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Presented by Ghada Abdelmoumin CS6204 Fall 2008/ Prof. Ing-Ray Chen

GARUDA Achieving Effective Reliability for Downstream Communication in Wireless Sensor Networks Park et. al. Presented by Ghada Abdelmoumin CS6204 Fall 2008/ Prof. Ing-Ray Chen. Reliable Data Delivery (RDD): Topics. Introduction; Background Information Basic Assumption Challenges

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Presented by Ghada Abdelmoumin CS6204 Fall 2008/ Prof. Ing-Ray Chen

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  1. GARUDAAchieving Effective Reliability for Downstream Communication in Wireless Sensor NetworksPark et. al Presented by Ghada Abdelmoumin CS6204 Fall 2008/ Prof. Ing-Ray Chen

  2. Reliable Data Delivery (RDD): Topics • Introduction; Background Information • Basic Assumption • Challenges • RDD Fundamental Problems • Related Work • Problem of Downstream Reliability • Definition and Key Goal. • Diverse Reliability or Reliability Semantics • Challenges • RDD Proposed Solution – GARUDA • Claims • Design Elements • Assumptions • Proposed Framework Approach • Reliability Variant. • Performance & Analysis

  3. Reliable Data Delivery (RDD): Assumptions • Inherent properties of WSNs such as redundancy increase the degree of Reliability, but can not guarantee Reliability Semantics. • Reliability in WSNs depends on the type of application, e.g., in security critical application any message from source has to reach the sensors reliably. • In a security critical application the source may send the following three classes of messages: Control Code, Query-Response-data, and Query-Request-information.

  4. Reliable Data Delivery (RDD): Challenges • The problem of RDD has been addressed in MANET. • MANET Proposed Approaches do not directly apply to the environment of WSN because of the three unique challenges imposed by: • Environment Considerations: substantially limited sensor lifetime, limited bandwidth, and limited energy. • MessageConsiderations: mostly small size messages/queries; What kind of loss recovery scheme can be employed? • Reliability Considerations: different notion of reliability; default  only a subregion  partial probabilistic reliability.

  5. Reliable Data Delivery (RDD): Fundamental Prob. • Redundancy can not guarantee any Reliability Why? Parameters: Message Size = 100 packets; Packet Size = 1 kb; NW = 650 m X 650 m grid, Nodes = 100 Wireless Random Channel Errors Congestion and Contention Broadcast Storm • WSNs requires diverse reliability semantics. • Separate Reliability Mechanism is needed!

  6. Reliable Data Delivery (RDD): Related Work

  7. Downstream Reliability: Problem Definition • Problem Name: Reliable sink-to-sensors downstream data delivery. • Problem Scope: Includes tackling the diverse reliability semantics required in WSNs. • Goal: Achieving reliability while minimizing bandwidth usage, energy consumption, and latency.

  8. Char 1: ReconfigureChar 2: Location-dependent Char 3: Redundancy DeploymentChar 4: Resolution Scoping Downstream Reliability: Diverse Reliability Semantics

  9. Downstream Reliability: Challenges (1) • Environment Constraint: • Minimize the number of retransmission overheads to ensure reliability and hence address energy and bandwidth constraints. • Topology Construction Mechanism: In case of node failure don’t rely on static construction mechanism, but use dynamic construction mechanism. Trade off:dynamic mechanisms that periodically refresh any constructions are not desirable. • Inherent characteristics such as spatial reuse to achieve best capacity and hence delay may be severely limited by a specific loss recovery mechanism. • Reliability Semantics: • Any reliability solution should support all types of semantics unique to WSNs.

  10. Downstream Reliability: Challenges (2) • Acknowledgment Paradox (ACK/NACK): • Stems from the constraints imposed by the typical sizes of messages; diverse message sizes (large-to-small). • NACK is an effective loss advertisement mechanisms, but it can not handle the unique case of all-packets-lost problem at a particular node; node is not aware that a message is expected. • ACK scheme would address all-packet-lost problem, but ACK implosion is problematic. • NACK scheme inherently require in-sequence forwarding of data by nodes to prevent NACK implosion; in-sequence forwarding limit spatial reuse.

  11. GARUDA: Claims • Provides Reliable point-to-multipoint data delivery from sink to sensors. • Scalable w.r.t network size, message characteristics, loss rate, and reliability semantics. • Reduce the size of the protocol inside each sensor node; provide services (Design Elements) with one framework.

