Adhoc Networks 2

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ADHOC NETWORKS

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INTRODUCTION

Adhoc networks are formed by devices that are able to

communicate with each other using a wireless physical

medium without having to resort to pre-existing network

infrastructure. These are also known as MANETS ie Mobile Adhoc

Networks.


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Fundamental characteristics of ADHOC

networks

They are able to configure themselves on the fly withoutthe intervention of a centralized administration.

The terminals in ADHOC networks can function not onlyas end systems (executing applications, sending

information) as source nodes and receiving the data asdestination nodes.

They also act as intermediate system i.e. forwarding thepackets from the other nodes.

Adhoc networks are also called multihop wireless

networks.


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Adhoc networks

Compared to cellular networks adhoc networks are moreadaptive to changing demands and physical conditions.

Attenuation characteristics of wireless networks are nonlinear.

Energy efficiency will be potentially superior and theincreased spatial reuse will yield superior capacity withincreased spectral efficiency.

These characteristics make adhoc networks attractive andis tightly linked to heterogeneous network and 4G

architecture.


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Challenges in adhoc networks

The need for self configurability and flexibility at

various levels i.e. (Dynamic Routing or distributed MAC

arrangements).

Gross layer optimization can significantly improve thesystem performance.


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Classification of adhoc networks

ADHOC networks are classified as follows

Body area network (BAN)

It is the set of variable devices that have a

communication range of 2 meters.

Personal area network (PAN)

It refers to the communication between different BANs ,

between a BAN and its intermediate surroundings.

Range of communication is approx 10 meters .


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Wireless local area network (WLAN)

WLAN has the range of 100s of meters.

ForWLAN the main option is the family of standards i.e.

IEEE 802.11

The main existing technology for implementing BANs

and PANs is Bluetooth.


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Routing is the most active research field in the adhoc

networks as it is related with different communication

layers .

Minimizing the hops is no longer the objective of therouting algorithm but optimization of multiple

parameters such as packets error rate over the route,

energy consumption, network survivability, routing

overheads, possibility of establishing a parallel route.


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Use of TCP over wireless links poses many problems .it

results in additional problems for wireless links.

Communication over wireless Route failures lead to

unnecessary congestion control. MAC congestion reduces throughput on longer routes.


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Power awareness

: since most of the w/l terminals can be expected to havelimited energy storage, power awareness is veryimportant.

This subject spans over several communication layers soattention is given to different power saving approaches.

The objectives are not only the reduction of transmissionpower but also the management of sleep states or

extention of network survivability through the routingwhich isenergy aware ..


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1

However if the medium remains idle for this period the

station will go to the back off state.

When entering the back off state MS selects aback off

interval (BI) between zero and the contention windowperiod (CW).

CW is the integer no of basic tine slots, if the medium

remains idle for the duration of BI time (i.e the value of

chosen BI minus the elapsed time since entering the back

off state).


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CSMA CD

Carrier sensed multiple access

technique/collision detection.

When the mobile gets a frame to transmit, it first senses

the channel to determine whether another MS istransmitting.

If MS senses the channel to be idle for a period which is

equal to the inter space frame, then it starts transmitting

the frame.


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When it senses the channel to be busy it will differ the

transmission and the station will keep on sensing the

channel.

At the point of time when the media becomes idle thestation will continue sensing and will wait for the period

which is equal to inter frame space to elapse again. If the

medium becomes busy during this period, the station will

go to the deffering state again.


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Collision will occur if two or more MSs select the same

BI provided the condition stated above , that the frame

coexist spatially at one or more of the receiving stations.

When the collision occurs the station that have causedthe collision senses the medium again for the inter frame

space and go again to back off state. Selecting a new BI.

Randomly with the value of contention window period

doubled


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The other station which stored their remaining BI times

also waits for inter frame space and then go to the back

off state.


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Basic principal

Mobile devices communicate in Peer to Peer fashion.

Self organizing network without the need to fixed

network infrastructure.

Multihop communication. Decentralized mobility-adaptive operation. This is the art

of networking without a network .


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Applications

Accident warning

Floating car data

Multihop extensions of Info stations.

Application for wireless sensor networks

Temperature. Measurement details

Detect vibrations

Make photos.

Environmental monitoring

Intrusion detection , detection of bush fires , earth quakewarning.


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ADHOC NETWORKS

Medical sector : Monitoring of body functions andImplants.

Biological sector : Animal tracking , underseaexploration

Industrial sector : Remote sensing in power plants

Home automation: Remote monitoring of resourcessuch as Electricity ,Water and Gas

Aerospace sector : Sensor equipped Robots on a plant

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Key advantages :-

y No expensive infrastructure must be involved.

y Making use of unlicensed frequency spectrum.

y Quick distribution of information around sender.

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KEY CHALLENGES

y All network entities must be mobile requirement of

very dynamic technology.

y Network functions must have high degree of

adaptability (mobility , outage).

y No central entities

operation in completely distributed manner.

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ROUTING FORADHOC MOBILENETWORKS :

Well known routings are:

Link state routing

Distance vector routing The Pro-active approach for routing

Always maintain all routes

Problems :

Topologies changes significant network traffic

Even when the route is not used

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UNICAST ROUTING PROTOCOLS :

Many protocols have been proposed some have been

invented specifically forMANETs other are adopted

from previously proposed protocols for wired networks.

No single protocol works well in all environments.

Some attempts made to develop adaptive protocols.

