Grid: Scalable Ad-Hoc Wireless Networking

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Grid Scalable Ad-Hoc Wireless Networking

• Robert Morris
• LCS
• http//pdos.lcs.mit.edu/grid

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Goal Networks out of Chaos
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Solution Multi-hop Forwarding
A to J Hello!
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System Status

• Software distributions for
• Linux, BSD
• PC, iPaq
• Works with unmodified Internet software
• Two Grid nets deployed

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LCS Grid Net
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• 17 static nodes on 5th/6th floors
• A dozen iPaq hand-helds

wired gateway
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Roof-Top Grid Net
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LCS
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Completed Research

• Scalable routing
• Geographic forwarding
• Distributed P2P location database
• Low-power forwarding
• Understanding capacity limits
• Avoiding malicious nodes

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Does Grid Find Useful Paths?
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Mistake Shortest-Path Routes
As max range
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Link Quality Isnt Bi-modal
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Obstacles to Better Routing

• Use low-loss paths, but
• Loss rate masked by 802.11 re-sends
• Changes quickly with time, motion
• Whats the best metric to minimize?
• Expected total packet transmissions
• Fight strong bias towards shortest paths

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Grid Summary

• Grid routing protocols are
• Self-configuring
• Easy to deploy
• Scalable
• http//www.pdos.lcs.mit.edu/grid

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Application Smart Devices
Remote Control
Print
Share
E-Mail
Internet
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Application Rooftop Nets
School/Homework Server
Internet Access
Game server
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Application Disaster Services

• Disaster may have damaged phone system c
• Want to avoid N2 plans for N services to
  communicate

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Direct Contact Scales Badly
Hello J!
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Design Challenges

• Cope with mobile nodes
• Finding routes
• Conserving battery power
• Coping with malicious/faulty nodes
• Scaling to large networks

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Topology Distribution Scales Badly
1. C can reach A and B.
3. Data from F to B.
2. D can reach A, B, and C.
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Geographic Forwarding Scales Well
Send towards latG / lonG.
Latitude
Longitude
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Location Database
DB
2. Where is G?
1. G is at latG / lonG
Latitude
Longitude
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Distributed Location Database

• Each node is DB for a few other nodes
• How to find a nodes location server(s)?
• Every node has an unchanging ID
• hash(ID) maps ID to position in unit square

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Gs Location Server is a Point
I
H
x
hash(G) 0.1,0.9
G
(0,0)
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Spatial Grid Hierarchy
All nodes agree on the global origin of the Grid
hierarchy
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Multiple Servers per Node
c
b
a
G
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Lookups Expand in Scope
c
b
a
G
?
A
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Grid Protocol Overhead Grows Slowly
Protocol Overhead (packets per second)
Number of nodes

• Protocol packets include Grid update, Grid
  query/reply.