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UNIT - I

1 Wireless Networks
and Ad hoc Networks

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Syllabus
Elements of Ad hoc Wireless Networks, Issues in Ad hoc wireless networks, Example commercial

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applications of Ad hoc networking, Ad hoc wireless Internet.

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Contents
1.1 Wireless Network
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1.2 Wireless Ad hoc Network
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1.3 Two Marks Questions with Answers [Part - A]
1.4 Long Answered Questions [Part - B] nee
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Ad hoc and Wireless Sensor Networks 1-2 Wireless Networks and Ad hoc Networks

1.1 Wireless Network

 Wireless networks are computer networks that are not connected by cables of any
kind. The use of a wireless network enables enterprises to avoid the costly process
of introducing cables into buildings or as a connection between different
equipment locations.

1.1.1 Introduction to Wireless Network

 The term wireless communication was introduced in the 19th century and wireless

ww communication technology has developed over the subsequent years. It is one of

the most important mediums of transmission of information from one device to

 wother devices.

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In this technology, the information can be transmitted through the air without
requiring any cable or wires or other electronic conductors, by using

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electromagnetic waves like IR, RF, satellite, etc. In the present days, the wireless
communication technology refers to a variety of wireless communication devices

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and technologies ranging from smart phones to computers, tabs, laptops,
Bluetooth technology, printers.

1.1.2 Types of Wireless Communication nee

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In the present days, wireless communication system has become an essential part
of various types of wireless communication devices, that permits user to
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communicate even from remote operated areas. There are many devices used for
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wireless communication like mobiles, cordless telephones, Zigbee wireless
technology, GPS, Wi-Fi, satellite television and wireless computer parts. Current
wireless phones include 3 and 4G networks, Bluetooth and Wi-Fi technologies.
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 The different types of wireless communication mainly include, IR wireless
communication, satellite communication, broadcast radio, Microwave radio,
Bluetooth, Zigbee etc.

1. Satellite Communication
 Satellite communication is one type of self contained wireless communication
technology, it is widely spread all over the world to allow users to stay connected
almost anywhere on the earth. When the signal (a beam of modulated microwave)
is sent near the satellite then, satellite amplifies the signal and sent it back to the
antenna receiver which is located on the surface of the earth. Satellite
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communication contains two main components like the space segment and the
ground segment. The ground segment consists of fixed or mobile transmission,
reception and ancillary equipment and the space segment, which mainly is the
satellite itself.

2. Infrared Communication
 Infrared wireless communication communicates information in a device or
systems through IR radiation . IR is electromagnetic energy at a wavelength that is
longer than that of red light. It is used for security control, TV remote control and
short range communications. In the electromagnetic spectrum, IR radiation lies

ww between microwaves and visible light. So, they can be used as a source of
communication. For a successful infrared communication, a photo LED

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transmitter and a photo diode receptor are required. The LED transmitter
transmits the IR signal in the form of non visible light, that is captured and saved

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by the photoreceptor. So the information between the source and the target is
transferred in this way. The source and destination can be mobile phones, TVs,

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security systems, laptops etc. supports wireless communication.

3. Broadcast Radio
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The first wireless communication technology is the open radio communication to
seek out widespread use, and it still serves a purpose nowadays. Handy
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multichannel radios permit a user to speak over short distances, whereas citizen’s
band and maritime radios offer communication services for sailors. Ham radio
enthusiasts share data and function emergency communication aids throughout .ne
disasters with their powerful broadcasting gear, and can even communicate
digital information over the radio frequency spectrum.
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 Mostly an audio broadcasting service, radio broadcasts sound through the air as
radio waves. Radio uses a transmitter which is used to transmit the data in the
form of radio waves to a receiving antenna (Different types of antennas). To
broadcast common programming, stations are associated with the radio N/W’s.
The broadcast happens either in simulcast or syndication or both. Radio
broadcasting may be done via cable FM, the net and satellites. A broadcast sends
information over long distances at up to two megabits/Sec. (AM/FM Radio).
 Radio waves are electromagnetic signals, that are transmitted by an antenna.
These waves have completely different frequency segments, and user will be
ready to obtain an audio signal by changing into a frequency segment.
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 For example, consider a radio station. When the RJ says you are listening to 92.7
BIG FM, what RJ really means is that signals are being broadcasted at a frequency
of 92.7 megahertz, that successively means the transmitter at the station is
periodic at a frequency of 92.700,000 Cycles/second.
 When listener would like to listen to 92.7 BIG FM, listener has to tune in the radio
to just accept that specific frequency and will receive perfect audio reception.

4. Microwave Communication
 Microwave wireless communication is an effective type of communication, mainly

ww this transmission uses radio waves, and the wavelengths of radio waves are
measured in centimeters. In this communication, the data or information can be


w transfers using two methods. One is satellite method and another one is terrestrial
method.
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Wherein satellite method, the data can be transmitted though a satellite, that orbit

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22,300 miles above the earth. Stations on the earth send and receive data signals
from the satellite with a frequency ranging from 11 GHz - 14 GHz and with a

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transmission speed of 1 Mbps to 10 Mbps. In terrestrial method, in which two
microwave towers with a clear line of sight between them are used, ensuring no

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obstacles to disrupt the line of sight. So it is used often for the purpose of privacy.

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The frequency range of the terrestrial system is typically 4 GHz - 6 GHz and with
a transmission speed is usually 1 Mbps to 10 Mbps.

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The main disadvantage of microwave signals is, they can be affected by bad
weather, especially rain. .ne
5. Wi-Fi
 Wi-Fi is a low power wireless communication, that is used by various electronic
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devices like smart phones, laptops, etc.In this setup, a router works as a
communication hub wirelessly. These networks allow users to connect only
within close proximity to a router. WiFi is very common in networking
applications which affords portability wirelessly. These networks need to be
protected with passwords for the purpose of security, otherwise it will access by
others

6. Cellular and Mobile Communication Systems

 The advancement of mobile networks is enumerated by generations. Many users
communicate across a single frequency band through mobile phones. Cellular and
cordless phones are two examples of devices which make use of wireless signals.
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Typically, cell phones have a larger range of networks to provide a coverage.But,

Cordless phones have a limited range. Similar to GPS devices, some phones make
use of signals from satellites to communicate.

Cellular systems
Cellular telephone systems are very popular and used worldwide. They were
primarily designed in the 1960’s to provide analog communication and later it was
enhanced to provide digital communication between mobile devices. The main goal of
cellular communication systems is to provide voice and data communication to
international level coverage. The working of cellular system is as follows,

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 The coverage area of cellular system is divided into non-overlapping cells which

 w comprises several mobile devices.

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Communication between the mobile devices is controlled by a fixed point base
station which is connected with a Mobile Switching Center (MSC).
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Each MSC acts as a central controller and takes the responsibility of allocating
channels within cells and managing hand-offs between MSCs.

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The essential components used in cellular systems are cheaper, faster and smaller in
size and require less power for radio propagation.
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The various developments of cellular systems are as follows : The first generation (1G)

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cellular system is called the Advance Mobile Phone Service (AMPS) which is based on
FDMA with 30 kHz FM-modulated voice channels. The second generation (2G) digital
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systems called Global System for Mobile communication (GSM) provides data rates of up
to 100 kbps. The third generation (3G) cellular system provides different data rates .ne
depending on mobility and location.

Cordless Phones
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Cordless telephones were first appeared in the late 1970’s. These phones are basically
designed for providing low cost, short wireless link communication. These devices use
radio waves with specific frequency for communication. Cordless phones replace the
handset cord or landline phone to radio link. The functionality of cordless phones is given
below :
 The cordless phone uses a base station and the handset which can be used
anywhere and at any time within a specified distance from the base station.
 The base station is connected to the phone line through a wire.

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 Base station acts as a normal telephone. It receives calls through the phone line as
electrical signals. Then it converts the received electrical signals to a radio signal
and forwards that signal to the handset of the user.
 The transmitted radio signal from the base station is received by the handset. This
signal is converted back to electrical signal and sent to the speaker.
 The speaker converts the electrical signal into the sound form that can be head.
 Again, when one talks via the handset, the voice is transmitted to the base station
as radio signal where it is converted to electrical signal and transmitted through
the phone line.

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The base station and handset operate on a frequency pair that allows to talk and listen
at the same time.

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7. Bluetooth Technology
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The main function of the Bluetooth technology is that it permits user to connect

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various electronic devices wirelessly to a system for the transferring of data. Cell phones
are connected to hands free earphones, mouse, wireless keyboard. By using Bluetooth

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device the information from one device to another device. This technology has various

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functions and it is used commonly in the wireless communication market.

8. ZigBee

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This wireless technology is mainly used in mesh networks and allows nodes to be

for providing communication with low cost and power consumption than Bluetooth g
connected together through multiple pathways. This radio specification is mainly used

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technology.
The main objective of using ZigBee technology is to provide radio communication for
prolong period without recharging. So, this technology is suitable in sensor networks and
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inventory tags. ZigBee technology was originally standardized as IEEE 802.15.4. ZigBee is
designed specifically to be used in Machine to Machine (M2M) networks.
ZigBee supports data rates of up to 250 kbps at a coverage range of upto 30 m.
However, these data rate is lower than Bluetooth technology. Furthermore, it consumes
less power and having more coverage area than Bluetooth technology.

9. WiMax
Worldwide Interoperability for Microwave Access (WiMax) is one of the broadband
wireless technologies. This technology was standardized as IEEE 802.16. This wireless
technology allows data to be transferred at a rate of 30 - 40 megabits per second. WiMax
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would operate similar to WLAN, but it transfers data at higher speeds over greater
distances and for a large number of users. It has the ability to provide service in the places
where implementing wired infrastructure is difficult.

1.1.3 Wireless Network - Building Blocks

1. Along with some services and other devices, the two main components of
wireless networks are wireless router or access point.
2. A high-speed broadband connection (that is DSL, cable, or fiber) internet
connection is necessary to connect any network to the Internet, there is need of.

ww3. A router is a network device that can connect one network to another,
determine what traffic can pass between them, and perform other functions on

w a network, such as assigning IP addresses. In addition to the phones, tablets,

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and laptops used in accessing a network, routers make up the hardware that
runs the network.
4.
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A wireless network adapter to connect other devices in the network. An older
laptop, television, or Blu-Ray player may not have built-in wireless support. In
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these devices a wireless network adapter is required to connect to the wireless

5.
network.
Role/Mode of Device in the wireless network nee
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There are three major “modes” a Wi-Fi device can use. These modes define the role a

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Wi-Fi device has in the network, and networks must be built out of combinations of
devices operating in these different modes. How the devices are configured depends on
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the types of connections used between various parts of the network.
1. A wireless router or access point - Most wireless networks are made using
Access Points - devices that host and control the wireless connection for
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laptops, tablets, or smart phones. If you use Wi-Fi in your home or office, it is
most likely through an Access Point. When a router is set up as an AP, it is said
to be in “Master” or “Infrastructure” mode.
An AP is sometimes a stand-alone device that bridges between a wireless and
wired (Ethernet) network, or is part of a router. APs can cover a range of areas
with a wireless signal, depending on the power of the device and the type of
antenna. There are also some APs that are weatherproof, designed to be
mounted outdoors.

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An access point is similar to a person on stage, addressing an audience or

crowd - they are providing the information for everyone else. Those audience
members can ask questions of the person on the stage, and receive a response.
They are the hardware devices that Internet service providers use to connect
any Wi-Fi enabled device to their cable or xDSL Internet network. A wireless
router, also called a Wi-Fi router, combines the networking functions of a
wireless access point and a router. A router connects local networks to other
local networks or to the Internet. A wireless access point connects devices to
the network wirelessly, using radio frequencies in the 900 MHz and 2.4, 3.6, 5,

ww and 60 GHz frequency bands. The latest wireless routers are based on the IEEE
802.11ac Wave 2 standard, often shortened to Wave 2. A wireless router is

w sometimes referred to as a WLAN (wireless local area network) device.

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Computers, tablets, and other devices connect to a wireless network via a
wireless access point or wireless router. In Wi-Fi-based wireless networks, the

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access point or router acts as an Ethernet switch. All devices connect to the
router, rather than directly with each other. Wireless router or access points
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should be installed in a way that maximizes coverage as well as throughput.

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The coverage provided is generally referred to as the coverage cell. Large areas
usually require more than one access point in order to have adequate coverage.

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An access point can also be added to the existing wireless router to improve

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coverage. Many DSL and cable modems today come equipped with integrated
wireless networking capabilities; these are called wireless modem routers.
Devices with wireless networking capabilities (wireless clients / Stations) - .ne
Devices such as computers, tablets, and phones are common Clients on a
network. Some routers can operate as Clients as well, which allows them to act
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like the wireless card in a computer, and connect to other Access Points. This
can bridge two Ethernet networks, or connect to more distant APs.
When a device is accessing a wireless hotspot, or the router in home or office,
the device is the client. This client mode is also known as “station mode” as
well.
A wireless client is similar to a person in the audience of a play or movie. They
are one of several or many people accessing information through the same
conduit - someone speaking.

