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8/3/2019 32-Mobile Ad Hoc Networks
http://slidepdf.com/reader/full/32-mobile-ad-hoc-networks 1/64
Mobile Ad Hoc Networks
• An ad hoc wireless network is a collection of two or more
devices equipped with wireless communications and networking
capacity.
• Ad hoc networks is a collection of wireless mobile nodes
dynamically forming a network without the aid of any network
infrastructure.
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B Y.
P. V I C T E R P A U L
D E A R ,
W E P L A N N E D T O S H A R E O U R E B O O K S A N D P R O J E C T / S E M I N A R
C O N T E N T S F O R F R E E T O A L L N E E D E D F R I E N D S L I K E U . . T O
G E T T O K N O W A B O U T M O R E F R E E C O M P U T E R S C I E N C E
E B O O K S A N D T E C H N O L O G Y A D VA N C E M E N T S I N C O M P U T E R
S C I E N C E . P L E A S E V I S I T. . . .
H T T P : / / F R E E - C O M P U T E R S C I E N C E - E B O O K S . B L O G S P O T . C O M /
H T T P : / / R E C E N T - C O M P U T E R - T E C H N O L O G Y . B L O G S P O T . C O M /
H T T P : / / C O M P U T E R T E C H N O L O G I E S E B O O K S . B L O G S P O T . C O M /
P L E A S E T O K E E P P R O V I D E M A N Y E B O O K S A N D T E C H N O L O G Y
N E W S F O R F R E E . E N C O U R A G E U S B Y C L I C K I N G O N T H E
A D V E R T I S E M E N T I N T H E S E B L O G .
8/3/2019 32-Mobile Ad Hoc Networks
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Multi-hop transmission
• May need to traverse multiple links to reach a
destination
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Mobility
Mobility causes route changes
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Advantages of Ad Hoc Networks
Ease of deployment
Speed of deployment
Decreased dependence on infrastructure
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Applications
• Military environments
soldiers, tanks, planes
• Emergency operations
Disaster recovery• Search-and-rescue
• Policing and fire fighting
• Taxi cab network
• Conference venues
• Meeting rooms
• Sports stadiums
•
Boats, small aircraft
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MANET Variations
• Fully Symmetric Environment
• all nodes have identical capabilities and responsibilities
• Asymmetric Capabilities
•
transmission ranges and radios may differ• battery life at different nodes may differ
• processing capacity may be different at different nodes
speed of movement
• Asymmetric Responsibilities• only some nodes may route packets
• some nodes may act as leaders of nearby nodes (e.g.,
cluster head)
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MANET vs. Traditional Routing
•Every node is potentially a router in a MANET. Topologies are
dynamic in MANETs due to mobile nodes, but are relatively static
in traditional networks
•Routing in MANETs must consider both Layer 3 and Layer 2
information, while traditional protocols rely on Layer 3 informationonly.
•A MANET “router” typically has a single interface.
•Interference is an issue in MANETs, but not in traditional
networks.
•Power efficiency is an issue in MANETs.
•There is limited physical security in a MANET compared to a
traditional network
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Challenges
• Limited wireless transmission range
Time-varying wireless link characteristics: unreliable
• Broadcast nature of the wireless medium
• Hidden terminal problem and broadcast storms
• Packet losses due to transmission errors
• Mobility-induced route changes
• Mobility-induced packet losses
•
Battery constraints• Potentially frequent network partitions
• Ease of snooping on wireless transmissions (security
issues)
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MANET Issues
Lack of a centralized entity
Network topology changes frequently and unpredictably
Channel access/Bandwidth availability
Hidden/Exposed station problem Lack of symmetrical links
Power limitation
Multipath Fading
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MANET Protocol Stack
• Physical Layer: 2.4/5.8 Ghz, FHSS/DSSS, OFDM,
OFDMA, MIMO, Directional Antenna, etc
• MAC Layer: CSMA, CSMA/CA, RTS/CTS, TDMA
with Scheduling Algorithm• Routing Layer: Addressing; DSR, AODV, OLSR,
TORA, ZRP, LAR, etc.
• Transport Layer: UDP, TCP, RTP, etc.
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MANET Protocols
Proactive Protocols
Table driven
Continuously evaluateroutes
No latency in route
discovery
Large network capacity to
keep info. current
Most routing info. may
never be used!
Reactive Protocols
On Demand
Route discovery by some
global search
Bottleneck due to latency
of route discovery
May not be appropriate for
real time commn.
