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VLM2: A Very Lightweight Mobile Multicast System For Wireless Sensor Networks

Anmol Sheth, Brian Shucker and Richard Han

University of Colorado, Department of Computer Science

IEEE WCNC 2003Speaker: earl

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OutlineIntroductionProtocol specificationPerformance analysisConclusions

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Introduction-sensor

sensor nodessensor field

uer

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Introduction-sensorResource constraints power (battery lift) Memory and CPU speed Simple communications devices Small form

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Introduction-sensor

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Network TopologyNetwork is anchored by base station Base station assumed to

have greater resources than sensor nodes

Base station is “gateway” to larger networks and users

Then create a multicast group

Arbitrary topology of nodesVLM2 runs at network layer

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TL

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temperature

Base station

location information

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Type of ServiceBasic routing services Unicast node to base (upstream) Muliticast base to nodes (downstream)Best-effort network Automatic node namingAutomatic mobility and fault recovery

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location informationtemperature

Base station

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Packet Formatsource immediate

source seqno destroute TTL DtB length

payload (variable length)

checksum

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Name AssignmentWhen a node startup, send name request to basestation

NAME_REQUEST packet is reserved addressBase station assigns network id by NAME_ASSIGN packet Reply packet includes global id of intended receiver

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locationtemperature

Base station

NAME_REQUEST

NAME_ASSIGN

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Distance to BaseNodes maintain hop count to base stationAt startup, DtB set to uniform network TTL(=20 hops)DtB inferred from TTL of downstream traffic Equal or lower DtB triggers immediate update

Timeout increments DtB, solicits updates

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DtB = 20DtB = 2DtB = 3DtB = 2

DTB_REPLYDTB_UPDATA

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Node to Base RoutingUnicast upstream routing(sender’s DtB – hops taken) v.s. (intermediate node’s DtB) If >=, then forward packet Otherwise ignore packet T

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LDtB=2

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DtB=5TTL=18Hops taken=2

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Base to Nodes RoutingMulticast downstreamNodes send subscribe messages upstream to join multicast groups Forwarding nodes add

group to downstream groups list

Downstream packets forwarded if address is in downstream groups list

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Subscribe packet

Check downstream groups list

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Performance analysisThe network consisted of ten nodes and a basestationAt fixed intervals, each node sends a data packet to the basestation (upstream)At startup, each node joins one multicast group in which it is the only memberThe basestation periodically sends a data packet to each multicast group (downstream)

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Performance analysis

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Performance analysis

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ConclusionsVLM2 provides multicast service appropriate for sensor networksBuilding multicast directly into network layer allows for very lightweight implementation