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VIRTUAL ROUTER
Kien A. Hua
Data Systems Lab
School of EECS
University of Central Florida
Outline
• Mobile Ad Hoc Networks
• Virtual Router Approach
– Routing
– Data Forwarding
• Cooperation Enforcement in Virtual Router
Approach
• Simulation Results
• Conclusions
2
Wireline Communications
Infrastructure
Router
Router
Router
Router
Router
S
Routers help
forward data
packets
D
What is Mobile Ad Hoc Network?
Infrastructureless → All nodes participate in the routing and
data forwarding process.
Source
Node
Destination
Node
Route Request
Source
Node
Destination
Node
Route Reply
Source
Node
Destination
Node
Data Transmission
Source
Node
The selected nodes participate in the
data forwarding process
Destination
Node
Link Break
Source
Node
Destination
Node
Issue Route Request
Source
Node
Selected New Route
Destination
Node
Handling High Mobility
• Using Physical Nodes as Routers:
Mobility
→ link breaks
→ reroute
→ overhead !
D
S
• Using Virtual Routers:
Virtual routers are stationary
→ links are robust
→ fewer reroute
S
→ less overhead !
Virtual
Router
D
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
S
Y
X
Virtual
Router
Z
D
11
Virtual Router – Example
Source
Node
Each node
has GPS &
grid map
Each cell is a
virtual router
How to apply this concept to
vehicular network ?
Destination
Node
Street Environment:
Mobility Model
• Streets constrain
node mobility
• Nodes can pause
and change direction
at intersections.
13
Street Environment:
Radio Range
Buildings block radio signal
→ Often no link between nodes on different streets
→ Broadcast range is not a circle
Street
Radio
Range of
m
Effective
Radio
Range of m
Radio
Range of
m
Mobile Node
m
Mobile Node
m
Cannot establish
direct communication
due
building
duetotothe
buildings
Street
Effective
Radio
Range of m
Cannot
Cannot
establish direct
establish direct
communication
communication
due to the
due to buildings
building
Street
14
Virtual Routers in
Street Environment
• Streets are divided into
small cells:
Buildings
Cell A
– 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
Cell B
Cell C
Buildings
Cell A
Cell B
Buildings
Cell A
Cell B
Cell C
Cell D
Buildings
15
Vehicular Network Using
Virtual 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
16
Location Discovery
• A source node broadcasts a Location
Discovery (LD) packet
Similar to
standard
route
request
• 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 ID’s of the source and
destination routers
17
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
Mid-Point of a
Destination Cell
( X D , YD )
Destination
Node
Destination Cell
Reference Line
Source node
Mid-Point of
Source Cell
( XS , YS )
Source Cell
18
Data Forwarding: Reference Points
Mid-Point of a
Destination Cell
( X D , YD )
Reference points
(RP’s) are the
intersections of the
reference line and
the streets
Destination
Node
Center of Streets
Destination Cell
Reference Point
Reference Line
Source node
Center of Streets
Mid-Point of
Source Cell
( XS , YS )
Source Cell
19
Data Forwarding:
Forwarding Zones
• There is one
forwarding zone for
each reference point
Forwarding Zone
• Three horizontal and
two vertical forwarding
zones in this example
• Some forwarding
zones overlap
Destination
Node
Reference Point
Source node
• The forwarding zones
make up the grid path
for data forwarding
20
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.
Forwarding Zone
Destination
Node
Reference Point
Source node
Selected Grid Path
How to do route maintenance
21
Connection Maintenance
Destination node moves away from current router
→ Reference line changes
→
→
→
Reference points changes
Forwarding zones changes
Need a new connection path
Essentially
no
overhead
Route Maintenance:
–
–
The destination node periodically updates its location
with the source node.
If this fails, source issues a location discovery packet
22
Selfish and Malicious Behavior
Destination
Node
It works
as long
Need
as nodes
cooperation
cooperate !!
enforcement
Malicious
Node
Source node
Selected Grid Path
23
Cooperation Enforcement
Step 1: Detect Malicious Node
Malicious
behavior
detected
Malicious
node
Malicious
behavior
detected
24
Cooperation Enforcement
Step 2: Penalize Malicious Nodes
Malicious Node tries
to establish
I knowby
about
connection
the misbehavior
No one will forward
radio range of
broadcasting
Location Discovery
malicious node
the Location
packet
I know aboutDiscovery packet
the misbehavior
Location
about
for the maliciousI knowLocation
Discovery
Discovery
the misbehavior
node.
