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Routing Protocols for Mobile
Ad Hoc Network
10/17/05
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Outline
Introduction to mobile ad hoc network
Ad hoc protocol routing requirementsCategorization of ad-hoc routing protocols
Representative Ad hoc protocols
Destination-sequenced Distance-vector(DSDV)
Ad-hoc On-demand Distance Vector(AODV)
Dynamic Source Routing (DSR)
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Mobile ad hoc network (MANET)
Self-configuring network of mobile stationsconnected by wireless links
Defined as Independent Basic Service Set(IBSS) in IEEE 802.11 standards
Peer-to-peer communication without usingAccess Point (AP) or any wired network
Dynamic topology
mobile nodes free to move randomly
mobile stations form an arbitrary topology
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Mobile ad hoc network (MANET)
Mobile station has router function
Peer to peer communication, no central control
Multi-hop routes between nodes
s
d
s
d
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Characteristics of MANETs
Dynamic topology
links formed and broken with mobility
Possibly uni-directional links
Constrained resources
battery power
wireless transmitter range
Network partitions
A B A
B
s d s
d
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Routing in MANETs
Goal:To find and maintain routes between
nodes in a dynamic topology with possiblyuni-directional links, using minimumresources.
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Ad Hoc Protocol Routing Requirements
Simple, reliable and efficient
Distributed but lightweight in natureQuickly adapts to changes in topology
Protocol reaction to topology changes shouldresult in minimal control overhead
Bandwidth efficient
Mobility management involving user locationand hand-off management
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Categorization of Ad-Hoc Routing
Protocols
Figure from Elizabeth M. Royer, CFigure from Elizabeth M. Royer, C--KKTohToh, A Review of Current Routing, A Review of Current Routing
Protocols for AdProtocols for Ad--Hoc Mobile Wireless Networks.Hoc Mobile Wireless Networks.
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Table Driven Based Routing
(Proactive)
Maintain table of all active links in network
Calculate the shortest path from table
Update table whenever nodes move
Immediate tell if node is reachable
Data can be sent immediately
Very high overheadsDSDV
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On-demand Routing(Reactive)
Find routes as needed
Cache information from other nodes requests
No static overhead
Slow start before transmitting data
AODV, DSR
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Representative Ad Hoc Routing
Protocols
Destination-Sequenced Distance-Vector
Routing (DSDV)- Proactive(table driven),next-hop routing, distance-vector
Ad hoc On-demand Distance-Vector Routing
(AODV)-reactive,next hop routing,distance-vector
Dynamic Source Routing (DSR)-reactive (ondemand),source routing,link state
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DSDV Routing
[Charles Perkins &Pravin Bhagwat]
Current in use on the MIT GRID projects
Route advertisements
Route table entry structure
Responding to topology changesRoute selection criteria
Summary
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Route Advertisements in DSDV
Each mobile node advertise its ownroute tables to its current neighbors
Routing tables update periodically toadapt the dynamic change and maintain
table consistency
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Route Table Entry Structure in DSDV
When advertisement, each mobile nodecontain its new sequence number and thefollowing information for each new route
The destinations address The number of costs (hops) required to reach the
destination
The sequence number of the informationreceived,originally stamped by the destination.
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Example of Advertised Table in DSDV
MHi-address for the mobile node, MH
4is the node
advertising the route table update
Table from Charles E.Perkins, AD HOC NetworkingTable from Charles E.Perkins, AD HOC Networking
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Responding to Topology Changes in DSDV
Two types of packets defined for route updates
full dump packets Carry all available routing information Size of multiple network protocol data units (NPDUs)
Transmitted infrequently during period of occasionalmovement
Incremental packets
Carry only information changed since last full dump Size of a NPDU
Transmitted more frequently
Additional table maintained to store the data from theincremental packets
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Route Selection Criteria
Routes are preferred if the sequence
numbers are newerIf the sequence numbers are the same, theone with better metric is preferred
Keep track of the settling time of routes-theweighted average time that routes to adestination will fluctuate before the route with
best metric is received (Why?)
R t S ttli Ti
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Route Settling Time
and SolutionA
CB
D
MN collection 1 MN collection 2
Problem
A initiated a route update with a new sequence number
Update from B arrives D 10 s before update from C
Metric of update from C is better (less hops)
Solutiondelay the broadcast of a routing by the length of thesettling time.
Exception:When broken link is found, broadcastimmediately
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Summary of DSDV Routing
Essentially a modification to Bellman-Fordrouting algorithm
Using sequence number to guarantee loop-freepaths
Relies on periodic exchange of routinginformation.
Inefficient due to periodic update transmissionseven no changes in topology
Overhead grows as O(n2) , limiting scalability
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Dynamic Source Routing (DSR)
[Dave J ohnson]
Internet drafts available on MANET webpage
Reactive (on demand)
Source routing
Based on link-state routing algorithm
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Route Discovery in DSR (1/6)
Sender floods RREQ through the network
Nodes forward RREQs after appending theirnames
Destination node receives RREQ andunicasts a RREP back to sender node
Y
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Route Discovery in DSR (2/6)
Represents node that has received RREQ originated
from S to D
B
A
S E
F
H
J
C
G
I
K
Z
Y
M
N
L
D
RREQ includes: the source IP address, the destination IP, a
unique request ID
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Route Discovery in DSR(3/6)
B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
YBroadcast transmission
M
N
L
[S]
[X,Y] Represents list of identifiers appended to RREQ
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Route Discovery in DSR (5/6)
B
A
S E
F
H
J
D
C
G
I
K
Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once
Z
Y
M
N
L
[S,C,G]
[S,E,F]
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Route Discovery in DSR(6/6)
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
Nodes J and K both broadcast RREQ to node D
N
L
[S,C,G,K]
[S,E,F,J]
Target Node Reaction
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Target Node Reaction
Node D examines its route cache, if a route to S found,use it as source route for RREP.Otherwise,
May perform its own route discovery to S,
piggyback the RREP on its own RREQ to S Simply reverse the sequence of hops in the
route record
Preferred by IEEE 802.11 that require abidirectional frame exchange
Avoids the overhead of a possible secondroute discovery
Tests the discovered route
Advantage : support asymmetric link
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Route Reply in DSR
B
A
S EF
H
J
D
C
G
I
K
Z
Y
M
N
L
RREP [S,E,F,J,D]
Represents RREP control message
Route reply with its associated route record back to thesource node
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Summary of DSR Routing
Potentially larger overhead
Intended for moderate speed mobile nodes, sourcerouting, not scalable to large networks
No network topology changes, no overhead
Support asymmetric link
Allow nodes keep multiple routes to one destinationin their cache, faster route recovery
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1. RomitRoy Choudhury and Nitin H. Vaidya, Impact of
Directional Antennas on Ad Hoc Routing.2. Elizabeth M. Royer, C-K Toh, A Review of Current
Routing Protocols for Ad-Hoc Mobile Wireless
Networks.3. Charles E. Perkins, AD HOC Networking
References