1. Efficient Flooding Techniques for Mobile Ad Hoc Networks
Special Topic for CS587x
Department of Computer Science
Iowa State University

2. Outline Introduction on MANET Existing flooding techniques
Proposed techniques
Future Works

3. Mobile Ad Hoc Networks (MANET)
Characteristics of MANET
No fixed network infrastructure
Hosts act as routers on demand
Flooding is a communication primitive
Frequently invoked for route discovery

4. Plain Flooding
Each host needs to forward a broadcast if the broadcast is received at the first time
Advantage : simple and reliable
Drawback : broadcast storm

5. Probabilistic Broadcasting [Tseng99, Sasson01]
Each host forwards only a certain percentage of the flooding packets it receives
Advantage : reduced network traffic
Drawback : not reliable

6. Multipoint Relaying [Laouite01, Peng02, etc.]
Each host selects some of its 1-hop neighbors to forward
Require 2-hop topology
Intensive computation B A 2 1 3 4 C D E

7. Research Motivation Problems of the existing schemes
Excessive network traffic
Reduced flooding reachability
Excessive control overhead
Excessive computation cost

8. Edge Forwarding – Partition
The broadcast coverage of each mobile host is divided into six partitions P2 P3 P1 A P6 P4 P5

9. Edge Forwarding - Subpartition
The location of a mobile host divides a given partition into six subpartitions
P12
P11
P13 B
P16
P14
P15 A

10. Observation
B does not need to forward A’s broadcast if at least one forwarding occurs in each of A’s subpartitions
P12
P11
P13 B
P16
P14
P15 A

11. Forwarding Rule
B must forward a broadcast from A if any P1i (i = 1, …, 6) contains no hosts
P12
P11
P13 B
P16
P14
P15 A

12. Proof of Reliability
If B does not forward, then at least one host in each P1i (i = 1, …, 6) will forward B A C
A host does not need to forward the broadcast if it is surrounded by other hosts A
If B does not need to forward the broadcast, there must at least one host, say C, in each of B’s partition
Similarly, C does not need to forward the broadcast, if there is at least one host, say D, in each of C’s partition.
As this process continues, the sizes of the partitions continue to reduce.
Eventually, some host F will not find another host in some of F’s partition, and F will have to forward the broadcast from A.

13. Advanced Forwarding
Push the forwarding responsibility to the hosts close to the broadcast perimeter 
P12
P11
P16
P13
P14
P15 B A
A host does not need to forward the broadcast if it is surrounded by other hosts A
If B does not need to forward the broadcast, there must at least one host, say C, in each of B’s partition
Similarly, C does not need to forward the broadcast, if there is at least one host, say D, in each of C’s partition.
As this process continues, the sizes of the partitions continue to reduce.
Eventually, some host F will not find another host in some of F’s partition, and F will have to forward the broadcast from A. 

14. Edge Forwarding Protocol
Receive a new packet P Y
Forward ? N
Overhearing To time units
Confirming Tc time units Y
Forward ? N
Forward P
Done on P

15. Why Wait ? Further deduction of redundant transmission
Make forwarding occur in better order
Overhearing phase (To)
Handle host uncertainty (eg., energy fading, movement, etc.)
Confirming phase (Tc) C B D A

16. Scalability with Network Size
2000
1800
Plain Flooding
1600
Edge Forwarding
1400
Average sending cost
1200
1000
800
600
400
200
100
200
300
400
500
600
700
800
900
1000
Network Area (x1000 meter^2)

17. Significant and Impact of
Edge Forwarding
Edge Forwarding is the first scalable and reliable 1-hop flooding technique
Low control overhead
Low computation cost
Minimum forwarding delay
Easy implementation

18. Reading Assignment 1 Read one of these two papers (search on Google)
Location-Aided Routing (LAR) in mobile ad hoc networks (MOBICOM 2000)
Energy Efficient Indexing on Air (SIGMOD 1994)
Prepare presentation slides (due Feb 18)
what is the problem
what is the state of the art and their limitation
how this is resolved
comments (originality, technical depth, drawback)
Two students will be chosen to present the paper in the class (TBD)