Download Introduction

Special Topics
on
Wireless Ad-hoc Networks
Lecture 1: Introduction
University of Tehran
Dept. of EE and Computer Engineering
By:
Dr. Nasser Yazdani & Farshad Lahouti
Univ. of Tehran
Wireless Ad Hoc/Sensor Networks
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Objectives of course
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Learn challenges in wireless networking
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Understand state-of-the-art in
wireless/ubiquitous systems
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What forces us to reconsider many traditional
designs?
Get a broad view of the ongoing research in the
wireless domain.
Have a good understanding of the
capabilities and limitations of them
Above all enjoy learning something new
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Wireless Ad hoc/Sensor Networks
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Course Materials
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Course Web page
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http://ece.ut.ac.ir/classpages/F85/Wireless/
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visit regularly
Research papers
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Pdf/ps version of the papers on the Web page
~30 papers, Combination of classic and recent
work. Some Optional reading!
Recommended textbook
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“Ad Hoc Wireless Networks: Architectures and
Protocols”, Ram Murthy & Manoj.
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Wireless Ad hoc/Sensor Networks
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Grading
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Homework assignments, around %20
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Paper review
Problems and hands-on assignments
Severe late penalties!
Project, ~ %30
Exam(s) ~%50
No Presentation: Except for PhD students
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Wireless Ad hoc/Sensor Networks
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How to survive the course
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Some Networking concepts are behavioral, then, do
not expect everything is as exact as mathematics.
Networking in general and wireless in particular is a
complicated field even though it sounds easy and
straightforward,
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Concentrates on concepts instead of a special technique or
technology.
The course is not a classic course like math 2, be
prepared for a lot of ideas.
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Then, class participation is extremely important.
Do not leave everything to the last minute.
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General ideas
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We will try to understand the wireless networking as
a whole. Believe or not Networking is fun and
applicable in many places.
You are supposed to be trained as researcher, then,
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Be open minded, nothing is final.
Try to understand the history and idea. It is important to
not repeat the same thing people have done previously
Capture concepts, then, you can easily say what is possible
or not possible.
Will try to follow layering perspective. Different from
the book
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Wireless Ad hoc/Sensor Networks
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General ideas (2)
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People from different background and different
interests. Makes course customization difficult
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Wireless realm is very vast, from communication to
computer.
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Try to give input
Be patient!
It is not possible to cover everything in one semester
We try to expose you to the whole realm without going
necessarily in all detail.
Notice: This course is the beginning not the end.
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Wireless Ad hoc/Sensor Networks
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Reading Papers
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Is this a vision/position/direction paper, or just
a measurement/implementation?
How the paper is compared to others? Can I
mentally slot this paper somewhere in the
taxonomy? “Differs from X as follows; has the
following in common with Y”
What is the most important contribution?
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Reading Papers (2)
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Does this advance the state of the art?
Did you learn anything new?
Does it provide evidence which supports/contradicts
hypotheses?
Is there experimental validation?
Any technical flaws?
Will the paper generate discussion in the class?
How readable is the paper?
Is the paper relevant to a broader community?
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Wireless Ad hoc/Sensor Networks
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Projects
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Goal: new research results
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Instructive projects okay too
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Ex: protocol visualization tool
System building, simulation-based
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Several publications from last years
Theoretical analysis
Must have strong networking concept
Try to work with 1–2 partners
Project proposal with presentation around 5-10 mins
Final report + presentation session
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Covered Topics (we try!)
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Overview
 The challenges, technologies, and trends
Wireless Fundamentals
 Source and channel coding
 Frequency spectrums
Wireless LAN
 MAC protocols
Wireless Internet – Mobile IP
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Covered Topics (2)
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Routing for Wireless
 Ad Hoc Routing
TCP in wireless enviroment
Power Management
wireless Sensor Networks
Quality of Services (QoS)
Hybrid Wireless Networks – Architectures– Pricing,
Power Control, Load Balancing
Special Topics
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Why wireless networks?
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Mobility: to support mobile applications
Costs: reductions in infrastructure and
operating costs: no cabling or cable
replacement
Special situations: No cabling is possible
or it is very expensive.
Reduce downtime: Moisture or hazards
may cut connections.
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Why wireless networks? (cont)
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Rapidly growing market attests to public
need for mobility and uninterrupted
access
Consumers are used to the flexibility
and will demand instantaneous,
uninterrupted, fast access regardless of
the application.
Consumers and businesses are willing
to pay for it
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Wireless Ad hoc/Sensor Networks
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The Two Hottest Trends in
Telecommunications Networks
700
600
Millions
Mobile Telephone
Users
500
400
Internet Users
300
200
100
0
1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
Source: Ericsson Radio Systems, Inc.
