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Introduction to Wireless Sensor Networks. Routing in WSNs 28 February 2005. Organizational. Class Website. www.engineering.uiowa.edu/~ece195/2005/. Class Time. Office Hours. Midterm Exam. Time: March 10, 2005. Routing. What is meant by “routing”? Internet (TCP/IP) - PowerPoint PPT Presentation
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1The University of Iowa. Copyright© 2005
A. Kruger
Introduction to Wireless Sensor Networks
Routing in WSNs
28 February 2005
2The University of Iowa. Copyright© 2005
A. Kruger
Organizational
Monday 4:30-5:20 Room 4511 SC
Thursday 12:30-1:20 Room 3220 SC
Please note that the room numbers are different for Mondays and Thursdays.
Class Website www.engineering.uiowa.edu/~ece195/2005/
Class Time
Midterm Exam Time: March 10, 2005
Monday 5:20-620 Room 1126 SC
Thursday 1:30-2:30 Room 1126 SC
Office Hours
3The University of Iowa. Copyright© 2005
A. Kruger
Routing• What is meant by “routing”?
• Internet (TCP/IP)– Routing tables often large– Can be updated frequently
• WSN– Frequent topology changes– Modest local storage– Expensive to update frequently– => Need local, stateless algorithms where
nodes know only immediate neighbors
4The University of Iowa. Copyright© 2005
A. Kruger
Routing• Consider the following
– The fundamental difference between classical routing and routing for sensor networks is that the separation between address and content of packet no longer viable
• What does it mean?– Network is a system, individual nodes come and go,
information sensed by one node can be sensed by another close by
• Data-centric view– Routing decision as based not on destination address, but
rather on destination attributes and relation to attribute of packet content
– Information providers and information seekers must be matched using data attributes and not (hard) network address
5The University of Iowa. Copyright© 2005
A. Kruger
Examples of Attributes• Node location
– But is this not just its address?– Get the rain data from the nodes at the Iowa City airport
• Types of sensor connected to a node– Send a control packet to all nodes that have a light sensor
connected to it
• Certain range of values in certain type of sensed data– Get max, min temperature values in from the sensor
network
• Pull model– Network is queried similar to a database
• Push model– Network can initiate flow of information based on events
6The University of Iowa. Copyright© 2005
A. Kruger
WSN Routing• Geographic routing (more traditional view)
– Greedy distance– Compass– Convex perimeter routing– Routing on a curve– Energy-minimizing broadcast
• Attribute-based routing (data-centric view)– Directed diffusion– Rumor routing– Geographic hash tables
7The University of Iowa. Copyright© 2005
A. Kruger
Graphs
8The University of Iowa. Copyright© 2005
A. Kruger
Greedy Distance and Compass Routing
• Greedy distance –pick the locally optimum (distance) neighbor
• Compass routing – pick the locally optimum (angle) neighbor
9The University of Iowa. Copyright© 2005
A. Kruger
Problem With Greedy Distance• Here both x’s neighbors are further
than destination
10The University of Iowa. Copyright© 2005
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Side-Bar Maze Solver
11The University of Iowa. Copyright© 2005
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Planar Graphs
not planar planar
12The University of Iowa. Copyright© 2005
A. Kruger
PlanerizationBasic idea – keep connectivity between nodes
Convex Polygon
Concave Polygon
13The University of Iowa. Copyright© 2005
A. Kruger
Planarization Requirements for WSN
• WSNs: local planarization algorithms, where edge xy is introduced if a geometric region (witness region) around xy is free of other nodes.
• Require accurate information about location of nodes
14The University of Iowa. Copyright© 2005
A. Kruger
Planerization• Basic idea – keep connectivity between nodes• Relative Neighborhood Graph (RNG)
– The edge xy is introduced if the intersection of circles centered at x and y with radius the distance d(x,y) is free of other nodes
• Grabriel Graph– The edge xy is introduced if the diameter xy is free of other
nodes
• Key for WSN: RNG and Gabriel graphs can be found with distributed construction
x y
x y
15The University of Iowa. Copyright© 2005
A. Kruger
Examples
RNG Gabriel
16The University of Iowa. Copyright© 2005
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Convex Perimeter Routing
• Objective: route from s to d (assume planar graph)• Start in the face just beyond s along sd and walk
around that face. Stop if d is reached. If the segment sd is about to be crossed, cross over to the next face along sd, and repeat
17The University of Iowa. Copyright© 2005
A. Kruger
Variations• Non-convex routing adaptation
• OFR – Other face routing
18The University of Iowa. Copyright© 2005
A. Kruger
Side-Bar Parametric Equations• Circle
– Non parametric: x2 + y2 = a2 – Parametric: x = a cos(t), y = a sin(t), t the
parameter
• Straight Line– Non parametric: y = mx+c– Parametric: line through point (a, b)
parallel to vector (u, v) is given by
(x, y) = (a, b) + t·(u, v), t the parameter
• Given t one can compute x and y
19The University of Iowa. Copyright© 2005
A. Kruger
Routing on A Curve• Specify a curve a packet should follow• Analytical description of a curve carried by the
packet• Curves may correspond to natural features of the
environment where the network is deployed• Can be implemented in a local greedy fashion that
requires no global knowledge• Curve specified in parametric form C(t)=(x(t),y(t))
– t – time parameter – could be just relative time
• Each node makes use of nodes trajectory information and neighbor positions to decide the next hop for the packet
• Also called trajectory-based routing
20The University of Iowa. Copyright© 2005
A. Kruger
21The University of Iowa. Copyright© 2005
A. Kruger
Optimal Path• What do we mean by “optimal”
– Minimum delay => fewest hops– Minimum Energy => frequent hops (why)
• Formally, cost of a path
– Where l(e) is the length of the edge in the graph– k is in range 1…5 – k = 0 => Hop length, measure delay– k = 1 => Euclidian path length– k > 1 => Capture energy of path, depending on
attenuation model
e
k elc )()(
22The University of Iowa. Copyright© 2005
A. Kruger
Review Questions• Write a short (5 sentence) paragraph contrasting the
needs and resources available in WSN as opposed to, say, the Internet.
• Explain the statement “When routing a packet in a WSN, more hops increase delay, but the advantage is that it increases energy efficiency for the WSN as a whole”
• Write a 6-7 sentence paragraph explaining the term “routing on a curve”
• Write a paragraph explaining the term “convex perimeter routing”
• True of False – a major disadvantage of perimeter routing in WSN is that path construction require knowledge of the global topology
• With the aid of a figure, explain how a greedy forwarding strategy can result in a packet being stuck at a node in a WSN
23The University of Iowa. Copyright© 2005
A. Kruger
Review Questions• Below is a connectivity graph for a WSN. (a)
Planerize it using the RNG method. Planerize it using the Grabriel method.
(figure goes here)
• True or False – a problem with “Routing on a Curve”
is that each nodes must know the location of all nodes along the routing path.
• Write a short (5 sentence) paragraph explaining what Trajectory-Based Routing is.