David E. Culler University of California, Berkeley

1. Wireless Embedded InterNetworkingFoundations of Ubiquitous Sensor Networks- Trickle -Polite Reliable Responsive Dissemination and Consistency David E. Culler University of California, Berkeley WEI short course - L9 trickle

2. 2 2 2 2 1 1 2 Network wide communication- Flood 0 WEI short course - L9 trickle

3. The Problem • Everybody responds! Ni, S.Y., Tseng, Y.C., Chen, Y.S., Sheu, J.P.: The broadcast storm problem in a mobile ad hoc network. MobiCom'99 WEI short course - L9 trickle

4. Flood Dynamics • Experimental Setup • 13x13 grid of nodes • separation 2ft • flat open surface • Identical length antennas, pointing vertically upwards. • Fresh batteries on all nodes • Identical orientation of all nodes • The region was clean of external noise sources. • Range of signal strength settings • Log many runs Ganesan, Krishnamachari, Woo, Culler, Estrin and Wicker, Complex Behavior at Scale: An Experimental Study of Low-Power Wireless Sensor Networks , UCLA Computer Science Technical Report UCLA/CSD-TR 02-0013 WEI short course - L9 trickle

5. Recast the problem • The goal is NOT to flood • The goal is to bring the network to a new consistent state • all nodes have the same piece of information • All nodes receive the same command • All nodes form a spanning tree • DHCP delegation • Multihop Router Advertisements • Respond rapidly to a change • Quiesce to very low communication rate • Never stomp on each other • High scalability • Extent AND density WEI short course - L9 trickle

6. A first step • Grow the tree slowly • Avoid Contention at every transmission • Avoid Redundant Transmissions • Adapt to huge range of density • Make sure it eventually gets to everyone • Even if they are not listening • Or arrive late • With very simple mechanism WEI short course - L9 trickle

7. Trickle – better than flood • Want the communication rate per unit area to be constant, regardless of the density of nodes • Lots of nodes, transmit infrequently • Few node, transmit more frequently • Nodes listen before transmitting • Estimate density based on how many nodes you hear from • Arrival during timer wait extends timer • If new value is disseminated by others, no need for you to transmit it. • Increase delay over time so ambient rate approaches zero. • Shorten delay when new epoch appears. WEI short course - L9 trickle

8. Epidemic NW protocols • Goal: scalable, robust communication algorithms that adapt to changing conditions with little state or protocol • Basic operation: • From time to time (based on local state and what you’ve heard) transmit a packet of information to whomever hears the message • From time to time, hear a packet which causes an update to local state • Continuous process to ensure full reliability • Adapt to density, coverage, interference, loss, schedule, … WEI short course - L9 trickle

9. 2 2 2 2 1 1 2 Trickle – till consisten 0 WEI short course - L9 trickle

10. Solution: Trickle • “Every once in a while, broadcast what data you have, unless you’ve heard some other nodes broadcast the same thing recently.” • Behavior (simulation and deployment): • Maintenance: a few sends per hour • Propagation: less than a minute • Scalability: thousand-fold density changes • Instead of flooding a network, establish a trickle of packets, just enough to stay up to date. • As long as each node communicates with others, inconsistencies will be found • Either reception or transmission is sufficient WEI short course - L9 trickle

11. Algorithm • Define a desired detection latency, t • Choose a redundancy constant k • k = (receptions + transmissions) • In an interval of length t • Trickle keeps the rate as close to k/t as possible • Choose timer t random in (t/2, t] • If inconsistent broadcast is heard before t, reset t to tmin. • If c < k consistent broadcasts are heard by t, broadcast • Otherwise suppress and double t up to tmax. • When there is nothing new to say, stay quiet WEI short course - L9 trickle

12. Example: K=1 WEI short course - L9 trickle

13. Work is logarithmic with loss rate WEI short course - L9 trickle

14. Short-Listen effect – why t/2 • With unsynchronized intervals and no min, some nodes get small t and broadcast even though they are hearing enough to suppress WEI short course - L9 trickle

15. Impact of listen-only period WEI short course - L9 trickle

16. Numerous Applications • Eliminates the “voodoo constants” in advertisement, route update, and the like. • Extends to dissemination of large object WEI short course - L9 trickle

