Efficient Flooding in Ad Hoc Networks Seminar: Pervasive Computing (SS 2004) Frank Radmacher Frank Radmacher, July 15, 2004 Betreuer: Stefan Penz Efficient Flooding in Ad Hoc Networks - p. 1/27
References [1] Sze-Yao Ni, Yu-Chee Tseng, Yuh shyan Chen, and Jang-Ping Sheu. Introduction ● References The Broadcast Storm Problem in a Mobile Ad Hoc Network. ● Contents ACM MobiCom , 1999. ● Mobile Ad Hoc Networks ● Multi-Hop Scenario The Broadcast Storm Problem [2] Jie Wu and Fei Dai. Self-Pruning Broadcasting in Ad Hoc Networks Based on Self-Pruning. IEEE Infocom , 2003. Simulation results [3] Hyojun Lim and Chongkwon Kim. Flooding in Wireless Ad Hoc Networks. Computer Communications 24(3-4) , 2001. [4] Yu-Chee Tseng, Sze-Yao Ni, and En-Yu Shih. Adaptive Approaches to Relieving Broadcast Storms in a Wireless Multihop Mobile Ad Hoc Network. IEEE Infocom , 2001. [5] Andrew S. Tanenbaum. Computer Networks, Fourth Edition . Prentice Hall PTR, 2002. Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 2/27
Contents ■ Introduction to Mobile Ad Hoc Networks Introduction ● References ■ The Broadcast Storm Problem ● Contents ● Mobile Ad Hoc Networks ● Multi-Hop Scenario ■ Self-Pruning The Broadcast Storm Problem ■ Simulation Results Self-Pruning ■ Conclusion Simulation results Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 3/27
Mobile Ad Hoc Networks (MANETs) ■ Consist of wireless mobile hosts which form a temporary network Introduction ● References ◆ without the aid of established infrastructure ● Contents ● Mobile Ad Hoc Networks (e. g. base stations) ● Multi-Hop Scenario The Broadcast Storm Problem ◆ without centralised administration Self-Pruning (e. g. mobile switching centers) Simulation results ■ Every host in a MANET ◆ can roam around freely ◆ can only communicate with hosts which are currently in its transmission range ➥ Multi-hop scenario: Packets must be forwarded to their destination Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 4/27
Mobile Ad Hoc Networks (MANETs) ■ Consist of wireless mobile hosts which form a temporary network Introduction ● References ◆ without the aid of established infrastructure ● Contents ● Mobile Ad Hoc Networks (e. g. base stations) ● Multi-Hop Scenario The Broadcast Storm Problem ◆ without centralised administration Self-Pruning (e. g. mobile switching centers) Simulation results ■ Every host in a MANET ◆ can roam around freely ◆ can only communicate with hosts which are currently in its transmission range ➥ Multi-hop scenario: Packets must be forwarded to their destination Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 4/27
Multi-Hop Scenario Introduction ● References ● Contents ● Mobile Ad Hoc Networks ● Multi-Hop Scenario The Broadcast Storm Problem Self-Pruning Simulation results Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 5/27
The Broadcast Storm Problem ■ Straightforward realisation of global broadcasting in a MANET Introduction ➥ Simple Flooding: The Broadcast Storm Problem ● Overview ● Redundancy Every host retransmits a received broadcast message once. ● Contention ● Collision ● Observation ■ This leads to the so called Broadcast Storm Problem Self-Pruning consisting of Simulation results ◆ Redundancy ◆ Contention ◆ Collision Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 6/27
The Broadcast Storm Problem ■ Straightforward realisation of global broadcasting in a MANET Introduction ➥ Simple Flooding: The Broadcast Storm Problem ● Overview ● Redundancy Every host retransmits a received broadcast message once. ● Contention ● Collision ● Observation ■ This leads to the so called Broadcast Storm Problem Self-Pruning consisting of Simulation results ◆ Redundancy ◆ Contention ◆ Collision Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 6/27
Redundancy (1) ■ Problem: Introduction When a mobile host retransmits a broadcast message, all its The Broadcast Storm Problem ● Overview neighbors might already have received this message. ● Redundancy ● Contention ● Collision ➥ The bandwidth of the network gets reduced by ● Observation unnecessary broadcasts. Self-Pruning Simulation results Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 7/27
