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

Formation

2003. 04. 18

ICNS LabNa 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

sourcedestination

A C DBA C DBA C DB

A Hello messages

Introduction

ᆞ 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 packets2. the probability of collision3. 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 messages2. It does not have any setup latency, and it saves energy with no

traffic3. Its maintenance is well adaptive to dynamic topology and

resource availability changes

Related Works

• Proposed several heuristics to reduce rebroadcasts1. Probabilistic scheme

Rebroadcast the packet with the randomly chosen probability2. 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 neighbo

rs

• 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 Total Number of Packets sent for one broadcast)– NDB (the Number of nodes Delivered the Broadcast)

– 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.