Wireless Ad hoc/Sensor Networks
Growth of Home wireless
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Wireless Ad hoc/Sensor Networks
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Wireless is THE Key Driver
for the Future Internet
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Historic shift from PC’s to mobile computing and
embedded devices…
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>2B cell phones vs. 500M Internet-connected PC’s in 2005
>400M cell phones with Internet capability, rising rapidly
Sensor deployment just starting, but some estimates ~5-10B
units by 2015
~750M servers/PC’s, >1B laptops, PDA’s, cell phones, sensors
~500M server/PC’s, ~100M laptops/PDA’s
Wireless
Edge
Network
INTERNET
INTERNET
Wireless
Edge
Network
Univ. of Tehran
2005
Wireless Ad hoc/Sensor Networks2010
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Market Size
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Wireless as the common case
vs. the exception
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Laptop (54%) vs. desktop sales
(46%)
>2B cell phones vs. 500M
Internet-connected PCs
Estimates of ~5-10B wireless
sensors by 2015
Staggering Market Statistics
• 9 million hotspot users in 2003
(30 million in 2004)
• Approx 4.5 million WiFi access
points sold in 3Q04
• Sales will triple by 2009
• Many more non-802.11 devices
Rapid deployment of new
technology
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Highly dynamic environment
Must accommodate
new/unexpected technologies
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Total
667
Classified
472
802.11b
379
802.11g
93
7/2004 wardrive (802.11g
standardized in 6/2003)
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Why is it so popular?
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Flexible
Low cost
Easy to deploy
Support mobility
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Applications ?
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Ubiquitous, Pervasive computing or nomadic
access.
Ad hoc networking: Where it is difficult or
impossible to set infrastructure.
LAN extensions: Robots or industrial
equipment communicate each others. Sensor
network where elements are two many and
they can not be wired!.
Sensor Networks: for monitoring, controlling,
e Univ. of Tehran
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Wireless Ad hoc/Sensor Networks
Infostations
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Mobile hosts traveling through fixed network
Good for periodic download or upload of bulky data
Wireless islands (interconnected by wired network)
 Gas stations
 Here and there on the freeway
Possibly an invisible infrastructure with mobile-aware
applications
 In reality, you may need to know to go to it
 Original paper assumes this: information kiosks
Coverage is spotty
Cost is lower than complete coverage
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Ad hoc networks
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Collection of wireless mobile nodes
dynamically forming a temporary network
without the use of any existing network
infrastructure or centralized administration.
Hop-by-hop routing due to limited range of
each node
Nodes may enter and leave the network
Usage scenarios:
Military
 Disaster relief
 Temporary groups of participants (conferences)
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Univ. of Tehran
Wireless Ad hoc/Sensor Networks
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Sensor networks
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Deployment of small, usually wireless sensor nodes.
 Collect data, stream to central site
 Maybe have actuators
Hugely resource constrained
 Internet protocols have implicit assumptions
about node capabilities
 Power cost to transmit each bit is very high
relative to node battery lifetime
 Loss / etc., like other wireless
 Ad-hoc: Deployment is often somewhat random
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Wireless Ad hoc/Sensor Networks
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Ad hoc networks, continued
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Very mobile – whole network may travel
Applications vary according to purpose
of network
No pre-existing infrastructure. Do-ityourself infrastructure
Coverage may be very uneven
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Wireless Ad hoc/Sensor Networks
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Networked Embedded Computers
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Connected to
network
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send and/or receive
May be embedded only
for network access  networked appliances
Network
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sensors
historical sites & other
locations
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Embedded Peer
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Composite devices
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security system
Distributed composites vs.
hardwired devices
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Network
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client-defined composites
reuse of constituents
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ease of change
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extendibility & scalability
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Networked Embedded Computers
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Issues
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Late binding
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Network
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Naming
Discovery
IPC
User-interface deployment
Multi-appliance control
Access control
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Existing social protocols not
supported by existing
mechanisms
All co-located users can use
appliance
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Wireless Ad hoc/Sensor Networks
 Children can see certain channels
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Location-Aware Computing
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Motivation
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location-based action
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nearby local printer, doctor
nearby remote phone
directions/maps
location-based
information
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real
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person’s location
history/sales/events
virtual
walkthrough
 story of city
Wireless Ad hoc/Sensor Networks
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Pose-Aware Computing
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Operations based
on locations and
orientations of
users and devices
Motivation
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Augmented reality
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Wireless Ad hoc/Sensor Networks
Magic Lens
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Wearable Pose-Aware Computers
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Computers on body
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track body relative
movements
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monitor person
train person
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Beyond Desktops/Servers
Embedded
Mobile
Location
Interactive
Sensor
Flight
Simulator
Active
badge
Wearable
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Summary
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Need to be connected from everywhere
and anytime.
Need to be connected on movement
Need to good quality service on those
situation.