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Most of the modern day devices have built-in wireless capabilities, either
802.11b/g, 802.11b/g/n, or even 802.11ac. These devices will be able to connect
directly to the wireless router.
3. Ad-hoc node (Mesh) - Some wireless devices (laptops, smart phones, or
wireless routers) support a mode called Ad-hoc. This allows those devices to
connect together directly, without an Access Point in-between controlling the
connection. This forms a different type of network - in Ad-hoc mode, all
devices are responsible for sending and receiving messages to the other devices
- without anything else in between. In an Ad-hoc network, every device must

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use this mode, and some have it as a “hidden” feature. Ad-hoc devices are

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“Mesh Nodes”.
An Ad-hoc or mesh node is similar to an individual in a group or roundtable

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discussion. They can take equal part in the conversation, raising their hand
when they want to speak so the others will listen. If someone at the end of the
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table cannot hear, one of the individuals in-between can repeat the original
message for the listener.
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Fig. 1.1.1 A wireless network

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1.1.4 Devices Connecting Procedure in to Wireless Network

A Wi-Fi-enabled device can connect to the network when it’s within the range of its
wireless router. If wireless security is enabled on the network, then there is a need to
enter password on each device to connect to wireless network. After that, the device will
be wirelessly connected to the router and there is no need to re-enter the password each
time).

Who connects to whom

1. Clients always need to connect to an access point, and mesh nodes all connect

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also prevents different roles from connecting to each other as well.

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3.
4.
Access points cannot connect to each other wirelessly.

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Clients cannot connect to each other wirelessly.
Clients cannot connect to Ad-hoc (Mesh) devices wirelessly.
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Access points cannot connect to Ad-hoc (Mesh) devices wirelessly.

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1.1.5 Wireless Operating Modes - Infrastructure Mode and Ad hoc Mode

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The IEEE 802.11 standards specify two operating modes - Infrastructure mode and Ad
hoc mode (Infrastructure-less )
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Infrastructure mode is used to connect computers with wireless network

help from wireless router or access point. g

adapters, also known as wireless clients, to an existing wired network with the

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In this mode each node is connected with other node through a fixed base
station. The fixed station is also known as Access Points (APs). An example for
infrastructure based network is cellular network in which base station or AP is
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used as fixed equipment. Each network area is divided into cells and the base
station provides each cell with the network coverage which can be used for the
transmission of high quality voice, data and other types of messages.
2. Ad hoc mode is used to connect wireless clients directly together, without the
need for a wireless router or access point. An ad hoc network consists of up to
9 wireless clients, which send their data directly to each other.
In this mode Each node can communicate with each other without using any
fixed infrastructure. Mobile ad hoc networks and Vehicular Ad hoc Networks
(VANETs) are the examples of infrastructure less networks. In Ad hoc

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networks, each node acts as a router to forward the information in a multi-hop

fashion.

Choice between Ad hoc and infrastructure mode

Deciding when to employ Ad-hoc versus infrastructure mode depends on the use. A
user who wants a wireless router to act as an access point should choose infrastructure
mode, but Ad-hoc mode might be a good option for a user setting up a temporary
wireless network between a small number of devices.

Comparative analysis of infrastructure network and Ad hoc network

Sr.
No. ww Characteristics Infrastructure network Ad hoc network

1.
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Communication

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Through an Access Point (AP),
APs act as a bridge to other
wireless/wired network.
Directly between devices, in ad-hoc
mode, each node communicates
directly with other nodes, so no

2. Security syE
More security options.
access point control is needed.

WEP (Wired Equivalent Privacy) or

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3. Range Determined by the range and

number of access points.
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individual devices on the network.

4. Speed Usually faster.

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Usually slower.

5. Complexity Designing is simple as most of

the network functionality lies
within AP and client is just a
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As no central co-ordination exists,

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it needs to use decentralized MAC
(Medium Access Control) protocols
simple machine. such as CSMA(Carrier Sense
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Multiple Access)/CA (Collision
Avoidance), with all nodes having
same functionality. This shoots up
the complexity and cost.

6. When can not be It can’t be used in critical It is not always fully connected as
used situations like disaster relief two mobile nodes may temporarily
where no infrastructure is left. be out of range.

7. Channel Access Most infrastructure based Most Ad-hoc based WLAN uses
WLAN uses TDMA-based contention MAC protocols (e.g.
protocols. CSMA).

8. Topology Based on topology, one main Ad-hoc WLANs are easier to set-up
advantage is the ability of and require no infrastructure.
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infrastructure WLANs to
provide wired network
applications and services.

9. Applications IEEE 802.11 & HIPERLAN2 are Bluetooth is a typical ad-hoc

based on infrastructure mode. network.

10. Figurative
depiction

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Requirements for all devices

1 Unique IP
(Internet
Yes required.
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Protocol)
address for nee
each device
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2

3
Mode set to

Same SSID
Infrastructure mode.

Yes, including the access point.

Ad hoc mode.

Yes.
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4
(Service Set
Identifier)

Same channel Yes, including the access point. Yes.

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Table 1.1.1 Comparative analysis of infrastructure network and Ad hoc network

1.1.6 Wireless Network - Classification

Based on how many devices are being connected in the network and how much
physical area is covered by the network the wireless there are four main types of wireless
networks namely,
1. Wireless Local Area Network (LAN) - Links two or more devices using a
wireless distribution method, providing a connection through access points to
the wider Internet.
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Ad hoc and Wireless Sensor Networks 1 - 13 Wireless Networks and Ad hoc Networks

2. Wireless Metropolitan Area Networks (MAN) - Connects several wireless

LANs.
3. Wireless Wide Area Network (WAN) - Covers large areas such as neighboring
towns and cities.
4. Wireless Personal Area Network (PAN) - Interconnects devices in a short
span, generally within a person’s reach.

1.1.7 Advantages and Disadvantages of Wireless Communication

Advantages of Wireless Communication

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2.
Any data or information can be transmitted faster and with a high speed.
Maintenance and installation is less expensive in wireless networks.

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3.
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The internet can be accessed from anywhere wirelessly.
Wireless networks are self-configuring and easy to use.
5.
6.
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Wireless networks are cost effective.
Wireless communication is a solution in certain areas where wired networks

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are difficult to install (e.g. military areas, flooded areas, hazardous areas, long

7.
distances etc.)
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Customers can work and access Internet anywhere and at anytime without

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carrying cables or wires wherever they go. This also helps to complete the

8.
work anywhere on time and improves the feasibility.
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Doctors, workers and other professionals working in remote areas can be in
touch with medical centers through wireless communication. .ne
9. Urgent situation can be alerted through wireless communication. The affected
regions can be provided help and support with the help of these alerts through
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wireless communication.

Disadvantages of Wireless Communication

The wireless network enables to use personal devices such as PDAs, cell phones etc
anywhere and at anytime. This has helped to improve in every field of life and in day to
day life; but this has led many threats as well. There are also some of the drawbacks
associated with the merits of wireless communication.
1. An unauthorized person can easily capture the wireless signals which spread
through the air hence more vulnerable to attack by unauthorized users. It is
very important to secure the wireless network so that the information cannot
be misused by unauthorized users.
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Ad hoc and Wireless Sensor Networks 1 - 14 Wireless Networks and Ad hoc Networks

2. It requires strong security protocols to secure the wireless signals.

3. Wireless communication is influenced by physical obstructions, climate
conditions, noise interference etc.
4. Wireless network suffers from bandwidth availability as there is limited
amount of bandwidth.
5. Tracing and capturing the intruder node is difficult.
6. Wireless connection set up is slow purpose.
7. Wireless network is many a times unstable.

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9.
To get constant coverage in some buildings is difficult.
The speed of the wireless transmission is slower and less efficient.

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1.1.8 Applications of Wireless Communication
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Applications of wireless communication involve security systems, television remote

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control, Wi-Fi, Cell phones, wireless power transfer, computer interface devices and
various wireless communication based projects.

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1.1.9 Difference between Wired and Wireless Communication

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Wired networks use cables or wires to transfer data between different communicating
devices. In general, wired networks use Ethernet cable to transfer data between

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interconnected devices. On the other hand, the wireless devices use infrared or radio
frequency signals to exchange information and other resources between devices. The
difference between wired and wireless communication is summarized in below
Table 1.1.2.
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Sr. No
l.
Parameters
Connectivity
Wired Communication
Nodes are connected via
t
Wireless Communication
Nodes are linked using
cables or wires. wireless links.

2. Data transmission Transmission of data Transmission of data occurs

occurs through cables. through radio waves.

3. Installation time Time to install network is Less time required to install

more. network.

4. Components Ethernet, cables, switches Wireless adapter and access

are available for data points are available for data
exchange. exchange.

5. Cost Cost of Ethernet, cables Cost of wireless adapter and

and switches are not access points are more.
expensive.
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Ad hoc and Wireless Sensor Networks 1 - 15 Wireless Networks and Ad hoc Networks

6. Mobility Limited mobility. High mobility.

7. Topology Static topology. Dynamic topology.

8. Link stability Infrequent link breakage. Frequent link breakage.

9. Security Efficient security Poor security mechanisms are

mechanisms are available. available.

10. Interference Less High

11. Connection set up Requires less time for Requires more time for
connection set up. connection set up.

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12. Quality of service Quality of service is better. Quality of service is poor due
to higher jitter, delays and

13.
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Bandwidth capacity High
longer connection set up times.

Low

14. Reliability
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Table 1.1.2 Difference between wired and wireless communication

1.2 Wireless Ad hoc Network

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A wireless Ad-hoc network (WANET) is a type of local area network (LAN) that is

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built spontaneously to enable two or more wireless devices to be connected to each other

are in Ad-hoc mode, each device in the network forwards data to the others. g
without requiring a central device, such as a router or access point. When Wi-Fi networks

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Since the devices in the Ad-hoc network can access each other's resources directly
through a basic point-to-point wireless connection, central servers are unnecessary for
functions such as file shares or printers. In a wireless Ad-hoc network, a collection of
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devices (or nodes) is responsible for network operations, such as routing, security,
addressing and key management.

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Fig. 1.2.1 Wireless Ad hoc network
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1.2.1 Ad hoc Network - Working
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Devices in the Ad-hoc network require a wireless network adapter, and they need to .ne
support a hosted network. When setting up a wireless Ad-hoc network, each wireless
adapter must be configured for Ad-hoc mode instead of infrastructure mode. All wireless
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adapters need to use the Same Service Set Identifier (SSID) and channel number.
Creating an Ad-hoc network for Windows 8 and 10 applications is more difficult than
it was for earlier Windows OSs. Networking experts offer pointers on how to tackle this
issue.

1.2.2 Wireless Ad hoc Network Features

1. Ad hoc networks adhere to dynamic topologies. Network topology which is
typically multi-hops, may change randomly and rapidly with time, it can form
unidirectional or bi-directional links. Expensive equipments are not necessary
to set up an on-the-fly ad hoc network. Nodes are free to move arbitrarily with
different speeds thus the network topology may change randomly and at
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Ad hoc and Wireless Sensor Networks 1 - 17 Wireless Networks and Ad hoc Networks

unpredictable time. The nodes in the MANET dynamically establish routing

among themselves as they travel around, establishing their own network.
2. Ad hoc networks suffer from bandwidth constrained and variable capacity
links. Wireless links usually have lower reliability, efficiency, stability and
capacity as compared to wired network. The throughput of wireless
communication is even less than a radio’s maximum transmission rate after
dealing with the constraints like multiple access, noise, interference conditions,
etc. The reliability, efficiency, stability and capacity of wireless links are often
inferior when compared with wired links. This shows the fluctuating link

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bandwidth of wireless links.
Each node in ad hoc network has autonomous behavior. Each node can act as a

w host and router, which shows its autonomous behavior. All nodes have

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identical features with similar responsibilities and capabilities and hence it
forms a completely symmetric environment.
4. syE
Nodal connectivity is intermittent that is not steady or it is irregular.
5.
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The terminals in the network are light-weight terminals. In maximum cases,
the nodes in ad hoc network are mobile with less CPU capability, low power

6.
storage and small memory size.
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Shared Physical Medium - The wireless communication medium is accessible

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to any entity with the appropriate equipment and adequate resources.