  12. GARUDA: Assumptions • Downstream Reliability • The algorithm limits reliability scope to source/sink-to-sensorsonly. • Communication and Node Failure: • The algorithms handles both link and node failure. • 100% Reliable Message Delivery/RMD: • Initially focuses on 100% reliability to all sensors • Extends focus to all other reliability semantics. • Message: • The message size consists of one or more packets. • Metrics: • Latency, retransmission overhead, and energy consumption. • Network Model: • The source/sink and sensors in the NW remains static. • Exactly one sink coordinating the sensors.

  13. GARUDA: Design Elements • Pulsing-based solution • For reliable message delivery. • Core/Virtual infrastructure: • It is a loss recovery infrastructure. • It is an approximation of the minimum dominating set (MDS) of the NW subgraph to which reliable message delivery is desired; optimal loss recovery designation servers  Optimization. • Instantaneously constructed during the course of a single packet flood. • Two-stage NACK-based recovery process • Minimizes retransmission process overhead. • Performs out-of-sequence forwarding to leverage spatial reuse. • Candidacy based solution • To support diverse reliability semantics.

  14. GARUDA: Core Rationale • When a Packet is sent from a source to sensors: • It is not possible that all nodes receives the packet without any error. • For any two packets broadcast, the set of node that has not received each packet can be different. • The set of nodes that have not received the packet can request for retransmission from any of the neighbor who received the packet successfully. • The retransmission by neighbor is sufficient to recover the loss of the same packet of all neighbors around it. • The Optimal Loss Recovery Server Designation Problem: • Tries to minimize the set of retransmitting nodes. • Can be abstracted to one of a Minimum Set Cover (MSC) to determine the recovery server set that covers the base set. • Recovery Server Set: The set of nodes that have received the packet successfully. • Base Set: The set of nodes that have not received the packet successfully. • MSC is NP-complete, but MDS is NP-hard. • MDS Problem is equivalent to MSC problem using L-reduction.

  15. GARUDA: Instantaneous Core Construction • The core is constructed using the first packet delivery. • The reliable delivery of the first packet determines the hop_count of each node. • If a node hasn’t heard from any other node and its hop_count is a multiple of 3 can elect it self as a core node. • To approximate the MDS problem select a node at 3i hop distance because it can cover the other nodes at 3i+1 and 3i-1.

  16. GARUDA: Loss Recovery Process • Out-of-Sequence Forwarding with A-Map Propagation • In-sequence forwarding suppress the forwarding of higher sequence number packet. • Out-of-sequence forwarding allow nodes with lost packets to continue to forward any higher (or lower) sequence number packets they might have received. • A-Map (Availability Map) propagation is used to address NACK implosion. • Any downstream core node initiates a request for a missing packet only if it receives an A-map from an upstream core node. • The core nodes initiate requests only when they are sure of an upstream core node having a particular packet. • There are two-stage loss recovery: Loss recovery for core nodes and Loss recovery for noncore node.

  17. GARUDA: Diverse Reliability Semantics • GARUDA Solution: • Find MDS within each partition • Connect MDS to the sink • Instance of reliability semantics require delivery to subset Gs of the nodes in the underlying graph G. • Gs consists of K components. • K components are connected but are not connected with each other. • GARUDA uses an approximation of the shortest path tree (SPT) to connect the components to the sink. • Nodes employ a candidacy check before participating in a the core construction algorithm. • Upon receiving the first packet the nodes determine whether or not they belong in Gs. • Node outside Gs that is required for Core construction are inducted in the core construction using a forced candidacy algorithm.

  18. GARUDA: Reliable Delivery of First Packet • GARUDA user ACK-based scheme instead of NACK-scheme • GARUDA uses the Wait-for-First-Packet (WFP) pulse to deliver the first packet reliably. • WFP addressed the ACK implosion problem. • WFP is a finite series of short duration pulses. • Pulse amplitude is larger than a regular data transmission, but its duration is smaller than that of a regular data transmission. • Any node irrespective of whether it is idle or receiving a packet can sense the pulse.

