VLM 2 : A Very Lightweight Mobile Multicast System For Wireless Sensor Networks

1. 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 2003 Speaker: earl

2. Outline • Introduction • Protocol specification • Performance analysis • Conclusions Earl

3. Introduction-sensor uer sensor nodes Earl sensor field

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

5. Introduction-sensor Earl

6. 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 VLM2 runs at network layer Network Topology temperature location information T L Base station B T L T T L L L T L Earl

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

8. Packet Format source immediate source seqno dest route TTL DtB length payload (variable length) checksum Earl

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

10. DTB_UPDATA DtB= 2 DtB = 2 DtB = 3 Distance to Base T • 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 L B T L T T L DTB_REPLY L L DtB = 20 T L Earl

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

12. Base to Nodes Routing T • 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 L B T L Check downstream groups list T T L L L T Subscribe packet L 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 • VLM2 provides multicast service appropriate for sensor networks • Building multicast directly into network layer allows for very lightweight implementation Earl