Redundancy (2) ■ We are interested in the additional coverage of a node (grey shaded area) πr 2 − INTC ( d ) ■ The additional coverage of B : √ � r r 2 − x 2 dx where INTC ( d ) = 4 d/ 2 � r 2 πx · [ πr 2 − INTC ( x )] dx ≈ 0 . 41 πr 2 ■ Expected additional coverage of a node: 0 πr 2 Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 8/27
Redundancy (3) ■ If a host received a broadcast message from more than one host, Introduction the expected additional coverage decreases. The Broadcast Storm Problem ● Overview ■ Expected additional coverage EAC ( k ) of a host ● Redundancy ● Contention after receiving a broadcast k times: ● Collision ● Observation Self-Pruning Simulation results ➥ Many rebroadcasts are superfluous in the case of simple flooding. Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 9/27
Contention (1) ■ Problem: Introduction If n nearby hosts try to rebroadcast a message nearly the The Broadcast Storm Problem ● Overview same time, they are likely to compete with each other. ● Redundancy ● Contention ■ Simple case of n = 2 : ● Collision ● Observation Self-Pruning Simulation results INTC ( x ) /πr 2 ■ The probability of contention is � r 2 πx · INTC ( x ) / ( πr 2 ) ■ For arbitrarily located B ’s: dx ≈ 59% 0 πr 2 Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 10/27
Contention (2) ■ The probability c f ( n, k ) of having k contention-free host Introduction among n receiving hosts: The Broadcast Storm Problem ● Overview ● Redundancy ● Contention ● Collision ● Observation Self-Pruning Simulation results ➥ Contention is likely to occur, especially in dense networks. Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 11/27
Collision ■ Problem: Broadcast messages are rather sent simultaneously, such that collisions get more probable. ■ Reason: CSMA/CA style communication ◆ without RTS/CTS dialogues ◆ without acknowledgement packets ■ Two problems: ◆ two hosts decide to transmit a message at around the same time ◆ the hidden station problem Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 12/27
Observation ■ Redundancy, Contention, Collision are serious problems. Introduction The Broadcast Storm Problem ■ All problems have one cause in common: ● Overview ● Redundancy ● Contention They increase with the number of hosts which ● Collision ● Observation unnecessarily rebroadcast a message. Self-Pruning Simulation results ■ Solution: Inhibit some nodes in the MANET from rebroadcasting. ➥ Select a forward node set Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 13/27
Introduction to Self-Pruning (1) ■ Self-Pruning: Every node decides on its own whether to Introduction forward a message or not. The Broadcast Storm Problem Self-Pruning ■ A forward node set has to form a connected dominating set . ● Introduction to Self-Pruning ● Coverage Condition I ● Coverage Condition II ◆ A set A of nodes is called dominating set of a graph G , if every ● Comparison ● k-Hop Neighbor Set node is either in the set or has a neighbor in the set. Simulation results ◆ dominating set: Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 14/27
Introduction to Self-Pruning (1) ■ Self-Pruning: Every node decides on its own whether to Introduction forward a message or not. The Broadcast Storm Problem Self-Pruning ■ A forward node set has to form a connected dominating set . ● Introduction to Self-Pruning ● Coverage Condition I ● Coverage Condition II ◆ A set A of nodes is called dominating set of a graph G , if every ● Comparison ● k-Hop Neighbor Set node is either in the set or has a neighbor in the set. Simulation results ◆ connected dominating set (CDS): Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 14/27
Introduction to Self-Pruning (2) ■ Ideal forward node set: Introduction The Broadcast Storm Problem minimum connected dominating set (MCDS). Self-Pruning ● Introduction to Self-Pruning ■ A minimum connected dominating set (MCDS) is a connected ● Coverage Condition I ● Coverage Condition II ● Comparison dominating set (CDS) with a minimal number of nodes. ● k-Hop Neighbor Set Simulation results ■ But: ◆ MCDS problem is NP complete. ◆ Global network information is needed for computation. ➥ Define coverage condition which only results in a nearly optimal CDS but is suitable for computation. Frank Radmacher, July 15, 2004 Efficient Flooding in Ad Hoc Networks - p. 15/27
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