The University of Iowa. Copyright© 2005 A. Kruger 1 Introduction to Wireless Sensor Networks Routing in WSNs 28 February 2005

The University of Iowa. Copyright© 2005 A. Kruger 2 Organizational Monday 4:30-5:20Room 4511 SC Thursday12:30-1:20Room 3220 SC Please note that the room numbers are different for Mondays and Thursdays. Class Website Class Time Midterm ExamTime: March 10, 2005 Monday 5:20-620Room 1126 SC Thursday1:30-2:30Room 1126 SC Office Hours

The University of Iowa. Copyright© 2005 A. Kruger 3 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

The University of Iowa. Copyright© 2005 A. Kruger 4 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

The University of Iowa. Copyright© 2005 A. Kruger 5 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

The University of Iowa. Copyright© 2005 A. Kruger 6 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

The University of Iowa. Copyright© 2005 A. Kruger 7 Graphs

The University of Iowa. Copyright© 2005 A. Kruger 8 Greedy Distance and Compass Routing Greedy distance –pick the locally optimum (distance) neighbor Compass routing – pick the locally optimum (angle) neighbor

The University of Iowa. Copyright© 2005 A. Kruger 9 Problem With Greedy Distance Here both x’s neighbors are further than destination

The University of Iowa. Copyright© 2005 A. Kruger 10 Side-Bar Maze Solver

The University of Iowa. Copyright© 2005 A. Kruger 11 Planar Graphs not planar planar

The University of Iowa. Copyright© 2005 A. Kruger 12 Planerization Basic idea – keep connectivity between nodes Convex Polygon Concave Polygon

The University of Iowa. Copyright© 2005 A. Kruger 13 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

The University of Iowa. Copyright© 2005 A. Kruger 14 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

The University of Iowa. Copyright© 2005 A. Kruger 15 Examples RNGGabriel

The University of Iowa. Copyright© 2005 A. Kruger 16 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

The University of Iowa. Copyright© 2005 A. Kruger 17 Variations Non-convex routing adaptation OFR – Other face routing

The University of Iowa. Copyright© 2005 A. Kruger 18 Side-Bar Parametric Equations Circle –Non parametric: x 2 + y 2 = a 2 –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

The University of Iowa. Copyright© 2005 A. Kruger 19 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

The University of Iowa. Copyright© 2005 A. Kruger 20

The University of Iowa. Copyright© 2005 A. Kruger 21 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

The University of Iowa. Copyright© 2005 A. Kruger 22 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

The University of Iowa. Copyright© 2005 A. Kruger 23 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.