Research in Wireless Ad-Hoc Sensor Networks: Routing and data transport protocols

1. Edo Biagioni presenting work done in collaboration with Kim Bridges and Brian Chee, and Shu Chen, Wei Chen, Lisa Fan, Dan Morton, Ben Roy, Yihua Xie April 23, 2004 Research in Wireless Ad-Hoc Sensor Networks:Routing and data transport protocols

2. Wireless Ad-Hoc networks • Each node has a radio transceiver • Each node generates and receives data • Each node must also transport data for other senders • Node distribution is planned or random • Some issues: where to send data (routing)? how to send data efficiently? • Could be mobile (MANet), fixed, or both

3. Sensor Networks • sensors are low-power (often battery powered), deployed for long periods in remote locations • data can be retrieved manually, but it is better to do so automatically over a network • some sensor networks might be very large, so scalability is an issue

4. Ad-hoc Wireless Sensor Networks • monitor remote sites over extended periods at low cost: science, agriculture, tourism, military applications • e.g. study endangered plants to find out why they are endangered • e.g. monitor crops to determine when to water or apply fertilizer • environmental monitoring, and also images, and intrusion or herbivore detection

5. Mobile Ad-Hoc Networks • Nodes are assumed to be moving continuously and at random • must minimize routing overhead • many protocols, including DSR, AODV • few applications: UAVs, vehicles • little study (so far) on performance e.g. transmitting TCP content

6. conserve power, e.g. by “sleeping” re-route around nodes that have failed and nodes that are congested deal sanely with disconnection support encryption, heterogeneity Challenges in WirelessAd-Hoc Sensor Networks • make sense of large amounts of data: visualization • minimize the data transmitted: model generation, distributed event detection

7. Protocol Design • efficient, reliable, high throughput, low delay (not unusual) • low power requires: low delay to completion (low packet delay and high throughput) and high efficiency (do not transmit unnecessary packets) • low power also requires synchronization • baseline is flooding broadcast

8. Wireless Ad-Hoc Sensor Network Protocol Examples

9. WSNs and MANets • Wireless sensor network nodes are even lower power than MANet nodes • nodes may be simpler than MANet nodes • no motion (fixed) or limited motion (fixed-mobile) • worth discovering and using good routes • nodes may know position

10. building an environmental sensor network: PODS • http://www.pods.hawaii.edu • high resolution images • sunlight, temperature, rain • V0: wired sensor boards • V1: PC-104, PC-compatibles running Linux, 802.11 for communications, BasicStamp power control board • V2: Compaq Ipaq, Linux, 802.11 • V3: in the planning stages

11. Multipath On-Demand Routing • Shu Chen • protocol to carry IP packets • establish routes on demand only: send a broadcast, reply along the reverse path • may be multiple routes to a destination: using all of them in turn provides load balancing, redundancy, and reliability • put routes on probation if they fail: keep trying them for a little while

12. MOR performance • faster transmission of fixed payload (over TCP) than DSR, AODV • multipath with reliability layer effectively routes around congestion • podr: long-term uninterrupted service in deployed pods, also works under ns-2 • hop-by-hop ack (e.g. 802.11) to decide whether to retransmit on this hop

13. Lusus Protocol • Dan Morton • Really low power is only available on really simple processors such as PIC and AVR, with < 1KB RAM, small programs • Need a really simple protocol: • only send data (not IP) • only send to nearest base station • hop-by-hop, not end-to-end reliability • short packets, very low overhead

14. Lusus Techniques • base stations regularly broadcast synchronization messages • each retransmission increases the distance • only send to nearest base station • data from different sources may be combined enroute • messages are retransmitted if there is no ack from the next hop • implementation is in progress

15. Sensor Network Data Transmission Protocol:SNDT • Lisa Fan and Yihua Xie • IP over MOR, can use ssh, but: • ssh has high overhead for small transfers • want connectionless, secure, and efficient protocol • use UDP, with explicit acks to minimize the overhead • rate-limit transmission to avoid generating congestion

16. SNDT security issues • initial secret is part of a node config • authentication to prevent bad data • encryption: data and commands should not be visible without the key • initial secret is leveraged to exchange session keys • nodes send data to base station • base station sends commands and configuration to nodes

17. SNDT open issues • distributing time must be done quickly, but authentication takes time • measuring RTT is hard if decryption is needed before ack • each key must have an ID, which must be present on packets: does this make the attacker's life easier? • maintaining session keys, and recovering from reboots, can be challenging

18. Distributed Route Table (DiRT) • Ben Roy • routing or forwarding to many hosts requires large routing tables • distribute the routing tables so each node has at most O(log(N)) routes, yet every node can reach every other • node IDs are set to be 0..N-1 • each node i has source routes for i±1, i±2, i±4, i±8, etc.

19. DiRT routing • for node i, if the destination D is in the routing table, send to it • otherwise, compute =D-i, the difference in addresses • for each destination j in i's routing table, find the one with the smallest , (will have at least one) and send to that node • packets require at most O(log(N)) legs, each of maximum length the diameter of the network

20. Distributed Routing Tables:Open Issues • Are there better ways to distribute large routing tables? • for example, among neighbors • if DiRT is used, what is the likelyhood of packets being rerouted along a better route encountered along the way? • analysis: how much better are we really doing than broadcast? • how does network geometry affect that?

21. Geographic Routing • each node knows its own position, e.g. via GPS • if the destination is identified by position, simply route to the neighbor nearest the destination • can cause routing loops, e.g. at dead ends • many refinements, but no good solutions

22. Geometric Routing: GEO • geographic routing works fine as long as the network is densely connected • only problems are at the edges of a connected area • communicate the geometry of the connected areas, and route around any “holes” • all the nodes on an edge must keep track of the geometry of that edge

23. GEO implementation • Wei Chen • on the ns-2 simulator • complex topologies simulated • many nodes simulated • scalability is good

24. Related work • Lots of protocols and ideas: Berkeley motes, diffusion, Zigbee • The Capacity of Wireless Networks, by Gupta and Kumar – there are limits to how much we can send • SPINS: security protocols for sensor networks, by Perrig et al. --practical secure transmission on tiny processors • http://www2.ics.hawaii.edu/~esb/prof/pub/ijhpca02.html, Biagioni and Bridges

25. Interesting Issues • new network, e.g. IP assumptions don't work, connectivity may be intermittent, and it is OK to design from scratch • low power operation is required, but there may be different ways to achieve it: physical layer, data link, network layer • should there ever be networks where data is unencrypted? How can automatic encryption be set up effectively?

26. More issues • Are there better ways of routing? • Are there reasonable “standard” benchmarks for routing? • Many problems to be solved: power aware routing, position determination, optimal node placement, architecture, operating system (e.g. TinyOS), scheduling, etc

27. Summary • Protocols to support goals of sensor network deployment: MOR, Lusus, SNDT, DiRT, GEO • building actual sensor networks to evaluate and motivate the ideas