Wireless Sensor Networks 7. Geometric Routing Christian Schindelhauer Technische Fakultät Rechnernetze und Telematik Albert-Ludwigs-Universität Freiburg Version 30.05.2016

Location Service How to inform all nodes about the position of the destination node(s) Categories Flooding-based location dissemination fastest and simplest way yet many messages Quorum-based and home-zone-based strategies reduces communication overhead Movement-based location dissemination location information is spread only locally table of location and time stamps is exchanged when to nodes come close to each other only applicable to mobile networks

Quorum based Location Services Location information at group of nodes Nodes need to be contacted to obtain information E.g. consider grid (Stojmenovic, TR 99) Destination information information is stored on a row Node needs to ask all nodes in a column to receive this information reduces traffic by a factor of O(n1/2) Grid Location Service (Li et al. MobiCom 00) location servers distributed by a hierarchical subdivision of the plane

Home based Location Services Each node has a home-zone in this home zone (possibly far away) another nodes is responsible for relaying position information Geographic Hash Tables (Ratnasami et al. 02) Node and location are key-value pair key is assigned to a location by a hash function In this location the home zone router is responsible for storing this information Each node updates his information at the home zone router Nodes looking for a node contact home zone router

Distributed Hash-Table (DHT) Pure (Poor) Hashing Hash table does not work efficiently for inserting and deleting Distributed Hash-Table peers are „hashed“ to a position in an continuos set (e.g. line) index data is also „hashed“ to this set Mapping of index data to peers peers are given their own areas depending on the position of the direct neighbors all index data in this area is mapped to the corresponding peer Literature “Consistent Hashing and Random Trees: Distributed Caching Protocols for Relieving Hot Spots on the World Wide Web”, David Karger, Eric Lehman, Tom Leighton, Mathhew Levine, Daniel Lewin, Rina Panigrahy, STOC 1997 peers 1 2 3 4 5 6 23 5 1 4 f(23)=1 index data f(1)=4 DHT index data peer range peers 10

Entering and Leaving a DHT Distributed Hash Table peers are hashed to to position index files are hashed according to the search key peers store index data in their areas When a peer enters neighbored peers share their areas with the new peer When a peer leaves the neighbors inherit the responsibilities for the index data black peer enters green peer leaves 11

Summary Geometric Routing is a scalable alternative with only local information Recovery strategies are necessary since barriers might occur Planarization underlying communication graph should be planar erase edges or use cell structure Beacon- and baconless Routing Location Service is necessary Real-world Solutions Flooding Alternating algorithm Greedy with right-hand recovery Greedy with flooding recovery

Wireless Sensor Networks 7. Geometric Routing Christian Schindelhauer Technische Fakultät Rechnernetze und Telematik Albert-Ludwigs-Universität Freiburg Version 30.05.2016