VIRTUAL ROUTER

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VIRTUAL ROUTER
Kien A. Hua Data Systems Lab School of
EECS University of Central Florida
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Outline

• Mobile Ad Hoc Networks
• Virtual Router Approach
• Routing
• Data Forwarding
• Cooperation Enforcement in Virtual Router
  Approach
• Simulation Results
• Conclusions

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Wireline Communications
D
Infrastructure
Router
Router
Router
Router
Router
S
Routers help forward data packets
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What is Mobile Ad Hoc Network?

• All nodes participate in the routing and data
  forwarding process.

Infrastructureless
Source Node
Destination Node
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Route Request
Source Node
Destination Node
6
Route Reply
Source Node
Destination Node
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Data Transmission
The selected nodes participate in the data
forwarding process
Source Node
Destination Node
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Link Break
Source Node
Destination Node
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Issue Route Request
Source Node
Destination Node
Selected New Route
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Handling High Mobility

• Using Physical Nodes as Routers
• Mobility
• ? link breaks
• ? reroute
• ? overhead !

D
S
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What is a Virtual Router ?

• A virtual router is a spatial area
• Physical nodes within this area alternate in
  forwarding data
• When a node leaves the area, it is no longer
  obliged to forward the data
• Virtual router is stationary
• More suitable for high mobility applications such
  as vehicular networks

Y
Virtual Router
X
D
Z
S
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Virtual Router Example
Source Node
Each node has GPS grid map
Each cell is a virtual router
Destination Node

• How to apply this concept to vehicular network ?

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Street Environment Mobility Model

• Streets constrain node mobility
• Nodes can pause and change direction at
  intersections.

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Street Environment Radio Range

• Buildings block radio signal
• Often no link between nodes on different streets
• Broadcast range is not a circle

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Virtual Routers in Street Environment

• Streets are divided into small cells
• Each intersection is an intersection cell
• A long road block can be divided into multiple
  block cells
• Radio range must cover any 2 consecutive cells
• Each cell is a virtual router

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Vehicular Network UsingVirtual Routers
Destination

• Green virtual routers form a connecting path
  between source and destination
• Data are transmitted from source to destination
  over these virtual routers

Source
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Location Discovery
Similar to standard route request

• A source node broadcasts a Location Discovery
  (LD) packet
• This LD packet propagates until it reaches the
  destination node
• When the LD packet arrives at the destination, it
  replies with a Location Reply (LR) packet that
  includes the location of the destination router
  (i.e., destination cell).

Subsequently, every data packet carries the IDs
of the source and destination routers
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Data Forwarding Reference Line

• Every data packet carries the locations of Source
  and Destination
• Reference line (RL) is the straight line
  connecting the center of the source router and
  the center of the destination router

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Data Forwarding Reference Points

• Reference points (RPs) are the intersections of
  the reference line and the streets

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Data Forwarding Forwarding Zones

• There is one forwarding zone for each reference
  point
• Three horizontal and two vertical forwarding
  zones in this example
• Some forwarding zones overlap
• The forwarding zones make up the grid path for
  data forwarding

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Data Forwarding

• Virtual routers within the forwarding zones are
  selected for data forwarding
• When a node leaves the forwarding area, it is no
  longer obliged to forward data.
• If a node enters the forwarding area, this node
  must participate in the data forwarding.

How to do route maintenance
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Connection Maintenance

• Destination node moves away from current router
• Reference line changes
• Reference points changes
• Forwarding zones changes
• Need a new connection path
• Route Maintenance
• The destination node periodically updates its
  location with the source node.
• If this fails, source issues a location discovery
  packet

Essentially no overhead
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Selfish and Malicious Behavior
It works as long as nodes cooperate
Need cooperation enforcement !!
Malicious Node
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Cooperation EnforcementStep 1 Detect Malicious
Node
Malicious behavior detected
Malicious node
Malicious behavior detected
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Cooperation EnforcementStep 2 Penalize
Malicious Nodes
No one will forward the Location Discovery packet
for the malicious node.
Malicious Node tries to establish connection by
broadcasting Location Discovery packet
I know about the misbehavior
I know about the misbehavior
I know about the misbehavior
Location Discovery packet is blocked by the
building
Location Discovery packet is blocked by the
building
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Network Layer Structure
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3C Module
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3C Module - Overview