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Conventional Routing Protocols
DBF shows a degradation in performance
Slow convergence due to “Count to Infinity” Problem
Creates loops during node failure, network partition or congestion
Protocols that use flooding techniques create excessive traffic andcontrol overhead
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MANET Protocol Considerations
Simple, Reliable and Efficient
Distributed but lightweight in nature
Quickly adapt to changes in topology and traffic pattern
Protocol reaction to topology changes should result inminimal control overhead
Bandwidth efficient
Mobility Management involving user location management
and Hand-off management
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Table Driven Routing Protocol
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Destination-Sequenced Distance Vector Protocol(DSDV)
Basic Routing Protocol
Based on Bellman ford routing algorithm with some
improvement
Each node maintains a list of all destinations and
number of hops to each destination. Each entry is marked with a sequence number.
Periodically send table to all neighbors to maintain
topology
Two ways to update neighbors:
Full dump
Incremental update
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Example of DSDV
Destination Next Hop Distance Sequence Number
A A 0 S304_A
B D 3 S424_B
C C 1 S297_C
D D 1 S687_D
E D 2 S868_E
F D 2 S164_F
Destination Next Hop Distance Sequence Number
A A 0 S205_A
B B 1 S334_B
C C 1 S198_C
D D 1 S567_D
E D 2 S767_E
F D 2 S45_F
A’s Routing Table Before Change
A’s Routing Table After Change
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Clusterhead Gateway Switch Routing(CGSR)
Similar to DSDV
Based on concept of clusters and cluster heads
Routing is done via the cluster heads and
gateways A routing table among cluster heads are
maintained
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Ad Hoc Networks and Automotive Applications
19
Clustering
Transforms the physical network into a virtualnetwork of interconnected node clusters
Cluster controllers act on behalf of other members of
the cluster to make control decisions Gateways establish communication between clusters
The objective is to improve efficiency of resource use by
Reducing channel contention
Forming routing backbones to reduce network diameter
Abstracting network state information to reduce its quantity and variability
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Example of CGSR
Data forwarding steps:
•from cluster head to
cluster head
– in a hierarchical manner•then from cluster head to
cluster members
•between two cluster heads,
gateways are used to forward
the packets
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Wireless Routing Protocol
Each node maintains a distance table, a routingtable,
link-cost table and a message retransmission list.
Distance table: Indicates the number of hops
between a node and its destination.
Routing table: Indicates the next hop node.
Link cost table:
Reflects the delay associated with a particular link.
Message retransmission list:
One or more retransmission entries
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Wireless Routing Protocol
Exchanged among nodes:
(routing table update messages ) Identifier of the sending node
A sequence number assigned by the sending node
An update list of updates or ACKs to update message
A response list of nodes that should send an ACK to the update
message
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Wireless Routing Protocol
Each node will communicate with its neighborsreporting any changes in the system
Each node will keep track of which node shouldsend an acknowledgement
Nodes will keep track of the changes in the system by periodic transmission of ‘hello’ messages
This protocol will force nodes to do consistent
check of their predecessor hence avoiding count-to-infinity problem.
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Flooding for Data Delivery
• Sender S broadcasts data packet P to all its neighbors •
Each node receiving P forwards P to its neighbors
• Sequence numbers used to avoid the possibility of forwarding the samepacket more than once
• Packet P reaches destination D provided that D is reachable from
sender S
• Node D does not forward the packet
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Flooding for Data Delivery-a wireless example
Y
Z
S E
FB C M L
J
A G
H DK
I N
Represents a node that has received packet P
Represents that connected nodes are within each
other’s transmission range
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Flooding for Data Delivery Y
Broadcast transmission
Z
S E
FB C M L
J
A G
H DK
I N
Represents a node that receives packet P for the first time
Represents transmission of packet P
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Flooding for Data Delivery Y
Z
S E
FB C M L
J
A G
H DK
I N
• Node H receives packet P from two neighbors:potential for collision
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Flooding for Data Delivery Y
Z
S E
FB C M L
J
A G
H DK
I N
• Node C receives packet P from G and H, but does not forward it
again, because node C has already forwarded packet P once
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Flooding for Data Delivery Y
Z
S E
FB C M L
J
A G
H DK
I N
• Nodes J and K both broadcast packet P to node D
• Since nodes J and K are hidden from each other, their
transmissions may collide
