Simulation of LargeScale Wireless Ad Hoc Networks

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Simulation of Large-Scale Wireless Ad Hoc
Networks

• Luiz Felipe Perrone
• Cybersecurity Research Group
• Institute for Security Technology Studies

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Acknowledments

• Some of the slides youll see have been recycled
  from other presentations.
• A few of the slides youll see come from
  presentations by Deborah Estrin (UCLA) and David
  Culler (UC Berkeley).

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Why wireless ad hoc networks?
Customizable
Easy to deploy
No infrastructure

• Good in changing environments.
• Allows for node mobility.
• Can be designed for self-configurability.
• Can be designed for scalability.

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Sensor Networks A Motivating Example
M
Intelligence, Surveillance, Emergency Response
M
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Technical Challenges

• Energy constraints no wires, no power source.
• Level of dynamics weather, terrain, RF
  interference, network traffic.
• Scaling very large number of nodes complicates
  protocol design.

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A Deeper Look into the Technical Challenges
Protocol Stack
Application
Transport
(Yes, I did throw away a couple of layers, but
who doesnt?)
Network
Link
Physical
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Physical Layer

• Design communication for maximum scalability and
  reliability
• Modulation (AM, FM, FSK, etc).
• Use of the spectrum (FDMA, TDMA, CDMA).
• Noise, interference, multipath effects, shadowing

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Data Link Layer Medium Access Control
(Coordinated access to a shared resource)

• Power is a scarce resource (so is the RF
  spectrum).
• Collisions lead to wasted power (AND wasted
  spectrum).
• Need to impose some kind of access discipline so
  as to avoid collisions.

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The Hidden Node Problem (MAC Layer)

• Station B can hear stations A and C.
• Stations A and C cant hear each other.
• How can we coordinate transmissions from A and C
  so as to avoid collisions?

A
B
C
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The Hidden Node Problem (MAC Layer)

• Station B can hear stations A and C.
• Stations A and C cant hear each other.
• How can we coordinate transmissions from A and C
  so as to avoid collisions?

A
B
C
Solution RTS/CTS/DATA/ACK handshake A sends
RTS to B, B sends CTS to A, C hears CTS and stays
quiet, A sends DATA to B, B replies to A with an
ACK.
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The Exposed Node Problem (MAC Layer)
A
B
C
D
An exposed node is one that is in range of the
transmitter, but outside range of the receiver.
Problem exposed nodes reduce bandwidth.
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The MAC Layer Challenge

• Maximize throughput
• Minimize collisions.
• Avoid exposed nodes.
• An interesting option schedule medium access.
• Related challenges
• Clock synchronization.
• Distributed coordination for determining
  schedule.

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The Network Layer Challenge

• How do we build routes dynamically?
• Pro-active algorithms.
• Reactive algorithms.
• Will the routing protocol scale up to LARGE
  networks?
• Can routing adapt to changes in network traffic,
  propagation conditions, etc.?
• Packet forwarding costs power. Can we do routing
  in a way that balances power consumption?

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Power Consumption Issues

• Nodes may not be rechargeable.
• Power conservation leads to maximum network
  lifetime.
• Communication is orders of magnitude more power
  hungry than computation (need for data
  compression, data fusion?).
• Actuation is orders of magnitude more power
  hungry than communication.

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Security Issues

• Desirable properties

• Availability
• Accessibility
• Self-organization
• Non-repudiation
• Flexibility

• Confidentiality
• Authenticity
• Integrity
• Freshness
• Scalability

• As of today, the network can be vulnerable at
  multiple levels
• PHY radio jamming.
• MAC DoS via fake requests or schedules.
• NET fake route advertisements (black hole
  attack).
• A funny but scary notion caveman attacks.

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The ISO/OSI RF Model and Wireless

• We need a good architecture for wireless ad hoc
  nets, but we dont have it yet.
• Current designs do not lend themselves to
  interoperability (try to plug out a layer and
  plug in a new one!).
• Power conservation spans multiple protocol layers.

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The Need for Simulation

• Protocol design has always been a tough problem.
  Protocol validation and verification have always
  been even tougher.
• We have a complex system that defies
  mathematical analysis.
• This system has several components tightly
  inter-connected interactions complicate
  behavior.
• Experiments will call for repeatability and
  controllability.

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Rapid Simulation A Tough Goal

• Radio propagation a continuous process in
  continuous time.
• Teletraffic a discrete process in continuous
  time.
• The simulation must cope with time scales of very
  different resolution. Mixing them and achieving
  high performance could be a tough goal.

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Wish List for a WAN Simulator

• Detail
• Completeness
• Performance
• Scalability

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Related Work

• CMU Monarch Project
• http//www.monarch.cs.cmu.edu/cmu-ns.html
• detailed radio propagation models, complete
  implementations of MAC and routing algorithms,
  scenario generation, visualization tools, network
  emulation, etc.
• UCLA SensorSim (pre-release stage)
  http//nesl.ee.ucla.edu/projects/sensorsim/
• sensing channel and sensor models, battery
  models, lightweight protocol stacks for wireless
  microsensors, scenario generation, and hybrid
  simulation.

Common major drawback they are based on ns-2.
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The Architecture of SWAN
Physical Process
read terrain features
Power Consumption Model
Protocol Graph
Terrain Model
Mobility Model
read terrain features
memory
OS Model (DaSSF Runtime Kernel)
time
run thread
Host Model
read terrain features
RF Channel Model
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Where Things Get Complicated

• Physical Processes We need to simulate different
  physical phenomena accurately and rapidly.
• RF Channel Model Propagation models are
  mathematically very complex. We need to abstract
  and take only the most relevant details, without
  this scalability is impaired.
• Scale Large number of nodes consume large
  amounts of memory. Large number of nodes mean
  large number of computing threads adding a big
  burden to scheduling.
• Direct execution Different code, potentially
  different behavior. We want to allow the
  simulator to run the same code that runs in the
  real system.

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The SWAN Protocol Stack Today
Application
AODV
Socket
TCP
UDP
IP
ARP
NIC
NIC
MAC
MAC
PHY
PHY
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What Were Doing with SWAN

• Evaluate routing protocols robustness to dynamic
  changes in propagation conditions.
• Evaluate routing protocols robustness to
  caveman attacks.
• Evaluate the impact of ARP in the simulation of
  wireless ad hoc networks.

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A Duckling Called TOSSF (TinyOSSSF)
TinyOS An event-driven component based
programming model that powers SmartDust platforms.
Goal Use existing SWAN framework to allow
simulation by direct execution of TinyOS
applications.
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A TinyOS Application a Protocol Graph

• Application graph of components scheduler

sensing application
application
Routing Layer
routing
Messaging Layer
messaging
packet
Radio byte
Temp
UART byte
byte
photo
SW
HW
RFM
i2c
ADC
bit
clocks
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Last Words

• Simulation is a key technology to the development
  of network protocols.
• However the behavior observed in simulations can
  be trusted only as long as the models used have
  been validated and verified.
• Do you like this kind of stuff? Want to work with
  us? Visit http//www.ists.dartmouth.edu