MANETs Routing
Dr. Raad S. Al-Qassas
Department of Computer Science
PSUT
raad@psut.edu.jo
Outline
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Routing challenges
Mobility patterns
AODV routing protocol
Performance metrics
MANET routing challenges
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No fixed infrastructure.
Nodes can have unlimited mobility.
Multiple hops to destination.
Unreliable communication medium.
All nodes need to participate in routing/forwarding.
Mobility patterns
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MANET nodes may follow one or more of the following
patterns :
–
–
–
–
Stationary nodes (e.g., sensor nodes).
Highly mobile nodes (e.g., vehicles).
Discrete versus continuous mobility.
Structured versus unstructured mobility.
Mobility patterns
Node mobility is characterised by:
 Speed.
 Direction.
 Pause time.
Unicast Route Establishment
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Unicast route is a route from a source node to a
destination node.
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Ad hoc On-demand Distance Vector
Routing (AODV)
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AODV has two phases:
– Route establishment
– Route maintenance
Route Request (RREQ) Message
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When node S wants to send a message to node D, S
searches its route table for a route to D.
If there is no route, S initiates a RREQ message with
the following components :
– The IP addresses of S and D
– The current sequence number of S and the last known
sequence number of D
– A broadcast ID from S. This broadcast ID is incremented
each time S sends a RREQ message.
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Processing a RREQ Message (I)
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The <broadcast ID, IP address> pair of the source S
forms a unique identifier for the RREQ.
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Suppose a node P receives the RREQ from S. P first
checks whether it has received this RREQ before.
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Each node stores the <broadcast ID, IPaddress> pairs
for all the recent RREQs it has received.
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Processing a RREQ Message (II)
S
Q
P
D
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If P has seen this RREQ from S already, P discards the RREQ. Otherwise, P
processes the RREQ :
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P sets up a reverse route entry in its route table for the source S.
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This entry contains the IP address and current sequence number of S, number of
hops to S and the address of the neighbour from whom P got the RREQ.
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Lifetime of a Route-Table Entry
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A lifetime is associated with the entry in the route
table.
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This is an important feature of AODV. If a route entry
is not used within the specified lifetime, it is deleted.
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A route is maintained only when it is used. A route
that is unused for a long time is assumed to be stale.
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Route Requests in AODV
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
D
N
Represents a node that has received RREQ for D from S
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Route Requests in AODV
Y
Broadcast transmission
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
D
N
Represents transmission of RREQ
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Route Requests in AODV
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
N
Represents links on Reverse Path
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Reverse Path Setup in AODV
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
D
N
• Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once
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Reverse Path Setup in AODV
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
I
D
N
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Reverse Path Setup in AODV
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
• Node D does not forward RREQ, because node D
is the intended target of the RREQ
N
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Forward Path Setup in AODV
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
N
Forward links are setup when RREP travels along
the reverse path
Represents a link on the forward path
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Handling More than one RREP
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An intermediate node P may receive more than
one RREP for the same RREQ.
P forwards the first RREP it receives and
forwards a second RREP later only if :
– The later RREP contains a greater sequence number
for the destination, or
– The hop-count to the destination is smaller in the
later RREP
– Otherwise, it does not forward the later RREPs. This
reduces the number of RREPs propagating towards
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the source.
Route Maintenance
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Once a unicast route has been established
between two nodes S and D, it is maintained as
long as S (source node) needs the route.
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If S moves during an active session, it can
reinitiate route discovery to establish a new
route to D.
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When D or an intermediate node moves, a
route error (RERR) message is sent to S.
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Route Maintenance
3´
RERR
RERR
1
S
3
2
D
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The link from node 3 to D is broken as 3 has moved away to a position 3´.
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Node 2 sends a RERR message to 1 and 1 sends the message in turn to S.
S initiates a route discovery if it still needs the route to D.
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Updating Route Tables
3´
RERR
RERR
1
3
2
D
S
4
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5
Suppose neighbours 4 and 5 route through 2 to
reach D. Node 2 broadcasts RERR to all such
neighbours.
Each neighbour marks its route table entry to D as
invalid by setting the distance to infinity.
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Updating Route Tables
3´
RERR
RERR
1
3
2
D
S
4
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5
Each neighbour in turn propagates the RERR
message.
Route entries with an infinity metric are not rejected
immediately as they contain useful routing
information for the neighbourhood.
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Local Connectivity
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Neighbourhood information is obtained through
hello messages. Each node broadcasts a hello
message to its neighbours at a regular hellointerval.
When a node M receives a hello message from a
neighbour N, node M updates the lifetime
associated with N in its route table.
Hello messages propagate only for one hop, in
the neighbourhood of a node.
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Performance measures
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Throughput
end-to-end delay
routing overhead
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Performance measures
(throughput)
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The throughput is the amount of data received
(measured in bits per second) at the final destination
over the simulated time averaged over the number of
flows.
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provides an indication of the efficiency of the routing
protocol as it shows the amount of data that the
protocol is able to deliver to destinations.
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Performance measures
(end-to-end delay )
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The end-to-end delay is the average time interval
between the generation of a packet in a source node
and the successful delivery of the packet at the
destination node.
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This delay accounts for all possible delays that can occur
in the source and all intermediate nodes.
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Performance measures
(routing overhead)
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The routing overhead is the number of routing (control)
packets generated during the simulated time in order to
establish and maintain paths and to exchange traffic
information among network nodes as dictated by the
operation of a given traffic aware metrics.
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routing packets sent over multiple hops, each hop
counts as one transmission.
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Performance measures
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The routing overhead measures the scalability of the
routing protocol and its efficiency in terms of consuming
a node’s battery power.
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The high routing overhead could affect the performance
in terms of data throughput and end-to-end delay.
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The high overhead is a result of factors like the
unsuccessful delivery of route requests and the
unsuccessful delivery of route replies.
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