  19. GARUDA Framework: Reliable Delivery of First Packet (RDFP) • RDFP consist of three modes: • Advertisement Notifies FP to all node using forced WFP pulses. • Delivery Sends FP packet using forwarding. • Recovery sends NACK using WFP to request retransmission. • Loss Recovery Optimization • Piggyback NACK info inside the packet. • NACK = Sequence # of the last msg. ID the node received successfully. • Any neighbor aware of a greater msg. ID and has the FP retransmit the FP. Latency:TC is proportional to the node hop distance

  20. GARUDA Framework: Core Construction • Core Construction Procedure: • When the sink sends the FP it stamps the FP with its band ID (bId =0). • When the sensor receives the FP, it increments its bId by 1 and sets the resulting value as its own bId (i.e., bId=2) • Only sensors located at 3i band can elect themselves as core nodes. • Every core node in the 3(i+1) band knows of t least one core in 3i. • Every Packet carries the previously visited node bId and A-map. • Concentric Circle • The FP delivery establishes band-IDs for node based on hop distance. • All nodes with the same ID form a band with a certain ID. • 3i [Hear=>elects self or receives solicitation message] 3(i+1) [Check=> knows or elects]  3(i+2) [forwards then elects].

  21. GARUDA Framework: Loss Recovery • Core Recovery • Loss Detection when a core node receives an out-of-sequence , it sends a request to an upstream core node only if notified through an A-map the missing packet is available at upstream core node. • Loss Recovery When a core node receives a unicast request from a downstream core node it performs a unicast retransmission for the request. • Noncore Recovery • Noncore node snoops all retransmission form its core node. • It initiates a retransmission request to its core node. • If it doesn’t hear from its core node for a core presence time, it sends an explicit request and the core node respond with its current A-map Opt: Core Node Packet (Cid, A-map, bId, vFlag) Forward Noncore Node Packet (Cid, NCid, A-map, bId, vFlag) ForwardNoncore Node Packet (Cid, Cid, Cid, A-map, bId, Null) Forward Core Node 2-Local A-maps (myBM, totBM), Core Node A-map (inBM) ReceiveCore Node (A-map has P*) Request (A-map*); Update (totBM); Set (Timer)Core Node (A-map*)Receive ; Update (myBM, totBM)Core Node (Timer Expire, Hear Not)  Request (A-map*, default Upstream Core Node)Default Upstream Core Node (A-map current) Send

  22. GARUDA Framework: Diverse Reliability Semantics • Reliability Variants: • Reliable Delivery to all nodes within a subregion • Reliable delivery to the minimal number of sensors required to cover entire sensing area. • Reliable delivery to p percent of the nodes. • Candidacy Problem: • Only a subset of the nodes in the network requires reliable delivery. • Which subset of nodes receives the message delivery? • FP is delivered to all nodes, but all subsequent packets are delivered based on candidacy. • FP carries info to identify eligibility of nodes for candidacy; i.e., coordinate-based description of the subregion. • Core nodes are the default candidates. • Each component on the candidate subgraph Gs has its own core node. • Forced candidacy to connect cores to sink and force non-candidate nodes in 3i band on the path from core nodes to sink to participate to ensure connectivity. • Downstream candidate core node requests explicitly from an upstream non-candidate core node to become a candidate if it hasn’t heard from any other candidate upstream node.

  23. GARUDA Framework: Diverse Reliability Semantics • Reliable Delivery Within Subregion(1): • Subregion can be specified in the form of coordinates. • Subregion can either be contiguous or noncontiguous. • Subregion coordinates are piggybacked on the First Packet delivered. • Each sensor receiving the packet can locally determine whether it is a candidate or not. • A sensor doesn’t elect itself as a core node if it is not a candidate. • Reliable Delivery to Cover Sensing Field(2): • Reliable delivery needs to be performed by a minimal subset of sensors such that the entire sensing field is covered. • Assume the sensing range S is always ≤ transmission range R . • Coordination between nodes is required to eliminate sensors covering a region that is already covered. • Core node perform coordination; it is adjacent to all noncore nodes and at distance 2R at least from the nearest core node. • Core nodes keep track of the region covered by 2(S+T). • Noncore nodes seek permission from coordinator and coordinator grants permission only if the node can cover an area that is not already covered by 2(S+T). • Reliable Delivery to Probabilistic Subset(3): • Useful when the sink intends to perform scoped sensing. • Candidacy is determined locally. • When receiving the FP, a sensor elects itself as a candidate with a probability P. • A sensor in a 3i band doesn’t elect itself as a candidate if it decides already not to be a noncore node.

  24. GARUDA Framework: Analysis and Evaluation

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