Group Communications in Group Communications in Mobile Ad hoc NetworksMobile Ad hoc Networks

Jian LiJian Lihttp://networks.cs.ucdavis.edu/~lijian/slides/ecs257/http://networks.cs.ucdavis.edu/~lijian/slides/ecs257/

ReferencesReferencesP. Mohapatra, C. Gui, and J. Li. Group P. Mohapatra, C. Gui, and J. Li. Group Communications in Mobile Ad hoc Communications in Mobile Ad hoc Networks. IEEE Computer Magazine, Networks. IEEE Computer Magazine, Feb. 2004, pp. 52-59.Feb. 2004, pp. 52-59.

AgendaAgendaIntroductionIntroductionGroup Comm. ModelsGroup Comm. Models– MulticastingMulticasting– BroadcastingBroadcasting– Geocasting & AnycastingGeocasting & AnycastingCommon IssuesCommon Issues– ReliabilityReliability– Energy efficiencyEnergy efficiency– QoSQoS– SecuritySecurityConcluding RemarksConcluding Remarks

ManetManetNo infrastructure, ad hoc deploymentNo infrastructure, ad hoc deploymentNodes are free to move aroundNodes are free to move aroundWireless mediaWireless mediaMultihop routingMultihop routingVarious potential applicationsVarious potential applications– Group Communication is a critical Group Communication is a critical

building blockbuilding block

Group Comm. In ManetGroup Comm. In ManetDiffer from wireline networksDiffer from wireline networksWireless medium has varying Wireless medium has varying characteristicscharacteristics– Signal strength and propagation Signal strength and propagation

fluctuation w.r.t time and placefluctuation w.r.t time and placeNode mobility is unpredictableNode mobility is unpredictable– Changing topologyChanging topologyLimited resourcesLimited resources– Bandwidth, battery, CPU, memory, etcBandwidth, battery, CPU, memory, etc

Multicasting: Exploiting Multicasting: Exploiting Characteristics of ManetCharacteristics of Manet

Variable topologyVariable topology– Mesh-based protocolsMesh-based protocolsSoft-state & state aggregationSoft-state & state aggregation– Stateless multicastStateless multicastKnowledge of locationKnowledge of location– Location aided multicastLocation aided multicastRandomnessRandomness– Gossip-based multicastGossip-based multicast

Mesh-based ProtocolsMesh-based ProtocolsCore-Assisted Mesh Protocol (CAMP)Core-Assisted Mesh Protocol (CAMP)On-demand Multicast Routing On-demand Multicast Routing Protocol (ODMRP)Protocol (ODMRP)

CAMP: FeaturesCAMP: Features

Assume the underlying unicast routing Assume the underlying unicast routing protocol can provide correct distance to protocol can provide correct distance to known destination within a finite timeknown destination within a finite timeEnsure reverse shortest paths from Ensure reverse shortest paths from receivers to sources are part of a group’s receivers to sources are part of a group’s meshmeshAnchorAnchor– Neighbor nodes which are required to re-Neighbor nodes which are required to re-

broadcast any non-duplicate data packets they broadcast any non-duplicate data packets they receivereceive

CAMP: OperationCAMP: OperationConsult a neighbor tableConsult a neighbor tableConfirm membership via a CAMP-UPDATEConfirm membership via a CAMP-UPDATEOtherwise, JOIN-REQUEST packet is sentOtherwise, JOIN-REQUEST packet is sentJOIN-ACK receivedJOIN-ACK receivedReceiver nodes periodically reviews packet Receiver nodes periodically reviews packet cache to determine whether it is receiving cache to determine whether it is receiving data packets from those neighbors are on data packets from those neighbors are on the reverse shortest paththe reverse shortest pathNodes periodically choose their “anchors”Nodes periodically choose their “anchors”

ODMRP: FeaturesODMRP: FeaturesA Mesh-Based & On-Demand protocolA Mesh-Based & On-Demand protocolForwarding group conceptForwarding group concept– A group of nodes participating in A group of nodes participating in

multicast packet forwardingmulticast packet forwardingRobustness to host mobilityRobustness to host mobilityScalability to large number of nodesScalability to large number of nodesProvide path redundancyProvide path redundancyJoin table, Member tableJoin table, Member table

ODMRP – Protocol OverviewODMRP – Protocol OverviewJoin tableJoin table– The table broadcasted by each multicast The table broadcasted by each multicast

receiver and forwarding node to establish / receiver and forwarding node to establish / update group memberships and routesupdate group memberships and routes