7.
Accordingly, access to the channel cannot be restricted.
g
In Ad hoc network the energy constrained operations can be critical in terms
.ne
of certain resource utilization. As some or all the nodes rely on batteries or
other exhaustible means for their energy. Mobile nodes are characterized with
less memory, power and light weight features.
t
8. Ad hoc networks offer limited security. Wireless network are more prone to
security threats. A centralized firewall is absent due to its distributed nature of
operation for security, routing and host configuration.
9. Less human intervention is required in Ad hoc network. They require
minimum human intervention to configure the network, therefore they are
dynamically autonomous in nature. Ad hoc network has mobile and
spontaneous behaviour which demands minimum human intervention to
configure the network.
10. There is no single point of failure in an Ad hoc network.

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11. In Ad hoc network multi hop routing is required as per situation. When a
node tries to send information to other nodes which is out of its
communication range, the packet should be forwarded via one or more
intermediate nodes.
12. High user density and large level of user mobility.
13. In ad hoc networks no central management hub is required from where all
devices can be controlled.
14. In Ad hoc network operations are performed in distributed manner.
Distributed nature of operation for security, routing and host configuration. A

ww centralized firewall is absent here. There is no background network for the

central control of the network operations, the control of the network is

w distributed among the nodes. The nodes involved in a MANET should

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cooperate with each other and communicate among themselves and each node

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acts as a relay as needed, to implement specific functions such as routing and
security.

1.2.3 Ad hoc Network-Architecture, Operations

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Ad hoc network is a decentralized network in which nodes are moving arbitrarily. It is
mainly used in the areas where costly network infrastructure cannot be deployed.

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Ad hoc network does not have any central access point. Every node is connected to
another node physically.
It is a temporary network setup generally for emergency purposes. g .ne
In this architecture communication is done directly between the nodes.
This type of network provides great flexibility.
Also this type of network is fit for smaller coverage area.
t
Interference and noise easily hinder the communication between the nodes. However,
detecting an error is easy in Ad hoc network as compared to infrastructure network.
Also configuring and re installation is quite economical as well. These networks do not
need much maintenance.
This network is costly for a small coverage area. In this network the transmission of
information is not reliable as compared to infrastructure network. But they are very
useful for emergency purposes like during flood, earthquakes etc.
The transmission is not very secure but offers good speed and serves the requirement
for communication in need.

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Ad hoc and Wireless Sensor Networks 1 - 19 Wireless Networks and Ad hoc Networks

A model of mobile ad hoc network is shown in below Fig. 1.2.2.

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Fig. 1.2.2 Mobile Ad hoc network

1.2.3.1 Ad hoc Network Architecture

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Ad hoc network is formed in emergency situations such as disasters, wars, flooded

g
areas by the mobile nodes such as laptops, mobile phones and desktop machines in the
air. Each ad hoc network node is allowed to move in any direction and can communicate
.ne
with its neighbours.

The mobile devices which are in the coverage range of other devices can communicate
t
with each other directly. Otherwise, if a mobile node (source) wants to transmit a message
to another mobile node (destination) which is in out of the communication range of
source node, then multiple intermediate nodes are used to forward the same message to
the designated destination.

The architecture of Ad-hoc Network is shown in below Fig. 1.2.3.

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ww
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Fig. 1.2.3 Ad hoc network architecture

The Ad hoc architecture comprises three categories,

1. nee
Enabling technologies - These technologies are further classified into several
classes :
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1. Body Area Network (BAN)
2. Personal Area Network (PAN) g .ne
3. Local Area Networks (LAN)
4. Metropolitan Area Network (MAN)
5. Wide Area Networks (WAN)
t
2. Networking - Due to the dynamic topology nature of the network, the routing
protocols which are designed for wired network are not suitable for ad hoc
scenario. So the routing protocols have to be re-designed to support for ad hoc
networks and to improve robustness and adaptability.
Enabling technologies are used to provide end-to-end reliable data delivery. In
ad hoc scenario, locating receiver node is difficult due to high mobility of
mobile nodes. Therefore, localization mechanisms are used to determine the
location of a mobile node. Localization is the process by which a mobile node
can determine its position with respect to other mobile nodes in the network.

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Location service is used to dynamically map the logical address of the receiver
device to its current location in the network.
3. Middleware and applications
Ad hoc systems do not have a middleware. However, it is developed to rely on
each application to handle all the services it needs in different environments.
Ad hoc networking applications are suitable mainly in specialized fields such
as emergency services, disaster recovery and environmental monitoring. In
addition, Ad hoc system can be widely used in home networking, search and
rescue operations, commercial and educational applications, sensor networks

ww etc.

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1.2.3.2 Communication

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There are two types of Ad hoc communication namely,
1. Single hop communication - Here, Direct Communication is possible between

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two mobile nodes.
2.
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Multi-hop communication - Here, each node forwards the message through
multiple hops (nodes) to deliver to the designated node (destination) which is
far away to source node.
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1.2.3.3 Ad hoc Network Operations
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responsibility to perform the following operations,
 Cooperate and organize to self-configure the network.
g
As mentioned earlier, in ad hoc network each mobile node acts as router and takes

.ne


Exchanges its own information to its neighbours as beacon messages periodically.
Receives beacons or other packets from neighbours.
t
 Discover forwarder nodes to forward packets to distant locations.
 Forward the received packet to a specified destination.
 Broadcast the packet to all other neighbours which are in its transmission range.
 Mobile node can join the network and can leave the network at any time.

1.2.3.4 Ad hoc Network - Routing

Routing is the process of finding path in a network to transmit a data packet from the
sender node to the intended receiver. Since each mobile node forms frequent dynamic
topology due to high mobility, routing is one of the big challenging issues in Ad hoc

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environment. Ad hoc routing protocols are broadly classified into three categories
namely,
1. Proactive or table-driven routing protocol
2. On-demand or reactive routing protocol
3. Hybrid routing protocol.
1. Proactive routing protocol - Each node maintains a routing table to listen and
update the details of its neighbours. Each node exchanges hello packet
including node identifier, message and time-to-live parameters. The node
which receives the hello packet will response using hello reply message. These

ww messages are used to update the routing table. So, whenever a mobile node
wants to transmit a packet to other node in the network, it can easily find the

w route from its routing table. Thus, these type of protocols are reducing the time

.Ea
needed to determine a route for data transmission. One of the examples of pro

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active routing protocol is Destination Sequenced Distance Vector (DSDV)
routing protocol.
2.
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Reactive routing protocol - Each node determines a routing path whenever it
is required to transmit a packet from a source node to the destination. Each

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protocol uses two key phases for finding a route : Route discovery and route
maintenance. Route discovery phase uses route request and route reply

rin
messages. If any reliable path is broken, then route maintenance phase can be

g
used. Route maintenance phase uses Route Error message for intimating the
broken route to the sender and will try to determine alternate route to reach
.ne
the source and destination. Some of the examples of reactive routing protocols
are Dynamic Source Routing (DSR) protocol and Ad hoc On demand Distance
Vector (AODV) routing protocol.
t
3. Hybrid routing protocol - This type of protocols combines the advantages of
proactive and reactive routing protocols. Each node uses proactive algorithm
within its visibility and uses reactive algorithm when a node wants to
communicate with other node which is in it’s out of the coverage area. Zone
Routing Protocol (ZRP) and Order One MANET Routing Protocol (OORP) are
the examples of hybrid routing protocols.

1.2.4 Types of Wireless Ad hoc Networks

Wireless Ad hoc networks are categorized into different classes depending upon the
nature of their applications.
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1.2.4.1 Mobile Ad hoc Network (MANET)

An Ad hoc network of mobile devices. This is a self configuring and self organizing
network of mobile devices.

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w .Ea
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Fig. 1.2.4 Mobile Ad hoc network (MANET)
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1.2.4.2 Vehicular Ad hoc Network (VANET) g .ne
Used for communication between vehicles. Intelligent VANETs use artificial
intelligence and Ad hoc technologies to communicate what should happen during
accidents. This network is formed by communication between moving vehicles and other
t
roadside devices.

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ww
w .Ea
syE
ngi
nee
Fig. 1.2.5 Vehicular Ad hoc network (VANET)
(Quick reference – RSU : Roadside Unit, Vehicle-to-Infrastructure (V2I) communication,
Vehicle-to-Vehicle (V2V) communication)
1.2.4.3 Smartphone Ad hoc Network (SPAN)
rin
g
Wireless Ad hoc network created on smart phones via existing technologies like Wi-Fi
and Bluetooth. These are peer to peer networks formed by smart phones within range of
each other without requiring any cellular carriers, wireless access point etc. .ne
t

Fig. 1.2.6 Smartphone Ad hoc network (SPAN)

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1.2.4.4 Wireless Mesh Network (WMN)

A mesh network is an Ad hoc network where the various nodes are in communication
directly with each other to relay information throughout the total network. The devices
connected to this network form a wireless mesh and depending upon the mobility
pattern, nature of devices and inter device distance.

ww
w .Ea
syE
ngi
nee
rin
Fig. 1.2.7 Wireless Mesh Network (WMN)
g .ne
1.2.4.5 Army Tactical MANET
Used in the army for "on-the-move" communication, a wireless tactical Ad hoc
t
network relies on range and instant operation to establish networks when needed.

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Ad hoc and Wireless Sensor Networks 1 - 26 Wireless Networks and Ad hoc Networks

ww
w .Ea
syE Fig. 1.2.8 Army tactical MANET
(Quick reference - Unmanned Aerial Vehicles (UAVs), LAN – Local Area Network)

1.2.4.6 Wireless Sensor Network

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Wireless sensors are portable devices that capture specific information from
environment ranging from temperature, humidity, pressure readings to noise level, traffic

rin
volume etc. These portable sensing devices can form an Ad hoc network to deliver
information to a home base without needing to connect directly to it. This network is
developed to collect the information on the fly.
g .ne
t

Fig. 1.2.9 Wireless sensor network

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Ad hoc and Wireless Sensor Networks 1 - 27 Wireless Networks and Ad hoc Networks

1.2.4.7 Disaster Rescue Ad hoc Network

Ad hoc networks are important when disaster strikes and established communication
hardware isn't functioning properly.

ww
w .Ea
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ngi
nee
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g .ne
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Fig. 1.2.10 Disaster rescue Ad hoc network

1.2.4.8 Intelligent based Mobile Ad hoc Network (iMANET)

This is used in linking fixed nodes and mobile nodes via routing protocol which
automatically establishes connection in decentralized manner.

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ww
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ngi
nee
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g .ne
t
Fig. 1.2.11 Intelligent based mobile Ad hoc network (iMANET)

1.2.4.9 Flying Ad hoc Network (FANET)

FANET is a special case of MANET. The topology of this network can change
frequently when compared to VANET. Here an Unmanned Aerial Vehicle (UAV) flies
autonomously without carrying any human help. It does this by simply connecting
directly to satellite or ground station to establish Ad hoc network. This type of wireless
networking architecture is called Flying Ad hoc Network (FANET).

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ww
w .Ea
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ngi
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Fig. 1.2.12 Flying Ad hoc network (FANET)
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1.2.5 Ad hoc Network - Commercial Applications
g
With the increased number of lightweight devices as well as evolution in wireless .ne
communication, the ad hoc networking technology is gaining effort with the increasing
number of widespread applications. t
Ad hoc networking can be used anytime, anywhere with limited or no
communication infrastructure.
The Ad hoc network architecture can be used in real time business applications,
corporate companies to increase the productivity and profit.
Ad-hoc networks are used frequently in new types of wireless engineering. Wireless
Ad-hoc networks require minimal configuration and can be deployed quickly, which
makes them suitable for emergencies, such as natural disasters or military conflicts.
There are dynamic and adaptive routing protocols so that these networks can be
configured quickly.

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These impromptu on-demand networks are useful for putting together a small,
inexpensive all-wireless LAN. They also work well as a temporary fallback mechanism if
equipment for an infrastructure mode network fails.
The importance of Ad hoc network has been highlighted in many fields as described
below,
1. Provincial level - Ad hoc networks can build instant link between multimedia
network using notebook computers or palmtop computers to spread and share
information among participants (e.g. Conferences).
2. Personal area network and home and enterprise network - A personal area

ww network is a short range, localized network where nodes are usually associated
with a given range. Conference meetings and lectures can be arranged.

w
3. Industry sector - Ad hoc network is widely used for commercial applications.

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Ad hoc network can also be used in emergency situation such as disaster relief.

