MANET:168

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Location-Aware Routing Protocolsin a Mobile Ad
Hoc Network

• Professor Yu-Chee Tseng
• Dept. of Computer Science and Information
  Engineering
• National Chiao-Tung University
• (???? ????? ???)

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Notebook GPS
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Location-Aided Routing

• LAR in MobiCom 1998.
• Main Idea
• Using location information to reduce the number
  of nodes to whom route request is propagated.
• Location-aided route discovery based on limited
  flooding

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Location Information

• Consider a node S that needs to find a route to
  node D.
• Assumption
• each host in the ad hoc network knows its current
  location precisely (location error considered in
  one of their simulations)
• node S knows that node D was at location L at
  time t0, and that the current time is t1
• Location services in ad hoc networks, refer to
• A survey on position-based routing in mobile ad
  hoc networks, M. Mauve, J. Widmer, and H.
  Hartenstein, IEEE Network, Vol. 15 No. 6,  2001.

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Expected Zone
expected zone of D ---- the region that node S
expects to contain node D at time t1, only an
estimate made by node S
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Request Zone

• LARs limited flooding
• A node forwards a route request only if it
  belongs to the request zone
• The request zone should include
• expected zone
• other regions around the expected zone
• No guarantee that a path can be found consisting
  only of the hosts in a chosen request zone.
• timeout
• expanded request zone

• Trade-off between
• latency of route determination
• the message overhead

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Membership of Request Zone

• How a node determines if it is in the request
  zone for a particular route request

• LAR scheme 1 inside or outside the request zone
• LAR scheme 2 based on whether there is any
  progress

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LAR Scheme 1
Two cases whether the source node is inside or
outside the expected zone?
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LAR Scheme 2
S knows the location (Xd, Yd) of node D at time
t0 Node S calculates its distance from location
(Xd, Yd) DISTs
Node I receives the route request, calculates its
distance from location (Xd, Yd) DISTi For some
parameter d, If DISTs d DISTi, node I
replaces DISKs by DISKi and forwards the request
to its neighbors otherwise discards the route
request
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GRID A Fully Location-Aware Routing Protocol
for Mobile Ad Hoc Networks

• Telecommunication Systems, 2001.

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Basic Idea

• Adopt Positioning Systems
• such as GPS receivers
• President Clinton ordered to discontinue SA
  (selective availability) in May 2000
• will increase the accuracy by an order
• Fully utilize location information
• route discovery
• data forwarding
• route maintenance
• We propose a new protocol called GRID.

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How to Utilize Location InformationObservation 1

• Determine route quality based on location
  information
• passing B is better than passing A

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How to Utilize Location InformationObservation
2 (Route Handover)

• Improving the vulnerability and quality of a
  route based on location information
• When B moves away, E can work on behalf of B.
• When F roams in, using F is more reliable.

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Comparison of Using Location Information
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The GRID Routing Protocol

• Partition the physical area into d x d squares
  called grid.

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Protocol Overview

• In each grid, a leader will be elected, called
  gateway.
• Routing is performed in a grid-by-grid manner.
• Responsibility of gateway
• forward route discovery packets
• propagate data packets to neighbor grids
• maintain routes which passes the grid

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Route Search

• We can adopt any existing route discovery
  protocol.
• Major features/differences
• limit the search range by the locations of source
  and destination
• only gateway will help with the discovery process
• The more crowded the area is, the more saving.
• routing table is indicated by grid ID (instead of
  host address)

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Route Search Example

• route search
  route reply

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Route Search Range Options
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Routing Table Format

• Next-hop routing
• the next hop is identified by grid ID (not host
  ID)

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Route Maintenance

• Two issues
• how to maintain a gateway in each grid
• how to maintain a grid-by-grid route
• Special Feature
• longer route lifetime
• as long as there is a host in each gateway, a
  route will be alive
• more robust
• In existing protocols, once a node in the route
  roams away, the route will be broken.

