32-mobile ad hoc networks

8/3/2019 32-Mobile Ad Hoc Networks

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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.



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 .

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Multi-hop transmission

• May need to traverse multiple links to reach a

destination



Mobility

Mobility causes route changes



Advantages of Ad Hoc Networks

Ease of deployment

Speed of deployment

Decreased dependence on infrastructure



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



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)



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



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)



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



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.



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.



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



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



Table Driven Routing Protocol



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



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



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



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



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



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




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




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.



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



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



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




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




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




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




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




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)




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)



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



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



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



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



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




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




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




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




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



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



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



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



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



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



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!



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



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



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



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.



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



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])



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



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



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



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



Re-active routing AODV(RFC3561)



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



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



ZRP Example



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



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

32-mobile ad hoc networks

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