Efficient Flooding in Ad hoc Networks using On-demand (Passive) Cluster Formation

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Efficient Flooding in Ad hoc Networks using
On
-
demand (Passive) Cluster Formation

2003. 04. 18


ICNS Lab

Na Gajin

Contents


Introduction


Blind Flooding / Efficient Flooding


Related Works and Motivations


Clustering in Ad hoc Networks


Passive Clustering


Simulation Studies


Conclusion






Introduction


Mobile ad hoc networks (MANET)


Self
-
creating, self
-
organizing and self
-
administrating without
deploying any kind of infrastructure


Wide application in military, commercial and educational
environments where fixed infrastructure is not easily acquired


Two nodes communicate directly or via a multi
-
hop route with
the cooperation of other nodes


To find a multi
-
hop path to another nodes, each MANET node
widely use
flooding

or
broadcast


Introduction


Route Discovery (DSR protocol)






Route Maintenance


A

B

C

D

“A”

“A,B”

“A,B,C”

id=2

id=2

id=2

source

destination

A

C

D

B

A

C

D

B

A

C

D

B

A

Hello messages

Introduction


Blind Flooding



Node transmits a message to all of its neighbors



The neighbors in turn relay to their neighbors and so on until the
message has been propagated to the entire network.



Neighbor degree gets higher, the blind flooding suffers from the
increases of

1.
redundant and superfluous packets

2.
the probability of collision

3.
congestion of wireless medium

Blind Flooding

redundant and superfluous packets

Introduction


Efficient Flooding



Only
a subset of neighbors

is required to participate in flooding
to guarantee the complete flooding



In MANET,
collecting topological information is very difficult

(huge extra overhead)



Many on
-
demand ad hoc routing schemes and service discovery
protocols simply use blind flooding



Introduction


New mechanism for efficient flooding suitable for

on
-
demand protocols based on
passive clustering


Several contributions with previous flooding
mechanisms


1.
It does not need any
periodic messages

2.
It does not have any
setup latency
, and it saves
energy with no
traffic

3.
Its maintenance is well adaptive to
dynamic topology

and
resource availability changes

Related Works


Proposed several heuristics to reduce rebroadcasts

1.
Probabilistic scheme


Rebroadcast the packet with the
randomly chosen probability

2.
Counter
-
based scheme


Rebroadcast if the
number of received duplicate packets

is less
than a threshold

3.
Distance
-
based scheme


Uses the
relative distance between hosts

to make the decision

4.
Location
-
based scheme


Based on
pre
-
acquired location information of neighbors

5.
Cluster
-
based scheme


Only
cluster heads and gateways

forward again



Related Works


Another approach : exploit topological information


Self
-
pruning


Each forwarding node piggybacks the list of neighbors of itself on
outgoing packet


Dominant
-
pruning


Extends the range of neighbor information to two
-
hop away
neighbors


Still depend on the
periodic hello messages

to collect
topological information


Extra hello messages consume resources and drop the network
throughput in MANETs

Motivations


Clustering


Reducing the routing table size



Reducing the communication overhead



Stabling network topology



Be ease of location management



Providing a simple and feasible power control mechanisms

Brief Overview of Clustering


Clustering

: Another method to select forwarding nodes



Cluster head : representative of each group (cluster)


Gateway : a node belongings to more than two clusters at the
same time


Ordinary nodes



Transmission area (radio range) of the cluster head defines a cluster



k
-
hop clustering

Efficient Flooding with Clustering


S

CLUSTER HEAD

GATEWAY

ORDINARY NODE

Flooding

Only cluster heads and gateways rebroadcast and ordinary nodes stop forwarding

Motivations


Clustering in ad hoc networks


Hierarchical routing schemes


Master election algorithms


Power control


Reliable and efficient broadcast



Cluster architecture commonly not used


Previous clustering schemes are based on the
complete knowledge of
neighbors


None of the clustering algorithms has proposed a gateway reduction
mechanism to select
the minimal number of gateways


The previous clustering requires
huge maintenance cost in high
mobility

Lowest
-
ID Clustering


Each node is assigned a
distinct ID



Periodically
, the node broadcasts the
list of nodes that it can hear



A node which only hears nodes with
ID higher than itself is a “
clusterhead








Clusterhead

Gateway

Ordinary Node

MPR (Multipoint Relays)


Reduce the flooding of broadcast
messages



Set of
one
-
hop neighbors

and
two
-
hop neighbors



To get the information about the
one
-
hop neighbors, most
protocols use some form of
HELLO messages periodically


