database Systems (MDS)
Mobile Agent Technology
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
Mobile Database Systems (MDS)
Mobile Agent Technology
Possible approaches

Agent broadcast on a dedicated wireless
channel

Pool of agents at every processing node

Agent migration to a required node.
Mobile Database Systems (MDS)
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.
Mobile Database Systems (MDS)
Mobile E-commerce
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.
Mobile Database Systems (MDS)
Mobile E-commerce
Requirements for a mobile E-system

Security

Reliability

Efficient

Customer trust

Quality of service
Mobile Database Systems (MDS)
Mobile E-commerce
These requirements are difficulty and complex to achieve
Security
Conventional
revision.
key
approaches
needs
Reliability
Hard to provide mainly because of the
unreliability and limitations of resources.
Mobile Database Systems (MDS)
Mobile E-commerce
These requirements are difficulty and complex to achieve
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.
Mobile Database Systems (MDS)
Mobile E-commerce
These requirements are difficulty and complex to achieve
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.
Mobile Database Systems (MDS)
Conclusions and summary
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.
Mobile Database Systems (MDS)
Conclusions and summary
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.
Mobile Database Systems (MDS)
References
1.
Acharya, S., Alonso, R., Franklin, M., and
Zdonik, S. Broadcast Disks: Data management
for Asymmetric Communication Environments.
Proc. ACM SIGMOD Conf., San Jose, May,
1995.
2.
Alonso, R., and Korth, H. Database Systems
Issues in Nomadic Computing. Proc. ACM
SIGMOD International Conf. on management of
Data, May 1993.
Mobile Database Systems (MDS)
References
3.
Barbara, D., and Imielinski, T. Sleepers and
Workaholics: Caching Strategies in Mobile
Environments. Proc. ACM SIGMOD Conf.,
Minneapolis, May, 1994.
4.
Chrysanthis, P. K., Transaction Processing in
Mobile Computing Environment, in IEEE
Workshop on Advances in Parallel and
Distributed Systems, October 1993.
Mobile Database Systems (MDS)
References
5.
Dhawan, C.
1997.
Mobile Computing.
McGraw-Hill,
6.
Dunham, M. H., Helal, A., and Balakrishnan, S., A
Mobile Transaction Model That Captures Both
the Data and Movement Behavior, ACM/Baltzer
Journal on Special Topics in Mobile Networks
and Applications, 1997.
7.
Forman, H. George and Zahorjan, J.
Challenges of Mobile Computing,
Computers, Vol. 27, No. 4, April 1994.
The
IEEE
Mobile Database Systems (MDS)
References
8.
Pitoura, E. and Bhargava, B., Maintaining
Consistency of Data in Mobile Distributed
Environments. Proceedings of 15th International
Conference on Distributed Computing Systems.,
1995.
9.
Pitoura, E.
and Bhargava, B., Building
Information Systems for Mobile Environments,
Proc. 3rd. Int. conf. on Information and
Knowledge Management, Washington, DC, No.
1994.
Mobile Database Systems (MDS)
References
10.
Vijay
Kumar,
“Timeout-based
Mobile
Transaction Commit Protocol”, 2000 ADBISDASFAA Symposium on Advances in Databases
and Information Systems, Prague, Sep. 5-8,
2000.
11.
Shaul Dar, Michael Franklin, Bjorn T. Johnsson,
Divesh Srivastava, and Michael Tan, “Semantic
Data Caching and Replacement”, Proc. Of the
22nd VLDB Conference, Mumbai, India, 1996.
Mobile Database Systems (MDS)
References
12.
E. Pitoura and G. Samaras, “Data Management
for Mobile Computing”, Kluwer Academic
Publishers, 1998.
13.
E. Turban, at. el., “Electronic Commerce: A
Managerial Perspective”, Prentice Hall, 2000.
14.
L. Loeb, “Secure Electronic Transactions”,
Artech House, 1998.