Transcript Wireless communication networks

CSE-302: Mobile Computing
Dr. R. B. Patel
Dr. R. B. Patel
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Breakthrough Technology
• Wireless communication networks
–
multiple networks “covering” the globe
–
world- wide deregulation and spectrum auctions
–
standard communication systems and air link
interfaces
• Portable information appliances
–
laptops, notebooks, sub- notebooks, and MNCs
–
hand- held computers
–
PDAs and smart phones
• Internet:
–
TCP/ IP& de- facto application protocols
Dr. R. B. Patel
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–
ubiquitous web content
New Forms of Computing
Distributed
Computing
(Client/ Server)
Wireless Computing
Nomadic Computing
Mobile Computing
Ubiquitous
Computing
Pervasive Computing
Invisible Computing
Dr. R. B. Patel
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Mobile Computing
Mobile Computing
• Using:– small size portable computers,
handheld, MNC, and other small wearable
devices,
• To run stand- alone or network based
applications via:– wireless networks: IR,
BlueTooth, W- LANs, Cellular,W- Packet Data
networks, SAT, etc.
•By : – nomadic and mobile users (animals,
agents, trains, cars, cell phones, ….)
Dr. R. B. Patel
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Mobile Computing
• An important question to ask is which technology drove mobile
computing to where it is today?
• Is it the wireless network technology or the miniaturization and
portable computing technology?
• Unfortunately, there is no easy answer. An individual with a Palm Pilot
will probably answer in favor of the portable technology, whereas a
UPS package delivery worker will be more thankful to the wireless
technology.
• Whatever the right answer might be, more important questions need to
be answered: where are we now?
• And what are the challenges and impediments facing mobile
computing?
Dr. R. B. Patel
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Mobile computing
• Mobile computing represents a shift in the distributed
systems paradigm.
• The potential of decoupled and disconnected operation,
location-dependent computation and communication, and
powerful portable computing devices gives rise to
opportunities for new patterns of distributed computation
that require a revised view of distributed systems.
• However, factors such as weak network connectivity,
energy constraints, and mobility itself raise new concerns
regarding the security, reliability, and even correct-ness of
a mobile computing system.
Dr. R. B. Patel
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Mobile Computing
• Migration is important for survival
• Mobility originated from the desire to move either toward
resource or away from scarcity
• Mobile computing about both physical and logical
computing entities that move
• Physical entities are computers that change locations
• Logical entities are instances of running user application or
a mobile agent
• Mobile agents can migrate any where over the Internet.
• But applications can only move to a local cluster of
computers
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Buzzwords
• Mobile, ubiquitous, nomadic, un-tethered (unsecured),
pervasive and any time, any where, any person computing
are used by the researchers to refer to computing that uses
small portable devices and wireless communication
network.
• Nomadic computing refer to limited migration
– Migration is within a building at a pedestrian speed
– Interleaved pattern of user relocation and indoor
connections
• In the same vein, users carrying laptop with Dialup
modems are engaged in nomadic computing
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Buzzwords (contd...)
• Mobile Computing requires: Wireless network to support
outdoor mobility and handoff from one network to the next
at a pedestrian or vehicular speed
• Traveler in car using laptop connected with a GSM phoneengaged in mobile computing
• Ubiquitous computing or pervasive computing refers to
access to computer network all the time at any location by
any person.
• Ubiquitous computing cannot be realized unless mobile
computing matures.
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Ubiquitous Computing = Nomadic
Computing + Mobile Computing
No
Network
Fixed
Network
Fixed
Wireless
Network
Nomadic Computing
Wireless
Network
(A)
Wireless
Network
(B)
Mobile Computing
Ubiquitous computing
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Nomadic computing
• It is another name for mobile computing, is the use
of portable computing devices (such as laptop and
handheld computers) in conjunction with mobile
communications technologies to enable users to
access the Internet and data on their home or work
computers from anywhere in the world.
• People using such a system are sometimes referred
to as technomads, and their ability to use that
system as nomadicity.
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Continued …
• Nomadicity is the tendency of a person, or group of
people, to move with relative frequency.
• The need to support today's increasingly mobile workers
with nomadic computing, the use of portable computing
devices and, ideally, constant access to the Internet and
data on other computers.
• The goal of nomadic computing is to enable a consistent
experience for users anywhere in the world, including as
they travel from one place to another.
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Continued …
• A nomadic environment is said to be one that is transparent
to the user, regardless of location, the device and platform
they're using, the available bandwidth, and whether or not
they are in motion at any given time.
• Standards such as the Internet Engineering Task Force’s
(IETF) Mobile IPv6 standards and Dynamic Host
Configuration Protocol (DHCP) can be said to support
nomadic computing.
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Ubiquitous Computing
• Ubiquitous computing names the third wave in
computing, just now beginning.
• First were mainframes, each shared by lots of
people. Now we are in the personal computing era,
person and machine staring uneasily at each other
across the desktop.