packet is
packet is
blocked by the
blocked by the
building
building
25
Network Layer Structure
Routing Layer (Network)
Routing Layer (Network)
MAC Layer (Data Link)
MAC Layer (Data Link)
Radio Layer (Physical)
Radio Layer (Physical)
26
3C Module
Routing Layer (Network)
Routing Layer (Network)
MODULE
MAC 3C
Layer
(Data Link)
(Temper Resistant)
MODULE
MAC3C
Layer
(Data Link)
(Temper Resistant)
Radio Layer (Physical)
Radio Layer (Physical)
27
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)
28
Misbehavior Detection: Overview
Add 3C
header
Routing Layer (Network)
Routing Layer (Network)
MODULE
MAC 3C
Layer
(Data Link)
(Temper Resistant)
MODULE
MAC3C
Layer
(Data Link)
(Temper Resistant)
Radio Layer (Physical)
Radio Layer (Physical)
Examine 3C
header for
misbehavior
Examine 3C
header
again before
forwarding
29
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
Let’s look at the operation at these nodes
30
Initiate Location Discovery
Upper Layer
Establish a
connection
Routing Layer
(Network)
Perform
Location Discovery
procedure
Submit a route
request
This is a reroute
request
An ongoing
communication
session?
3C MODULE
(Temper Resistant)
Add to
Session Table
Yes
Add 3C header
to the packet
MAC Layer
(Data Link)
No
Increment Location
This is Discovery
a new Counter
communication
request
Broadcast location
discovery packet
31
Receive Location Discovery
VRA Protocol
Routing Layer
(Network)
Penalize
the
Reset TTL for
requester
this entry
Increment
Forward Request
Counter
Discard Packet
Yes
Insert new
No
Therequest
forwarding
into
Session
Tablethis
node
initiates
route request
More on this
Is the packet
module
later…
in Session
Table?
3C MODULE
Is from
misbehavior
node?
No
No
Yes
No
(Temper Resistant)
Initiated
by
sender?
Yes
Need
to detect
misbehavior
?
Yes
Misbehavior
Detection
MISBEHAVIOR DETECTION MODULE
MAC Layer
(Data Link)
Location discovery
packet arrives
32
Forward Location Discovery (1)
The Virtual Router
has already
forwarded the Start delay period
packet
No
Discard Packet
Yes
Hear same
packet from a
neighbor node?
The route has
been found
Yes
No
Have seen the
packet before?
No
Is destination
node?
No
End of Delay?
Yes
(Reply)
Routing Layer
(Network)
3C MODULE
VRA Protocol
Yes
(Forward)
Increment
Forward Request
Counter
Reset TTL for
this entry
(Temper Resistant)
33
Forward Location Discovery (2)
Routing Layer
(Network)
Is destination
node?
End of Delay?
Yes
(Reply)
3C MODULE
Yes
(Forward)
(Temper Resistant)
Increment
Forward Counter
MAC Layer
(Data Link)
Broadcast location
discover/reply packet
34
Network Attack:
Sending Dummy Packets
Routing Layer
(Network)
3C MODULE
(Temper Resistant)
Flood the
network with a
dummy record
Generate & “forward”
a dummy route
request packet
Is
packet in
Session
Table?
No
Discard Packet
Increment
Forward Counter
MAC Layer
(Data Link)
Broadcast location
discover/reply packet
35
Data Transmission
• Source node transmits a data packet
• Intermediate nodes forward the packet until it reaches the
Destination node
Data
S
Data
Data
Data
D
Let’s look at the data forwarding operation at a node
36
Receive Data Packet
Routing Layer
(Network)
Forwarding
Procedure in
VRA
VRA Protocol
Reset TTL for
this entry
Increment
Forward Request
Counter
3C MODULE
(Temper Resistant)
Yes
Is
packet in
Session
Table?
MAC Layer
(Data Link)
No
A node new to
the virtual router
might not know
about this ongoing session
Insert new
request into
Session Table
Data packet arrives
37
VRA Protocol Forwarding Procedure
(Data Packet)
Start delay period
These
No
Discard
steps
are Packet
the
same as in Location
Discovery packet
Yes
Hear same
packet from a
neighbor node?
Yes
No
Have seen the
packet before?
No
No
The packet has
reached its
destination
Is destination
node?
End of Delay?
Yes
Routing Layer
(Network)
VRA Protocol
Yes
3C MODULE
Increment
Forward Request
Counter
Reset TTL for
this entry
(Temper Resistant)
38
Forward Data Packet
Routing Layer
(Network)
Is destination
node?