• It maintains three Counters
• Forward Request Counter Number of forward
  requests (both discovery and data packets)
  received by a node.
• Forward Counter Number of packets forwarded by a
  node.
• Location Discovery Counter Number of Location
  Discovery packets initiated by a node (i.e.,
  number of connections requested)
• It adds a 3C header which contains the values of
  these three counters to every Location Discovery
  packet.
• Based on this header, neighboring nodes analyze
  the behavior of the source node, and decide to
  forward or discard the packet (i.e., penalize the
  source node)

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Misbehavior Detection Overview
Examine 3C header for misbehavior
Add 3C header
Examine 3C header again before forwarding
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Route Discovery

• Source node initiates Route Request packet
• Intermediate nodes forward the packet until it
  reaches the Destination node
• The Destination node receives the Route Request
  packet and sends back a Route Reply packet

Request
Request
Request
Request
S
D
Reply
Reply
Reply
Reply
Lets look at the operation at these nodes
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Initiate Location Discovery
Upper Layer
Submit a route request
Routing Layer (Network)
This is a reroute request
Add to Session Table
This is a new communication request
MAC Layer (Data Link)
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Receive Location Discovery
Routing Layer (Network)
Penalize the requester
More on this module later
The forwarding node initiates this route request
Initiated by sender?
MISBEHAVIOR DETECTION MODULE
MAC Layer (Data Link)
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Forward Location Discovery (1)
The Virtual Router has already forwarded the
packet
The route has been found
Routing Layer (Network)
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Forward Location Discovery (2)
Routing Layer (Network)
MAC Layer (Data Link)
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Network AttackSending Dummy Packets
Routing Layer (Network)
Flood the network with a dummy record
Generate forward a dummy route request packet
MAC Layer (Data Link)
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Data Transmission

• Source node transmits a data packet
• Intermediate nodes forward the packet until it
  reaches the Destination node

Data
Data
Data
Data
S
D
Lets look at the data forwarding operation at a
node
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Receive Data Packet
Forwarding Procedure in VRA
Routing Layer (Network)
A node new to the virtual router might not know
about this on-going session
MAC Layer (Data Link)
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VRA Protocol Forwarding Procedure (Data Packet)
These steps are the same as in Location Discovery
packet
The packet has reached its destination
Routing Layer (Network)
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Forward Data Packet
Routing Layer (Network)
Packet arrives at destination
MAC Layer (Data Link)
Receive Data Packet
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Network Attack Dummy Packets
Routing Layer (Network)
Flood the network with a dummy record
Generate forward a dummy data packet
MAC Layer (Data Link)
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Receive Location Discovery
Routing Layer (Network)
We now discuss this module
MISBEHAVIOR DETECTION MODULE
MAC Layer (Data Link)
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Misbehavior Detection Metrics

• 3C Module at each node i maintains the following
  information
• Forward Ratio (FR) Percentage of arriving
  packets forwarded
• FRi
• Local Average Forward Ratio (LAFR)
• LAFRi ,
• where, n is the number neighbor nodes of i
• Request Ratio (RR) Offer enough service
• to use the network ?
• RRi

Forward Request Counter Number of forward
requests (both discovery and data packets)
received by a node. Forward Counter Number of
packets forwarded by a node. Location Discovery
Counter Number of Location Discovery packets
initiated by a node (i.e., number of connections
requested)
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Initiate Misbehavior Detection
Need to establish a communication connection with
someone
If m is not the source node, n proceeds to
forward the packet
else, n checks 3C header of this packet.
Is the forwarder the initiator of this packet ?
Location Discovery packet
m
n
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Misbehavior Detection Check Forward
Ratio
FRm lt FRn ? n suspects m has been dropping
packets
FRm lt FRn means that n is not forwarding enough
packets
m is a suspect
Location Discovery packet
m
n
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Misbehavior DetectionCheck Request Ratio
RRm gt 1.2RRn ? n suspects m has been dropping
packets
RRm gt 1.2 RRn means that m made many
connection requests but it has not provided
enough service to other nodes.
n needs to exchange counter information with
neighboring nodes
m is a suspect
Location Discovery packet
m
n
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Initiate Misbehavior DetectionCompare to Local
Average
k is the number of neighbor nodes of n
x
FRm lt LAFRn ? m is a suspect according to local
average
n exchanges counters information with neighboring
nodes
m
n
y
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Enter Detection Mode Listening State
m is a suspect. Enter Detection mode Listening
State
x
n enters Detecting state by invoking Misbehavior
Detection procedure.
m is a suspect. Enter Detection mode Listening
State
m
n
m is a suspect. Enter Detection model Listening
State
y
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Detection Mode Detecting State (1)
x resets the delay timer and stays in Listening
State
x
n generates and broadcasts a Detection packet
n broadcasts a Detection packet two more times
m
n
Detection packet is just a dummy data packet
y resets the delay timer and stays in Listening
State
y
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Detection Mode Detecting State (2)
x exits Listening State
x
If m forwards the Detection packet
n exits Listening State
m
n
n forwards ms Location Discovery packet
y exits Listening State
y
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Detection Mode Detecting State (3)
x marks m as misbehavior
x drops ms Location Discovery pakcet
x
If m drops all three Detection packets
n drops ms Location Discovery packet
n marks m as misbehavior
m
n
y drops ms Location Discovery packet
y marks m as misbehavior
y
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Simulation Setting

