1. Protocols for Wireless Sensor Networks

2. Outline Introduction Conventional Protocols Flat Routing Protocols
Directed Diffusion
SPIN
Hierarchical Routing Protocols
LEACH
PEGASIS

3. Introduction
A sensor network is a computer network of many, spacially (location) distributed devices using sensors to monitor conditions at different locations.
Involve three areas:
sensing,
communication, and
computation.

4. Types of Routing Protocol for WSN
Single-hop Networks
Packets are transmitted from sources to destinations directly.
Multi-hop Networks
The final destination of a packet might not be reached directly and the other nodes can be used to route the packet to the final destination.

5. What is the ideal protocol?B D E F G
Using shortest path routes
Avoids overlap and implosion
Minimum energy
Need global topology information

6. Conventional Protocols

7. Conventional Protocols
Classic Flooding (Send to all neighbors but not the neighbors that have sent a message)
B will not send a message to A A C B D E F G

8. Deficiencies Implosion A B C D (a) A B C (r,s) (q,r) q s r
Data Overlap
Resource blindness

9. Gossiping Forward data to a random neighbor Avoids implosionC
Forward data to a random neighbor
Avoids implosion
Disseminates information at a slower rate
Fastest rate = 1 node/round

10. Flat Routing Protocols
Flat Networks
Every incoming packet is sent out on every outgoing line except the one it arrived on.
Vast numbers of duplicate packets are generated.
Routing Protocols: Directed Diffusion, SPIN.

11. The Directed Diffusion Protocol
Directed Diffusion consists of several elements:
Interests
Data messages
Gradients (paths)
Reinforcements

12. Gradients
gradient is a generalization of the usual concept of derivative of a function in one dimension to a function in several dimensions.

13. Directed Diffusion - Interest & Data
type = wheeled vehicle
interval = 1 s
rect = [-100, 200, 200, 400]
timestamp = 01:20:40 // hh:mm:ss
expiresAt = 01:30:40
Data
type = wheeled vehicle // type of vehicle seen
instance = trunk // instance of this type
location = [125, 220] // node location
intensity = 0.6 // signal amplitude measure
confidence = // confidence in the match
timestamp = 01:20:40 // local event generation time

14. Directed Diffusion - Interest Propagation
The sink periodically broadcasts an interest message to each of its neighbors.
Every node maintains an interest cache

15. Directed Diffusion - Gradient (path) Establishment
That every pair of neighboring nodes establishes a gradient toward each other.
This technique can enable fast recovery from failed paths or reinforcement of empirically better paths.

16. Directed Diffusion - Data Propagation
A sensor node that detects a target, computes the highest requested event rate among all its outgoing gradients.
To resend a received data message, a node needs to examine the matching interest entry's gradient list.

17. Directed Diffusion - Reinforcement
The node might choose that neighbor from whom it first received the latest event matching the interest to reinforce.
It is very reactive to changes in path quality.

18. SPIN Sensor Protocols for Information via Negotiation
Starts with a source node sending its data to all of its neighbors.

19. SPIN - Flooding deficiencies
Implosion & Overlap
(a) A B C D
(r, s)
(q, r) A B C q s r
Implosion Problem
Overlap Problem

20. SPIN has three types of messages
ADV (advertisement)
When a SPIN node has data to share, it can advertise an ADV message containing meta-data.
REQ
A SPIN node sends a REQ message when it wishes to receive some actual data.
DATA
contain actual sensor data with a meta-data header.

21. The SPIN Protocol
Steps C
DATA
ADV
REQ D B
DATA
REQ
ADV A E F

22. Hierarchical Routing Protocols
Hierarchical Networks
The main aim of hierarchical routing is to efficiently maintain the energy consumption of sensor nodes.
Performing data aggregation and fusion in order to decrease the number of transmitted messages to the sink.
Routing Protocols: LEACH, PEGASIS, TEEN.

23. LEACH Protocol Low-Energy Adaptive Clustering Hierarchy.
Distributed cluster formation technique that enables self-organization of large numbers of nodes.

24. LEACH - Cluster
Algorithms for adapting clusters and rotating cluster head positions to evenly distribute the energy load among all the nodes
The nodes organize themselves into local clusters, with one node acting as the cluster head.
The cluster head performs signal processing functions on the data, and transmits data to the remote Base Station (sink)

25. LEACH - Set-up phase Cluster Head Non-Cluster Head
Each cluster head node broadcasts an advertisement message (ADV) to let all the other nodes that they have chosen this role for the current round.
Non-Cluster Head
They transmit a join-request message (Join-REQ) back to the chosen cluster head.

26. LEACH - Set-up phase
The cluster head node sets up a TDMA schedule and transmits this schedule to the nodes in the cluster.
Ensures that there are no collisions among data messages.
Allows the radio components to be turned off at all times except during their transmit time.

27. LEACH - Steady-state phase
Broken into frames, where nodes send their data to the cluster head at most once per frame during their allocated transmission slot.
Once the cluster head receives all the data, it performs data aggregation.

28. The PEGASIS Protocol
Power-Efficient GAthering in Sensor Information Systems.
The key idea in PEGASIS is to form a chain among the sensor nodes so that each node will receive from and transmit to a close neighbor.

29. PEGASIS - Chain
The nodes will be organized to form a chain, which can be accomplished by the sensor nodes themselves using a greedy algorithm starting from some node.
When a node dies, the chain is reconstructed in the same manner to bypass the dead node.

30. PEGASIS - Leader
The main idea in PEGASIS is for each node to receive from and transmit to close neighbors and take turns being the leader for transmission to the Base Station.
Nodes take turns transmitting to the BS, and use node number i mod N (N represents the number of nodes) to transmit to the BS in round i.

31. PEGASIS - Token
Token passing approach N0 N1 N2 N3 N4 BS
Token
Data