End of Delay?
Yes
Yes
3C MODULE
Increment
Forward Counter
(Temper Resistant)
Packet arrives at
destination
MAC Layer
(Data Link)
Receive Data
Packet
Broadcast Data Packet
39
Network Attack: Dummy Packets
Routing Layer
(Network)
3C MODULE
(Temper Resistant)
Generate & “forward”
a dummy data packet
Is
packet in
Session
Table?
No
Flood the
network with a
dummy record
Discard Packet
Increment
Forward Counter
MAC Layer
(Data Link)
Broadcast Data Packet
40
Receive Location Discovery
VRA Protocol
Routing Layer
(Network)
Reset TTL for
this entry
Increment
Forward Request
Counter
Insert new
request into
Session Table
Yes
No
Is the packet
Weinnow
discuss
Session
Table?
this module
3C MODULE
Yes
Is from
misbehavior
node?
No
No
Discard Packet
No
(Temper Resistant)
Is initiated
by last hop?
Yes
Need
to detect
misbehavior
?
Yes
Misbehavior
Detection
MISBEHAVIOR DETECTION MODULE
MAC Layer
(Data Link)
Location discover
packet arrives
41
Misbehavior Detection Metrics
3C Module at each node i maintains the following information:
– Forward Ratio (FR): Percentage of arriving packets forwarded
• FRi =
Forward Counteri
Forward Re quest Counteri
– Local Average Forward Ratio (LAFR)
n

• LAFRi =
( FR j )  FRi
j 1
n 1
,
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)
Location Discovery Counteri
Forward Counteri
42
Initiate Misbehavior Detection
Need to
establish a
communication
connection
with someone
m
If m is not
the
Is
the
else, n checks
source
node, nthe
forwarder
3C header of
proceeds
to
initiator
of this
this packet.
forward
the ?
packet
packet
Location Discovery
packet
n
43
Misbehavior Detection:
Check Forward Ratio
Forward Counterm
FRm =
Forward Re quest Counterm
Forward Countern
FRn =
Forward Re quest Countern
FRm < FRn means that n is not
forwarding enough packets
m is a
suspect
m
Location Discovery
packet
FRm < FRn
→ n suspects m
has been
dropping packets
n
44
Misbehavior Detection:
Check Request Ratio
RRm =
Location Discovery Counteri
Forward Counteri
RRn =
RRm > 1.2 ∙ RRn means that m
made many connection
requests; but it has not
provided enough service to
other nodes.
m is a
suspect
m
Location Discovery
packet
Location Discovery Counteri
Forward Counteri
RRnmneeds
> 1.2*RR
to n
→
n suspects
exchange
counterm
information
with
has been
neighboringpackets
nodes
dropping
n
45
Initiate Misbehavior Detection:
Compare to Local Average
k
k is the number of
neighbor nodes of n
LAFRn =
x
m
 ( FR )  FR
i 1
i
n
k 1
n
n exchanges
FRmcounters
< LAFRn
→ m is awith
information
neighboring
suspect
nodes to
according
local average
y
46
Enter Detection Mode:
Listening State
m is a suspect.
Enter Detection
mode –
Listening State
x
Radio range of m
m
n
y
n enters
m
is a suspect.
Detecting
state
byEnter
invoking
Detection
Misbehavior
mode –
Detection
Listening
State
procedure.
m is a suspect.
Enter Detection
model –
Listening State
47
Detection Mode:
Detecting State (1)
x resets the
delay timer and
stays in
Listening State
x
m
n
Detection packet is just a
dummy data packet
y
generates
nnbroadcasts
and
a Detection
broadcasts
packet twoa
Detection
more
times
packet
y resets the
delay timer and
stays in
Listening State
48
Detection Mode:
Detecting State (2)
x exits
Listening
State
x
If m forwards the
Detection packet
n exits
Listening
State
m
n
n forwards m’s
Location Discovery
packet
y
y exits
Listening
State
49
Detection Mode:
Detecting State (3)
x drops m’s Location
Discovery pakcet
If m drops all three
Detection packets
m
y drops m’s
Location
Discovery
packet
x marks m as
misbehavior
x
n drops m’s
Location
Discovery
packet
y
n
n marks m as
misbehavior
y marks m as
misbehavior
50
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.
51
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.
52
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
53
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.
54
Misbehaving Node Detection Ratio (D)
Average
about
87%
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%
55
False Accusation Rate (F)
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)
56
False Accusation
Forward detection
packet
Send detection
packet
m
False
accusation
n
m is bad
57
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
58