[AD Hoc Networks]

by: Farhad Rad

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Agenda :

Definition of an Ad Hoc Networks routing in Ad Hoc Networks IEEE 802.11 security in Ad Hoc Networks Multicasting Protocols for Ad Hoc Networks

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Introductin:

MANET (Mobile Adhoc NETworks) An ad hoc network is a collection of wireless mobile

hosts forming a temporary network without the aid of any established infrastructure or centralized administration”

Military Applications Rescue Operations Mobile Ad hoc Networks

Virtual Classroomssolution

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Routing in Ad Hoc Networks: Challenges to Routing in MANETsChallenges to Routing in MANETs Routing Protocols for MANETsRouting Protocols for MANETs Ad-hoc On Demand Distance Vector (AODV)Ad-hoc On Demand Distance Vector (AODV) Comparisons andComparisons and ConclusionsConclusions

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Challenges to Routing in Challenges to Routing in MANETs MANETs

Lack of a fixed infrastructureLack of a fixed infrastructure

Each node in the network must route messages Each node in the network must route messages towards their destinationtowards their destination

Nodes operate on battery powerNodes operate on battery power ( (Routing of Routing of messages may cause faster battery messages may cause faster battery consumption, leading to node going consumption, leading to node going offlineoffline))

Nodes are constantly moving, leaving, or joiningNodes are constantly moving, leaving, or joining

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Routing Protocols for Ad-hoc Routing Protocols for Ad-hoc Networks:Networks:

Destination-Sequenced Distance Vector Protocol (DSDV)

Dynamic Source Routing (DSR) Ad-hoc On Demand Distance Vector (AODV)

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Ad-hoc On Demand Distance Vector : Ad-hoc On Demand Distance Vector : (AODV)(AODV)

Routes are discovered on demandRoutes are discovered on demand

AODV is capable of both unicast and multicast routing

AODV uses sequence numbers to ensure the freshness of routes

It is loop-free scales to large numbers of mobile nodes AODV maintains routes for as long as the route

is active.

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Route Discovery:Route Discovery:

Node can initiate route discovery by broadcasting a Node can initiate route discovery by broadcasting a Route Request (RREQ) messageRoute Request (RREQ) message

RREQ contains:RREQ contains:Source and Destination addressesSource and Destination addressesSequence number of sourceSequence number of sourceLast known sequence number of destinationLast known sequence number of destinationBroadcast ID (incremented with each RREQ)Broadcast ID (incremented with each RREQ)Number of hopsNumber of hops

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يا DVالگوريتمهاي بردار فاصله

يكي از روشاي پويا در مسيريابي •

ARPA مورد استفاده در شبكه •

استفاده در مسيريابهاي كوچك•

DV نامهاي متفاوت روش •

RIP پروتكل •

- Bellman الگوريتم مسيريابي •Ford

– Ford الگوريتم مسيريابي •Fulkerson

Distance Vector Routing الگوريتم •

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DVاصول كار روش

بPا • فPيزيكي صPورت بPه كPه را خطPوطي محاسPبه مسيريابهاي ديگر دارد و درج در جدول مسيريابي

هزينPة خطPوطي كPه مسPيرياب بPا بينهPايت درنظرگPرفتن • آنها در ارتباط مستقيم نيست

ارسPPال • سPPتون هزينPPه از جPPدول مسPPيريابي بPPراي توسPط هPاي زمPاني مشPخص، در بازه مسPيريابهاي مجPاور

(“يعPني فقPط بPراي مسPيريابهائي كPه بPا آن هPر مسPيريابدريPافت اطالعPات در ارتبPاط اسPت نPه تمPام مسPيريابها ”).

اي ثانيهTدر فواصل جديد ا زمسيريابهاي مجاور در

مسPيريابي • جPدول نمPودن هنگPام بPه پس از دريPافت جPPداول مسPPيريابي از مسPPيريابهاي مجPPاور ، طبPPق يPPك

الگوريتم بسيار ساده

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Jجدول مسيريابي مربوط به مسيرياب

زيرساخت ارتباطي يك شبكة فرضي

با دوازده مسيرياب

يا بردار فاصلهDVالگوريتمهاي

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DVمشكل عمده پروتكلهاي

هنگام خرابي يك مسيرياب يا يك عدم همگرايي سريع جداول مسيريابي شمارش تا بينهايت = مشكل كانال ارتباطي

: راه حل

هايش بدهد خواهد اطالعاتي را به همسايه وقتي يك مسيرياب ميهزينه رسيدن به آنهايي را كه قطعا{ بايد از همان مسيرياب بگذرند را

)كنند اعالم مي (يا. كند اعالم نمي

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مسئله شمارش تا بينهايت

به خبرهاي خوب واکنش سريع ولي به خبرهاي بد .واکنش کندي نشان مي دهد

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هرگاه مسيريابي از زيرشبکه خارج شود هرکدام از ساير مسيرياب هاي .فعال احساس مي كنند از طريق ديگري مسيري بهتر به آن وجود دارد

مسئله شمارش تا بينهايت

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AODV introduction:

Generating Route Request Processing and Forwarding Route Requests Generating Route Replies Receiving and Forward Router Replies

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Aodv Algorithm:

AB

D

C

G

H

EF

I

Source: A Dest. : I

A broadcast Route Request packet.

