1 Nancy Lynch Massachusetts Institute of Technology, CSAIL Workshop on Critical Research Areas in Aerospace Software MIT August 9, 2005 Virtual Node Layers

2 Collaborators: – Shlomi Dolev, Alex Shvartsman, Jennifer Welch, – Seth Gilbert, Sayan Mitra, Calvin Newport, Tina Nolte, – Limor Lahiani, Elad Schiller, – Matthew Brown, Mike Spindel

3 Virtual Nodes Small computers can be equipped with sensors, actuators, wireless communication. Potentially, people, robots, vehicles, could use this hardware to establish mobile ad hoc networks, coordinate in running applications. Examples: – Rescue workers in disaster areas – Soldiers in urban battle – Robots exploring a novel location – Cars on highway Set up network, use network to collect and process data, produce models of environment, plan activities.

4 That would be nice, but… Application design for ad hoc networks is hard. Networks change unpredictably. New idea for simplifying application design: – Use a Virtual Node layer Abstract layer containing virtual computing nodes that are better behaved than actual physical nodes. – Program applications on top of the virtual node layer.

5 Virtual Node Layers Abstraction layers containing virtual active nodes. Virtual Nodes may be associated with fixed geographical locations, or VNs may move: – Along a pre-planned path, or – Along a path that is calculated dynamically. Program applications over the VN layer. Application Virtual Node Layer

6 Virtual Node Layers

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8 Route message to a designated geographical region Application: GeoCast

9 Gather, analyze, aggregate,and distribute data. Data Management

10 Region Coordination Coordinate behavior of nodes in region.

11 Circulate token region by region. Token Circulation

12 Location Tracking Service Support queries about current locations of (cooperative) PNs. Implement Location Tracking Service over VN layer: – Each PN has a Home Location: VN that keeps track of PN’s current location (VN region). Determined by hash function from PN id. – PN keeps Home Location up-to-date by sending periodic messages. Use GeoCast (implemented over VN layer). – Queries, responses also use GeoCast. – For reliability, use several, redundant Home Locations. – Easier than solutions using distributed hashing directly over physical layer. Use this Location Tracking Service to implement (easily) point-to- point message routing between PNs.

13 Coordination Oracles Oracle associated with a given VN location: – Gathers and analyzes information about that location. – Sends summarized information to other Oracles. – Builds a suitable model of the environment. PNs query nearby Oracles and use response to help plan their actions. Use for advanced global coordination.

14 Location A My model predicts fierce fighting here. Stay here, take cover! Coordination Oracles

15 Location A My model predicts quiet here. Location A needs reinforcements. I will suggest a safe route there. Coordination Oracles Location B

16 Application: Motion Coordination Given curve Γ, and a finite, unknown set of physical mobile nodes (PNs), move the PNs so that they are (approximately) evenly spaced on Γ.

17 VN Virtual Node Approach Divide region into zones, one VN per zone. VN coordinates client nodes in its zone Directs motion of CNs in its zone: – Towards Γ. – On Γ, to even out spacing. Communicates with neighboring VSNs, sends “extra” clients to neighboring zones. CN

18 Experimental project Undergrad programmers: Mike Spindel, Matthew Brown PhD students: Gilbert, Newport, Nolte Building small network of virtual nodes on a bunch of HP Ipaqs, equipped with and GPS sensors. Demo applications: – Virtual traffic light – Tracking cooperative mobile devices (using home location service) Sponsor: Quanta, Inc.

19 Relevance to Aero/Astro? Virtual Node Layer consisting of Virtual Air-Traffic Controllers? For congestion management, in free flight.