Interworking with the existing networks
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Classification of Wireless
Networks
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Mobility: fixed wireless or mobile
Analog or digital
Ad hoc (decentralized) or centralized
(fixed base stations)
Services: voice (isochronous) or data
(asynchronous)
Ownership: public or private
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Classification of Wireless
Networks
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Area: wide (WAN), metropolitan (MAN),
local (LAN), or personal (PAN) area
networks
Switched (circuit- or packet-switched) or
broadcast
Low bit-rate (voice grade) or high bit-rate
(video, multimedia)
Terrestrial or satellite
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Wireless Ad hoc/Sensor Networks
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What is special on wireless?
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Channel characteristics
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Resource limitation
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Half-Duplex
Location dependency
Very noisy channel, fading effects, etc.,
Bandwidth
Frequency
Battery, power.
Wireless problems are usually optimization
problems.
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Wireless Ad hoc/Sensor Networks
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What is special on wireless?
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Mobility in the network elements
Very diverse applications/devices.
Connectivity and coverage (internetworking)
is a problem.
Maintaining quality of service over very
unreliable links
Security (privacy, authentication,...) is very
serious here. Broadcast media.
Cost efficiency
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Wireless Ad hoc/Sensor Networks
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Big issues!
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Integration with existing data networks
sounds very difficult.
It is not always possible to apply wired
networks design methods/principles here.
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Internet Design Goals
0
Connect existing networks
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1.
Survivability
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2.
3.
4.
5.
6.
initially ARPANET and ARPA packet radio network
ensure communication service even in the
presence of network and router failures
Support multiple types of services
Must accommodate a variety of networks
Allow distributed management
Allow host attachment with a low level of effort
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Tehran
Wireless Ad hoc/Sensor Networks
Allow
resource
accountability
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Problems
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Host mobility is not considered in the
design.
There is a hierarchal design. How Ad
hoc wireless networks can be handled
A layered design. Layer should be
independent of each other. It is not
work at all in wireless
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TCP
Battery shortages;
Etc,.
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Disconnection / store & forward
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Many Internet protocols assume frequent
connectivity
What if your node is only on the Internet for 5
minutes every 6 hours?
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How do you browse the web?
Receive SMTP-based email?
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High availbility requirements
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No QoS assumed from below
Reasonable but non-zero loss rates
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What’s minimum recovery time?
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But conservative assumptions end-to-end
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1rtt
TCP RTO - min(1s)!
Interconnect independent networks
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Federation makes things hard:
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My network is good. Is yours? Is the one in the middle?
Scale
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Routing convergence times, etc.
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Trends
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Multimedia over IP networks
Next Generation Internet with features for “soft”
QoS
 RSVP, Class-based Queuing, Link Scheduling
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Voice over IP networks
Packet Voice and Video
 RTP and ALF
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Intelligence shifts to the network edges
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Better, more agile software-based voice and video
codecs
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Issues
Scalability
 Must scale to support hundreds of thousands
of simultaneous users in a region.
 Functionality
 Computer-phone integration
 Real-time, multipoint/multicast, locationaware services, security
 Home networking, “active” spaces,
sensors/actuators
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Issues(2)
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First Principles-based Design
 Leverage evolving IP traffic models
 Provisioning the network for the extrapolated traffic
and services
 ProActive Infrastructure
 Computing resources spread among switching
infrastructure
 Computationally intensive services: e.g., voice-totext
 Service and server discovery
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Wireless Differences 1
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Physical layer: signals travel in open
space
Subject to interference
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From other sources and self (multipath)
Creates interference for other wireless
devices
Noisy  lots of losses
Channel conditions can be very dynamic
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Wireless Differences 2
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Need to share airwaves rather than wire
Don’t know what hosts are involved
Hosts may not be using same link technology
Interaction of multiple transmitters at receiver
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Collisions, capture, interference
Use of spectrum: limited resource.
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Cannot “create” more capacity very easily
More pressure to use spectrum efficiently
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Wireless Ad hoc/Sensor Networks
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Wireless Differences 3
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Mobility
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Must update routing protocols to handle
frequent changes
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Changes in the channel conditions.
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Requires hand off as mobile host moves in/out
range
Coarse time scale: distance/interference/obstacles
change
Fine time scale: Doppler effect
Other characteristics of wireless
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Slow
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49
Growing Application Diversity
Collision Avoidance:
Car Networks
Mesh Networks
Wired Internet
Access
Point
Sensor
Relay Node
Ad-Hoc/Sensor
Networks
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Wireless Home
Wireless Ad hoc/Sensor Networks Multimedia
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Challenge: Diversity
Wireless
Edge
Network
INTERNET
INTERNET
Wireless
Edge
Network
2005
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2010
New architectures must accommodate rapidly
evolving technology
Must accommodate different optimization goals
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Power, coverage, capacity, price
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Spectrum Scarcity
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Interference and unpredictable behavior
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Need better management/diagnosis tools
Lack of isolation between deployments
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Cross-domain and cross-technology
Why is my
802.11 not
working?
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52
Other Challenges
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Performance: Nothing is really work well
Security: It is a broadcast media
Cross layer interception
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TCP performance
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