1 VLM 2 : 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 2003 Speaker: earl

Earl 2 Outline Introduction Protocol specification Performance analysis Conclusions

Earl 3 Introduction-sensor sensor nodes sensor field uer

Earl 4 Introduction-sensor Resource constraints power (battery lift) Memory and CPU speed Simple communications devices Small form

Earl 5 Introduction-sensor

Earl 6 Network Topology Network 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 nodes VLM 2 runs at network layer T BT L T T L T L L L L temperature Base station location information

Earl 7 Type of Service Basic routing services Unicast node to base (upstream) Muliticast base to nodes (downstream) Best-effort network Automatic node naming Automatic mobility and fault recovery T BT L T T L T L L L L location information temperature Base station

Earl 8 Packet Format source immediate source seqnodest routeTTLDtBlength payload (variable length) checksum

Earl 9 Name Assignment When a node startup, send name request to basestation NAME_REQUEST packet is reserved address Base station assigns network id by NAME_ASSIGN packet Reply packet includes global id of intended receiver T BT L T T L T L L L L location temperature Base station NAME_REQUEST NAME_ASSIGN

Earl 10 Distance to Base Nodes maintain hop count to base station At 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 T BT L T T L T L L L L DtB = 20 DtB = 2DtB = 3DtB = 2 DTB_REPLY DTB_UPDATA

Earl 11 Node to Base Routing Unicast upstream routing (sender ’ s DtB – hops taken) v.s. (intermediate node ’ s DtB) If >=, then forward packet Otherwise ignore packet T BT L T T L T L L L L DtB=2 L DtB=5 TTL=18 Hops taken =2

Earl 12 Base to Nodes Routing Multicast downstream Nodes 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 T BT L T T L T L L L L Subscribe packet Check downstream groups list

Earl 13 Performance analysis The network consisted of ten nodes and a basestation At 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 member The basestation periodically sends a data packet to each multicast group (downstream)

Earl 14 Performance analysis

Earl 15 Performance analysis

Earl 16 Conclusions VLM 2 provides multicast service appropriate for sensor networks Building multicast directly into network layer allows for very lightweight implementation