=> Packet P may not be delivered to node D at all,despite the use of flooding
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Flooding for Data Delivery Y
Z
S E
FB C M L
J
A G
H DK
I N
• Node D does not forward packet P, because node Dis the intended destination of packet P
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Flooding for Data Delivery Y
Z
S E
FB C M L
J
A G
H DK
I N• Flooding completed
• Nodes unreachable from S do not receive packet P (e.g., node Z)
• Nodes for which all paths from S go through the destination D
also do not receive packet P (example: node N)
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Flooding for Data Delivery Y
Z
S E
FB C M L
J
A G
H DK
I N
• Flooding may deliver packets to too many nodes(in the worst case, all nodes reachable from sender may receive the packet)
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Flooding for Data Delivery: Advantages
• Simplicity
• Efficient for:
- Low information exchangerate - High mobility
In these cases, the overhead of explicit routediscovery/maintenance incurred by other protocols may berelatively higher e.g. nodes transmit small data packets relativelyinfrequently, and topology changes occur between consecutive
packet transmissions• Potentially higher reliability of data delivery
- Because packets may be delivered to the destination on multiple paths
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Flooding for Data Delivery: Disadvantages
• Potentially, very high overhead
- Data packets may be delivered to too many nodes who do not
need to receive them
• Potentially lower reliability of data delivery (or higher delay)
- Flooding uses broadcasting -- hard to implement reliablebroadcast delivery without significantly increasing overhead
- Broadcasting in IEEE 802.11 MAC is unreliable
- In our example, nodes J and K may transmit to node Dsimultaneously, resulting in loss of the packet
- in this case, destination would not receive the packet at all
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Dynamic Source Routing (DSR)
• When node S wants to send a packet to node D, but doesnot know a route to D, node S initiates a route discovery
• Source node S floods Route Request (RREQ) • Each node
appends own identifier when forwarding RREQ
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Route Discovery in DSR Y
Z
S E
F
B C M LJ
A G
H DK
I N
Represents a node that has received RREQ for D from S
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Route Discovery in DSR YBroadcast transmission
[S] Z
S E
F
B C M LJ
A G
H DK
I N
Represents transmission of RREQ
[X,Y] Represents list of identifiers appended to RREQ
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Route Discovery in DSR Y
Z[S,E]S E
F
B C M LJ
A [S,C] G
H DK
I N
• Node H receives packet RREQ from two neighbors:potential for collision
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Route Discovery in DSR Y
Z
S E
F [S,E,F]
B C M LJ
A G
H DK
[S,C,G]I 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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Route Discovery in DSR Y
Z
S E
F [S,E,F,J]
B C M LJ
A G
H DK
I [S,C,G,K] N
• Nodes J and K both broadcast RREQ to node D • Since nodes
J and K are hidden from each other,transmissions may collide
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Route Discovery in DSR Y
Z
S E[S,E,F,J,M]
F
B C M LJ
A G
H DK
I N
• Node D does not forward RREQ, because node D is the
intended target of the route discovery
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Route Discovery in DSR
• Destination D on receiving the first RREQ, sends a RouteReply (RREP)
• RREP is sent on a route obtained by reversing the routeappended to received RREQ
• RREP packet contains the route from S to D that wasdiscovered using the RREQ packet
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Route Reply in DSR Y
ZRREP [S,E,F,J,D]S E
F
B C M LJ
A G
H DK
I N
Represents RREP control message
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Dynamic Source Routing (DSR)
• Node S on receiving RREP, caches the route included inthe RREP
• When node S sends a data packet to D, the entire route isincluded in the packet header
- hence the name source routing
• Intermediate nodes use the source route included in apacket to determine to whom a packet should beforwarded
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Data Delivery in DSR Y
DATA [S,E,F,J,D] Z
S E
F
B C M LJ
A G
H DK
I N
Packet header size grows with route length
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When to Perform a Route Discovery?
• When node S wants to send data to node D (i.e. on-demand ), but does not know a valid route to node
D
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DSR Optimization: Route Caching
• Each node caches a new route it learns by any means •When node S finds route [S,E,F,J,D] to node D, node Salso learns route [S,E,F] to node F
• When node K receives Route Request [S,C,G] destined fornode D, node K learns route [K,G,C,S] to node S • Whennode F forwards Route Reply [S,E,F,J,D], node F learnsroute [F,J,D] to node D
• When node E forwards Data [S,E,F,J,D] it learns route
[E,F,J,D] to node D• A node may also learn a route when it overhears Data
packets!
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Use of Route Caching
• When node S learns that a route to node D is broken, it uses another route from its local cache, if such a route to D exists in its cache.
