1. A Survey on Sensor Networks
Ian F. Akyildiz, Weillian Su, Yogesh Sankarasubramaniam, Erdal Cayirci
IEEE Communications Magazine, August 2002
Presented by Alexandra Czarlinska

2. Goals and Structure of this Paper
Survey Communication Protocols for the 5 Layers
Analysis and Conclusions
Communication in Sensor Networks
Introduction
Special constraints of Sensor Networks
Communication Topology
Do these protocols work for Sensors? Encourage new research

3. Communication Topology
Multi-hop wireless
Sink / Base Station
Internet or Satellite
area A
Cluster-Head or Aggregator
Task Manager Node
Density of nodes μ(R) = N πR2/A
N = # of nodes in area A
R is radio range
Self-organizing, non-homogenous Sensor Network
End User

4. UC- Berkeley mote
Tiny sensor node with 7 sensing devices ; Photoresistor, Temperature, Barometric pressure, Barometric Pressure and Temperature, Humidity, Thermopile and Thermistor

5. Inside a Sensor Node Actuator Location Finder Mobilizer Power Unit
ADC
Processor
Storage
TX/RX
Power Generator

6. Special Constraints for Communication in Sensor Networks
Fault Tolerance
Handle loss of nodes
Scalability
Handle high density of nodes
Security ?
Confidentiality, Authentication etc
Power
Limited Tx, computation, and lifetime
Costs
Nodes die, make them low cost
Hardware Limitations
Nodes are tiny
Transmission Media
wireless: RF, optical, infrared
Hostile Environment
Survive and maintain communication
Changing Topology
Nodes moving, new nodes, loss of nodes

7. Protocol Stack and Sensor Network Management
5. Application Layer
4. Transport Layer
Sensor Network Manage-ment
3. Network Layer
Power
Moving
Collaboration
2. Data Link Layer
1. Layer Physical

8. 1. Physical Layer
Responsible for frequency selection, modulation and data
Encryption. The big issue here is Power!
source
modulation
freq 915 MHz?
encryption
???
Transmit
Sink
d distance
Low-lying antenna
Power to transmit
≈ dn where 2 ≤ n ≤ 4
High antenna

9. 1. Physical Layer
Have/Know
Binary Modulation needs less energy than M-ary modulation
Direct Sequence Spread Spectrum is low power (transmission and security)
Ultra wideband (UWB) uses low power, does well under multi-path and has simple Tx/Rx
Need
More research on smaller hardware that uses less power (battery!)
Protocols that exploit node density and multi-hop redundancy

10. 2. Data Link Layer
Responsible for multiplexing of data streams, Medium
Access control (MAC) and Error Control
Cellular MAC
Base
wired
wireless
Bluetooth and MANET
Master
slave
Problem: MAC ensures QoS and Bandwidth, not Power conservation, central base
Problem: MAC ensures QoS under mobility. Not enough nodes, Tx power needed is too much, central base

11. What we still need to improve
2. Data Link Layer
MAC Protocol
Method
SMACS and EAR
Fixed allocation of duplex time slots at fixed freq.
Hybrid TDMA/ FDMA
Sensors
Centralized freq. and time division
CSMA-based for Sensors
Contention-based random access
Power Conservation
Random wake up during setup and turning radio off while idle. Exploits large bandwidth available compared to sensor data rate.
Min energy use in Hardware. Picks the mix of TDMA/FDMA to min energy use
Uses constant “listening time” to min energy.
What we still need to improve
Not great for very mobile networks (good for mostly stationary nodes).
Should use more computation over handshaking. Use more Power-saving modes (sleeping). Need to derive bounds on energy needed by sensors.

