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A Survey on Position-Based
Routing in Mobile Ad-Hoc Networks
Alok Sabherwal
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Overview
Introduction Location Services
Distance Routing Effect Algorithm for Mobility
Quorum-Based Location Service
Grid location Service
Homezone Forwarding Strategies
Greedy Packet Forwarding
Restricted Directional Flooding
DREAM
LAR Hierarchical Routing
Terminodes Routing
Grid Routing
Comparisons
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Routing in MANET
Static vs. Mobile
Flooding-based routing
Reactive vs. Proactive
Source routing vs. Table driven routing
Flat vs. Hierarchical routing
Non-location based vs. Location based routing
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Position-based routing
Position-based routing algorithms eliminate some ofthe limitations of topology-based routing by usingadditional information.
A location serviceis used by the sender of a packetto determine the position of the destination and toinclude it in the packets destination address.
Position-based routing thus does not require the
establishment or maintenance of routes.(Forwarding Strategy)
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Location Services
In order to learn the current position of a specificnode, the help of a location serviceis needed. Difficult to get the position of location server!
(Egg & Chicken)
No guarantee for one position server in each adhoc network.
Location services can be classified according tohow many nodes host the service Some-for-some Some-for-all All-for-some All-for-all
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Location Services
Distance Routing Effect Algorithm for Mobility (DREAM)
Quorum-Based Location Service
Grid Location Service (GLS)
Homezone
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Distance Routing EffectAlgorithm for Mobility (DREAM)
Proactively disseminate location information
Distance Effect:
Closer nodes are updated more frequently
age field in location update Mobility Effect:
rate of location update controlled by mobility
No bandwidth wastage for no movement
Routing policy If no entry for destination in table, flood
Otherwise forward data to mneighbors in thedirection of destination
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** All for all approach
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Quorum Based Location Services 1 of 3
Known from information
replication
Update and request
performed on different nodesubsets
If subsets intersect up todate information can always
be found
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Quorum Based Location Services 2 of 3
A some-for-some scheme Node subset hosts position databases
Virtual backbone between those nodes (non-position-based routing algorithm)
Send position update and query to the nearestbackbone node
Backbone node contacts the nodes of a (usuallydifferent) quorum
Timestamps to choose most current information
Tradeoff: Quorum size
(communication cost and resilience against
unreachable backbone nodes)
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Quorum Based Location Services 3 of 3
How to deal with the movement ofbackbone node?
The topology of the backbone will be
rearranged
If a backbone node has been disconnectedfrom the network for more than a threshold
amount of time, a new node will be chosenas the replacement
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Grid Location Service (GLS)
Geographic Forwarding
- Each node maintains its position usingGPS and broadcast HELLO packet to itsneighbors
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Geographic Forwarding more..
Each node maintains a routing table for allnodes within two hops
Forward a packet to the neighbor nodeclosest to the destination
** All for some approach
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An Example of Grid
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The Grid Location Service (Cont.)
Three main activities
Location server selection
Location query request Location server update
Handling Failures
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Selecting Location Servers
Unique ID using hash function
Select nodes with ID closest to its own ID
Closest means the least ID greater than
the nodes ID
ID space is circular
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Location Server Organization
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Location Query Request
The query request packet is forwarded toa node that is closest to the destination,within the order-2 square
The packet is forwarded through thehigher order grid square until it reachesthe location server of the destination
The destination responds directly with itsdestination to the source node
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Location Server Update
Each node maintains two tables
- A location table
- A location cache
Update packet is sent to location servers
Update distance threshold
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Location Query Failures
Two types of failures
- A location server has out-of-date
informationSolution: use the old location information
- A node moves out of its current grid
Solution: forwarding pointers
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Homezone
A virtual homezone where position informationfor a node is stored
The position C of the homezone for a node can
be derived by applying a well-known hashfunction to the node identifier
All nodes within a disk with radius R centered atC have to maintain position information for the
node If the homezone is sparsely populated, R may
have to be increased
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Comparisons of Location Service
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Forwarding Strategies
Greedy Packet Forwarding
Restricted Directional Flooding
Hierarchical Routing
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Greedy Packet Forwarding
MFR Most Forward within R It tries to minimize the number of hops a packet has
to traverse in order to reach D
NFP Nearest with Forward Progress The packet is transmitted to the nearest neighbor of
the sender which is closer to the destination Better than MFR
Compass routing It selects the neighbor closest to the straight line
between sender and destination
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Greedy Routing Strategies
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Greedy Routing Failure
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Restricted Directional Flooding
DREAM Sender will forward the packet to all one-hop
neighbors that lie in the direction of destination
Expected region is a circle around the position of
destination as it is known to source The radius r of the expected region is set to (t1-
t0)*Vmax, where t1 is the current time, t0 is thetimestamp of the position information source has
about destination, and Vmax is the maximum speedthat a node may travel in the ad hoc network
The direction toward destination is defined by the linebetween source and destination and the angle
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DREAM
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Location-Aided Routing (LAR)
Each node knows its location in everymoment
Using location information for route
discoveryRouting is done using the last known
location + an assumption
Route discovery is initiated when: S doesnt know a route to D
Previous route from S to D is broken
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LAR - Definitions
Expected Zone
S knows the location L of D in t0
Current time t1 The location of D in t1 is the expected zone
Request Zone
Flood with a modification
Node S defines a request zone for the routerequest
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LAR
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Hierarchical Routing
Terminodes Routing
TLR (Terminode Local Routing)
It uses a proactive routing scheme if the
destination is close to the source node.
TRR (Terminode Remote Routing)
TRR allows data to be sent to non-TLR-reachabledestination
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Terminodes Routing
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Grid Routing
It is similar to Terminodes Routing
A proactive distance vector routing is usedat local level
Intermediate Node Forwarding (INF) isused for long-distance routing
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Comparisons of ForwardingStrategies
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Work done
How to discover the position of thedestination ?
How to forward the packets based onabove ?
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Results
All for some services like GLS incombination of greedy packet forwardingis the most promising in general position
based routing.
DREAM & LAR could be useful insituations where a small number of
packets need to be transmitted veryreliably.
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References
Martin Mauve, et al, A Survey on positionbased routing in ad-hoc networks , IEEENetwork Magazine 15 (6), pp. 30-39,
November 2001.
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Thank you!!