Member tableMember table– The table maintained by multicast receivers The table maintained by multicast receivers

containing information of multicast sources containing information of multicast sources for each multicast group it is associated withfor each multicast group it is associated with

Suffers from excessive control packet Suffers from excessive control packet transmission overheadtransmission overheadControl PacketsControl Packets– JOIN-REQ, JOIN-TABLEJOIN-REQ, JOIN-TABLE

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State MaintenanceState MaintenanceUnconstrained stateUnconstrained state– Both member and non-memberBoth member and non-memberConstrained state Constrained state – Through abstraction via application-Through abstraction via application-

layer multicasting layer multicasting – By aggregation via hierarchical By aggregation via hierarchical

multicastingmulticastingZero stateZero state– No state information is maintainedNo state information is maintained

Location Aided MulticastingLocation Aided MulticastingODMRP ODMRP – can utilize location and mobility can utilize location and mobility

information to estimate route lifetimeinformation to estimate route lifetimePosition Based Multicasting (PBM)Position Based Multicasting (PBM)– Greedy forwardingGreedy forwarding– Perimeter forwardingPerimeter forwarding

Gossip-based MulticastingGossip-based MulticastingAnonymous Gossip (AG)Anonymous Gossip (AG)Route Driven Gossip (RDG)Route Driven Gossip (RDG)

Anonymous GossipAnonymous GossipEnhancement technique atop any Enhancement technique atop any tree- or mesh-based protocoltree- or mesh-based protocolA member node does not know any A member node does not know any other member nodesother member nodesTwo phasesTwo phases– Data packets are multicast to the groupData packets are multicast to the group– Anonymous gossip in the background: Anonymous gossip in the background:

attempt to recover lost data packets attempt to recover lost data packets from other group membersfrom other group members

Route Driven Gossip (RDG)Route Driven Gossip (RDG)Rely on an underlying unicasting Rely on an underlying unicasting protocol for guidanceprotocol for guidanceCSMA/CA MAC (e.g., IEEE 802.11) CSMA/CA MAC (e.g., IEEE 802.11) provides reliable, sequenced single-provides reliable, sequenced single-hop unicast by RTS/CTShop unicast by RTS/CTS––Data/Ack Data/Ack handshake sequencehandshake sequence

Data packets, digests of missing packets, view

RDG: Data Structures and OperationsRDG: Data Structures and Operations

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Operations

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BroadcastingBroadcastingImportant building block for on Important building block for on demand route discoverydemand route discoveryCategorizationsCategorizations– Simple floodingSimple flooding– Probability based broadcastingProbability based broadcasting– Area-based broadcastingArea-based broadcasting– Neighbor knowledge based broadcastingNeighbor knowledge based broadcasting

Self pruningSelf pruningInformation:Information:– Hello message (1-hop)Hello message (1-hop)– Piggyback adjacent node list in broadcast Piggyback adjacent node list in broadcast

packetspackets (2-hop)(2-hop)– Store adjacent node list in cacheStore adjacent node list in cacheForwarding node decision:Forwarding node decision:– Node Node vvjj who receives the packet from who receives the packet from vvii checks checks

whether the set whether the set NN((vvjj)-N()-N(vvii)-{)-{vvii} is empty} is empty

vi vj

GeocastingGeocastingGroup membership is defined by Group membership is defined by geographical coordinatesgeographical coordinatesSuitable for delivering messages to Suitable for delivering messages to every node in a specific areaevery node in a specific areaExamplesExamples– Flooding based geocastingFlooding based geocasting– Route based geocastingRoute based geocasting

LBM: Flooding based GeocastingLBM: Flooding based GeocastingScheme IScheme I

LBM: Flooding based GeocastingLBM: Flooding based GeocastingScheme IIScheme II

Route Based Geocasting: GeoTORARoute Based Geocasting: GeoTORA

Based on TORABased on TORA– Temporally Ordered Routing AlgorithmTemporally Ordered Routing Algorithm– Destination-orientedDestination-oriented directed acyclic directed acyclic

graphs (DAGs)graphs (DAGs)– Uses “Link-Reversal” techniques to Uses “Link-Reversal” techniques to

maintain DAGsmaintain DAGsGeoTORAGeoTORA– Modify TORA to do anycastingModify TORA to do anycasting– Modify further to do geocastingModify further to do geocasting