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The rapid development of non-existing infrastructure makes the Ad hoc
network easily to be used in emergency situation.
4.
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Bluetooth - Bluetooth can provide short range communication between the
nodes such as a laptop and mobile phone.
5.
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Tactical/military networks - Military communication and operations can be

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carried out. In this network the coordination of military object moving at high
speeds such as fleets of airplanes or ship can achieved. An Ad hoc networking

g
allows the military battle ground to maintain an information network among

.ne
the soldiers, vehicles and headquarters. Automated battlefields can be set such

6.
as in determining the position of troops during war fare.
Sensor networks - These network support collection of embedded sensor
devices used to collect real time data to automate everyday functions. Sensor
t
network can be deployed in the monitoring and measurement of variables
such as change in pressure, temperature etc especially in pipelining. This
network can be use in tracking of positions and movement of objects and
animals.
7. Emergency services - Ad hoc network can be used in search, rescue, crowd
control operations and in disaster control and recovery. It can be used in
replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire
etc. It can be deployed for policing and fire-fighting. It can support doctors and
nurses in medical field.

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8. Commercial and Civilian Environment - With the emergence of Ad hoc

network E-commerce, e.g., electronic payments from anywhere (i.e., in taxi)
have been very efficient and fast. The business databases can be accessed as per
need from anywhere.
9. Educational Applications - Ad hoc network can be used in universities and
campus for setting up virtual classrooms or conference rooms and for data
sharing.
10. Entertainment - Ad hoc networks can be used in multi-player games. The
network can deploy robotic pets outdoor.

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1.2.6 Ad hoc Network Advantages and Disadvantages

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Ad hoc network advantages
1.
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There is separation from central network administration.
2.
3. syE
The self-configuring nodes are also routers.
It is adaptive in nature. There are self configuring and self healing nodes, does

4.
not require human intervention.
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It is very cheap to set up since there is no wiring of nodes.
5.
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Ad hoc networks are scalable in nature and incorporate the addition of more

6.
nodes.
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Mobility allows Ad hoc networks being created on the fly in any situation

7.
where there are multiple wireless devices.
g
Ad hoc networks are flexible and can be temporarily setup at anytime, in any .ne
8.
place.
Ad hoc networks have lower startup costs due to decentralized administration.
t
9. The nodes in ad hoc network need not rely on any hardware and software. So,
it can be connected and communicated quickly.
10. Lack of infrastructure makes the network robust in network failure.
11. Ad hoc networks do not restrict access to channels.

Ad hoc network disadvantages

1. In Ad hoc network the resources are limited due to various constraints like
noise, interference conditions, etc.
2. Ad hoc networks do suffer from slow data rate.
3. Ad hoc networks lack the authorization facilities.

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4. Ad hoc networks are more prone to attacks due to limited physical security. If
an attacker comes within range of the ad hoc network, the attacker can easily
get in inside the network.
5. For file and printer sharing, all users need to be in the same workgroup, or if
one computer is joined to a domain, the other users have to have accounts on
that computer in order to access shared items.

1.2.7 Issues and Challenges in Ad hoc Networks

1. Limited bandwidth - The limited radio band results in reduced data rate

ww compared to wireless networks. Hence, optimal usage of bandwidth is

necessary by keeping low overhead as possible. The wireless networks have a

w limited bandwidth in comparison to the wired networks. Wireless link has

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lower capacity as compare to infrastructure networks. The effect of fading,
multiple accesses, interference condition is very low in Ad hoc networks in

2.
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comparison to maximum radio transmission rate.
Variability in capacity links due to bandwidth constraint - Being a link of

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wireless the nodes have tendency to continue with low capacity in comparison

3.
to the hardwired.
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Dynamic topology - In dynamic topology the nodes are free to move in any

rin
direction. Topology of network changes rapidly and unpredictably by the time.

g
Due to this topology the bidirectional and unidirectional routing exists.
Challenging task is to transferring the packets between the nodes because the
topologies are changes continuously. Due to dynamic topology the nodes have .ne
less trust between them. If some settlements are found between the nodes that
also makes trust level questionable.
t
4. Multicast routing - Another challenge of Ad hoc network is multicast.
Multicast stands for multiple communication between wireless devices. Ad hoc
networks are the multicast dynamic networks because the nodes randomly
change their positions. The nodes have multiple hopes instead of single hop
and they are complex. As the nature the multicast is not remains for longer
period so that the protocol has to maintain mobility which includes the leaving
and joining of nodes. The new device adds in the network need to know all the
other nodes. To facilitate automatic optimal route selection dynamic update is
necessary due to existence of node.

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5. High Routing (Routing overhead ) - In Ad hoc networks due to dynamic

topology some nodes changes their position which affects the routing table.
Due to the mobility of nodes within the Ad hoc network, stale (and not
available now) routes are generated in the routing table leading to routing
overhead.
6. Mobility - Due to the dynamic behavior and changes in the network topology
by the movement of the nodes, Ad hoc networks faces path breaks and it also
changes in the route frequently.
7. Problem of hidden terminal - The collision of the packets are held due to the

ww transmission of packets by those node which are not in the direct transmission
range of sender side but are in range of receiver side.

w
8. Packet loss due to transmission error - The vulnerable nature of wireless

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networks often lead to frequent packet loss due to traffic collision caused by

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hidden terminals, interference and frequent path breaks caused by mobility of
nodes. By increase in collisions , hidden terminals, interference, uni-directional

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links and by the mobility of nodes frequent path breaks a higher packet loss
has been faced by ADHOC networks.
9.
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Frequent network partitions - The random movement of nodes often leads to
network partitions. This affects mostly the intermediate nodes.

rin
10. Power-constrained and operation - This is considered as a major challenge for

g
the Ad hoc network. Most of the nodes rely on limited battery life. Some of the
power of the batteries is used for data transmission, data processing and for
.ne
Ad hoc network. In Ad hoc network all the nodes rely on the batteries or some
exhaustible source of energy. Conversion in the energy is the optimized criteria
t
routing packets to their destination. This is a critical issue in the design of an

and an important system design. Lean power consumption is also used for the
light weight mobile terminals. Conservation of power and power-aware
routing is another aspect which needs to be considered in Ad hoc network.
11. Diffusion hole problem - The excess energy consumption is faced by the
nodes which are present in the boundaries of the holes. If the bypass holes are
wish to omit then the packets are delivered along the holes boundaries. This
enlarges the hole due to consumption of very much of the nodes and its
boundaries.
12. Quality of service - In Ad hoc network the environment changes constantly so
that it provides different quality of service levels which are challengeable. The
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random nature in the quality communication of Ad hoc it is difficult to serve

good guarantee of service of the device. To support multimedia services
adaptive quality of services can be implemented over traditional resources.
13. Inter-networking - Communication with fixed networks is also expected from
Ad hoc networks in many cases. The existence of routing protocols in both the
networks is quite challengeable for pleasant mobility management.
14. Security, security threats and reliability - New security challenges are raised
by Ad hoc networks due to wireless nature. In Ad hoc networks or wireless
networks the trust management between the nodes leads to numerous security

ww attacks. A nasty neighbor node, relaying the packets is also a security problem
along with other vulnerabilities. Different schemes are used for authentication

w and key management in distributed operations.

.Ea
Reliability problem is also a wireless link characteristic due to limited wireless

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transmission. Due to the broadcast nature of wireless medium packets loss and
errors do occur in the transmissions. In comparison to the wired network the

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wireless networks are more vulnerable to security threats.
There are various security threats in Ad hoc networks. Mobile nodes are

nee
usually more vulnerable to attacks within the network as well as outside the
network.

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External Threats - Performing communication in free space exposes Ad hoc networks

g
to attacks as anyone can join the network, and eavesdrop (being hidden and listening) or
inject messages. External attacks are accomplished by entities which are outside of the
.ne
network or by nodes which are not authorized. These attacks generally threaten the
lower layers that is physical and data link layer. As, in Ad hoc network the nodes inherit
the mobile nature it is intrinsically difficult to secure this layer. These threats can be
t
further classified in following categories based on their action,
(i) Passive Attacks - Passive eavesdropping is a technique where an unauthorized
node silently listens the network traffic, even the route updates. It gathers the
data and attempts to discover nodes information (for example, IP addresses,
location of nodes, etc.) by listening to routing traffic. Such information can be
used to threaten the network by interfering the topology, knowing the
geographical location of the nodes and identifying the heavily used nodes.
Passive attack signifies that the attacker does not send any message, but just
listens to the channel. A passive attack does not disrupt the operation of a
protocol, but only attempts to discover valuable information. Passive attack is
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Ad hoc and Wireless Sensor Networks 1 - 35 Wireless Networks and Ad hoc Networks

usually impossible to detect this attack, as it does not produce any new traffic
in the network.
(ii) Active Attacks - Active attacks are designed to disrupt the network by sending
signals or data. An active attack attempts to destroy or modify the data being
exchanged in the network, hence disrupting the normal functioning of attacks.
In contrast to passive attack, during an active attack, information is inserted
into the network. Active attacks involve actions such as the replication,
modification and deletion of exchanged data. Certain active attacks can be
easily performed against an Ad hoc network. These attacks can be classified as

ww impersonation, denial of service, and Disclosure attack. Denial of service attack

is one of the major active attacks causing the communication channel to be

w blocked.

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Further these attacks are divided into two categories,

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External attacks - These are carried out by the outsider nodes, those nodes that do not
belong to the concerned network.

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Internal attacks - These attacks occur because of compromised nodes present inside
the network.

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Routing Attacks - These attacks are aimed on the routing protocols and are being
performed in a manner to disrupt the operation of the network. These attacks are

rin
further categorized as routing table overflow and routing table poisoning.

1.2.8 Ad hoc Wireless and Cellular Network and their Comparative Analysis g .ne
A cellular network is a radio network distributed over land through cells where each
cell includes a fixed location transceiver known as base station. These cells together
provide radio coverage over larger geographical areas. User Equipment (UE), such as
t
mobile phones, is therefore able to communicate even if the equipment is moving through
cells during transmission.
Cellular networks give subscribers advanced features over alternative solutions,
including increased capacity, small battery power usage, a larger geographical coverage
area and reduced interference from other signals. Popular cellular technologies include
the global system for mobile communication, general packet radio service, 3GSM and
code division multiple access.
Cellular network technology supports a hierarchical structure formed by the Base
Transceiver Station (BTS), Mobile Switching Center (MSC), location registers and Public
Switched Telephone Network (PSTN). The BTS enables cellular devices to make direct
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communication with mobile phones. The unit acts as a base station to route calls to the
destination base center controller. The Base Station Controller (BSC) coordinates with the
MSC to interface with the landline-based PSTN, Visitor Location Register (VLR), and
Home Location Register (HLR) to route the calls toward different base center controllers.

Cellular networks and Ad-hoc networks

Following table compares cellular network versus Ad hoc network with respect to
various system parameters :
Sr. No. Parameters Cellular network Ad Hoc network

ww 1. Network routing Centralized, all the traffic

goes through the base
Distributed, No
centralized system such

w
2.
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Infrastructure
requirements
station

Infrastructure required
as Base station needed

No infrastructure
required

3.
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Switching Type Circuit Switching Packet Switching

4.

5.
Number of Hops

Topology Star ngi

Single hop type Multiple hops

Mesh

6. Application Designed and developed

for voice traffic
nee Designed to meet best
effort data traffic

rin
requirements

7. Cost and time for

installation
Higher cost and takes more
time for deployment g
Lower cost and does not

.ne
take more time for
deployment

8. Call drops Low call drops during

mobility due to seamless
t
Higher breaks in the
path during mobility
connectivity across region

9. Network maintenance Requires periodic Nodes are self

maintenance and hence it is organising and hence it
costly. is less costly.

10. Frequency re-use It utilizes same frequency Dynamic frequency re-

channels in the nearby cells use is employed using
with proper RF planning carrier sense mechanism.
and antenna placement.
This is known as static
frequency re-use.

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11. Bandwidth (BW) The allocation of BW is The allocation of BW is

mechanism guaranteed and easy. based on shared channel
using complex MAC
algorithms.