If the receiving node has a route to the If the receiving node has a route to the destination:destination:

Set up reverse path entry as Set up reverse path entry as beforebefore Sends back a Route Reply Sends back a Route Reply message message (RREP) to the source (RREP) to the source containing :containing :

o Last known sequence number Last known sequence number of destinationof destinationo Number of hops to destinationNumber of hops to destination

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Comparisons :Comparisons :

Percentage of Packets Received CorrectlyPercentage of Packets Received Correctly

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Routing Overhead in PacketsRouting Overhead in Packets

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Conclusions:Conclusions:

Routing protocols for MANETs will become Routing protocols for MANETs will become important due to of wireless devicesimportant due to of wireless devices

Different routing protocols for different needsDifferent routing protocols for different needs DSDV does not perform well with highly mobile DSDV does not perform well with highly mobile

nodesnodes DSR and AODV seem to give similar resultsDSR and AODV seem to give similar results

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An overview of IEEE 802.11

802.11 refers to a set of WLANs that was approved by IEEE in 1997.

Specifies the lowest two layers of the OSI model

802.11g

802.11a

802.11b

802.11

Standard

54 Mbps Max.

54 Mbps Max.

11 MpbsMax.

1-2 Mbps

Data rate

OFDM

OFDM

DSSS/HR-DSSS

FHSS/DSSS

Physical Layer

2.4 GHz

5.5 GHz

2.4 GHz

2.4 GHz

Operating Frequency

802.11g

802.11a

802.11b

802.11

Standard

54 Mbps Max.

54 Mbps Max.

11 MpbsMax.

1-2 Mbps

Data rate

OFDM

OFDM

DSSS/HR-DSSS

FHSS/DSSS

Physical Layer

2.4 GHz

5.5 GHz

2.4 GHz

2.4 GHz

Operating Frequency

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IEEE 802.11

IEEE 802.11 was first designed for wireless fixed networks

Many problems occur when building ad hoc Networks with the IEEE 802.11 standard as the lowest two layers

Until now, IEEE 802.11 doesn’t function well in wireless ad hoc netwroks

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Modes of operation:

Infrastructure-based: The main most mature technology for

WLANs Most commonly used to construct Wi-Fi

hotspots Costly for dynamic environments

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Modes of operation:

Infrastructureless-based: Also called Ad Hoc mode Stations form an Independent Basic

Service Set (IBSS) Any stations within the same

transmission range can communicate

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IEEE 802.11 Architecture:

Physical Layer : infrared, FHSS, or DSSS in 1997 OFDM and HR-DSSS were added in 1999

MAC Layer: Distributed Coordination Function

(DCF): Provides the basic access method to the

802.11 MAC protocol Uses random backoff time following a busy

signal Based on CSMA/CA Point Coordination Function (PCF): Only used in infrastructure-based

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Common Problems in Wireless Ad Hoc Networks:

The hidden-station problem * The exposed-station

problem Collision occurs * Degradation in

throughput

CBACBA D

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Solution for the hidden and exposed station problems:

Hidden Station Problem Solution:

Extension for the DCF protocol by a virtual carrier sensing mechanism.

Adding two control frames: Ready-To-Send (RTS), Clear-To-Send (CTS)

Sending station transmits RTS to receiver and waits for CTS Receiver will not send CTS if receiving from another station Avoiding collision Exposed Station Problem Solution: A node can identify itself as an exposed node if it hears an RTS

frame but not a CTS frame from the other transmitting node. Therefore, it concludes that it can have a simultaneous transmission

Avoiding the reduction in throughput

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Exposed node problem:

Add info of your choice here

Add text, graphic or photo at left

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Mobility Problem:

In ad hoc networks nodes can change their positions anytime

TCP protocol cannot distinguish between congestion on one hand and route failure or packet loss due to transmission on the other hand

This results in reduction in the performance of the network because of the slow start mechanism of the TCP protocol

Mobility Problem Solutions: Route Failure and Rout Re-establishment notifications Explicit Link Failure Notification (ELFN) signal Ad hoc TCP (ATCP) : by adding a thin layer between TCP and IP

layers

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MAC Protocol & TCP :

IEEE 802.11 was designed for wireless infrastructure LANs not for multi-hop ad hoc networks

802.11 doesn’t function well ad hoc networks because of the TCP protocol mechanisms and the difference among the transmission, sensing and interference ranges

Three major problems will occur: Instability problem In-compatibility problem One hop Un-fairness problem

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Instability Problem:

If station 1 is sending to station 5, the throughput can drop down to zero in some scenarios because of the following

The hidden and exposed station problems that may prevent station 2 from receiving RTS or sending CTS to station 1

The random backoff time High window size that the TCP uses

Solutions for the Instability Problem Decreasing the maximum window size of the TCP layer making the interfering range the same as the

communication range

1 2 3 4 5

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In-Compatibility Problem:

This problem is defined as two simultaneous TCP traffics cannot coexist in the network. Once one session develops, the other one is shut down. The overturn can happen at any time randomly.

the main causes of this problem are the hidden station problem, the exposed node problem and the exponential back-off scheme in the MAC layer.

