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Submitted to Submitted by Submitted by

Mr.Hemant Kumar Jyotendra Sharma

(EC-A III Yr)

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Acknowledgement

“There are the times when silence speaks so much more

loudly than the words of praise to only as good as belittle a

person, whose words do not express, but only put a veneer

over true feelings, which are of gratitude at this point of time.”

Firstly, I would like to express my sincere gratitude to my

mentor Mr. Hemant Kumar, for her vital support, guidance

and encouragement – without which this report would not

have come forth.

Heartily, I would like to thank God, dear parents, my friends,

respected HOD sir and all readable books which help me to

make such a knowledgeable report.

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Certificate

This is to certify that Jyotendra Sharma of Electronics &

Communication, 5th Semester, Shri Vaishnav Institute of

Technology and Science has successfully completed his

project on the topic:

“Ad-Hoc wireless communication” under supervision and

guidance of Mr. Hemant Kumar.

Teacher in charge:

Mr. Hemant Kumar

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Declaration

I hear by declare that the present work on the Topic: “Ad-Hoc

wireless communication” is done by me myself only under the

guidance of Mr.. Hemant Kumar

. Jyotendra Sharma

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Index

Table of contents Page no.

1)-Introduction 1

2)-History

2.1)-Motes 7

2.2)-PRNet 9

3)-Important keywords 11

4)-Features of Ad-Hoc 12

5)-Establishment of Ad-Hoc 13

6)-Network Architecture 15

7)-Disadvantages 16

8)- References 17

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1-Introduction

An ad-hoc network is a local area network (LAN) that is

built spontaneously as devices connect. Instead of relying

on a base station to coordinate the flow of messages to

each node in the network, the individual network nodes

forward packets to and from each other. It is a type of

peer to peer networking.

In the Windows operating system, ad-hoc is a

communication mode (setting) that allows computers to

directly communicate with each other without a router.

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2-History

2.1-MOTES:

Ad-Hoc, in beginning, was used as a mode of

communication between military elements.

DARPA first used motes to detect enemy’s truck

movement in a remote area. A mote is an electronic

sensor that can sense vibrations caused by massive

vehicles such as trucks, tanks etc. A mote is equipped

with a magnetometer and GPS (Global Positioning

System) receiver that helps it to pin point its location and

then can inform an administrator to know whereabouts of

enemy artillery.

An airplane flies over the area and scatters thousands of

motes in target area.

Each mote wakes up, on sensing vibration generated by

heavy vehicles, senses its position and then sends out a

radio signal to find its neighbors.

Neighboring motes pick up the transmissions and forward

them to their neighbors and so on, until the signals arrive

at the collection node and are transmitted to the

commander. The commander can now display the data on

a screen and see, in real time, the path that the truck is

following through the field of motes.

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(Figure depicting motes communicating with each other)

(Figure depicting close view of motes)

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2.2-PRNET : ANOTHER APPLICATION OF AD-HOC

PRNet (Packet Radio Network) was to provide an efficient

means of sharing broadcast radio channel among many radios.

Packet radio is a form of packet switching technology used to

transmit digital data via radio or wireless communications

links.

Few characteristics of PRNet are:

Presence of mobile repeaters : Used to receive, amplify and retransmit signals. They operates

in zones i.e. they act as transmitter for terminals falling under

there zone. Mobile terminals :

These are the end users who shall receive data transmitted by

mobile repeaters.

Static station for routing: This is the type of routing which is used to transmit data

between various nodes. Data flow in certain pattern within

various nodes. This path followed by data is called route and

route can be specified by maintaining routing table.

Static routing means that there is no automated way of route

formation and it has to be specified manually by an

administrator.

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Not entirely infrastructure less: Unlike actual Ad-Hoc PRNet is not completely infrastructure

less as it does require mobile repeaters for transmission of data

and routing table has to be manually maintained unlike Ad-Hoc

which uses dynamic routing.

Static station:

It is responsible for maintenance of routing table and transmission of

data to mobile terminals.

Figure depicting implementation of PRNet

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3-Important keywords:

3.1-Routing table:

In computer networking a routing table, or Routing Information Base (RIB), is a data

table stored in a router or a networked computer that lists the routes to particular

network destinations, and in some cases, metrics (distances) associated with those

routes.

The routing table contains information about the topology of the network immediately

around it. The construction of routing tables is the primary goal of routing protocols.

Static routes are entries made in a routing table by non-automatic means and which

are fixed rather than being the result of some network topology "discovery" procedure.