• Next comes ubiquitous computing, or the age of
calm technology, when technology recedes into
the background of our lives.
• This is also called "Third Paradigm" computing.
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Sentient computing
• Sentient computing is a form of ubiquitous
computing which uses sensors to perceive
its environment and react accordingly.
• A common use of the sensors is to construct
a world model which allows location-aware
or context-aware applications to be
constructed.
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Mobile Environment
Wireless
radio Cells
Fixed
host
Fixed
host
Fixed
host
High-speed wireline network
Fixed
host
Fixed
host
Fixed
host
Satellite
link
Wireless
LAN
Base
station
Mobile
host
Dr. R. B. Patel
Wireless
link
Comm.
cell
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Wireless
Networks
Telecommunication
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Emerging Portable Information Devices
The First Wrist PC: Ruputer
The Nokia 9000 Communicator
Motorola
marco
The
Vadem
Clio
Subscriber Identification
Module (SIM)
The Power
Ring
The Pocket PC
Motorola Envoy
The Dr.
Sharp
R. Zaurus
B. Patel
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Fujitsu Stylistic
2300/ 3400
Japan’s PHS
Phone, Year
Wearable
Computers
Applications for mobile computing
• There are several applications for mobile computing
including wireless remote access by travelers and
commuters, point of sale, stock trading, medical
emergency care, law enforcement, package delivery,
education, insurance industry, disaster recovery and
management, trucking industry, intelligence and military.
• Most of these applications can be classified into: (1)
wireless and mobile access to the Internet, (2) wireless and
mobile access to private Intranets, and (3) wireless and
adhocly mobile access between mobile computers.
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Beneficiaries of ubiquitous computing
Internet
Education
Insurance
Emergency
Trucking
Intelligence
Military
Intranet
Servers
Commuters
Travelers
Stock traders
Medical
Law enforcement
Ad-hoc network
Dr. R. B. Patel
Clients
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Limitations of the
Environment
–
–
–
–
–
–
Mobile
Limitations of the Wireless Network
Heterogeneity of fragmented networks
Frequent disconnections
Limited communication bandwidth
Limitations Imposed by Mobility
Limitations of the Mobile Computer
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Continued…
Frequent Disconnections
– Handoff blank out (>1ms for most cellular
system)
– Drained battery disconnection
– Battery recharge down time
– Voluntary disconnection (turned off to
preserve battery power, also off overnight)
–
Theft and damage (hostile environment)
–
Roam-off disconnections
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Continued…
Limited Communication Bandwidth
–
Orders of magnitude slower than fixed
network
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Higher transmission bit error rates (BER)
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Uncontrolled cell population
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Difficult to ensure Quality of Service (QoS)
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Asymmetric duplex bandwidth
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Limited communication bandwidth
exacerbates the limitation of battery lifetime.
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Continued…
Limitations of the Mobile Computer
–
–
Short battery lifetime (max ~ 5 hours)
Subject to theft and destruction =>
unreliable
–
Highly unavailable (normally powered-off to
conserve battery)
–
Limited capability (display, memory, input
devices, and disk space)
–
Lack of de- facto general architecture:
Handheld, communicators, laptops, and other
devices
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Continued…
Limitations Imposed by Mobility
Lack of mobility- awareness by
applications
–
inherently transparent programming
model (object-,components- oriented,
but not aspect- oriented)
–
lack of environment test and set API
support
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Continued…
Lack of mobility- awareness by the system
–
network: existing transport protocols are
inefficient to use across heterogeneous mix of
fixed/wireless networks
–
session and presentation: inappropriate for
the wireless environment and for mobility
–
operating systems: lack of environment
related conditions and signals
–
client/server: unless changed,
inappropriate and inefficient
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Continued…
Mobile and Wireless Networking Issues
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Mobile IP
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Wireless Transport
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Ad- Hoc Networks
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Location Management
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Wireless Network Benchmarking
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Ad- Hoc Network Simulation
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Wireless Link Simulation
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Continued…
Wireless and Mobile Computing Models
–
Mobility- aware Client/ Server using
Proxies
–
Disconnected Operations
–
Application- aware Adaptations
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Mobile Agents and Objects
–
Thin Client/ Server
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Mobile Caching and Replication
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Broadcast Disks
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Service Advertisement and Brokering
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Smart Pones
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Continued…
Mobile file and Database Systems
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Wireless File System Access
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Disconnected File Systems
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Mobile Access to C/ S or Distributed
Databases
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Ad- Hoc Database Systems
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Checkpointing
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Database recovery
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Mobile Database Design
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Continued…
Mobile Transaction and Workflow
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ACID Relaxation
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Mobile Transaction Models
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Optimistic Data Replication
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Semantic- based Conflict Resolution
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Consensus in Mobile Environment
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Continued…
Wireless and Mobile Applications and Services
–
Application Design for Wireless networks
–
Application Design for Mobility
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Wireless WWW Access
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Active Badges (Teleporting)
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Wireless Classroom (Wireless Campus!)
