1. Data-Centric Storage in Sensornets Submitted to Sigcomm 2002 Authors: Sylvia Ratnasamy et al. ICIR, UCLA, UC-Berkeley Presenter:Shang-Chieh Wu (meou@cs)

2. Sensornets Sensornets are large-scale distributed sensing networks comprised of many small sensing devices equipped with memory, processors, and short-range radio Monitor temperature in an active volcano, keep track of the seismic waves in an earthquake region, or even save rare and endangered species.

3. Sensornets Scalable, self-organizing and energy- efficient data dissemination algorithm required. Data-centric routing algorithm. Data-centric storage.

4. Terminology Observations: The low-level output from the sensors. Events: Certain constellations of low-level observations. Task: The code running on each sensor. Query: Elicit the event information from the sensornet.

5. External, Local, and Data-Centric Storage External Storage(ES): On detection of events, the relevant data is sent to external storage. Local Storage (LS): Event information is stored locally. Data-Centric Storage (DS): After an event is detected, the data is stored by name within the sensornets.

6. ES, LS, DS Assume n nodes totally and the diameter of the sensornet is O(n 0.5 ) ESLSDS Cost for Saving EventO(n 0.5 )0 Cost for Query Event0O(n)O(n 0.5 ) Cost for Query Result0O(n 0.5 ) Communication Costs per each

7. ES, LS, DS D total : The total number of events detected. Q: the number of event types for which queries are issued. D q : the number of events detected for the types of events queried for. No more than one query for each event type, so there are Q queries in total. Assume hotspot occurs on packets sending to the access point.

8. ES, LS, DS ESLSDS TotalD total n 0.5 Qn + D q n 0.5 Qn 0.5 + D total n 0.5 + D q n 0.5 Or Qn 0.5 + D total n 0.5 + Qn 0.5 HotspotD total Q + D q Q + D q or 2Q DS is preferable in Sensornet is large D total >> max[Q + D q ] (??) Summarises are used. Approximate Communication Costs

9. Data-centric storage Based –GPSR geographic routing algorithm. –Efficient peer-to-peer lookups system. Relevant data is stored, by name, at nodes within the sensornet. All data with the same general name will be stored at the same sensornet node. As an alternative method.

10. GPSR Strongly geographic routing algorithm. Each mode determines its own geographic coordinates and periodically announces its address and coordinates to its neighbors. Each mode is aware of the identifications and positions of all its neighbors. Special rule to handle dead-ends.

11. GPSR

12. Right-hand rule: Each node to receive a packet forwards the packet on the next link counterclockwise about itself from the ingress link.

13. Distributed Hash-Table Given an event name, we hash the name into a key. The key is a location somewhere in the sensornets. Put(key, value) command sends a packet with the given payload into the sensornet routed towards the location key. MIT’s GLS is a good candidate. Some extra concepts are proposed to handle failure, mobility, and scalability.

14. Conclusion Storages are involved in sensornets, another option. A detail evaluation for transmission cost from collecting data to answering queries.

15. My opinions Database approaches for sensornets. No serious contribution in real key issue.(routing and hashing) Oversimplify the difficulty of “summary events”. Lengthy introduction for sensornet. The cost of failure for storages is neglected, On purpose ? Data consistence in storages ?