localized operations for distributed minimum energy multicast algorithm in mobile ad hoc networks
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DESCRIPTIONPaper by Song Guo and Oliver Yang; supporting images and definitions from Wikipedia Presentation prepared by Al Funk, VT CS 6204, 10/30/07. Localized Operations for Distributed minimum energy multicast algorithm in mobile ad hoc networks. Table of Contents. Background and related work - PowerPoint PPT Presentation
Paper by Song Guo and Oliver Yang; supporting images and definitions from Wikipedia
Presentation prepared by Al Funk, VT CS 6204, 10/30/07
Table of ContentsBackground and related workModels: system, network, mobilityDMEM algorithmOperationsPerformanceConclusions
Background and related workMulticast: communication technique which enables a source to send a single packet to reach multiple receivers.Objective: Create a distributed algorithm to solve the Minimum Energy Multicast (MEM) problemDefinition of MEM: Find a route for multicast transmission with the minimum total energy consumption for a given communication session.Challenges: MANET changing network topology, lack of central authority; problem is NP-hard
Background and related workPrior research focused on:Creating centralized, not distributed, algorithmsEfficient heuristic algorithm designWeaknesses of prior researchExamination of static, not dynamic, network topologiesLittle examination of performance impact of node mobility
Models: System ModelDiscrete Power Level Management ModelTransmission range based on power level, but power level increases at an exponential rate as distance increasesIdentify discrete power levels appropriate to reach nodes at various distances from the transmitterVary transmitter power in granular increments to balance power use with the bandwidth usage necessary to constantly adjust transmission strength
Models: System Model
Pvu = Power level required to transmit from node v to node ulvu = Layer (concentric ring from prior slide) of u relative to vK = Number of discrete power levels of the transmitter (and therefore number of layers)rK = Distance of ring K = Parameter (2 to 4) representing rate of signal attenuation
Models: Network ModelRepresent network as a directed graph, G(N,A,p)N = set of nodes, A = set of arcs, p = function representing power required for each arcRooted tree: directed acyclic graph with a source node that has no incoming arcs and where other nodes have a single incoming arcLeaf vs. internal/relay nodes
Models: Network ModelFor any node v in the rooted tree, there exists a single acyclic source route vOur goal is to set lv, the transmission layer of node v, to the minimum necessary for v to reach all of its child nodesOnce this is known, we can calculate pv, the necessary power level for the node
Models: MobilityMobility is a differentiator for the contribution, as alternative models require the significant overhead associated with central coordination.Authors use Random Waypoint ModelCalculate random speeds bounded by Vmin and Vmax; assume random start and end points; introduce pause between journeys.Objective: calculate the steady-state average speed:
Algorithm: Data Structure
We need to store the forwarding state at each tree node v.Membership status sender, receiver, forwarder (can be receiver and forwarder)Source route directed path from the source to node v (used to avoid loops)Tree neighborhood table TNv stores neighbors, along with whether is a father, child or other, along with layer lvu
Algorithm: Tree ConstructionMinimum Spanning Tree: Given a connected, undirected graph with weighted edges, an MST is a subgraph which connects all vertices together resulting in the minimum total weight.
Algorithm: Tree ConstructionMULTICAST-JOIN-REQUEST (MJREQ): Broadcast message initiated by the source used when no route information is knownMULTICAST-JOIN-REPLY (MJREP): Response message sent to previous hop nodeMJREQ: Transmitted at maximum transmission powerMJREP: Returned at necessary powerNecessary power determined by strength of the original MJREQ message
Algorithm: Tree FloodMULTICAST-ALIVE (MA): Message sent periodically during session to refresh the tree (otherwise tree routes are cleared)Message sent at maximum powerUsed to adjust power dynamicallyOnly sent if received from father (but then always sent)Supports tree repair and energy saving operationsNodes update neighborhood information to identify nearby nodes
Localized OperationsNormal Energy Saving (NES): Upon receipt of MA from children, node adjusts its transmission power to the minimum necessary.Reactive approach which could lower total power utilizationKeeps the tree connected but not with maximum efficiency
Localized Operations: SHOSoft Hand-Off (SHO): Initiated by a node that detects it is leaving its fathers transmission range (K).Goal is to identify a new father s.t. and power utilization is minimizedNode severs link with previous father (via MULTICAST-LEAVE (ML) message), selects the new fatherTree is maintained.
