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

2. 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

3. 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

9. 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

10. 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

11. 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

13. 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

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