12. Time synchronization Easy time synchronization. Difficult to do time

synchronization

13. Technologies IS-95, IS-136, GSM, Mobile WLAN 802.11e

WiMAX, CDMA, LTE

ww Table 1.2.1 Difference between cellular networks and Ad-hoc networks in tabular form

1.2.9 Design Issues of Ad hoc Wireless Network

w .Ea
The various design issues of wireless ad hoc network are discussed below,
1. Medium access scheme
2. Routing syE
3. Multicasting
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4.
5.
Transport layer protocol
Pricing scheme nee
6. Quality of service provisioning
rin
7.
8.
Self-organization
Security
g .ne
9. Addressing and service discovery
10. Energy management
t
11. Deployment considerations.
1. Medium access scheme - The major issues considered while designing a MAC
protocol for Ad hoc wireless network are as follows : Distributed operation,
synchronization, hidden terminals, exposed terminals, throughput, access
delay, fairness, real time traffic support, resource reservation, ability to
measure resource availability, capability for power control, adaptive rate
control and use of directional antennas.
2. Routing - It is the process of determining a route based on hop count, need of
power and life time of the link in order to exchange information from one node
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to other node. The major design issues of a routing protocol are as follows :
Mobility, bandwidth constrained, error-prone and shared channel, location
dependent contention and other resource constraints such as computing and
battery power, storage capacity etc.
Other requirements of routing protocols in Ad hoc networks are minimum
route acquisition delay, quick route reconfiguration, loop free routing,
distributed routing approach, minimum control overhead, scalability,
provisioning of Quality of Service (QoS), support for time sensitive traffic and
security.

ww3. Multicasting - Transmission of same message to a group of mobile nodes in

w single transmission is called multicasting. The major design issues of

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multicasting protocols are as follows : Robustness, efficiency, control overhead,
QoS, efficient group management, scalability and security.
4.
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Transport layer protocols - Transport layer protocols are used to set up and
maintain end-to-end connection. Further, it provides reliable data delivery in

ngi
wired networks. It is also focused to perform flow control and congestion
control.

nee
Transmission Control Protocol (TCP) is one of the reliable connection oriented

rin
protocols which is widely used in wired networks. However, the performance
of TCP is degraded in Ad hoc networks due to the factors such as frequent

g
path breaks, high mobility, bandwidth and power constrained, high channel
.ne
error rate and frequent network partitions. If a TCP connection is divided into
two in Ad hoc network, then it will lead to much packet loss. This would be an
intolerable when the network partitions exist for prolong period. Therefore, the
development of transport protocols for Ad hoc networks should take into
t
consideration the aforementioned issues.
5. Pricing scheme - In Ad hoc network, if any mobile node is not interested in
relaying a packet to its neighbours, it can decide to power off. In spite of that a
node is having an optimal path to communicate with other node and any
intermediate node on the path supposed to relay the packet is decided to
power down, then the sender node cannot use that optimal path; instead it
may force to determine or consider a costlier alternate path which is non-
optimal, consumes more resources and hence highly affects the throughput of
the system.

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6. QoS provisioning - It is the performance level of services which is offered by a

service provider. If there is a better coordination and cooperation between
service provider and the user, then high QoS can be achieved. Some of the QoS
parameters, QoS-aware routing and QoS frameworks are discussed below :
a. QoS parameters differ from application to application. For instance,
bandwidth and delay are the important key parameters of multimedia
applications. Identifying trusty nodes and routing the packets through
them are key parameters of defense applications. Multiple link disjoint
paths and availability are the key parameters of emergency and rescue

ww operations related applications. Energy conservation and battery life are

the major QoS parameters in sensor networks.

w b. QoS aware routing protocol should possess QoS parameters for

.Ea
determining routing path. The routing measures considered are network
throughput, packet delivery ratio, packet loss rate, delay, reliability, bit

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error rate and bandwidth consumption.
c.
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QoS framework is a complete system that is used to provide the assured
services to the concerned user or application. The key component of QoS

nee
framework is a QoS service model that defines the serving way of user
requirements. One of the design issues is whether to provide service in

rin
per-session basis or per-class basis. The other key components are QoS

scheduling schemes. g
routing, QoS signaling, QoS MAC, connection admission control and

.ne
7. Self-organization - The mobile nodes in ad hoc networks would self-configure
the network by itself. Self-organization includes neighbour discovery, topology
organization and reorganization. Beacon signals would be exchanged between
t
mobile nodes during neighbour discovery. For organizing topology, every
node gathers information from other nodes. During topology reorganization,
every node maintains the updated information. The topology of the network
would be changed due to high mobility, node failures and frequent network
partitioning.
8. Security - Security is a challenging one in Ad hoc wireless networks, especially
in military areas. The attacks in Ad hoc wireless network are broadly classified
into two types :
1. Passive attack
2. Active attack.
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In general, passive attacks would be caused by malicious nodes present in the network
to obtain the information being exchanged in the network. This type of attack would not
interfere in network operations. Active attacks would disturb the network operation. If
the network operation is disrupted by mobile nodes (attackers) available within the
network are called internal attackers; if the network operation is interrupted by the
mobile nodes (attackers) which is in external network are called as external attackers.
Some of the security threats exist in ad hoc wireless network are Denial-of-Service (DoS),
resource consumption, host impersonation, information disclosure and interference.
9. Addressing and service discovery - Address of a mobile node is a globally

ww unique identifier used for communication in Ad hoc wireless network. Since

nodes join into a new network and leave from the current network any time,

w any auto-configuration addressing scheme is required to allocate non-duplicate

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addresses to the nodes. Ad hoc wireless network also requires a duplicate
address-detection mechanism in order to maintain unique addressing

syE
throughout the network. Since the Ad hoc network forms frequent dynamic
topology, efficient service advertisement mechanism also required to locate
services that other nodes provide.
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nee
10. Energy management - It is the process of managing the sources and consumers
of energy in a node to boost up the lifetime of the node in the network. Energy
management can be classified into four categories -
rin
I.
II.
Transmission power management
Battery energy management g .ne
III. Processor power management
IV. Device power management.
Some of the functions of energy management mechanisms are enhancing battery life of
t
a node by shaping the energy discharge pattern, determining routing path with minimum
energy consumption, using distributed scheduling schemes to enhance battery life of a
node and to minimize the power consumption of processor and other computing devices
during data transfer.
11. Deployment considerations - The deployment considerations of Ad hoc
wireless networks when compare with wired networks are low cost of
deployment, incremental deployment, short deployment time, re-
configurability and non-estimation of future traffic growth in network.

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1.2.10 Ad hoc Wireless Internet

The Ad hoc wireless Internet extends the services of the Internet to the end users in an
ad hoc wireless network environment. Important applications of the Ad hoc wireless
Internet are wireless mesh networks, provisioning of temporary Internet services to
meeting venues, sports venues, temporary military settlements, battlefields, and
broadband Internet services in rural regions. A Below figure depicts the Ad hoc wireless
Internet protocol stack and structure of network.
Extends the services of the internet to end users over an Ad hoc wireless networks.

ww
w .Ea
syE
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nee
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g .ne
t
Fig. 1.2.13 Ad hoc wireless internet protocol stack and structure of network

Major issues in ad hoc wireless internet

1. Gateways - Gateway nodes in the Ad hoc wireless Internet are the entry points
to the wired Internet. The major part of the service provisioning is
incorporated in the gateway nodes. Gateways are usually owned and operated
by a service provider. Gateways can perform the tasks like, keeping track of
the end users, bandwidth management, load balancing, traffic shaping, packet
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filtering, bandwidth fairness, address discovery, service discovery, location

discovery and various such network crucial tasks.
2. Address mobility - The Ad hoc wireless Internet faces the challenge of address
mobility. This problem is worse here as the nodes operate over multiple
wireless hops. Mobile IP can provide temporary solution for this.

3. Routing - Routing is a major problem in the Ad hoc wireless Internet, due to

the dynamic topological changes, the presence of gateways, multi-hop
relaying, and the hybrid character of the network. The possible solution for this
is the use of a separate routing protocol for the wireless part of the Ad hoc

ww wireless Internet. Routing protocols that exploit the presence of gateway nodes
are more suitable here.

w
4.
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Transport layer protocol - Even though several solutions for transport layer
protocols exist for Ad hoc wireless networks, unlike other layers, the choice lies

syE
in favor of TCP's extensions proposed for Ad hoc wireless networks. Split
approaches that use traditional wired TCP for the wired part and a specialized

ngi
transport layer protocol for the Ad hoc wireless network part can also be
considered where the gateways act as the intermediate nodes at which the

nee
connections are split. Various factors are required to be considered here, like
the state maintenance overhead at the gateway nodes.
rin
5.
g
Load balancing - There is 100 % chance that the Ad hoc wireless Internet
gateways experience heavy traffic. Hence the gateways can be saturated much
earlier than other nodes in the network. Load balancing techniques are .ne
essential to distribute the load so as to avoid the situation where the gateway
nodes become bottleneck nodes.
t
6. Usage pricing/billing - Since Internet bandwidth is expensive, it becomes very
important to introduce pricing/billing strategies for the Ad hoc wireless
Internet. Gateway is the preferred choice for charging the traffic to and from
the Internet. It is very complex to calculate the Pricing for the local traffic
(traffic within the wireless part, that is, it originated and terminated within the
wireless part without passing through the gateway nodes), where it becomes
necessary to have a dedicated, secure, and lightweight pricing/billing
infrastructure installed at every node.

7. Security provision - The inherent broadcast nature of the wireless medium

attracts not just the mobility seekers but also potential hackers who love to
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snoop on important information sent unprotected over the air. Hence security
is a prime concern in the Ad hoc wireless Internet.

Since the end users can utilize the Ad hoc wireless Internet infrastructure to
make e-commerce transactions, it is vital aspect to include security
mechanisms in the Ad hoc wireless Internet.

8. QoS support - Voice over IP (VoIP) is widely used all over and there is huge
multimedia applications usage over the Internet. Therefore, provisioning of
QoS support in the Ad hoc wireless Internet becomes a very important issue.

ww9. Service, address, and location discovery - By service discovery in any network
it means the activity of discovering or identifying the entity which provides a

w particular service or resource. In wired networks, service location protocols

.Ea
exist to do the same, and similar systems need to be extended to operate in the
Ad hoc wireless Internet as well. Address discovery refers to the services such

syE
as those provided by Address Resolution Protocol (ARP) or Domain Name
Service (DNS) operating within the wireless domain. Location discovery refers

ngi
to different activities such as detecting the location of a particular mobile node

nee
in the network or detecting the geographical location of nodes. Location
discovery services can provide enhanced services such as routing of packets,
location-based services, and selective region-wide broadcasts.
rin
g
Below Fig. 1.2.14 depicts wireless mesh network that connects several houses
to the Internet through a gateway node. Such networks can provide highly
.ne
reliable broadband wireless networks for the urban as well as the rural
population in a cost-effective manner with fast
reconfiguration. This wireless mesh network is a special case of the Ad hoc
t
deployment and

wireless Internet where mobility of nodes is not a major concern as most relay
stations and end users use fixed transceivers. In the Fig. 1.2.14 House-1 is
connected to the Internet over multiple paths (path 1 and path 2).

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ww
w .Ea
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Fig. 1.2.14 Ad hoc wireless Internet implemented by a wireless mesh network

1.3 Two Marks Questions with Answers

nee
Q.1 What is an Ad hoc network ?
Part - A

rin
g
Ans. : An Ad hoc network is a multi hop, infrastructure less network which has no
centralized server to control the communication between the nodes and resources .ne
cannot be reserved beforehand. It is used in battlefields and military applications.
Q.2 Why are Ad hoc networks needed ? t
Ans. : Ad hoc networking is often needed where an infrastructure network cannot be
deployed and managed. The presence of dynamic and adaptive routing protocols
enables quick formation of Ad hoc networks and is suitable for emergency situations
like natural disasters, spontaneous meetings or military conflicts.
Q.3 List the characteristics and applications of MANETs.
Ans. : The characteristics of MANETs are,
1. Dynamic topologies
2. Bandwidth-constrained and variable capacity links.
3. Energy-constrained operation.
4. Limited physical security.
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The applications of MANET are,

1. Defense applications
2. Crisis-management applications
3. Telemedicine
4. Tele-geo processing applications
5. Virtual navigation
6. Education via the internet.
Q.4 Define MANET.

ww
Ans. : MANET is defined as an autonomous system of nodes or Mobile Stations (also
serving as routers) connected by wireless links, the union that forms a communication

w
networks, modeled in the form of an arbitrarily communication graph.

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Q.5 What are various operating modes in wireless networks ?
Ans. : Operating modes in wireless networks are infrastructure mode and Ad hoc

syE
mode. The IEEE 802.11 standards specify two operating modes - infrastructure mode
and Ad hoc mode (Infrastructure-less )
1. ngi
Infrastructure mode is used to connect computers with wireless network

nee
adapters, also known as wireless clients, to an existing wired network with
the help from wireless router or access point. In this mode each node is

rin
connected with other node through a fixed base station. The fixed station is

g
also known as Access Points (APs). An example for infrastructure based
network is cellular network in which base station or AP is used as fixed
equipment. Each network area is divided into cells and the base station .ne
provides each cell with the network coverage which can be used for the
transmission of high quality voice, data and other types of messages.
t
2. Ad hoc mode is used to connect wireless clients directly together, without the
need for a wireless router or access point. An Ad hoc network consists of up
to 9 wireless clients, which send their data directly to each other. In this
mode Each node can communicate with each other without using any fixed
infrastructure. Mobile Ad hoc networks and Vehicular Ad hoc Networks
(VANETs) are the examples of infrastructure less networks. In Ad hoc
networks, each node acts as a router to forward the information in a multi-
hop fashion.

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Q.6 What are VANETs ?