12. 3. Network Layer Have/Know Also have: Pegasis, GEAR
Routes data supplied by the Transport Layer
Scheme
Description
Flooding
Broadcasts data to all neighbor nodes
Gossiping
Sends data to one randomly selected neighbor
LEACH
Forms a clusters to minimize energy loss
SPIN
Sends data to sensor nodes only if they are “interested”, has 3 types of messages (ADV, REQ, DATA)
Directed Diffusion
Sets up gradients for data to flow from source to sink during interest dissemination
Also have: Pegasis, GEAR

13. 3. Network Layer Have/Know allow higher topology changes Need
Scheme
Description
Power Efficiency Routing
Pick a route based on: max Power Available (PA) or, min Energy (ME), or Min Hop (MH) or Max Min PA.
SMECN
Creates a sub-graph of the sensor network that contains the minimum energy path
SAR
Creates multiple trees where the root of each tree is one hop neighbor from the sink
Need
allow higher topology changes
Allow higher scalability

14. 3. Network Layer Power Efficiency Routing
1- Max Power Available (PA) route, 2- Min Energy (ME) route, Min Hop (MH) route and 4 - Max Min PA route
1- Max Power Available route
4 -Max Min
Route along which the min PA is larger than the min PA of other routes A
P = 1
P = 2
P = 3
Total P = 6
P = 2
P = 4 B
P = 2

15. 4. Transport Layer
Helps to maintain the flow of data if the Application Layer
requires it. Needed if End-User accesses the Sensor
Network through the Internet
Current TCP:
has a window mechanism that may not suit Sensor Networks
uses end-to-end Global Addressing (nodes may have Attribute-based or Location-based addressing)
TCP and UDP not based on power conservation and scalability
Have/Know

16. TCP Splitting: TCP on one side, modified UDP on the other
Need
4. Transport Layer
More research is needed to see if we need new protocols and what they might be. Suggestion by authors:
TCP Splitting: TCP on one side, modified UDP on the other
UDP
Sink
Task Manager Node
Internet
TCP
End User

17. 5. Application Layer
Makes the hardware and software of the lower layers
transparent to the Task Manager Node (and End-User)
Task Manager Node
Internet
Sink
End User

18. Sensor Query and Data Dissemination Protocol
5. Application Layer
SMP
TADAP
SQDDP
Task Assignment and Data Advertisement Protocols
Sensor Query and Data Dissemination Protocol
Sensor Management Protocol
Rules for Data Aggregation, Time sync. Moving, turning nodes on/off
Issue queries,
collect replies
Allows for Attribute-based and Location-based addressing
Interest Dissemination from:
- user to nodes
- nodes to user

19. 5. Application Layer Data Centric Routing (not Address Based Routing):
Attribute-Based Addressing:
The locations of nodes that sense temperature higher than 70 degrees
Location-Based Addressing:
What are the temperatures read by sensors in region A
Need
In general, more research is needed in all the areas mentioned

20. Strengths and Contributions
“A Survey on Sensor Networks”
Great overview of what exists, why it’s good or not good for Sensor Networks
Gives a table of on-going Sensor Network research projects
Identifies and motivates new areas of research that are needed
Identifies certain general “design principles”

21. Analysis: Weaker side
Does not mention security enough (should be designed right into the system, not after)
Does not mention Asymmetric Links
Does not mention Distributed Protocols sufficiently (could have no Base Station)

22. Keep in Mind
Paper assumes that nodes do not have much energy but there is new research in:
solar cells, temperature gradients, vibrations, RF Transfer, Micro Heat Engines (using MEMS)
Assumes high density of cheap nodes vs. a few high quality nodes (keep in mind NASA)
Does not always assume the most General Topology (ie: there could be no Base Station, there could be multiple sensing devices on one node etc)

23. References
I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, E. Cyirci, “ A survey on Sensor Networks”, Computer Networks, 38(4): , March 2002
Chee-Yong Chong, S. P. Kumar, “Sensor networks: evolution, opportunities, and challenges”, Proceedings of IEEE, pp , August 2003

24. Additional slides with more detail
Appendix
Additional slides with more detail

25. Sensor Network Communication Architecture
area A
Fault Tolerance rk(t) = e – λk t
λ k is failure rate of node k
t is time period
Density of nodes μ(R) = N πR2/A
N = number of nodes in area A
R is radio range

26. Authors of this Survey Georgia Institute of Technology Ian F. Akyildiz
School of Electrical and Computer Engineering
Ian F.
Akyildiz
Yogesh
Sankarasu-
bramaniam
Weilian Su
Erdal
Cayirci
Prof: wireless and satellite networks, next-gen Internet
Phd: Timing recovery, ad hoc routing and Sensor Networks
Phd: Sensor Networks and next-generation wireless
Sensor Networks, mobile comm., tactical and military