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Gateway Election in a Grid

• Any leader election protocol in distributed
  computing can be used.
• Weaker than leader election
• It is acceptable that there are multiple leaders
  in a grid.
• But without leader is less acceptable.
• Preference in electing a gateway
• near the physical center of the grid
• likely to remain in the grid for longer time
• once elected, a gateway will remain so until
  leaving the grid
• to avoid ping-pong effect

X
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Gateway Election Details
BID(g, loc)
GATE(g, loc)
RETIRE(g, T)
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How to Maintain a Grid-by-Grid Route

• Strength more robust route
• mobility-resistant
• Problems
• Gateway moves away
• The gateway election will find the new gateway.
• So the route will remain alive.
• Source moves away (see next page)
• getting closer
• getting farther away
• Destination move away (similar)

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(a) getting closer (b) same length (c) getting
farther, remaining connected (d) getting
farther, but disconnected
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Relationship of Grid Size and Transmission
Distance

• r radio transmission distance
• d grid size

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Simulation Model

• Physical area of size 1000m?1000m
• n number of hosts 100300
• r300m
• d grid size
• GRID-1
• GRID-2
• GRID-3
• Roaming speed 30 km/hr, 60 km/hr

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Route Lifetime

• With better route maintenance, our route lifetime
  is longer.
• 30 km/hr
  60 km/hr

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Routing Cost (s30 km/hr)

• n 100, 200, 300
• (number of hosts)
• GRID is better in
• more crowded area.

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Delivery Rate

• With less routing cost (and thus less traffic
  load), our packets can be delivered with higher
  success rate.
• 30 km/hr
  60 km/hr

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Route Length

• Limited by gateway positions, the route length
  could be longer for GRID approach.
• 30 km/hr
  60 km/hr

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Implementation Experience

• Platform
• Red Hat Linus
• building our routing protocol in the kernel
• 5 10 notebooks
• WaveLAN cards
• Application
• ad hoc classroom (????)
• ????????
• anytime, anywhere classroom

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Conclusions

• A FULLY location-aware routing protocol
• route discovery by gateways only
• data forwarding by gateway ID, instead of host
  ID
• route maintenance like handoff in GSM systems
• Taking advantage of geometric property of
  network.
• instead of graph property in other approaches
• Less routing cost
• longer route lifetime, more resilient route
• less traffic load

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Geographical Routing Using Partial Information
for Wireless Ad Hoc Networks

• Pahul Jain, Anuj Puri, Raja Sengupta
• University of California, Berkeley
• IEEE Personal Communication, 2001

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Basic Idea

• to use the geographical position of the
  destination in making routing decisions
• acyclic routes

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Rule 1 Packet Forwarding

• When a node S receives a packet for destination
  D, it finds the neighboring host X which is
  closest to D than any other neighbors.
• then forward the packet to X

X
D
S
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Rule 2 Route Discovery

• If S itself is closest to D than any other hosts.
  We say that the packet is stuck.
• Node S initiates a route discovery to destination
  D, following the DSR protocol.

D
S
Stuck, initiating route discovery
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Example
physical location
Initially, everyone only knows its neighbors.
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• Case 1 node A needs a route to destination C at
  (3, 1).
• Forward the packet to node B (closest to (3, 1)).
• B forwards the packet to C.
• Case 2 node A needs a route to destination D at
  (2.5, 0)
• It gets stuck (no one is closer to (2.5) than
  itself).
• A initiates Route Discovery.
• finding a new path ltA,B,C,D gt
• A updates its routing table.
• then forward the packet.
• See Table 5 (next page).

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newly learned
learned from snooping
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• Case 3 node A needs a route to destination E
• D is the nearest to E in As routing table.
• forward the packet to Next(D) B
• Node B forwards the packet to node C.
• Node C forward the packet to node E.
• note C will behave based on its own routing
  table.

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Conclusion

• Advantage
• Routing table is small in size.
• Routing tables are cycle-free.
• Low communication overhead.
• Disadvantage
• Destination position is known by the source
  before routing.
• A location discovery service is required.

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Geocasting

• Geocasting
• sending a message to everyone WITHIN a specific
  geographical region
• Application
• emergency messages to a building, or an assembly
  ground
• geographic advertisement

Geocast region
Geocast group