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

Outline Introduction on MANET Existing flooding techniques Proposed techniques Future Works

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

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

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

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

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

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

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

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

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

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.

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. 

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

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

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)

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

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)