selected topic Pervasive Computing edited 02.pdf

Wireless Technologies - Overview
Wireless technologies represent a rapidly emerging area
providing pervasive/ubiquitous access to the network.
Internet-enabled cell phones and Personal Digital Assistants (PDAs)
have emerged as the newest products that can connect to the Internet
across a wireless network or facilitate communication among devices.
Among such technologies are:
 Infrared
 RF (RFID Tags and Readers - Sensors)
 Bluetooth
 WLAN - IEEE 802.11/WiFi (Wireless Fidelity) and
 WiMAX 802.16 (World Interoperability for Microwave Access)
 GPRS/CDMA based wireless access to the Internet

Infrared: IrDA
IrDA is a point-to-point, narrow-angle (30° cone), ad
hoc data transmission standard designed to operate over
a distance of zero to one meter.
RF: RFID
 Radio Frequency Identification (eg. Bar code replacement)
 Exists as RFID readers and tags
 Tags exist in the form of Passive Tags and Active tags

Bluetooth
Low-cost, short-range wireless links between mobile PCs,
mobile phones, and other portable handheld devices (to
avoid annoying wires)
Connection between cell phone and headset
Point to point (serial wire replacement)
Point to multipoint (Pico-net, ad-hoc networking)

WLAN (WiFi)
 Wireless Local Area Networks (WLAN) are implemented as an
extension to wired LANs based on the IEEE 802.11 standard
 New protocols such as Wireless Application Protocol (WAP)
are introduced
 New languages such as WML (Wireless Markup Language) have
been developed
 Requires Access Point (WiFi direct also exists)
 An access point/base station connects to a LAN by means of
Ethernet cable
 Access point usually installed in the ceilings

WLAN (WiFi) – cont.
 Access points receive, buffer, and transmit data between the
WLAN and the wired network infrastructure.
 A single access point supports on average of twenty users at a
time
 Has a coverage varying from 20 meters in areas with obstacles
(walls, stairways, elevators) and up to 100 meters in areas with
clear line of sight.
 A building may require several access points to provide
complete coverage and allow users to roam seamlessly between
access points.
 Wireless Client Adapter - A wireless adapter connects users via
an access point to the rest of the LAN.

WLAN (WiFi) – Standards
 WiFi standard exists as IEEE 802.11a/b/g/n
 The number "11" indicates the IEEE working group assigned to 802 standards, and
the a/b/g/n refers to a special Task Group within this body, known as TGa, TGb,
TGg and TGn.
 The 802.11n is a newer standard of WiFi LAN. It operates on the 2.4 gigahertz
(GHz) band, like 802.11b and 802.11g. This frequency does not require line-of-
sight availability like 802.11a, which works in the regulated 5 GHz band.
 802.11n uses MIMO (multiple-input multiple-output) technology and incorporate
OFDM (orthogonal frequency-division multiplexing) that splits signal frequencies
up into several modulated channels for increased throughput.
Standard
802.11b
Frequency
2.4 GHz
Speed
5-11 mbps
802.11g 2.4 GHz 25-54 mbps
802.11a 5.0 GHz 25-54 mbps
802.11n 2.4 GHz 100-200+ mbps

WiMax (802.16)
 WiMax is a superset of WiFi
 Designed for wide area networking
 Designed specifically for last-mile distribution and mobility
 Promises high speed (30 Mbps+)
 Relatively new standard; thus, WiMax products are expensive
GPRS/CDMA: General Packet Radio Service extends GSM
(Global System for Mobile communications) ands it is packet
oriented mobile data service on 2G and 3G cellular
communication system (WAP, MMS, P2P, Always on Internet)
• CDMA 1X, CDMA2000, …

Wireless Mesh Networks
 “Mesh” refers to many types of technology that enable wireless
systems to automatically find each other and self-configure
themselves to route information among themselves.
Wide
Range
of
Applications

Pervasive Infrastructure
Applications need to
Become autonomous
Place greater reliance on knowledge of context reducing
interactions with users.
Cope with highly dynamic environments in which resources,
such as network connectivity and software services,
frequently vary over time.
As computing devices become more pervasive, the nature of
interactions between users and computers must evolve.