Localized Operations: MTRMulticast Tree Repair (MTR): In the case where loss of a node results in a tree partition, we need a way to repair the multicast tree.Occurs when a forwarder or receiver fails to receive successive MAs from its fatherNodes furthest from the source attempt to reconnect firstMULTICAST-JOIN-SOLICITATION (MJS): Hop-limited message
Localized Operations: MTRDisconnected node closest to source notifies the subtree that it is initiating repair procedures using an MA messageThe closest node to the source initiates an MJREP message and attempts to reconnect the subtree back to the multicast treeIf an appropriate node responds, the tree is reconnected; if not, other nodes in the subtree attempt to reconnect, and the node(s) that failed must rejoin through a network flood.
Localized Operations: AESAdvanced Energy Savings (AES): A proactive method of reallocating child nodes s.t. overall power utilization of the system is reduced.The major contribution of the paperWe must be able to retain the MST structure for multicastOperation performed as part of MAApproach: Each child node attempts to extend its transmission range to become the parent of a current child of its father but only if such a change reduces the total power utilization of the systemMore sophisticated than NES They are not mutually exclusive
Localized Operations: AESUsing the MA message header means that no separate message is necessary for the operationUse of MA messages fits the algorithm -- father to child propagation enables communication of power levels and supports child decision-making.At each transmission from its father, a node modifies header with its own information and propagates to its neighborsBecause MA messages are at full power, neighbors of multicast tree nodes will receive.As a result, non-multicast tree nodes can join, but must consider potential added cost of the link from a father node
Localized Operations: AESAES-REQUEST: When a node identifies a power savings, it sends an AES-REQUEST to the sourceSource reviews AES-REQUEST messages and sends AES-REPLY to the node with the greatest power savings
Localized Operations: AESFinalizing the updateSelected node sends local broadcast TREE-UPDATE and assigns itself as father to the node to moveMoving node leaves father, sending MULTICAST-LEAVE.If selected node is a non-tree node, it must find a fatherIt will be a forwarding node only, otherwise it would have been part of the original treeMultiple nodes may become children of the selected node if power savings justify
Localized Operations: AESExamples of AES tree revision
Performance EvaluationSimulationsAd hoc network with size 1,000 meters sq.Each node can transmit 250 metersK=10 = 2Modeled max node movement speeds of: 1, 5, 10, 15, 20 and 25 m/sMulticast groups 5, 25, 50, 75, 100Static networks considered50 scenarios for each multicast group
Performance EvaluationMeasuresRelative tree power: Ratio of actual total tree power for heuristic algorithm vs. ideal of MST algorithmAverage tree power: Power used over time for the treeCommunication overheads: Overhead for AES, SHO and MTR as a total number of these operations over each simulation
Performance EvaluationStatic network evaluationCompared DMEM against prior workNot key to the paper, but demonstrates that DMEM is a useful heuristic compared with prior research
Performance EvaluationMobile network evaluation: Consider with and without optional protocol components
Performance EvaluationExamine AES performance considering node speed and multicast group size.
Performance EvaluationExamine SHO operations given node speed and multicast group size.
Performance EvaluationMTR operations considering node speed and multicast group size.
ConclusionsIn a static network, DMEM is superior to alternative algorithms for medium and large multicast groups.Measures heuristics, but major contribution is on dynamic networkDMEM is efficient in reducing energy utilizationAES provides significant value relative to base caseSHO is mostly redundant when using AESDMEM proven correct for maintaining tree structure using localized operations
CritiqueGraphs are not presented in such a way to visually support the analysise.g., authors require visual comparison of separate charts to compare AES and SHO, rather than presenting a single chartIs it scalable? Authors indicate that AES becomes saturated; this seems to occur rapidly in large networks even at slow speed.Authors indicate that it is scalable with regard to mobility but AES saturation seems to put this in question, as do some of their comments right before the conclusionIf scalability is an issue, possible approaches to address it would have been welcomeDo the arbitration performed by the source node along with the broadcast approach amount to centralization that reduces scalability and creates a bottleneck?