• Simulator GloMoSim.
• Constant-bit-rate sessions of 512-byte packets.
• Radio propagation range is 375 meters, and
  channel capacity is 2 Mbits/sec.
• Street width is 10 meters, and building block
  size is 100m by 100m.
• Initial nodes placement 2 nodes per
  intersection, and 8 nodes per block.
• Mobility model At intersections, a node pauses
  for a period of time, and then probabilistically
  changes its direction of movement.
• Speed random between 0 m/s and 25 m/s (or 56
  miles/hr).
• Pause time random between 0 and 20 seconds.
• 100 simulation runs with different seed numbers
  for each scenario.
• Number of misbehaving nodes 5, 10, 20, and
  30 of total number of nodes.

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Schemes and Malicious Behavior

• Schemes compared
• Reference scheme All nodes act collaboratively
  and relay data for each other.
• Defenseless scheme No detection mechanism is
  implemented. The network is totally
  defenseless.
• 3CE (3-Counter Enforcement) scheme misbehaving
  nodes are detected and punished.
• Malicious Behavior
• A malicious node recognizes that it is being
  punished when its Location Discovery packet has
  been dropped four consecutively times.
• Once malicious nodes recognize the punishment,
  they participate in data forwarding to rejoin the
  network.

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Performance Metrics

• Packet Delivered Ratio (P)
• Percentage of data packets successfully delivered
  to their destination.
• Misbehaving Node Detection Ratio (D)
• Percentage of misbehaving nodes detected
• False Accusation Rate (F)
• Percentage of detected nodes incorrectly accused

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Packet Delivered Ratio (P)
Reference
VRA
Defenseless

• 3CE is significantly better than the defenseless
  system
• 3CE incurs little overhead. Its performance does
  not decrease significantly compared to the
  Reference scheme.

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Misbehaving Node Detection Ratio (D)
Average about 87
  Detection Ratio Detection Ratio Detection Ratio Detection Ratio
Speed (m/s) 10 15 20 25
5 misbehaving nodes 89 88 83 81
10 misbehaving nodes 93 91 86 88
20 misbehaving nodes 91 85 89 87
30 misbehaving nodes 91 87 84 85
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False Accusation Rate (F)
  False Accusation Ratio False Accusation Ratio False Accusation Ratio False Accusation Ratio
Speed (m/s) 10 15 20 25
5 misbehaving nodes 0 2 3 2
10 misbehaving nodes 1 2 2 3
20 misbehaving nodes 1 1 2 2
30 misbehaving nodes 2 2 4 5

• Overall, false accusation is very low.
• False accusation is higher when nodes move
  faster.
• Suspect node forwards the detection packet after
  moving out of the radio range of the detecting
  nodes causing false accusation (i.e., not
  forwarding the detection packet)

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False Accusation
Forward detection packet
Send detection packet
m
n
m is bad
False accusation
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Conclusions

• The Virtual Router approach has been shown to
  provide better performance than standard routing
  based on physical nodes
• 3CE (3 Counters Enforcement) cooperation
  enforcement technique further improves the
  Virtual Router approach
• Our simulation results indicate
• improved network throughput (better data delivery
  rate)
• effective detection of most (87) misbehaving
  nodes
• almost no false accusation