Three Important Observations

1.
The selection mechanism to choose the dominant set
should be efficient and dynamic


2.
In a MANET, collecting accurate topological information
is very hard and carries the huge overhead


3.
Clustering schemes is independent of the network
topology




With keeping advantages of clustering, our scheme
eliminates the main control overhead

Overview of Passive Clustering


On
-
demand protocol



Constructs and maintains the cluster architecture only when there
are
on
-
going data packets

that piggyback “cluster
-
related
information”



Each node collets neighbor information through
promiscuous packet
receptions



First Declaration Wins


Node that first claims to be a cluster head “rules” the rest of nodes in its
clustered area


Gateway Selection Heuristic


Elect the minimal number of gateways


Construction and Maintenance


The IP option field for cluster information


Node ID

: the IP address of the sender node


State of cluster

: the cluster state of the sender node


If a sender node is a gateway, then it tags
two IP addresses of
cluster heads

which are reachable from the gateway



Initially joining node or floating node sets the cluster
state to
INITIAL




Passive Clustering Algorithm


Cluster states


INITIAL, CLUSTER_HEAD, ORDINARY_NODE, GATEWAY,
CH_READY, GW_READY and DIST_GW



Packet handling


Upon sending a packet, each node piggybacks
cluster
-
related information


Upon a promiscuous packet reception, each node
extracts cluster
-
related information of neighbors and
updates neighbor information table


Passive Clustering Algorithm


A cluster head declaration


INITIAL


CH_READY : packet arrives from another node that
is not a cluster head


With outgoing packet, a CH_READY node can declare as a
cluster head


Becoming a member


A node becomes a member of a cluster once it has heard or
overheard a message from any cluster head.


A member node can serve as a gateway or an ordinary node
depending on the collected neighbor information


A member node can settle as an ordinary node only after it has
learned enough neighbor gateways


Gateway Selection Heuristic


Gateway : a bridge node that connects two adjacent clusters



Only one gateway is needed for the each pair of two adjacent
clusters



Gateway selection mechanism that eventually allows only one
gateway for each pair of two neighboring cluster heads




Gateway Selection Heuristic


candidate gateway

: a node belongs to more than two clusters at the
same time



If the node finds 2 cluster heads, then it finalizes its role as a
gateway and announces 2 cluster heads to neighbors



If a gateway has received a packet from another gateway which has
announced the same pair of CHs, then this node compares the node
ID of itself with that of the sender.



If this node has the lower ID, it keeps its role as the gateway
.



Otherwise it changes the pair of CHs or changes its state

Gateway Selection Heuristic


CLUSTER HEAD

GATEWAY

ORDINARY NODE

GW_READY NODE

1

7

4

5

(1,7)

(1,4)

(4,5)

(5,7)

There is at most one gateway between


any pair of two cluster heads

Simulation Studies


Flooding efficiency with passive clustering


Apply passive clustering to representative reactive ad
hoc routing protocols (AODV, DSR)



Flooding Experiments


TNP (the
T
otal
N
umber of
P
ackets sent for one broadcast)


NDB (the
N
umber of nodes

D
elivered the

B
roadcast)



BF

(Blind Flooding)


MPR
-
F

(Flooding with MPR scheme)


AC_LID
-
F
(Flooding with active clustering with Lowest Id )


PC_LID
-
F

(Flooding with passive clustering)

Flooding Experiments


Fixed network size with node mobility (100 nodes)

Total Number of Packet sent

Delivery Count (NDB)

On
-
demand Routing
-
AODV

Delivery Ratio

Normalized Control Overhead

On
-
demand Routing
-

DSR

Normalized Control Overhead

Delivery Ratio

Conclusion


Passive Clustering protocol



Effective
gateway selection heuristic



Efficient flooding based on
topological information



Applicability of passive clustering to a few
reactive routing
protocols

References


Taek Jin Kwon

,


Mario Gerla, “
Efficient Flooding in Ad hoc
Networks using On
-
Demand (Passive) Cluster Formation
”, ACM
SIGCOMM Computer Communication Review ,2002.



Gerla, M.; Taek Jin Kwon; Pei, G., ”
On
-
demand routing in large ad
hoc wireless networks with passive clustering
”, Wireless
Communications and Networking Conference, 2000.



Amir Qayyum, Laurent Viennot, Anis Laouiti, “
Multipoint relaying: An
ecient technique for flooding in mobile wireless networks
”, Technical
Report RR
-
3898, INRIA, February 2000.