TORA – Link ReversalTORA – Link ReversalWhen a node has When a node has nono downstream links, it downstream links, it reversesreverses the direction of one or more links the direction of one or more links

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Anycasting with Modified TORAAnycasting with Modified TORAIn GeoTORA, the TORA protocol is modified In GeoTORA, the TORA protocol is modified to be able to perform anycastto be able to perform anycast– AnycastAnycast - deliver to - deliver to any oneany one node in the node in the anycast anycast

groupgroup– ProtocolProtocol

Maintain a DAG for Maintain a DAG for eacheach anycast groupanycast groupMake each member of the anycast group a Make each member of the anycast group a sinksinkNo logical direction for links between sinksNo logical direction for links between sinksFollowing the directed links results in packets being Following the directed links results in packets being delivered to delivered to any oneany one sinksink

Anycasting ExampleAnycasting Example

Anycast group = {A, B, C, D},DAG structure for the anycast group

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Geocasting using Modified AnycastingGeocasting using Modified AnycastingSmall variation on the previous Small variation on the previous anycastinganycasting– All nodes within a specified All nodes within a specified

geocasting region are made sinksgeocasting region are made sinks– Maintain a single DAG for a given Maintain a single DAG for a given

geocast groupgeocast group– Source first performs an Source first performs an anycastanycast

to the geocast group membersto the geocast group members– When a group member receives When a group member receives

a packet, a packet, it it floodsfloods it within the it within the geocast region geocast region

Geocast Region

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Common IssuesCommon IssuesReliabilityReliabilityEnergy efficiencyEnergy efficiencyQualify of serviceQualify of serviceSecuritySecurity

ReliabilityReliabilityClustering structure + Clustering structure + acknowledgement along reversal acknowledgement along reversal pathpathProbabilistic reliabilityProbabilistic reliability– RDG approachRDG approachReliable MAC supportReliable MAC support– BMW protocolBMW protocol

Energy Efficiency: RoutingEnergy Efficiency: RoutingWireless transmissions are major Wireless transmissions are major energy consumersenergy consumersProtocols attempt to reduce Protocols attempt to reduce forwarding set of nodesforwarding set of nodesBroadcast Incremental Power (BIP) Broadcast Incremental Power (BIP) protocolprotocol– Add new node one at a timeAdd new node one at a time– Increment transmission power to add Increment transmission power to add

one new nodeone new node

Energy Efficiency: MACEnergy Efficiency: MACReception and idle-listening also Reception and idle-listening also major energy consumersmajor energy consumersPower aware MACPower aware MACExample: PAMAS MACExample: PAMAS MAC– Separate signaling channelSeparate signaling channel– Turn off nodes when appropriate Turn off nodes when appropriate – Overhear RTS/CTS to determine when to Overhear RTS/CTS to determine when to

sleep, for how long, sleep, for how long, – What to do if destination node is asleep?What to do if destination node is asleep?

Energy Efficiency: Wakeup Energy Efficiency: Wakeup Mechanisms Mechanisms

On-demand wakeupOn-demand wakeup– Use a wakeup toneUse a wakeup toneScheduled wakeupScheduled wakeup– Require synchronization among nodesRequire synchronization among nodesAsynchronous wakeupAsynchronous wakeup– Guaranteed overlap active time over a Guaranteed overlap active time over a

certain durationcertain duration

Quality of ServiceQuality of ServiceA set of measurable service attributesA set of measurable service attributes– Bandwidth, delay, loss rateBandwidth, delay, loss rate– Power consumption, service coveragePower consumption, service coverageQoS support are desirable in various QoS support are desirable in various applicationsapplicationsResource limitation and variability add to Resource limitation and variability add to the need of QoS supportthe need of QoS supportQoS aware group comm. Remains an open QoS aware group comm. Remains an open problemproblem

SecuritySecurityBroadcast medium is more prone to active Broadcast medium is more prone to active and passive attacksand passive attacksDynamic nature of Manet adds to the Dynamic nature of Manet adds to the challengeschallenges– Lack of trusted centralized infrastructureLack of trusted centralized infrastructure– Ad hoc linkAd hoc link– Group comm. models are differentGroup comm. models are different– Light weight requirementLight weight requirementAlso an open problemAlso an open problem

Concluding RemarksConcluding RemarksGroup Communication is essential for Group Communication is essential for ad hoc networksad hoc networksMore efforts are neededMore efforts are needed– MACMAC– TransportTransport– QoSQoS– SecuritySecurity