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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [ Wireless Mesh Personal Area Networks ] Date Submitted: [ 4 November , 2006 ]

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Wireless Mesh Personal Area Networks] Date Submitted: [4November, 2006] Source: [Inhwan Lee (1), Sungrae Cho (2), Bong Soo, Kim (1), and Cheol Sig Pyo (1)] Company [ETRI (1), School of Computer Science and Engineering, Chung-Ang University (2)] Address [221 Heukseok, Dongjak, Seoul 156-756, Republic of Korea] Voice:[+82-2-820-5766], FAX: [+82-2-820-5766], E-Mail:[ihlee@etri.re.kr] Re: [IEEE P802.15.5 WPAN MESH Networking Call for Additional Contributions dated on July, 2006 at IEEE P802.15-06-0333-04-0005] Abstract: [This document is a summary of the proposed Timer-based Reliable Broadcast (TRB) for WPAN mesh networks.] Purpose: [A response to the call for additional contributions.] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. <Inwhan Lee>, <ETRI>

  2. Timer-based Reliable Broadcast for WPAN Mesh Networks Inhwan Lee (1), Sungrae Cho (2), Bongsoo Kim (1),and Cheol-Sig Pyo (1) (1) ETRI (2) Chung-Ang University <Inwhan Lee>, <ETRI>

  3. Contents • Introduction • Motivation • Timer-based Reliable Broadcast (TRB) for WPAN Mesh Networks • Examples • Summary <Inwhan Lee>, <ETRI>

  4. INTRODUCTION • Broadcast is necessary for disseminating data for various reasons, e.g., sensor network query dissemination, S/W updates at mesh nodes, etc. • Reliability should be guaranteed in some or most cases. → Reliable Broadcast <Inwhan Lee>, <ETRI>

  5. MOTIVATION (1/2) • Suppose that every receiver node acknowledges (with ACK or NAK) for broadcast data, e.g., • The broadcast node will be overwhelmed by acknowledge messages (a.k.a. ) ACK/NAK implosion problem. <Inwhan Lee>, <ETRI>

  6. MOTIVATION (2/2) • This implosion problem also causes the problems of • Unnecessary Collision • Unnecessary Power Consumption • Solution: limit the number of acknowledgements • How?: • Use timers • Timer-based Reliable Broadcast (TRB) <Inwhan Lee>, <ETRI>

  7. TRB (1/4) • Transmitter Behavior (when it has broadcast data): • UPSTREAM: If the data is from its child, it does the following in its appropriate schedule: • It broadcasts the data (piggybacked by ACK/NAK) to its children (not siblings), and sets its timer D. • It unicasts the data to its parent and associated neighbors, and sets its timer D. • DOWNSTREAM: If the data is from its parent • it broadcasts its data to its children (not siblings) and associated neighbors, and sets its timer D. • THE OTHER CASES: If the transmitter is the originator of the data, it does the following in its appropriate schedule: • It broadcasts the data to its children (not siblings), and sets its timer D. • It unicasts the data to its parent and associated neighbors, and sets its timer D. • In all cases, a node that received a broadcast data from other node does not unicast back to that other node. • If timer D expires before receiving feedback (ACK/NAK), it retransmits the original data as above. <Inwhan Lee>, <ETRI>

  8. Error NAK timer ACK timer TRB (2/4) • Receiver Behavior (after receiving broadcast data) • When a node receives a broadcast data, it delays its acknowledgement by a random timer described below: • If the received data is erroneous, the node activates a NAK timer. • If the received data is OK, the node activates an ACK timer. • If its timer expires, the node responds (with unicast) its feedback (NAK or ACK) to its transmitter. <Inwhan Lee>, <ETRI>