Solutions for the In-Compatibility Problem: Changing the back-off policy by penalizing stations that transmit

too much data, so the other stations can still use the media.

Adjusting the interfering and the sensing range

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One-hop unfairness problem: If there are two simultaneous

TCP connections one is a single-hop connection and the other is a multi-hop connection, the single-hop connection will be activated even if the multi-hop connection started first.

Causes are hidden station problem, the exposed node problem and the exponential back-off scheme

1 2 3 4 5 6

First Connection

Second Connection

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Unicast and Multicast:

Unicast : With n receivers,

sender must replicate the stream n times

128.146.222.0/24

128.146.116.0/24128.146.199.0/24

ReceiverSender

128.146.222.0/24

128.146.116.0/24128.146.199.0/24

ReceiverSender

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Multicast:

Source transmits one stream of data for n receivers

Replication happens inside routers and switches

128.146.222.0/24

128.146.116.0/24

Receivers

128.146.199.0/24

Receiver

ReceiverSender

128.146.222.0/24

128.146.116.0/24

Receivers

128.146.199.0/24

Receiver

ReceiverSender

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Multicast Routing Protocols for Ad hoc Networks:

Tree Based ProtocolsAd hoc Multicast Routing (AMRoute)Ad hoc Multicast Routing Protocol utilizing

Increasing id numberS (AMRIS)

– Mesh Based ProtocolsOn-Demand Multicast Routing Protocol

(ODMRP)Core-Assisted Mesh Protocol (CAMP)

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Multicast Routing Protocols:

protocol AMRoute ODMRP AMRIS CAMPConfigurat

ion Tree Mesh Tree Mesh

Loop - Free No Yes Yes Yes

Dependency on unicast Protocol

Yes No No Yes

Periodic Messagin

g

Yes Yes Yes Yes

Control Packet Flood

Yes Yes Yes No

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On-Demand Multicast Routing Protocol (ODMRP):

Source broadcasts periodically Join Request.

Nodes receiving the request, save upstream node id and rebroadcast the message.

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ODMRP:

When a receiver gets the request, it updates its member table and return message Join Table to its neighbors.

Nodes that are on the path from receiver to source, become part of the Forwarding Group

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ODMRP:

If source wants to leave the group, simply stop sending JOIN REQUEST packets

If a node wants to leave the group it stops sending JOIN TABLE packets for that group

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Simulation:

Metrics Packet Delivery Ratio: The ratio of the number of data packets

actually delivered to the destinations versus the number of data

packets supposed to be received. Number of control packets transmitted per data packet delivered:

The ratio of control packets transmitted to data packets delivered gives a measure of efficient utilization of control packets in delivering data.  

Number of data packets transmitted per data packet delivered Number of control and data packets transmitted per data packet

delivered

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Simulation Model:

network of 50 mobile hosts

Radio propagation range for each node was 250 meters and channel

capacity was 2 Mbits/sec. There are 21 nodes in the

multicast group and 5 nodes are chosen as sources

….

Data Packets TXed/Data packet Delivered as a function of Mobility

0

0.5

1

1.5

2

2.5

0 1 2 5 10 20

Mobility (m/sec)

Dat

a P

acke

ts T

Xed

/Dat

a P

acke

t D

eliv

ered

ODMRP

AMRIS

ODMRP transmits more data packets than AMRIS because it exploits

multiple redundant routes for data delivery

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Simulation Model:

AMRIS has the smallest number of packet transmissions because it uses a tree

ODMRP transmits more data packets on redundant paths

All Packets TXed/Data Packet Delivered as a function of Mobility

0

0.5

1

1.5

2

2.5

0 1 2 5 10 20

Mobility (m/sec)

All

Pack

ets

TXed

/Dat

a Pa

cket

Del

iver

ed

ODMRP

AMRIS

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Network Traffic Load:

AMRIS is very sensitive to traffic load

ODMRP is also affected at higher loads, but the packet loss rate is

much lesser than AMRIS PDR as a function of Network Traffic Load

0

0.2

0.4

0.6

0.8

1

1.2

1 5 10 25

Netw ork Traffic Load(pkts/sec)

Pac

ket

Del

iver

y R

atio

AMRIS

ODMRP

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Challenges:

Security in Ad Hoc Networks Qos Routing Protocol Multicasting

………..

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