Download - Geographic Routing Made Practical
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Geographic Routing Made Practical
Y.-J. Kim, R. Govindan, B. Karp and S. Shenker
NSDI 2005, To Appear
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Geographic Routing
� Each node knows � its geographic location� its 1-hop neighbors
� Greedy forwarding� GPSR, compass routing
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Greedy Protocol Can Get Stuck
� No where to go
� Recovery strategy for planar graph� Perimeter routing� Other-face routing
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Planarization
RNG: Gabriel:
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
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Challenges
Unit-disk graph assumption!
� Nodes communicate if within unit distance
� No communication if longer than unit distance
Planarization may fail!
� Anisotropic
� Obstacles presence
� Unidirectional links
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Pathologies
Partition graph Asymmetric links Cross links
x
wu
y
x
u
y y
x
wu
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Problems
� Partitioned graph
� Cross links
Pathologies may cause Routing failures!
s
d
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Example
floor plan Gabriel graph
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not necessarily planar
This Paper …
� CLDP� Cross-Link Detection Protocol
� Given an arbitrary communication graph� Produce a subgraph that a face routing will not fail
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High Level Idea
� For every link, probe to find crossings
x
wu
y
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Right-hand Rule
x
w
y
x
wu
y
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Correct Crossings
� Under the constraint to maintain connectivity
y
x
wu
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Multiple Cross-links
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Concurrent Probing
� Lock links being probed
� Re-probe after face change
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Correctness
Theorem AIf a connected graph G has at least one crossing, then there is at least one face that has a crossing.
Theorem BGeographic routing never fails on a connected
CLDP-stable graph.
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mutual witness
Simulations Setup
� CLDP Implemented in TinyOS� Simulator: TOSSIM
� Performance compared with:� GPSR� GPSR-PLAN� GPSR-MWP� GPSR-PLAN-CLDP
Greedy forwarding on FULL communication graph
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Success Rate vs. Density
Network: 200 nodes, many obstacles
unit radio range random-linkage graph
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Stretch Factor vs. Density
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Others
� Overhead:� 85 - 90% links see less than 4 messages� But ~10% can see up to 100 messages
� Convergence rate
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Summary
� Greedy forwarding + CLDP� Remove unrealistic assumptions on communication
� Always guarantee routing success� Reasonable routing paths� Low overhead, converge fast� Works under network dynamics