17. Request Maintain Transmit Robust OTA Programming • Every byte must (eventually) be correctly received by all nodes! • Reliable Pipelined Epidemic Distribution of series of pages • Constrained storage hierarchy • Packet (32 bytes) << RAM (4K) << program (128K) < external flash (512K) • Lossy links, Critical Contention • Density-aware • Robust to asymmetric links • Dynamic adjustment of advertisements • Minimize set of concurrent data broadcasts • Spatial multiplexing • Page Advertise, Request/Fix, Xfer • Density-aware suppression and snoop on each • Packet CRC + Page CRC • 159 Byte memory footprint flash … WEI short course - L9 trickle

18. OTA Programming • Learn about the environment after deployment • sensing range, network characteristics, etc. WEI short course - L9 trickle

19. OTA Programming • Learn about the environment after deployment • sensing range, network characteristics, etc. WEI short course - L9 trickle

20. OTA Programming • Learn about the environment after deployment • sensing data, network characteristics, etc. • Embedded nature of sensor networks • Network scales reaching thousands of nodes • A necessity in debugging and testing cycle WEI short course - L9 trickle

21. Program 0101010101010101011010101101010101010101 What is Deluge? • A reliable data dissemination protocol for program images over a multihop network. • Combined with a bootloader (TOSBoot)  Network Programming WEI short course - L9 trickle

22. Data Representation • Program divided into pages, each consisting of Npackets. Program 101 110 110 010 010 000 101 111 000 011 Packets 1 2 3 4 N • Reduced RAM requirements • Allows for spatial multiplexing WEI short course - L9 trickle

23. How Does Deluge Work?(Glossing over many details) • Nodes periodically advertise • Suppress similar advertisements I only have version 1. Version 2here. I only have version 1. WEI short course - L9 trickle

24. How Does Deluge Work?(Glossing over many details) • Neighboring nodes request data • Suppress similar requests Send mepage 1! Send me page 1! WEI short course - L9 trickle

25. How Does Deluge Work?(Glossing over many details) • Requested data is broadcast Packet 12 of page 1! WEI short course - L9 trickle

26. How Does Deluge Work?(Glossing over many details) • Dropped packets are NACKed Repeat packet 4of page 1! Repeat packet 32of page 1! WEI short course - L9 trickle

27. How Does Deluge Work?(Glossing over many details) • Dropped packets are sent again Packet 4 of page 1! WEI short course - L9 trickle

28. How Does Deluge Work?(Glossing over many details) • Advertise for propagation to next hop Version 2here. I only have version 1. WEI short course - L9 trickle

29. Spatial Multiplexing • Propagate in “waves” • Exploit limited radio range for concurrent broadcasts. • Reduced completion time • o(d + Sobj) vs. o(d *Sobj) Page 1 Page 0 WEI short course - L9 trickle

30. Epidemic Propagation • Epidemic propagation from one source WEI short course - L9 trickle

31. Epidemic Propagation • Epidemic propagation from one source or many WEI short course - L9 trickle

32. Deluge Features • Epidemic propagation from one source or many • Continuous propagation effort by all nodes • Turn on/off radios at will • Reach nodes with intermittent connectivity Will find a path if it exists • Aggressive message suppression • Scales with density • Ultra low quiescent traffic WEI short course - L9 trickle

33. Program Name Compile Time UserID Hostname Platform ProgA ProgB ProgC 0101010101010101011010101101010101010101 0101010101010101011010101101010101010101 0101010101010101011010101101010101010101 CRC CRC CRC CRC CRC CRC CRC CRC CRC 0101010101010101011010101101010101010101 CRC CRC CRC CRASH! Deluge Features • Management • Multiple program images • Image metadata • User confirmation on expensive operations • Minimize operator error • Robustness • Redundant CRCs • Golden Image with write protect • Load Golden Image • Watchdog trigger • Golden gesture • TOSBoot • TOSBoot as isolated code • Verify CRCs • Verify system voltage WEI short course - L9 trickle

34. Deluge - Lessons Learned • Advantages • Ease of reprogramming 100’s-1000’s of nodes • Does not erase node IDs • Golden Image is immensely useful • Quickly switch between images • More reliable than uisp or msp430-bsl • Deluge over 802.15.4 more efficient that 802.11! • Disadvantages • Ease of reprogramming 100’s-1000’s of nodes WEI short course - L9 trickle

35. Take-aways • Many embedded network applications will be built as “application overlays” on UDP • Use trickle as a “polite gossip” adaptive congestion control. • Additional optimizations through scheduling WEI short course - L9 trickle