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Mobile Groupware
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Location- sensitive Yellow Service
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Pervasive Computing and Smart spaces
–
•.....
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Continued…
Performance and QoS
–
QoS Measures in Wireless and Mobile
Environments
–
QoS Guarantees
–
Simulators and Emulaors of Wireless Links
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Simulators of Mobile and Ad- hoc
Networks
–
Wireless Networking Benchmarking
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Continued…
Emerging Standards
–
The 802.11b
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The BlueTooth Standard
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The Wireless Application Protocol (WAP)
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The CompactHTML
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The Network Computer Reference
Specification
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Telecom Standards: UMTS
–
…
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Continued…
Commuters
Travelers
Stock traders
Medical
Law enforcement
Internet
Intranet
Education
Insurance
Emergency
Trucking
Intelligence
Military
Intranet
Ad-hoc network
Servers
Dr. R. B. Patel
Clients
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Challenges
•
•
•
•
•
•
•
Mobility/context aware applications
Naming and locating
Routing data and messages
Reliability in presence of disconnection
Data management
Transaction models
Security
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Continued…
• Mobile computing affects entire spectrum of
issues in computing
• First of all it is distributed + mobile computing
• Distributed computing as we know works on static
wired network
• Node may initiate computation somewhere and
migrate to another place.
• So two major problems that arise due to mobility
– Searching for current location of a mobile node
– To impose a communication structure among nodes
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Continued…
• Physical location of mobile host is not the network
address, so how do we route the message to a
mobile host.
• This question is being addressed by two different
communities- Internet community and cellular
community
• Work of Internet community involves Mobile IP
– Aims at standards that can extend IP in order to deal
with location of mobile host
– Mobile IP work assumes connectionless packet
switching scenario
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Continued…
• Cellular community’s effort based on location
management of cellular phone users
• It deals with connection-oriented communication,
since it is motivated by issues in call-setup in
telephony
• Main problem in mobility management is to find
an appropriate tradeoff between searching and
informing
• Searching is performed when address of the
message recipient is not known- at least not
known precisely
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Continued…
•
•
Informing is a responsibility of the mobile
host when it migrates
Extreme situations can be
1. Mobile host never informs- works for hosts
receiving few messages and for hosts which
do not move during receiving
2. Always informs – works well for hosts
receiving messages frequently
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Continued…
•
•
Ad hoc network routing is the ultimate challenge
Ad hoc networks arise in rapid development scenarios
1.
2.
3.
•
•
Emergency disaster management
Military operation in remote sites
Business meeting venues without infrastructure support
Many routing algorithms are designed: such as fisheye,
state routing, dynamic source routing, ad hoc on demand
routing, etc.
There are interesting application of conventional graph
theoretic problems in ad hoc network routing
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Continued…
(b) Ad hoc network
(a) Infrastructure-based wireless network
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Continued…
• Main cause of loss of packets in wired network is
congestion because error rates are very low
• In wireless network congestion still remains a
problem, but the situation is somewhat reversed
• Wired and wireless network require different
techniques to achieve reliability and flow control
• TCP works is unsuitable for wireless network as it
interprets errors packets loss
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Continued…
ITCP (split/indirect TCP) splits TCP into two
parts
– One between sender and local MSS of the
recipient
– The other between local MSS and recipient
– If MH switches cell during lifetime of a ITCP
connection center point of connection moves to
new MSS sender remains completely unaware
about it
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Continued…
• Disconnection/weak connection support is
important
• CODA file system provides support for this
• It is implemented as client side cache management
system
• The issue concerns making a file system highly
available while maintaining consistency
• Caching in mobile environment is quite different.
MSS cannot keep state information (due to scale)
for all clients. So invalidation by notification
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Continued…
•
Categories of information dissemination
1. Wide area services – such as stock quotes on
national scale
2. Macro services- such weather on a regional
scale
3. Micro services- traffic condition is an
immediate vicinity
•
Can be extend to even picocells – such
finding a parking slot
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Continued…
Proving services will require addressing of following
new issues
– Interoperability
and
adaptability
to
network
environments ranging from high to low bandwidths and
infrared communication links
– Energy efficient data access
– Support for mobility and disconnection
– Support for active services, triggers (even notification),
and periodic data delivery.
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Continued…
•
•
•
Two modes of information dissemination are
1. Publish
2. Provide on demand
Publish data is filtered by client and server provides
directory information for assisting the filtering
Advantages of information dissemination by publishing
are
– Hot spots can be broadcast frequently-which saves
energy at client, avoid congestion
– Directory helps client to tune in selectively
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Continued…
• Handoff management – an MH moves from
one cell to another while being connected
• Desirable features are
– Probability of call dropping is minimized
– Ping-pong handoffs avoided
– Interruption is minimized
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Mobile Computing Models
• The following models of computing in the
mobile environment are currently being
researched and investigated:
–
–
–
–
–
Client/Server
Client/Proxy/server
Disconnected Operation
Mobile Agents
The Thin Client Model
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