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ROUTING PROTOCOLS :

Proactive Protocols :

y Determines the route independent of traffic pattern

y Traditionally link state and distance vector routingprotocols are proactive

Reactive protocols :

y

Maintain routes only if needed

Hybrid protocols :

y Combines Pro-active and re-active elements

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Position based protocols

Use the geographic position of nodes for

forwarding decisions


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TRADE OFF

Latency of route discovery

Proactive protocols may have lower latency since the

routes are maintained at all times

Reactive protocols may have higher latency because a

route from X to Y will be found only when X attempts to

send Y

Overhead of route discovery /maintenance

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Reactive protocols may have lower overhead since routes

are determined only if needed

Proactive protocols can (but not necessarily) result in

higher overhead due to continuous route updating

Which of the protocols achieve a better trade off depends

on the traffic and mobility patterns

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FLOODING FOR DATA DELIVERY

SenderSbroadcast data packet P to all neighbours

Each node receiving P forwards P to its neighbours

Sequence no's are used which avoid the possibility of

forwarding the same packet more than once

Packet Preaches the destination D provided that D is

reachable from senderS

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B

S

A

C

H

E

I

G

F

K

J

D

M

N

L

i.e. S represent a node that has

received packet P

represents that connected nodes are

within each other transmission range

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Node D does not forward a packet


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RELIABILITY OF ADHOC NETWORKS

Wireless links are prone to errors

y Either because of interference

y Or because of collisions

(collision detection does not work for half duplex

networks)

High packet loss rate detrimental to transport layer

performance

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THE MECHANISM ARE NEEDED TO

INCREASE THE RELIABILITY :

Forward error correction (FEC) include the redundancy

in the packet

Automatic repeat request (ARQ) use acknowledgementsand re-transmission

y ARQ for multi hop AD-HOC networks

Implicit assumptions :-

y

Packet loss is caused by interference or collisionsy Retransmission seems to be appropriate

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WHAT HAPPENS IF PACKET LOSS OCCURS DUE TO

A NODE LEAVING THE TRANSMISSION RANGE

i. Multiple re-transmission before a sender gives up

ii. Massive increase in network congestion

Unlikely

y No route discover strategies favour shortest (i.e.

minimal) path

Note:- Broadcast (used for rote discovery) are not

protected by ARQ

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PROBLEM WITH RANGES FOR MULTI-HOP

ADHOCNETWORKS :

1. Large interference , dramatically reduces the capacity

2. Ranges depend on the transmission rate

Low rate less vulnerable to interference

3. Broadcast use a lower rate than Uni casts in IEEE

802.11

( to make the transmission more reliable)

4. Broadcasts are used for route discovery

5. Uni casts used for data delivery

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CONSEQUENCES :-

Routes found via broadcast may not be usable for data traffic

y It is called Grey zone

IEEE 802.11 is used and will be used for multi hop ADHOCnetworks

Inter-vehicle communication

Also as access networks

It is certainly not optimal : focus is on single hop networks

There are many pit falls when blindly using existing MAC

mechanism

There is also the need & integrated routing /MAC approach

Building a new MAC is hard and expensive

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SECURITY IN MOBILE ADHOCNETWORKS

1. Security needs and threats1/28/2012

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Security

features and need

Privacy

/Anonymity

features and

need

Dependability

features and need

Subject /object

authentication

Confidentiality sort off Availability

Data integrity No unauthorizeddissemation of personal

data

Availability

Accountability Location , Address

,service privacy


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NETWORK SECURITY SEEN AS CUSTOMER-

PROVIDER RELATIONSHIP

End user perspective : wants secure end to end

communication

Operator perspective : Has to provide secure n/w organization

as basis for offering a secure communication service

Attack types and building blocks of counter measures

y

Passive attack -F

abricating or stealing of packetsy Get content - modification of packets

y Profiling -Active attacks

y Other types of attacks

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SECURITY GOALS WITH RESPECT TO

ADHOC ROUTING

Routing signaling cannot be spoofed

Fabricating routing messages can not be integrated in the

network

Routing messages cannot be altered in transit exceptaccording to the normal functionality of the routing

protocol

Routing loops cannot be formed through malicious

action route cannot be re-directed from the shortest path

by malicious action

Managed open environment

Unauthorized nodes should be excluded from route

computation and discovery

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Managed hostile environment

The network topology must be exposed neither to adversaries nor

to authorized nodes by the routing messages

The solutions for secure routing

ARAN : Authenticated routing for Adhoc networks

Assumptions : MOE (Managed Open Environment )

Trusted certificate server to its public key is known to all nodes

Each nodes has non certificate signed by T

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Counter measures used are :

Cryptography

Monitoring

Difference in service classes and ADHOC network

1)Key managed infrastructure2)Intrusion detection

3)Single administration domain

4)Transiently unavailable

Only local monitoring

Multiple domains , no clear line of defense

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ADHOC SPECIFIC ATTACK TYPES ARE AS

FOLLOWS :

Equipment/battery : no obvious line of defense ,Side

channel attacks

Radio jamming

DLC : attacks on MAC , MAC address

Routing : no infrastructure support , no clear line of

defense

Co-ordination : based on principal of mutual assistance ,

simple attacks and packet drops

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Security procedures:

Route

y Signed discovery packet (RDP) propagates to sought

destination

y

Destination sends back signed route reply (REP)y At each hop the following action is taken

Validation of original signature

Validation of last hop signature

When last hop is neither source nor destination

replace the last hop signature by your own signature

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ARAN (authentication routing for ADHOC

networks )

check list :

Unauthorized participation , managed by trusted

authority

Spoofed route signaling everything is signed

Fabricated routing messages

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Adhoc Networks 2

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