Pervasive Infrastructure Requirements
Devices
Software components
Users
User interfaces
Components that place requirements on both the supporting
infrastructure and the manner in which software components
and user interfaces are constructed include

Heterogeneity
 Devices in a pervasive computing environment include sensors
and actuators; embedded devices in objects such as watches
and vehicles; home and office appliances such as videos and
telephones; mobile devices such as PDAs, cell phones and
notebooks; desktop machines, etc.
 Heterogeneous devices will be required to interact seamlessly,
despite wide differences in hardware and software capabilities.
 Requires an infrastructure that maintains knowledge of device
characteristics and manages the integration of devices into a
coherent system that enables arbitrary device interactions.
Device related requirements that must be addressed
by pervasive computing infrastructure include:
Heterogeneity and Mobility

Mobility
 Mobility introduces problems such as the maintenance of
connections as devices move between areas of differing
network connectivity, and the handling of network
disconnections.
 While protocols for wireless networking handle some of
the problems of mobility, such as routing and handovers,
some problems cannot be solved at the network level, as
they require knowledge of application semantics.
 It should be the role of the computing infrastructure to
cooperate with applications in order to perform tasks
related to device mobility.
Device related requirements …

Context awareness
Adaptation
Mobility and distribution
Interoperability
Development and deployment
Component discovery services
Scalability
Software related requirements that must be addressed by
pervasive computing infrastructure include

Context awareness
 Invisibility of applications will be accomplished in part by reducing
input from users and replacing it with knowledge of context.
 Context-aware software components will exploit information such as
the activities in which the user is engaged, proximity to other devices
and services, location, time of day and weather conditions, etc.
 Knowledge of context will also be required to enable adaptation to
changing environmental conditions, such as changing bandwidth and
devices, which can be brought about by mobility.
 The infrastructure for pervasive computing should support context
awareness by facilitating the gathering of information from sources
such as sensors and resource monitors; performing interpretation and
dissemination of contextual information in a scalable and timely
fashion; and providing models for programming context-aware
applications.
Software related requirements …

Adaptation
 Adaptation is required in order to overcome the dynamic
nature of pervasive computing. Mobility of users, devices
and software components can occur, leading to changes in
the physical and virtual environments of these entities.
 It should be the role of the infrastructure for pervasive
computing to facilitate adaptation, which may involve
adapting individual software components and/or
reconfiguring bindings of components by adding,
removing or substituting components.

Mobility and distribution
As users can be mobile and able to exploit the
capabilities of several devices simultaneously,
mechanisms will be required to enable the
mobility and distribution of software.
These mechanisms should be largely transparent
to component developers, who should not be
concerned with program and data migration or
synchronization and coordination of distributed
components.

Interoperability
 The infrastructure for pervasive computing must support
diverse types of software component.
 The infrastructure is required to integrate software
components to successfully interact and cooperate to achieve
common tasks.
 Applications are formed dynamically from available software
components. This will require dynamic interoperability at the
component level.
 Components will need to be capable of dynamically acquiring
knowledge of each other’s interfaces and behaviour, in order
to learn how to interact with previously unknown
components.

Development and deployment
The number and diversity of software components
that will be required in pervasive computing
environments will necessitate methods for their
rapid development and deployment.
Infrastructural support for rapid application
deployment can be achieved through the provision
of execution environments into which applications
can be placed regardless of configuration or
adaptation.

Component discovery services
 The issue of discovery of software components has been
addressed in various research areas. In open distributed
computing, resource discovery is supported by a type
management repository, which maintains descriptions of
service interface types. Resource discovery is also addressed
by network directory protocols such as LDAP, and in other
technologies such as Jini and Bluetooth.
 The main challenge in pervasive computing environments,
which are characterized by their heterogeneity, will be to
integrate the different approaches into a single scalable
resource discovery system by mapping requests between
resource discovery domains.

Scalability
One of the features of pervasive computing is the
increasing ubiquity of devices and software. Thus,
the infrastructure, the interactions between
components, and the software services provided in
pervasive computing environment must all be
scalable.
A powerful software platform on which scalable,
fault-tolerant and distributed components can be
built is essential.

Maintaining knowledge of users context
Managing tasks related to user mobility
User related requirements that must be addressed by

Maintaining knowledge of users context
 The infrastructure should maintain context data related to
users, including their preferences, current activities and
active computing sessions.
 The uses of user-related context includes allowing
applications to provide adaptation to user requirements and
enabling the amount of input that applications require from
users to be reduced.
 For example: With knowledge that a user is engaged in
driving a car, an application can ensure interaction is
carried out through a speech-based interface, rather than a
screen based one, in order to enable the user to focus on the
road.
User related requirements …

Managing tasks related to user mobility
User mobility between devices should be
supported by enabling automated migration (or
re-instantiation in a new location) of application
components.
The tasks of identifying the need for application
migration and then carrying out the migration
should be performed by the computing
infrastructure in a manner that makes the
migration as transparent as possible.
User related requirements …

Universal Interface
 Users in pervasive computing environments will demand
ubiquitous access to their computing applications, which will
create a requirement for universally available user interfaces.
Adaptation
 Device heterogeneity introduces a further requirement for user
interfaces that are highly adaptable.
Usability
 User interfaces for pervasive computing must be carefully
designed with several factors like ergonomics and novelty in
mind.
User interface related requirements that must be addressed by

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