3.2-Routers:

A router is a device that forwards data packets between computer networks, creating

an overlay internetwork. A router is connected to two or more data lines from different

networks. When a data packet comes in one of the lines, the router reads the address

information in the packet to determine its ultimate destination. Then, using

information in its routing table or routing policy, it directs the packet to the next

network on its journey.

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4-Features of Ad-Hoc:

Ad-Hoc provides us with following features, which gives it ace over

wired networks:

It doesn’t require any established infrastructure like wired

network. Wired network transmits data through system of

complex network via. Gateways, nodes, routers etc. Whereas,

Ad-Hoc just require two devices which have transmission and

reception capabilities and some set of protocols to transmit data.

Ad-Hoc wireless network can be established on the go i.e. even

devices in motion can establish connection.

As depicted earlier that even devices in motion can establish

connection, hence Ad-Hoc is very flexible and is capable of

handling situations like change in geography, or addition of new

user.

Supports short range communication.

Ad-Hoc does feature encryption of data however is not as secure

as other data transmission techniques.

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5-Establishment of Ad-Hoc

5.1-Bringing up an ad-hoc:

Ad hoc network begins with at least two nodes broadcasting their

presence (beaconing) with their respective address information.

They may also include their location info if they are GPS equipped

Beaconing messages are control messages. If node A is able to

establish a direct communication with node B verified by

appropriate control messages between them, they both update their

routing tables.

If Third node C joins the network with its beacon signal, two

scenarios are possible:

I. A & B both try to determine if single hop communication is

feasible

II. Only one of the nodes e.g. B tries to determine if single hop

communication is feasible and establishes a connection.

The distinct topology updates consisting of both Address and the

route updates are made in three nodes immediately.

In first scenario, all routes are direct i.e. A->B, B->C, and A->C

(Let’s assume bi-directional links).

In the second scenario, the routes are updated

First between B & C,

then between B & A,

Then between B & C again confirming that A and C both

can reach each other via B.

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5.2-Topology update due to link failure:

Mobility of nodes may cause link breakage requiring route

updates. Assume link between B & C breaks because of some

reason however observe that nodes A & C are still reachable via D

and E.

So old route between A &C was A->B->C is replaced by

A->D->E->C

All five nodes are required to incorporate this change in their

routing table

This change will happen

First in nodes B & C

Then in A & E

Then in D

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6-Network architecture of Ad-Hoc

All ad hoc networks operate in TDD (Time division duplexing)

mode. Time Division Duplex (TDD) refers to multiplexing of

transmission and reception in different time periods in the same

frequency band .Time-division duplexing (TDD) is the application

of time-division multiplexing to separate outward and return

signals. It emulates full duplex communication over a half-duplex

communication link.

FDD is another mode of communication, however is not employed

in present Ad-Hoc system as it increases circuit complexity. FDD

is Frequency Division Duplex (FDD); it refers to using different

frequency bands for uplink and downlink transmissions.

Ad-Hoc is a type of distributed wireless type network. It acts as a

whole i.e. there are no dedicated hardware, all is done by devices

themselves. Wireless nodes communicate with each other without

any fixed infrastructure.

Terminals have an RF or infrared interface to communicate with

each other.

All data transmission and reception occurs in the same frequency

band (there is no special node to do the frequency translation).

There is no centralized control for managing the network e.g. node

failures etc. And Ad-Hoc operates in unlicensed frequency band of

2.4 GHz, thus no transmission fee!!

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7-Disadvantages of wireless / Ad-Hoc communication

Wired transmission is much more secured because it consists of

physical cables that have fixed destination and are buried deep

inside ground so that no one can easily dig them out.

Wireless transmission is much more prone to hacking techniques

such as masking- in which the hacker shows himself as a host

and lures the user to enter his vital information on his computer.

It is very hard to avoid packet collisions in case of wireless

transmission.

Mobility affects routing- routing table changes.

Wireless transmission, reception, retransmission, beaconing,

consumes power that calls for use of huge power sources.

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8-References:

1. “How Stuff Works” – Perfect guide for beginners to understand

Ad-Hoc.

2. “Wikipedia”- Wireless Ad-Hoc network.

3. Carroll, Robert T. (23 February 2009), "Ad hoc hypothesis".

4. Article on “Design and Implementation of Ad Hoc” by Chih-

Yung Chang and Jang-Ping Sheu ,Department of Computer and

Information Science, Aletheia University.