  9. αD (NAK Period) (1-α)D (ACK Period) D Broadcast Data Received TRB (3/4) • NAK timer is generated at random in range of [0, αD] while ACK timer is generated at random in range of [αD, D]. • Shorter timer for NAK causes early rebroadcast of the original data to fix errors. • Longer timer for ACK is for the case that all nodes successfully received the data. • Transmitter Behavior (after receiving feedback) • Once the transmitter receives a NAK, it retransmits its data as described in Slide 7 to fix the error, and sets its timer D. • When an ACK received, the transmitter transmits its next broadcast data if it has as described in Slide 7, and sets its timer D. <Inwhan Lee>, <ETRI>

  10. Broadcast Rebroadcast TRB (4/4) • Receiver Behavior (after receiving rebroadcast data) • The receiver node cancels its timer (NAK or ACK). • This will reduce unnecessary feedbacks to the transmitter. • Based on the result of error detection/correction, the receiver uses NAK/ACK timer. • This series of procedure will continue up to predefined number of times. • Overall behavior will look like as the following for an example: Tx ACK NAKs NAK Rx’s Many of receivers will suppress their timer <Inwhan Lee>, <ETRI>

  11. Downstream Example (1/7) • @ T=t0, parent (node A) broadcasts. • Dotted lines: association relations Level N-1 A OK B OK C D Level N OK Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  12. Downstream Example (2/7) • @ T=t0+0.75D, node B replies with ACK. Level N-1 A ACK B C D Level N Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  13. Downstream Example (3/7) • Before or after T=t0+0.75D, node C may forward it to its children. Level N-1 A B C D Level N OK Error Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  14. Downstream Example (4/7) • @ T=t0+0.8D, node F replies with NAK. • About the same time, node E forwards the data to its children. Level N-1 A B C D Level N NAK Level N+1 E F OK OK OK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  15. Downstream Example (5/7) • @ T=t0+0.9D, node C rebroadcasts to its children. • Node E suppresses its ACK for the previous broadcast data, and also ignore silently the rebroadcast data. Level N-1 A B C D Level N OK Level N+1 E F ACK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  16. Downstream Example (6/7) • After T=t0+0.9D, node F forwards the data to its children. Level N-1 A B C D Level N Level N+1 E F OK OK OK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  17. Downstream Example (7/7) • @ T=t0+1.5D, node F replies with ACK. Level N-1 A B C D Level N Level N+1 E F ACK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  18. Upstream Example (1/4) • @ T=t-1, child (node E) of node C broadcasts to its children. • Dotted lines: association relations Level N-1 A B C D Level N Level N+1 E F Broadcast Originator OK OK OK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  19. Upstream Example (2/4) • @ T=t0, child (node E) unicasts to node C. Level N-1 A B OK C D Level N Level N+1 E F ACK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  20. Upstream Example (3/4) • After T=t0, node C broadcasts data piggybacked with ACK which is ignored by node F in this example. • Also, node C unicasts data to its parent in its appropriate schedule. Level N-1 A OK B C D Level N Data/ACK Data/ACK OK Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  21. Upstream Example (4/4) • After receiving C’s unicast data, nodes A broadcasts the data piggybacked with ACK. Level N-1 A Data/ACK Data/ACK Data/ACK B C D Level N Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

  22. Simple Analysis (1/3) • Consider a simple star network consisting of a parent and N children associated with the parent. • Assume that NAK/ACK never be lost. • prob. of transmission error. • Let us define energy efficiency, • If , • If , <Inwhan Lee>, <ETRI>

  23. Simple Analysis (2/3) Time that both nodes receive a broadcast data • So, <Inwhan Lee>, <ETRI>

  24. Simple Analysis (3/3) • So, we will have better energy efficiency • Even for large N • Even for large number of receivers with error • and have to be selected so that <Inwhan Lee>, <ETRI>

  25. Summary • ACK/NAK in reliable broadcast may cause problems of • Feedback implosion, • Unnecessary collisions, and • Unnecessary power consumption, • Due to unnecessary feedback messages • Timer-based Reliable Broadcast (TRB) algorithm effectively solves the above mentioned problems. <Inwhan Lee>, <ETRI>

  26. This work has been supported partially by HNRC of IITA. <Inwhan Lee>, <ETRI>

  27. Thank You! <Inwhan Lee>, <ETRI>

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