Collection Tree Protocol

1. Collection Tree Protocol ACM SenSys’09 Slides revised from Omprakash Gnawali

2. Outline • Introduce • Control Plane (two principles of CTP) • Datapath validation • Adaptive beacons • Data Plane • Evaluation

3. Data collection protocols • Three phases in handling sensory data in IoT: • Sensory data acquisition • Sensory data collection • Sensory data computation • CTP is a kind of data collection protocol • Base Requirement • Reliability: > 90% of packet • Robustness: Operate without tuning or configuration • Efficiency: Use minimum of transmissions • Hardware Independence: no specific chip feature

4. CTP sink • Is a protocol that computes routes from sensor to one or more sinks(base stations) • Build and maintains minimumcost tree(s) with the sink(s) as root • A distance vector protocol

5. Parent Selection b e 10 • Minimize transmission costs(ETX) • Every node maintains an estimate of the costs of a route to sink 3 1 2 d sink a 4 3 2 2 2 f 3 c e: EXT(e) = 1 f: EXT(f) = 2 d: 2 + EXT(e) < 2 + ETX(f) b: 10 + EXT(e) c: 3 + EXT(f) a: 4 + EXT(d) < 3+ EXT(b) and 2 + EXT(c)

6. Challenges for data collection • Link dynamics • Links can be highly dynamic, particularly in the 2.4 GHz frequency space • Wireless links can change in the order of a few hundred milliseconds • Routing inconsistencies • Rapid topology change can cause routing inconsistencies and route loops, cause packet loss in the data plane

7. Common Architecture Control Plane Data Plane Routing Engine Application Fwd Table Link Estimator Forwarding Engine Link Layer

8. CTP Noe • Enable control and data plane interaction • Two mechanisms for efficient and agile topology maintenance • Datapath validation • Adaptive beaconing Control Plane Data Plane Routing Engine Application Link Estimator Forwarding Engine Link Layer

9. Outline • Introduce • Control Plane(two principles of CTP) • Datapath validation • Adaptive beacons • Data Plane • Evaluation

10. Routing Consistency • Next hop should be closer to the destination • Maintain this consistency criteria on a path • Inconsistency due to stale state ni+1 nk ni

11. Routing Inconsistency X • Cost does not decrease • Route inconsistency can cause routing loops 3.2 8.1 C 4.6 B A D 6.3 5.8

12. Datapath validation • Use data packets to validate the topology • Inconsistencies • Loops • Receiver checks for consistency on each hop • Transmitter’s cost is in the data packet header

13. Datapath validation • Datapath validation • Cost in the packet • Receiver checks • Inconsistency • Larger cost than on the packet • On Inconsistency • Don’t drop the packets • One beacon interval pause in forwarding • Immediately Signal the control plane 3.2 < 4.6? 8.1 < 4.6? X 3.2 8.1 C 4.6<5.8? 4.6 < 6.3? 5.8 8.1 4.6 4.6 6.3 4.6 B 5.8 < 8.1? A D 6.3 5.8

14. Outline • Introduce • Control Plane(two principles of CTP) • Datapath validation • Adaptive beacons • Data Plane • Evaluation

16. How Fast to Send Control Beacons? • Control beacons are broadcasts • Other protocols typically use periodic beacons to update network topology and link estimates • Using a fixed rate beacon interval • Faster rate lead to higher cost • Slower rates lead to less agility • Agility-efficiency tradeoff • Agile+Efficient possible? • CTP use Trickle Algorithm[Levis, 2004]

17. Increasing interval Reset interval Control Traffic Timing • In CTP: • Start with lowest intervals of 64ms • When interval expires double it up to 1 hour • Reset to lowest interval when inconsistent • Reset the interval on three events • Receive packet ETX <= self ETX • Its routing cost decreases Significantly • It receives a packet with P bit set TX

18. Adaptive vs Periodic Beacons Total beacons / node 1.87beacon/s 0.65beacon/s Time (mins) Tutornet Less overhead compared to 30s-periodic

19. Node Discovery A new node introduced Total Beacons Path established in < 1s Tutornet Time (mins) Efficient and agile at the same time

20. Outline • Introduce • Control Plane(two principles of CTP) • Datapath validation • Adaptive beacons • Data Plane • Evaluation

21. Data Plane Design • Queueing discipline • Per-client queueing [top-level] • each client may have one outstanding packet • achieves better fairness than a shared queue • Hybrid send queue [lower-level] • contains both route-through and locally-generated traffic • duplicate packets are dropped [i.e., not inserted in the queue]

22. Data Plane Design • Transmit Timer • Self-interference between packets • Rate Control: delay the transmission of packets: randomized between (1.5, 2.5) packet times

23. Data Plane Design • Transmission cache • For each transmitted packet insert(origin, seqNo, THL) • Determine if a packet is duplicate

24. Outline • Introduce • Control Plane(two principles of CTP) • Datapath validation • Adaptive beacons • Data Plane • Evaluation

25. Experiments • 12 testbeds • 20-310 nodes • 7 hardwareplatforms • 4 radiotechnologies • 6 link layers Variations in hardware, software, RF environment, and topology

26. Reliable, Efficient, and Robust False ack Retransmit High end-to-end delivery ratio(but not on all the testbeds!)

27. Reliable, Efficient, and Robust

28. Reliable, Efficient, and Robust CTP Noe Tutornet Low data and control cost

29. Reliable, Efficient, and Robust Tutornet No disruption in packet delivery Delivery Ratio 10 out of 56 nodesremoved at t=60 mins Time (mins)

30. Reliable, Efficient, and Robust Nodes reboot every 5 mins Routing Beacons ~ 5 min Tutornet Delivery Ratio > 0.99 High delivery ratio despite serious network-wide disruption(most loss due to reboot while buffering packet)

31. Summary of Results • 90-99.9% delivery ratio • Testbeds, configurations, link layers • Compared to MultihopLQI • 29% lower data delivery cost • 73% fewer routing beacons • 99.8% lower loop detection latency • Robust against disruption • Cause for packet loss vary across testbeds

32. Thank you!