1. Wireless Sensor Networks

2. Puzzle Three bulbs inside a room Three switches outside the room
Room initially locked
You can initially play with the switches
You then need to enter the room and be able to match switches to their respective bulbs
Devise a strategy

3. Puzzle Turn switch 1 ON Wait for 10 minutes Turn switch 1 OFF
Enter room
Lit bulb: switch 2
Unlit bulb that is warm: switch 1
Unlit bulb that is cold: switch 3

4. Grades Exam 1: 10 points Exam 2: 15 points Final exam: 40 points
Assignments: 18 points
Project: 12 points
Class participation: 5 points

5. Exam 2
Max = 15
Min = 6
Average = 12.96
Stdev = 2.24

6. Directed Diffusion
A node requests data by sending interests for named data
The request “How many pedestrians do you observe in region X” is broadcasted to region X
Data matching the interest is then “drawn” down towards the node
When a node in region X receives the request, it activates its sensors, and returns sensed information along reverse path of interest propagation
Intermediate nodes can cache, or transform data
Combine reports from multiple sensors to more accurately pinpoint pedestrian’s location

7. Elements of Directed Diffusion
Interests
Query of what the user wants
Data messages
Collected or processed information of a physical phenomenon
Gradients
Direction state created in each node that receives the interest
Reinforcements
Of one or a small number of the available paths

8. Naming Attribute-value pairs Example: Vehicle detection task (query)
(Type=wheeled, interval=20ms, duration=10seconds, rect=[-100,100,200,400])
VDT (response)
(type=wheeled,instance=truck,location=[125,220],intensity=0.6,confidence=0.85,timestamp=01:20:40)

9. Interests Can be initiated by the sink
Exploratory interest with a large interval, followed by reinforcements
e.g. to detect any wheeled vehicles
Soft-state refreshing of interests
reliability & overheads
Each node maintains one entry per interest in an interest-cache

10. Interests (contd.)
Each interest entry contains a gradient (neighbor, report rate, and lifetime)
Interest entry possibly created upon receipt of interest
Interest possibly forwarded to a sub-set of neighbors
e.g. based on cached data

11. Gradient Establishment
A generic notion
Can be implemented in several ways: binary values, probabilistic forwarding, load balancing
Gradients might be set-up differently for different tasks

12. Data Propagation Nodes in “rect” sense data
Propagates data according to the gradients to the corresponding interest entry
If an intermediate node receives data, but finds no interest entry, it drops the data
Gradients can change as data is being forwarded
e.g. down-sampling : 100 events/second to 50 events/second

13. Reinforcement Exploratory gradients vs. data gradients
Sink reinforces one (or a subset) of the neighbors reporting back exploratory events
Data gradients can have a higher reporting rate – positive reinforcement
Allows sink to reinforce selective paths and reduce multi-path routing for the real heavy data

14. Other Issues MAC Topology control (with sensing reliability)
Sensor placement
Reliable transport
Congestion control

15. CtS

16. Puzzle A bridge can carry at most two people at a time
It is dark and a flashlight is required to cross the bridge
Four people A, B, C, D at one end of the bridge want to cross the bridge
Have only one flash light
A will take 10 minutes to cross the bridge, B will take 5 minutes, C will take 2 minutes, and D will take 1 minute
If two people cross the bridge together, time taken is determined by the slowest of the two
What is the minimum amount of time in which all four can cross the bridge?