Ans. : Vehicular Ad hoc network (VANET) - Used for communication between vehicles.
Intelligent VANETs use artificial intelligence and ad hoc technologies to communicate
what should happen during accidents. This network is formed by communication
between moving vehicles and other roadside devices.
Q.7 What are passive attacks in the network ?
Ans. : Passive eavesdropping is a technique where an unauthorized node silently
listens the network traffic, even the route updates. It gathers the data and attempts to
discover nodes information (for example, IP addresses, location of nodes, etc.) by

ww
listening to routing traffic. Such information can be used to threaten the network by
interfering the topology, knowing the geographical location of the nodes and

w
identifying the heavily used nodes. Passive attack signifies that the attacker does not

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send any message, but just listens to the channel. A passive attack does not disrupt the
operation of a protocol, but only attempts to discover valuable information. Passive

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attack is usually impossible to detect this attack, as it does not produce any new traffic
in the network.
Q.8 What is wireless network ? ngi
nee
Ans. : Wireless networks are computer networks that are not connected by cables of
any kind. The use of a wireless network enables enterprises to avoid the costly process

rin
of introducing cables into buildings or as a connection between different equipment
locations.
Q.9 What is Wi-Fi network ? g .ne
Ans. : Wi-Fi is a low power wireless communication, that is used by various electronic
devices like smart phones, laptops, etc. In this setup, a router works as a
communication hub wirelessly. These networks allow users to connect only within
t
close proximity to a router. WiFi is very common in networking applications which
affords portability wirelessly. These networks need to be protected with passwords for
the purpose of security, otherwise it will access by others.
Q.10 What is Bluetooth technology ?
Ans. : The main function of the Bluetooth technology is that it permits user to connect
various electronic devices wirelessly to a system for the transferring of data.Cell
phones are connected to hands free earphones, mouse, wireless keyboard. By using
Bluetooth device the information from one device to another device. This technology
has various functions and it is used commonly in the wireless communication market.

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1.4 Long Answered Questions

Part - B
Q.1 Explain in detail about cellular and Ad hoc wireless networks. (Refer section 1.2)
Q.2 What are various types of wireless communication ? (Refer section 1.1)
Q.3 Devices connecting procedure in to wireless network. (Refer section 1.1)
Q.4 Explain in detail about applications of Ad hoc wireless. (Refer section 1.2)
Q.5 Explain in detail about Issues in Ad hoc wireless networks. (Refer section 1.1)
Q.6 Explain the Ad hoc network architecture. (Refer section 1.2)
Q.7 List the advantages and disadvantages of wireless communication. (Refer section 1.1)

ww
Q.8 Explain various wireless communication. (Refer section 1.1)

w
Q.9 What are the various components of wireless networks ? (Refer section 1.1)

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Q.10 Classify wireless network and explain it. (Refer section 1.1)

syE 

ngi
nee
rin
g .ne
t

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Ad hoc and Wireless Sensor Networks 1 - 48 Wireless Networks and Ad hoc Networks

Notes

ww
w .Ea
syE
ngi
nee
rin
g .ne
t

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UNIT - I

2 Routing in Ad hoc Networks

Syllabus
ww
Issues in Designing a Routing Protocol for Ad Hoc Wireless Networks, Classifications of
Routing Protocols, Table Driven Routing Protocols - Destination Sequenced Distance Vector

w
(DSDV), On-Demand Routing protocols - Ad hoc On–Demand Distance Vector Routing
(AODV).
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Contents
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2.1 Introduction to Routing
2.2 Types of Ad hoc Routing Protocols
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2.3 Advantages and Disadvantages of Ad hoc Wireless Routing Protocols
2.4 Two Marks Questions with Answers [Part A]
2.5 Long Answered Questions [Part B]
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g .ne
t

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Ad hoc and Wireless Sensor Networks 2-2 Routing in Ad hoc Networks

2.1 Introduction to Routing

An ad hoc network is a collection of mobile nodes forming a network without the help
of any centralized administration. Usually, mobile hosts use wireless radio frequency
transceivers for communicating with other mobile nodes. Since mobile nodes are not
fixed and changes network topology from time to time, establishing a communication
path between two nodes is a big challenging one.

2.1.1 Routing Concept and Process

ww
1. Routing is the process of establishing a path between the sender and receiver nodes
for transmitting the packet along the path. Different types of routing protocols are

wwidely used to discover a path between two nodes and take the responsibility of

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routing the packet to the intended destination with minimized delay, efficient
bandwidth consumption and maximizing reliability.

syE
2. Since two hosts wishing to exchange packets cannot be able to communicate
directly, some form of routing protocol is necessary to relay the packets between

ngi
nodes. When the destination is few hops away from the source node, multi-hop
communication need to be used for establishing path between the source and
destination.
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2.1.2 Major Issues in Designing Routing Protocols for Ad hoc Networks
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Routing protocols used in wired networks cannot be directly applied to ad hoc
wireless networks because of the following design constraints, g .ne
1.
2.
Node mobility
Bandwidth constrained t
3. Error-prone shared broadcast radio channel
4. Hidden and exposed terminal problems
5. Resource / energy constrained
6. Security
7. Highly dynamic topology
8. No infrastructure for centralized administration
9. Establishing end-to-end path.
Therefore, the design of new routing protocol has to consider the design constraints of
ad hoc wireless networks to meet out the requirements of an efficient routing protocol.

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Ad hoc and Wireless Sensor Networks 2-3 Routing in Ad hoc Networks

Ad hoc wireless networks are dynamic in nature. So establishing end-to-end

connection is too difficult in ad hoc environment. There are many design challenges that
need to be considered while designing a new routing protocol in ad hoc wireless
networks. The major issues in designing a routing protocol in ad hoc networks are
explained in the following sections.

1. Node Mobility
The nodes used in ad hoc network are highly dynamic due to the movement of nodes.
Mobility nature of nodes causes frequent path break. Sometimes, the node which acts as a
forwarder node may move away and leads to path break. The frequent path break occurs

ww
due to the movement of intermediate nodes or end nodes along the path. So the design of
routing protocol has to consider this issue to introduce efficient algorithms for

w .Ea
determining alternate path with little delay.

2. Bandwidth Constraint

syE
Wireless link has limited bandwidth due to limited radio spectrum. Hence the wireless
links carrying large amount of data is not possible in ad hoc network. Frequent dynamic
ngi
topology leads to high control overhead. The bandwidth is affected by multiple access,

nee
fading, noise, interference conditions etc. Message aggregation exceeds network capacity
frequently.

3. Error-Prone Shared Broadcast Radio Channel rin

g
The capacity and link error probability of wireless link varies from time to time.
Collisions may occur at node because of hidden terminal problem and exposed terminal .ne
problem. So the newly designed routing protocol has to take this as a serious issue and
must introduce specific algorithms to avoid collisions. t
4. Hidden and Exposed Terminal Problems
Consider node-A and node-C are in the transmission range of node-B, but is hidden
from each other. If both the nodes try to communicate with node-B simultaneously,
collision may occur at node-B. This event cannot be identified by node-A and node-C.
This happens because node-A is hidden from node-C. So node-A is not aware of the
transmission between node-C and node-B, similarly, node-C is not aware of the
transmission between node-A and node-B. The typical solution for this situation is so
called “Hidden terminal” problem. This scheme uses two control messages - RTS and
CTS. When node-A wants to transmit a packet to node-B, it first sends RTS packet to
node-B. This packet can be heard by neighboring nodes and received by node-B. As the
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Ad hoc and Wireless Sensor Networks 2-4 Routing in Ad hoc Networks

reply message, node-B transmits CTS packet to node-A, this can be received by node-A
and heard by node-C. So, node-C defers its transmission for the time period specified in
CTS packet as there is a transmission between node-A and node-B.
Consider the scenario where node-D exists in the transmission range of node-C. When
node-B wants to transmit to node-A, at the same time, node-C cannot communicate with
node-D due to false conclusion by node-C. This problem is often referred to as “the
exposed terminal problem”. Both the hidden and the exposed terminal problems cause
reduction of network throughput when the traffic load is high.

5. Resource Constraints

ww
Mobile nodes have limited battery power, processing power, memory and energy.

w
Increasing the battery power and processing ability makes the nodes bulky and less

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portable. Hence the design of a routing protocol has to consider the resource constraints
of mobile nodes.

6. Security Issues syE

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Mobile ad hoc wireless networks are prone to security threats. The attacks such as
eavesdropping, spoofing, and denial-of-service should be considered while designing a

nee
new routing protocol. Unauthorized access of others data is known as snooping.
Tunneling a packet between two colluding attackers is referred to as a wormhole. In

rin
wormhole attack, a malicious node receives packets at one location in the network and

g
forwards them to another location where these packets are resent into the network. In
black hole attack, a node (attacker) designs a routing protocol as having a shortest path
between itself and the node whose packets it wants to intercept. .ne
7. Highly Dynamic Topology
Frequent changes in local topology and changes in the topology of parts of the
t
network with which the node does not have any traffic correspondence, are required be
considered appropriately.

8. No Infrastructure for Centralized Administration

In ad hoc network, due to dynamic nature there is no provision for centrally
positioned administration node. This puts additional load on protocol as it needs to
manage the overall administrative operations for each node individually.

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Ad hoc and Wireless Sensor Networks 2-5 Routing in Ad hoc Networks

9. Establishing end-to-end path

It is very critical job in ad hoc network to establish the end-to-end path because the
network topology is dynamic and the devices can come in and out of the network. The
routing protocol needs to consider the dynamic aspects of ad hoc network.

2.1.3 Characteristics of an Ideal Routing Protocol for Ad hoc Wireless

Networks
It can be understood that there are various issues in an ad hoc wireless network
environment therefore wired network routing protocols cannot be used in ad hoc wireless

ww
networks. Hence ad hoc wireless networks require specialized routing protocols that
address the challenges described above.

w
A routing protocol for ad hoc wireless networks should have the following
characteristics,
.Ea
1. It must be fully distributed, as centralized routing involves high control overhead

syE
and hence is not scalable. Distributed routing is more fault tolerant than centralized
routing, which involves the risk of single point of failure.
ngi
2. It must be adaptive to frequent topology changes caused by the mobility of nodes.

nee
3. Route computation and maintenance must involve a minimum number of nodes.
Each node in the network must have quick access to routes, that is, minimum
connection setup time is desired.
rin
control overhead. g
4. It must be localized, as global state maintenance involves a huge state propagation

.ne
5. Protocol should be loop-free and free from stale routes.
6. The number of packet collisions must be kept to a minimum by limiting the number
of broadcasts made by each node. The transmissions should be reliable to reduce
t
message loss and to prevent the occurrence of stale routes.
7. It must converge to optimal routes once the network topology becomes stable. The
convergence must be quick.
8. It must optimally use scarce resources such as bandwidth, computing power,
memory, and battery power.
9. Every node in the network should try to store information regarding the stable local
topology only. Frequent changes in local topology and changes in the topology of
parts of the network with which the node does not have any traffic correspondence,
should not affect the node in any ways, that is, changes in remote parts of the

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network must not cause updates in the topology information maintained by the
node.
10. It should be able to provide a certain level of Quality of Service (QoS) as
demanded by the applications, and should also offer support for time-sensitive
traffic.

2.2 Types of Ad hoc Routing Protocols

Ad hoc routing protocols can be broadly classified into three categories namely,
1. Proactive or table driven routing protocols

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2. Reactive or on-demand routing protocols
3. Hybrid routing protocols.

w .Ea
2.2.1 Proactive Routing Protocols (Table Driven Routing Protocols)
1. Proactive routing protocols are also called as table-driven routing protocols in

syE
which each node maintains a routing table.

ngi
2. Routing table contains up-to-date routing information of the entire network.
Whenever a node wants to send a packet to the receiver node, it looks up its own

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routing table to find the routing path from itself to the intended receiver.
3. These routing tables have to be updated periodically to maintain the current stable

rin
or available paths. This can be achieved by exchanging or broadcasting the periodic
beacon signals between the nodes.
4. Therefore, each node can have the knowledge about the complete network g .ne
topology. Hence each node can update its routing table based on the beacon signal
it has received from its neighbors. t
Advantage
1. Minimum time is required to find out a route for data transmission

Disadvantages
1. Due to the frequent change of network topology, the exchange of up-to-date
information has to be done periodically
2. Network overload is high
3. Bandwidth consumption is high in large networks
4. This type of protocol is not suited for large networks

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Various Proactive Routing Protocols

The various protocols which use the concept of proactive routing are as follows,
1. Destination sequenced distance-vector routing protocol
2. Wireless routing protocol
3. Cluster-head gateway switch routing protocol
4. Fisheye state routing.