Otherwise, node S initiates route discovery by sending a route request
• Node X on receiving a Route Request for some node D can send aRoute Reply if node X knows a route to node D
• Use of route cache
- can speed up route discovery
- can reduce propagation of route requests
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Use of Route Caching
[S,E,F,J,D][E,F,J,D]
S [F,J,D],[F,E,S]E
F
[J,F,E,S]B C M LJ
[C,S]A G
H D[G,C,S] K
I N
Z
[P,Q,R] Represents cached route at a node
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Use of Route Caching:
Can Speed up Route Discovery
[S,E,F,J,D][E,F,J,D]
S [F,J,D],[F,E,S]E
F
[J,F,E,S]B C M L[G,C,S]J
[C,S]A G
H DK[K,G,C,S]
RREPI N
RREQZ
When node Z sends a route request for node C, node K sends back a routereply [Z,K,G,C] to node Z using a locallycached route
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Use of Route Caching:
Can Reduce Propagation of Route Requests Y[S,E,F,J,D]
[E,F,J,D]
S [F,J,D],[F,E,S]E
F
[J,F,E,S]B C M L[G,C,S]J
[C,S]A G
H DK[K,G,C,S]
I NRREP
RREQZ
Assume that there is no link between D and Z. RouteReply (RREP) from node K limits flooding of RREQ. Ingeneral, the reduction may be less dramatic.
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Route Error (RERR) Y
RERR [J-D] Z
S E
F
B C M LJ
A G
H DK
I N
J sends a route error to S along route J-F-E-S when its attempt toforward the data packet S (with route SEFJD) on J-D fails
Nodes hearing RERR update their route cache to remove link J-D 36
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Route Caching:Disadvantages
• Stale caches can adversely affect performance
• With passage of time and host mobility, cached routes may become
invalid
• A sender host may try several stale routes (obtained from local cache,or replied from cache by other nodes), before finding a good route
•(An illustration of the adverse impact on TCP can be found in[Holland99])
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Dynamic Source Routing: Advantages
• Routes maintained only between nodes who need tocommunicate (ie. on-demand )
- reduces overhead of route maintenance
• Route caching can further reduce route discovery overhead
• A single route discovery may yield many routes to thedestination, due to multiple intermediate nodesreplying from local caches
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Dynamic Source Routing: Disadvantages
• Packet header size grows with route length due to sourcerouting
• Flood of route requests may potentially reach all nodes inthe network
• Care must be taken to avoid collisions between routerequests propagated by neighboring nodes
- insertion of random delays before forwarding RREQ
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Ad Hoc On-Demand Distance Vector Routing
(AODV)
• DSR includes source routes in packet headers
• Resulting large headers can sometimes degrade performance
- particularly when data contents of a packet are small
• AODV attempts to improve on DSR by maintaining routing tables atthe nodes, so that data packets do not have to contain routes
• AODV retains the desirable feature of DSR that routes are maintainedonly between nodes which need to communicate (on-demand)
47
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AODV
• Route Requests (RREQ) are forwarded in a manner similar to DSR
• When a node re-broadcasts a Route Request, it sets up a reverse path
pointing towards the source- AODV assumes symmetric (bi-directional) links
• When the intended destination receives a Route Request, it replies bysending a Route Reply
• Route Reply travels along the reverse path set-up when Route Requestis forwarded
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Re-active routing AODV(RFC3561)
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Re-active routing AODV(RFC3561)
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Summary: AODV
• Routes need not be included in packet headers
• Nodes maintain routing tables containing entries only for routes thatare in active use
• At most one next-hop per destination maintained at each node
- DSR may maintain several routes for a single destination
• Unused routes expire even if topology does not change
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Zone Routing Protocol
A Hybrid Routing Protocol
A Zone is defined for each node
Proactive maintenance of topology within a zone (IARP)Distance Vector or Link State
Reactive query/reply mechanism between zones (IERP) With Route Caching : Reactive Distance Vector W/O Route Caching : Source Routing
Uses ‘Bordercast’ instead of neighbor broadcast
Neighbor Discovery/Maintenance (NMD) and BorderResolution Protocol (BRP) used for query control, routeaccumulation etc.
l
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ZRP Example
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Zone Routing Protocol cont.
Routing Zone and IntrAzone Routing Protocol Zone Radius may be based on hop count
Identity and distance of each Node within the Zone isproactively maintained
The Interzone Routing Protocol
Check if destination is within the routing zone
Bordercast a route query to all peripheral nodes
Peripheral nodes execute the same algorithm
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Zone Routing Protocol cont.
Route Accumulation :
Provide reverse path from discovery node to source node
May employ global caching to reduce query packet
length Query Detection/Control :
Terminate Query thread in previously queried regions
Intermediate nodes update a Detected QueriesTable [Query Source, ID]
Route Maintenance may be reactive or proactive