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Routing In (Mobile) Ad-Hoc Networks
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Outline
FloodingTopology-based Routing Protocols
Proactive Algorithms [DSDV – Destination Sequenced Distance-Vector Routing]Reactive (on demand) Algorithms [AODV – Ad-hoc On-Demand Distance Vector Routing], [DSR – Dynamic Source Routing]
Geographic Routing Protocols[FR – Face Routing], [GPSR – Greedy Perimeter Stateless Routing]
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Communication by flooding
ProsSimpleWork also in highly dynamic networks
ConsLots of messages duplicateAll nodes always involvedScalability
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Routing In (Mobile) Ad-Hoc Networks
Proactive, table-driven algorithms
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Proactive Routing
Each node floods the network with its own local topology informationOn the basis all this information each node computes the global topology of the network.Each node can calculate complete routes.
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DSDV – Destination Sequenced Distance-Vector Routing
A
B
C
EDA-B
A-C
C-A
C-D
B-A
B-D
D-B
D-C
D-E
E-D
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DSDV – Destination Sequenced Distance-Vector Routing
A
B
C
ED
A-B
A-C C-A
C-D
B-A
B-D
D-B
D-C
D-E
E-D
Graph Algorithm
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DSDV – Destination Sequenced Distance-Vector Routing
A
B
C
ED
A-B
A-C C-A
C-D
B-A
B-D
D-B
D-C
D-E
E-D
StandardGraph Algorithm
SEND: Ciao
TO: E
ROUTE: A-B-D-E
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Routing In (Mobile) Ad-Hoc Networks
Reactive, on-demand algorithms
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Ad Hoc On-Demand Distance Vector Routing (AODV) 1/2
Routes are created on demand, only when actually needed.A node S wishing to communicate with node D starts a discovery process to find where is DD replies creating a communication channel between S and DCommunication travels through the established channel
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Ad Hoc On-Demand Distance Vector Routing (AODV) 2/2
Route Requests (RREQ) are flooded across the network, implementing a breadth-first, expanding-ring algorithm.When a node re-broadcasts a Route Request, it sets up a reverse path pointing towards the source
AODV assumes symmetric (bi-directional) linksWhen the intended destination receives a Route Request, it replies by sending a Route Reply (RREP)Route Reply travels along the reverse path set-up when Route Request is forwarded
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Route Requests in AODV
B
A
S EF
H
J
D
C
G
IK
Z
Y
Represents a node that has received RREQ for D from S
M
N
L
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Route Requests in AODV
B
A
S EF
H
J
D
C
G
IK
Represents transmission of RREQ
Z
YBroadcast transmission
M
N
L
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Route Requests in AODV
B
A
S EF
H
J
D
C
G
IK
Represents links on Reverse Path
Z
Y
M
N
L
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Reverse Path Setup in AODV
B
A
S EF
H
J
D
C
G
IK
• Node C receives RREQ from G and H, but does not forwardit again, because node C has already forwarded RREQ once
Z
Y
M
N
L
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Reverse Path Setup in AODV
B
A
S EF
H
J
D
C
G
IK
Z
Y
M
N
L
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Reverse Path Setup in AODV
B
A
S EF
H
J
D
C
G
IK
Z
Y
• Node D does not forward RREQ, because node Dis the intended target of the RREQ
M
N
L
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Forward Path Setup in AODV
B
A
S EF
H
J
D
C
G
IK
Z
Y
M
N
L
Forward links are setup when RREP travels alongthe reverse path
Represents a link on the forward path
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Communication and Link FailureCommunication
Once forward and backward routes have been established S and D can communicate without flooding the network.Moreover, subsequent discovery of routes toward S and D can takeadvantage of the established route constraining flooding.
Link FailureWhen node X is unable to forward packet P (from node S to node D) on link (X,Y), it generates a RERR message to S.When node S receives the RERR, it initiates a new route discovery for DThe routing structure is adjusted on-demand
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Routing In (Mobile) Ad-Hoc Networks
Geographic algorithms
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What is Geographic Routing?
A.k.a. location-based, position-based, geometric, etc.Each node knows its own position and position of neighborsSource knows the position of the destination. No routing tables stored in nodes!Geometric routing is important:
GPS/Galileo, local positioning algorithm,overlay P2P network, Geo-casting
The Problem with Greedy Routing
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Greedy Routing…. Problems
Forward to the node closer to the destination…..
S
D
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Related Work in Geometric Routing
Worst-case optimal and average-case efficient, percolation theory
GOAFRMobiHoc 2003Kuhn, Wattenhofer, Zollinger
Improved GOAFR for average case, analysis of cost metricsGOAFR+PODC 2003Kuhn, Wattenhofer, Zhang, Zollinger
First worst-case analysis. Tight Ω(c2) bound.AFRDialM 2002Kuhn, Wattenhofer, Zollinger
A new name for GFGGPSRMobiCom 2000Karp, Kung
First average-case efficient algorithm (simulation but no proof)
GFGDialM 1999Bose, Morin, Stojmenovic, Urrutia
First correct algorithmFace RoutingCCCG 1999Kranakis, Singh, Urrutia
Geometric Routing proposedMFR et al.Various 1975ffKleinrock et al.
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Face RoutingBased on ideas by [Kranakis, Singh, Urrutia CCCG 1999]Here simplified (and actually improved)
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Face Routing
It applies to planar graph only.Remark: Planar graph can easily (and LOCALLY!) be computed with the Gabriel Graph, for example
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Gabriel Graph
A planar (Gabriel) graph is computed from an ad-hoc network by dropping crossing-linksThe Gabriel Graph GG(V) is defined as an undirected graph (with E being a set of undirected edges). There is an edge between two nodes u,v iff the disk(u,v) inclusive boundary contains no other points. disk(u,v)
U V U V
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Gabriel Graph Example 1/2
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Gabriel Graph Example 2/2
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Face Routing
s t
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Face Routing
s t
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Face Routing
s t
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Face Routing
s t
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Face Routing
s t
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Face Routing
s t
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Face Routing
s t
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All necessary information is stored in the messageSource and destination positionsPoint of transition to next face
Completely local:Knowledge about direct neighbors‘ positions sufficientFaces are implicit
Planarity of graph is computed locally (not an assumption)Computation for instance with Gabriel Graph
Face Routing Properties
“Right Hand Rule”
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Conclusions
ProactiveSuitable for only relatively static networks.
ReactiveSuitable for highly mobile networks, with mainly 1-1 communication
GeographicRequire localization. Opens new scenarios (decoupling).