2.2.1.2 Destination Sequenced Distance Vector Routing

Destination Sequenced Distance Vector (DSDV) routing protocol is one of the popular

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proactive routing protocols of ad hoc network. In DSDV, each node keeps record of route
information in the form of routing table. Each table contains the following information :


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ID of destination node
Details of next hop


Metric
Sequence number
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 Time-to-live parameter.
ngi
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Each route broadcast message includes the list of ID of destination node, number of
hops required to reach the destination node, next hop, recent sequence number and

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metric parameter. Each node exchanges its updated routing table with each other.
Updates in the routing table can be sent to other nodes in two ways :


Full dump update g .ne
Incremental update.
In full dump update method, a node sends the whole routing table to the neighbors
and thereby increases network overhead. In incremental update method, only the recent
t
updated entries are sent. The incremental update method is more suitable when the
network is large and stable so that heavy traffic can be avoided.

Table Maintenance in DSDV

The steps followed for maintaining a routing table at each node is given below,
 Each node receives the route information with most recent sequence number from
other nodes and updates its table.
 The node looks at its routing table in order to determine the shortest path to reach
all the destinations.

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 According to the shortest path information, each node constructs another routing
table where the node has recently updated route information to reach destination
with minimum distance.
 This new routing table will be broadcast to its
neighbours.
 On receipt of these messages, the neighbour
nodes update its routing table. Fig. 2.2.1 Network topology in
In the Fig. 2.2.1, the connectivity between nodes are DSDV
shown using wireless links. The routing table

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maintained at node-A is shown in Table 2.2.1.

w Destination

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B
Next Hop

B
Metrix

1
Sequence No

342

D
syE C

B
1

2
168

121

E C ngi 2 24

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Table 2.2.1 Routing table at node A

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If node-B is the destination for node-A, then node-A can directly transmit the packet

g
with metric 1 and next hop is node-B. But, if node-A wants to transmit a packet to node-E,
then it can find the route from the routing table. In this case, the node-E is not in the .ne
visibility of node-A. Therefore, the packet can be transmitted through the next hop C with
metric 2. t
Maintaining Metric Field
In ad hoc wireless network, all the nodes are moving and relocate its position from
time to time. When topology changes dynamically each node will broadcast a routing
table update packet to its neighbours. The procedure for updating metric field in the
routing table update packet is as follows,
• The routing table update packet starts with a metric of one.
• When the neighbour nodes receive this packet, it will increment this metric by one
and then re-broadcast the updated packet to its neighbours.
• This process will be repeated until all the nodes in the network receive the copy of
update message.
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• When a node receives more than one packet, then the update packet with smallest
metric value will be considered to ensure the shortest path. Other packets will be
ignored.

Significance of Sequence Number

When a node broadcasts a routing table update packet, it has to increase the sequence
number by one. This is used to find out the updated route packet.
When a node receives an update packet from its neighbour node and if the sequence
number is equal to or greater than the sequence number of already received packet, then

ww
the routing packet will be updated in the table. Else, the received packet will be assumed
as a stale or old packet and hence discarded.

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2.2.1.2 Wireless Routing Protocol

.Ea
Wireless Routing Protocol (WRP) is one of the proactive routing protocols in ad hoc
wireless networks.
syE
When compare with DSDV, the WRP differs in table maintenance and the procedure
used in updating routing tables.
ngi
In order to maintain the accurate information in the routing table, in WRP, each node
maintains four tables. These tables are explained below,
nee
1. Distance table
2. Routing table rin
3. Link cost table
4. Message re-transmission list.
g .ne
1. Distance Table
In this table, each node contains information such as destination node, next hop,
t
distance and the previous node (predecessor) of the destination.

2. Routing Table
It contains the shortest distance and the up-to-date information of all destinations. In
order to determine the shortest path, each node maintains the ID of destination node, next
hop, distance (cost) and predecessor node.

3. Link-Cost Table
Each node contains the cost of link and the ID of direct nodes with which the node can
communicate directly. The cost of other links is represented as infinity.

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4. Message Retransmission List (MRL)

This list contains the message to be transmitted in the route update packet. It also
maintains the details of the nodes from which it has to receive acknowledgement. So, this
table contains the sequence number of the update message to be transmitted, counter
value used for retransmission, list of updates sent in the update message and
acknowledgments received from other nodes.

Table Maintenance
This protocol requires larger memory to store four tables and more processing for

ww
maintaining accurate information about nodes in the network.
It is also not suitable for large networks with high mobility.

w
In order to update the table, each node periodically

.Ea
broadcast hello message to its neighbours. If the sending
node is a new one, then all the neighbouring nodes will

syE
update its table. Otherwise, the nodes will ignore the

ngi
message. The exchange of hello message is used to ensure Fig. 2.2.2 Example topology
the availability and the connectivity of node in the network. for WRP protocol
Fig. 2.2.2 shows an example network topology of WRP
protocol. nee
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Consider that node-A is the source and node-E is the destination. The routing table
maintained at each node with destination node-E is shown in Table 2.2.2.
Node ID Next Hop Predecessor Costg .ne
A

C
C

E
C

C
7

2
t
D C C 5

E E E 0

Table 2.2.2 Routing table at node-A with destination node-E

From the routing table, node-A can identify that there is a path to node-E with next
hop C and the predecessor is also C with cost value 7.

Route Maintenance
When a link break occurs, the node which detects link breakage will send an update
message by setting the cost of broken link to infinity. The nodes receive this update
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message will update its routing table. The node which had been initiated the update
packet will detect an alternate path and broadcast the new path information to its
neighbors. Based on the reception of this message, all the neighbors will update its
routing table.

2.2.1.3 Cluster-Head Gateway Switch Routing Protocol

The Cluster-head Gateway Switch Routing (CGSR) protocol forms hierarchical
network topology rather than forming flat network topology. In CGSR, clusters are
formed in the network. Nodes present in the cluster are called as members of the cluster.

ww
Each cluster contains a special node called cluster-head which controls its cluster. Each
cluster-head maintains the information of the members of that cluster.

w
CGSR uses Least Cluster Change (LCC) algorithm to select cluster-head. Clusters can

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overlap with other clusters. Communication between the clusters can take place through
the common nodes (members of more than one cluster) exists in the overlapping area of

syE
each cluster. The common nodes are called as gateways or border nodes. Data
transmission can be carried out through the cluster-heads of each cluster.

ngi
When a cluster-head enters in another cluster, it cannot act as cluster-head; it acts as

 A cluster-member table nee

the member of new cluster. In CGSR, each node contains two tables namely,

 A routing table.
rin
node in the network. g
Cluster-Member Table - This table maintains the cluster-head of each destination

.ne
Routing Table - This table contains routing information such as destination node, next
hop, metric and the sequence number.
Each table is updated periodically at every node. Before performing actual packet
t
transmission, each node has to receive a token from its cluster-head. This token includes
the information of destination cluster-head and the next hop node information taken from
the cluster-member table and the routing table of its cluster-head. The steps involved in
packet transmission using CGSR are given below,
 When a node wants to send a packet to the node belongs to same cluster, it
forwards the packet directly to the cluster-head.
 Cluster-head checks whether the destination node belongs to that cluster or not.
 If the destination node belongs to that cluster, then the cluster-head forwards the
packet to the destination node directly.

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 Otherwise, the packet has to be forwarded to other cluster using gateways. This
step will be repeated until finding the destination node’s cluster-head.
 Once the destination node’s cluster-head is identified, then the packet is
transmitted to the cluster-head of the destination node. This cluster-head will in
turn forward the packet directly to the intended destination.

ww
w .Ea
syE
ngi
nee
Fig. 2.2.3 Network topology of CGSR

In the above Fig. 2.2.3, cluster-heads, border nodes (gateways) and cluster members

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are shown. When node H wants to transmit a packet to node M, it follows the path H-A-

g
F-B-L-C-M. Packet transmission between clusters is carried out through border nodes.
Since node F and node L are border nodes, the packet transmission between node H and
.ne
node M are taken place through these border nodes. If a path break occurs or any node
moves away, then the source node will reestablish the path between the source and
destination. If any cluster-head or border node moves away, then the time taken to find
t
an alternate path by the source node will lead to long delay.

2.2.1.4 Fisheye State Routing

Fisheye State Routing (FSR) is one of the table-driven routing protocols. In FSR, each
node broadcasts and exchanges the details of farthest node rather than broadcasting
neighbours information frequently in order to reduce the control overhead. FSR protocol
comprises three phases namely,
1. Neighbour Discovery
2. Information Dissemination
3. Route Computation.
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1. Neighbour Discovery - Each node maintains neighbour list and topology table.
Initially these tables are maintained as empty. Once the node initiates this
neighbour discovery phase, then it can fill the table with neighbour relationships. In
order to identify the presence of neighbours, each node broadcasts ‘hello’ packet
including its ID, time-to-live parameters. The nodes hearing the packet will
response with the reply message. Thus each node maintains relationship between
each other.
Information Dissemination - This phase propagates Link State Packets (LSP). This
phase handles two functions namely, LSP integrity and updating interval. In LSP

ww
integrity, when a node generates a new LSP, it must be flooded throughout the
network. Most recently generated LSP contains highest sequence number. Each

w
node keeps track of sequence number that it is used for the last LSP and inserts a

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next sequence number for the new LSP. A sequence number is a counter value. For
each new LSP, counter value is incremented. Most recent sequence number

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indicates the freshness of the message. The update interval is that the time gap
between sending first LSP and next LSP by a node.

ngi
When a node receives a LSP to retransmit, it calculates interval time to wait before

nee
sending out the LSP to other nodes based on Update_Interval calculation.
Update_Interval = Constant_Time * hop_count^ 

rin
Where, Constant_Time is the user defined refresh period to send out LSPs (in the 1st

g
scope), hop_count is the number of hops the LSP has traversed, alpha is a parameter that
determines how much effect each scope has on the Update_Interval. Values for alpha are
.ne
0 or ≥ 1.
Route Computation - This phase is responsible for computing route based on the
information available in LSP. Using Dijkstra's algorithm, each node computes
t
shortest path to reach other nodes. The hop count value is taken as cost of the path.
Data can be transmitted through shortest path.

2.2.2 Reactive Routing Protocols

1. Reactive routing protocols are also called as on-demand routing protocols. In this
type of routing protocols, each node determines the routing path whenever it is
ready for transmitting data to other node in the network.
2. Unlike proactive routing protocols, no node maintains routing table. Routing paths
are discovered only when required (on-demand).

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3. In order to find a route, the sender node has to broadcast route discovery control
messages to neighbor nodes until receiving reply from the intended receiver.

Advantages
1. Needs to broadcast less control messages for discovering route when required
2. Network overhead is low
3. Suitable for large networks
4. Bandwidth wastage is low.

Disadvantage

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1. Time taken to discover a route is non-predictable.

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Various Reactive Routing Protocols

.Ea
Reactive routing protocols are also called as on-demand routing protocols. The
protocols which use reactive routing concept are as follows,

syE
1. Dynamic source routing protocol
2. Ad hoc on-demand routing protocol
3. Temporarily ordered routing algorithm ngi
4. Location aided routing
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5. Associativity-based routing
6. Signal stability-based routing protocol rin
7. Flow oriented routing protocol.
g .ne
2.2.2.1 Dynamic Source Routing (DSR) Protocol
Dynamic Source Routing (DSR) protocol is one of the popular reactive routing
protocols that discover a route between the source and destination whenever required.
t
The operation of this protocol is based on source routing. The sender knows the complete
route to reach the destination. Each data packet carries the source route in the packet
header.
Since each packet carries the complete route information in the packet, the
intermediate nodes do not maintain routing information to route the packets to the
destination. Nodes which use reactive routing protocol does not maintain routing table.
Therefore, the number of message exchanges between nodes is very low and hence leads
to less network overhead.
So, the major advantage of this protocol is that the bandwidth usage is limited by
avoiding the periodic table updates. However, at the time of route discovery, the sender
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node has to exchange control messages to establish a path between source and the
destination. DSR protocol comprises two phases : Route discovery and route
maintenance.

Route Discovery Phase

Route discovery phase is also known as route construction phase. This phase follows
the steps given below,
 The sender node broadcasts (floods) the Route Request (RREQ) packet in the
network if it does not have a route to the intended destination.

ww The neighbouring nodes which receive the RREQ packet will attach its ID and
rebroadcast the RREQ packet. This process continues till any intermediate node


whas the information about destination or until the destination node receives this
packet.
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One node may receive multiple numbers of RREQ packets. Then, the destination


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node selects only one path with shortest distance.
On receipt of RREQ messages, the actual destination will send a Route Reply

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(RREP) message to the sender node through the selected path.

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After receiving the RREP packet, actual data transmission will be started between
the sender and the receiver nodes.

