1. Architectures and Applications for Wireless Sensor Networks (01204525) Network Architecture
Chaiporn Jaikaeo
Department of Computer Engineering Kasetsart University
Materials taken from lecture slides by Karl and Willig

2. Outline Network scenarios Optimization goals Design principles
Service interface
Gateway concepts

3. Typical Views of WSN Self-organizing mobile ad hoc networks (MANETs)
Peer-to-peer networks
Multi/mobile agent systems and swarm intellegence

4. Sensor Network Scenarios
Sources: Any entity that provides data/measurements
Sinks: Nodes where information is required
Sink
Source
Sink
Source
Source
Internet
Sink

5. Single-Hop vs. Multi-hop
Multi-hop networks
Send packets to an intermediate node
Intermediate node forwards packet to its destination
Store-and-forward multi-hop network
Store & forward multi-hopping NOT the only possible solution
E.g., collaborative networking, network coding
Source
Sink
Obstacle

6. Multi-hopping Always Efficient?
Obvious idea: Multi-hopping is more energy-efficient than direct communication
Suppose we put a relay at distance d/2
Energy for distance d is reduced from cd to 2c(d/2)
c - some constant
 - path loss coefficient ( 2)
Usually wrong, or over-simplified
Need to take constant offsets for powering transmitter, receiver into account

7. Multiple Sinks, Multiple sources

8. Different sources of mobility
Node mobility
Sink mobility
Event mobility

9. Sink Mobility
Request
Propagation
of answers
Movement
direction

10. WSN Event Mobility

11. Outline Network scenarios Optimization goals Design principles
Service interface
Gateway concepts

12. Goal: Quality of Service
QoS in WSN is more complicated (compared to MANET)
Event detection/reporting probability
Event classification error, detection delay
Probability of missing a periodic report
Approximation accuracy (e.g, when WSN constructs a temperature map)
Tracking accuracy (e.g., difference between true and conjectured position of the pink elephant)
Related goal: robustness
Network should withstand failure of some nodes

13. Goal: Energy efficiency
Many definitions
Energy per correctly received bit
Energy per reported (unique) event
Delay/energy tradeoffs
Network lifetime
Time to first node failure
Network half-life (how long until 50% of the nodes died?)
Time to partition
Time to loss of coverage
Time to failure of first event notification

14. Sharpening the Drop
Sacrifice long lifetimes in return for an improvement in short lifetimes

15. Goal: Scalability
Network should be operational regardless of number of nodes
At high efficiency
Typical node numbers difficult to guess
MANETs: 10s to 100s
WSNs: 10s to 1000s, maybe more
Requiring to scale to large node numbers has serious consequences for network architecture
Might not result in the most efficient solutions for small networks!
Carefully consider actual application needs before looking for scalable solutions

16. Outline Network scenarios Optimization goals Design principles
Service interface
Gateway concepts

17. Distributed Organization
WSN participants should cooperate in organizing the network
Centralized approach usually not feasible
Potential shortcomings
Not clear whether distributed or centralized organization achieves better energy efficiency
Option: “limited centralized” solution
Elect nodes for local coordination/control
Perhaps rotate this function over time

18. In-Network Processing
WSNs are expected to provide information
Gives additional options
E.g., manipulate or process the data in the network
Main example: aggregation
Apply aggregation functions to a collection tree in a network
Typical functions: minimum, maximum, average, sum, …
Not amenable functions: median

19. Aggregation Example 1 3 6

20. Signal Processing Another form of in-network processing E.g.,
Edge detection
Tracking/angle detection of signal source
Exploit temporal and spatial correlation
Observed signals might vary only slowly in time
Signals of neighboring nodes are often quite similar
Compressive sensing

21. Adaptive Fidelity
Adapt data processing effort based on required accuracy/fidelity
E.g., event detection
When event occurs, increase rate of message exchanges
E.g., temperature
When temperature is in acceptable range, only send temperature values at low resolution
When temperature becomes high, increase resolution and thus message length

22. Data Centric Networking
Interactions in typical networks are addressed to the identities of nodes
Known as node-centric or address-centric networking paradigm
In WSN, specific source of events might not be important
Several nodes can observe the same area
Focus on data/results instead
 Data-centric networking
Principal design change

23. Implementation Options
Publish/subscribe (NDN – Named Data Networking)
Nodes can publish data, can subscribe to any particular kind of data
Once data of a certain type has been published, it is delivered to all subscribers
Databases
SQL-based request

24. Other Design Principles
Exploit location information
Exploit activity patterns
Exploit heterogeneity
By construction
By evolution
Cross-layer optimization of protocol stacks for WSN
Goes against grain of standard networking
Promises big performance gains

25. Outline Network scenarios Optimization goals Design principles
Service interface
Gateway concepts

26. Interfaces to Protocol Stacks
The world’s all-purpose network interface: sockets
Good for transmitting data from one sender to one receiver
Not well matched to WSN needs (ok for ad hoc networks)
App as another component
Well-designed interface

27. Outline Network scenarios Optimization goals Design principles
Service interface
Gateway concepts

28. Gateways in WSN/MANET Allow remote access to/from the WSN
Bridge the gap between different interaction semantics
E.g., data vs. address-centric networking
Need support for different radios/protocols

29. WSN to Internet Communication
E.g., deliver an alarm message to an Internet host
Issues
Need to find a gateway (integrates routing & service discovery)
Choose “best” gateway if several are available
How to find Alice or Alice’s IP?

30. Internet to WSN communication
How to find the right WSN to answer a need?
How to translate from IP protocols to WSN protocols, semantics?
Gateway nodes
Remote requester
Internet
Gateway

31. WSN tunneling
Use the Internet to “tunnel” WSN packets between two remote WSNs
Gateway nodes
Internet
Gateway

32. 6LoWPAN IPv6 over Low-power Wireless Personal Area Networks
Nodes communicate using IPv6 packets
An IPv6 packet is carried in the payload of IEEE data frames

33. Example 6LoWPAN Systems

34. Summary
Network architectures for WSNs look quite different from typical networks in many aspects
Data-centric paradigm opens new possibilities for protocol design