1. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 1 NEST Retreat, Lake Tahoe, June 17-19 2002

2. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 2 End-to-end reliability Routing resilient to failures is needed for sensor networks –Random link or node failures –Patterned node failures –Fail-fast vs. Byzantine Traditional approach: TCP –End-to-end acknowledgements –Assumes the main source of loss in the network is congestion

3. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 3 End-to-end reliability Sensor networks –Major source of loss is due to packet loss, corruption, and collisions, not congestion –Retransmission over a lossy path is unlikely to be beneficial –Acknowledgements are likely to be lost as well (network links may be asymmetric) –Easy to send packets to the base station, but harder for base station to address individual nodes Simple solution: Periodic flooding –Expensive in terms of messages sent/power consumption

4. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 4 ARRIVE Design Goals Reliable (one-way) communication between nodes and the base station –Resilient against isolated and patterned node and link failures –Primary metric is event delivery ratio Limit the dependency on flooding Leverage the broadcast medium and high density of nodes Rely on localized information Basis for secure routing

5. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 5 Key Ideas A forward approach to end-to-end reliability –Avoidance vs. detection –Source multiple packets representing a single event –Promote diversity in the paths taken by these packets Probabilistic determination of the next hop –Weighted by an estimation of link reliability using implicit link layer acknowledgements Detect packet convergences to prevent packets from using the same nodes or links in their paths Passive participation –Neighboring nodes can help detect when a transmission has failed and take responsibility for forwarding the packet

6. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 6 Algorithm Use flooding once to assign each node a level, representing the number of hops to the base station –nodes are not assigned a parent For a node at level n, –Parents are those nodes within radio range with level n-1 –Neighbors are those nodes within radio range with level n

7. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 7 Algorithm Each node maintains a reputation history for each parent and neighbor –Estimation of link/node reliability –Ratio of packets relayed to packets sent (using implicit link acknowledgements) –Sliding window weighted with exponential decay 4 8 5 5 2 5 0 1 4 6 1 2 8 8 6 6 1286432168421weighting: # sent: # relayed: Reputation = (.5*128 + 1*64 +.4*32 +.66*8 +.5*4 + 1*2 + 1*1) / 255 = 0.58 more recent

8. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 8 Algorithm Forwarding probability –Each packet carries a forwarding probability to suggest if the next hop should be a parent or neighbor –The outgoing forwarding probability may be modified by each node Fanout –Number of packets corresponding to a single event sent by the sourcing node (k)

9. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 9 Algorithm Passive Participation A node may decide to passively accept packets with a different destination. For robustness, passively processing packets and forwarding them can assist in recovery from failures or dropped packets without end-to-end retransmission Threshold Processing: Nodes are filtered by reputation relative to a specified threshold. Convergences of packets representing the same event are detected, and previous recipients are discarded from consideration.

10. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 10 Algorithm Parent or Neighbor? Selection is randomly determined by the forwarding probability included in the received packet. Adjust Forward Probability Outgoing forwarding probability is altered according to the type (parent or neighbor) of the destination and distance from the sink. This process maintains a “beam” from source to sink. Destination Selection Each node is weighted by their reputation. The destination is randomly chosen from the available nodes remaining after threshold detection.

11. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 11 Algorithm Parameters Changing the Parameters Yields Different Algorithm Behavior: –Reputation History Currently a sliding window weighted exponentially Simpler methods may be possible via: –Link layer acknowledgements –Continuous weighted average –Alec Woo’s Max Reliable Path Routing

12. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 12 Algorithm Parameters Changing the Parameters Yields Different Algorithm Behavior: –Redefining the Pr[forward] Function We use: (limits pushing near the base) Or use level-independent pushing: –If forwarding: Lower forwarding probability by: »1/c * (Pr[f]) –If pushing: Raise forwarding probability by: »1/d * (1 – Pr[f]) –Intuitionally want 1/c << 1/d

13. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 13 Analysis : Basic Java Simulator Nodes are 90% reliable and fixed via random uniform distribution. Horrible performance for 1 sourced packet over all densities As sourced packets increase and density increases, reliability increases. Reliability of Multiple Sourced Packets

14. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 14 Passive Participation When a neighboring node observes that a packet hasn’t been relayed, it relays the packet (with some probability) by passively processing it For a graph with a density of 10 and 4 sourced packets (fanout): –A 5% chance of passively participating yields a 15% increase in event delivery to the base station A B C D E F

15. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 15 Ns-2 Experiments Alterations to the ns-2 simulator to model the motes’ radio model: –40kbps radio speed –802.11 MAC layer set in broadcast mode no link-layer ACKs –Current consumption of the RFM TR1000 included in model to monitor energy usage

16. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 16 Ns-2 : Patterned node failures Increasing fanout dramatically increases reliability “Network effects” Effect of Fanout with Patterned Failures

17. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 17 Ns-2 : Random Node Failures

18. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 18 Discussion Application of ARRIVE to other routing paradigms –eg: geographic routing Passive participation vs. link retransmission Security

19. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 19 Future Work Future work includes: –Further evaluation of destination selection Incorporation of new link layer acknowledgements Evaluation of Alec’s neighbor weighting method Probability adjustment algorithms –Analysis on Berkeley MICA platform Implementation exists, not debugged –Applying TDMA/Scheduling for low power operation (wrt passive participation) –Security Analysis

20. Monday, June 01, 2015 ARRIVE: Algorithm for Robust Routing in Volatile Environments 20 Conclusion Sensor network routing algorithms should leverage the broadcast medium. Packets should be sourced over both space and time. Probabilistic forwarding and maintaining neighbor reputations yield quick recovery to failures and misbehaving nodes. –Visualization!