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The route discovery phase of DSR protocol using RREQ packet is shown in below
Fig. 2.2.4,
g .ne
t
Fig. 2.2.4 Route construction in DSR protocol

When node A wants to transmit a packet to node F, it broadcasts RREQ packet in the
network. The key fields of RREQ packet are ID of source node and ID of destination node.
The RREQ packet is received by node B. Node B checks that whether the packet has to be
rebroadcast or not. If so, it attaches its own ID and rebroadcast it. This happens until the
packet received by node F. Node F may receive multiple RREQ packets with different

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paths like A-B-E and A-C-D-H. Node F selects

shortest path and sends a reply message by
attaching complete path in the packet as shown
in below Fig. 2.2.5,
On receipt of reply message from node F,
node-A uses the path that is specified in the
packet for actual data transmission. Each node
maintains a routing catch. All the routes learned
Fig. 2.2.5 Route reply in DSR
by a node are recorded in a route cache of that
protocol

ww
node. This route information can be used by the
node in future. This concept reduces the time required to discover a new route.

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Route Maintenance Phase
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In this phase, if any node finds that the path is broken, then a Route Error (RERR)

syE
message will be forwarded to the sender node. So, the sender node again starts the route
construction phase by broadcasting RREQ packet to discover an alternate path in order to
reach the actual destination node.
ngi
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Furthermore, if a node detects an error along the path of a packet transmission, then
the node forwards a route error packet to the sender. The route error packet contains the

rin
IDs of the upstream and downstream nodes at both ends of the node in error. When a
route error packet is heard by neighbors, the link in error is removed from any route
caches.
g .ne
2.2.2.2 Ad-hoc On-demand Distance Vector (AODV) Protocol
It is one of the reactive or on-demand routing protocols used widely in mobile ad hoc
networks. As DSR protocol, AODV protocol also operates on two phases namely, route
t
discovery and route maintenance mechanism. The major difference between DSR and
AODV protocols, in AODV, the source route will not carry the complete path. Each node
only knows its previous hop and next hop information of the established path.

Route Discovery
In AODV, each node maintains a routing cache to save the information about the
reachable destinations. When to a node wants to transmit a packet to the destination the
sender node initiates to broadcast the RREQ packet. All the neighbouring nodes receive
the RREQ packet and rebroadcast it if it is not the intended recipient. The RREQ contains
the following information.

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 ID of source node
 ID of destination node
 Most recent sequence number
 Broadcast ID
 Hop count
 Time-to-live.
Each broadcast packet contains broadcast ID. The hop count is the number of hops the
packet passes through to discover the destination. If any one of the neighboring nodes

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which had received the RREQ packet and knows the path for destination, then it sends
RREP packet through a selected path to the sender node. Otherwise, the neighbor node

w
rebroadcasts the RREQ packet.

.Ea
Consider that node-A wants to send a packet to node H. Node-A initiates broadcasting
RREQ packet. Node-B and node-C are the neighbors of node-A and received the packet. If

syE
node-B and node-C has route information of node-H, then it replies with RREP packet.
Otherwise, node-B and node-C will re-broadcast the RREQ packet which is shown in
Fig. 2.2.6 (a).
ngi
nee
rin
g .ne
Fig. 2.2.6 (a) Broadcasting RREQ packet in AODV protocol
t
Finally, node-H receives more number of RREQ packets through different paths. In
general, a shortest path will be selected
to route the RREP packet. When the
RREP sends back to the sender node-
A, all the intermediate nodes on the
path will update their routing cache
with the reachable destination
information. Fig. 2.2.6 (b) shows the
transmission of RREP packet from
Fig. 2.2.6 (b) Transmission of RREP packet in
node-H to the source node-A. AODV protocol
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Once the sender node receives RREP packet, then it saves the route in the cache and
starts to send the packet to the destination through the established path. Unlike DSR, in
AODV, each node does not store the complete path required for data transmission.
Instead, each node stores only the next hop information of the established path. The
routing packets are transmitted by specifying sequence numbers to indicate the freshness
of the packet.

Route Maintenance
When a node moves away or fails from the established path, then the broken path has
to be intimated by sending Route Error (RERR) packet to the sender node. RERR message

ww
can also be sent when a node has no route or if the node cannot communicate with its
neighbors.

w .Ea
2.2.2.3 Temporarily Ordered Routing Algorithm

syE
Temporarily Ordered Routing Algorithm (TORA) is one of the reactive routing
protocols and works based on 'link reversal' algorithm. The main motive of TORA is to

ngi
reduce the transmission of control messages in mobile environment. TORA performs the
following functions,
1. Route discovery
nee
2. Route maintenance
3. Removing route if not valid. rin
g
Every node maintains local topology based on the information received from its
neighbors. In TORA, nodes have an ability to discover the network partitions. .ne
Route Discovery
When a node wants to transmit a packet to the
t
destination, it starts route discovery. A destination
oriented Directed Acyclic Graph (DAG) is formed
using TORA. DAG is a directed graph with no
cycles. If a DAG does not have any downstream
nodes then it is called as destination oriented
DAG. DAG can be created based on two
Fig. 2.2.7 (a) Operation of TORA
messages, Query and Update messages. The
Fig. 2.2.7 (a) illustrates the operation of TORA.
Consider, node-A that wants to transmit a packet to destination D. For that, node-A
initiates broadcasting Query packet. All the neighbor nodes (B, E) rebroadcast the
received packets if it is not the intended recipient. Node-C again rebroadcast the Query
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packet and it can be received by node-D. Since node-D is the intended recipient, it does
not re-broadcast the Query packet further.
On receipt of Query packet, node-D replies with Update message to the sender node.
Update packet contains the information about distance from the destination. When a
node receives Update packet, it sets the distance higher than the existing value in the
packet. Thus direct links from the sender node-A to the destination node-D is created.
This links forms a DAG. After establishing a path to destination, data transfer will take
place.

Route Maintenance and Removing Route

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If any intermediate node identifies
that the path with destination is broken

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or becomes invalid, then it changes its

.Ea
distance value higher than the existing
one and again starts to broadcast Update

using syE
packet. In this case, DAG has to be
recomputed link reversal
algorithm. The neighbor node which
ngi Fig. 2.2.7 (b) Route maintenance in TORA

receives the update packet will reverse the path as shown in Fig. 2.2.7 (b).

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Node-E broadcasts Update packet. On receiving this, node-A reverses the path

rin
between E and A. Similarly, if the path between node-C and node-D breaks, then the link
(C-D) will be removed. This leads to separate the node-D from the network. Now nodes

g
A, E and C remain in a network and node-D is partitioned from the network. This will in
turn make changes in DAG. This representation also makes network partitions. Using .ne
Clear message, the existing path in the partition with respect to destination is removed.

2.2.2.4 Location Aided Routing

t
Location Aided Routing (LAR) protocol uses Global Positioning System (GPS) for
identifying the positional information of a node in order to perform well-organized
routing. LAR exchanges control packets on two regions,
 Expected region
 Request region.
Expected Region - Based on the past mobility information of destination node, the
expected region is constructed. Therefore, the expected region is the region of the
destination node where it is assumed to be present. This zone can be determined based on
the available mobility information about the destination.

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Ad hoc and Wireless Sensor Networks 2 - 20 Routing in Ad hoc Networks

If a node can collect more information about destination’s mobility, then the expected
region can be determined perfectly. This helps to route the packet efficiently with
minimum latency.
Request Region - The control packets used for determining a path can be propagated
in a region called request region. Usually, sender node itself may determine the request
region.

Transmission of Control Packets

Control packets can be flooded on the request region. If any node receives the control

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packet in outside of the request region, then the packet will be discarded at the node. If
sender node does not find any forwarder node in the particular request region, then the

w
region of request zone (region) will be extended.

.Ea
TORA uses two algorithms for taking decisions in forwarding and rejecting the
packets which had been received from other nodes. They are,
1. LAR1 2. LAR2
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These two algorithms are discussed in detail below.

LAR1 Algorithm ngi

nee
Each node broadcasts route request packet to identify the path to destination. The

rin
route request packet contains the information about the request region. The Fig. 2.2.8 (a)
shows expected and request regions.

g .ne
t

Fig. 2.2.8 Expected and request regain in LAR1

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The request region is specified as a rectangle area and the coordinates used for
specifying the rectangle is (x1, y1), (x2 + r, y1), (x1, y2 + r) and (x2 + r, y2 + r). Request region
contains source node and the expected region of destination node. When the sender node
presents within the expected region, then the size of request region may shrink to the size
of the expected region.
As explained earlier, if the intermediate nodes C, B and E are present within the
request region and receives route request packet from node-A, then the intermediate
nodes will rebroadcast the same packet. Otherwise, the nodes will drop the packet. In the
given example, node-I discards the packet since it is present out of the request zone.
When node-D receives route request packet from node-A, it will send route reply

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packet to the sender node. This packet contains the current location of node-E and current
time.

w
LAR2 Algorithm

.Ea
In LAR2, source node attaches the (x, y) position of destination in the route request
packet. It does not attaché the information about the expected region of the destination in

syE
the route request packet explicitly. In addition to the position of destination, the sender
node also attaches the distance between source and destination in the route request
packet. ngi
nee
When the intermediate node receives route request packet, it calculates the distance
between the node-A and node-D which is shown in Fig. 2.2.8 (b).

rin
g .ne
t
Fig. 2.2.8 (b) LAR2 algorithm

If the calculated distance is smaller than the distance between node-A to destination
D+Δ (Δ is the locality error), then it forwards the received packet. Otherwise the packet
will be dropped at the node.
As shown in Fig. 2.2.8 (b), when node-C receives route request packet and calculates
the distance between itself and node-D, it identifies that the newly computed distance
value is smaller than the distance between node-A and node-D. So it decides to forward
the packet. But, node-B discards the packet since the newly computed distance value is
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greater than the existing one. When node-D receives the route request packet, then it
sends route reply message to the sender node. After that, actual data transmission will be
started.

2.2.2.5 Associativity-based Routing

Associativity - Based Routing (ABR) protocol is one of the on-demand routing
protocols. The route can be selected based on link stability (temporal stability). The
wireless links between nodes can be classified as,
• Stable link
•
ww Unstable link.
Temporal stability refers the count of beacon signal a node receives from its neighbors.

•
w
Based on temporal stability, each neighbor can be classified as,

.Ea
Stable neighbour
•
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Unstable neighbor.
Each node maintains route cache to store the information about destination.

Route Establishment
ngi
nee
The sender node broadcasts route request packet in order to discover a path between
sender node and the receiver. Each route request packet contains the path it has visited
and the beacon count of the node along the path.
rin
g
When a destination node receives first route request packet from its neighbors, it waits
for some more time to receive multiple route request packets from other nodes. Finally,
when time expires, the destination node selects a path with stable links. When more than .ne
one path contains stable links, then a path with shortest distance will be considered.
t

Fig. 2.2.9 Operation of ABR protocol

In above Fig. 2.2.9 node-A wants to transmit a packet to node-E. In the Fig. 2.2.9, solid
lines represent stable links and other links are unstable links. In ABR, in spite of receiving
two routes from node A (A-B-H-E, A-B-D-F-E), node-E selects second route even the
length of second path is longer than the first path. This happens because the second path
contains stable links.
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Route Maintenance
If a link break occurs, then the previous intermediate node near the broken link will
discover a new route by broadcasting route repair packet or route error packet. This
process continued until repairing the route or establishing a new route from the source to
the destination nodes.

2.2.2.6 Signal Stability-based Adaptive Routing Protocol

Single Stability-based Adaptive (SSA) routing protocol uses the concept of beacon-
based on-demand routing. It uses the stability of signal for determining efficient and

ww
stable routes. The signal strength of each beacon is measured and is classified as,
 Stable signal

w Unstable signal.

.Ea
SSA protocol comprises two protocols,

 syE
Forwarding Protocol (FP)
Dynamic Routing Protocol (DRP).

ngi
Forwarding Protocol - FP routes the packets to the intended destination through
specific path.

nee
Dynamic Routing Protocol - DRP communicates with other DRP processes to collect

 Beacon count rin

information and maintain a routing table. Each routing table maintains two fields,

 Signal strength of its neighbours.

g
Based on the received beacons from neighbor nodes, one node can classify the weak .ne
and strong links. If a node receives more number of strong beacons from other nodes,
then the link is assumed as strong link. Other links are weak or unstable links. The
t
strength of the signal is maintained in a table called Signal Stability Table (SST).

Route Establishment
When a node forwards a packet to the destination, it refers SST for identifying the
stable links. After identifying the stable links, the sender node broadcasts route request
packet.
When a neighour node receives route request packet, it forwards the packet if the
packet has been received only through strong link. Otherwise, the node will drop the
packet. On receipt of route request packet, the destination node sends route reply packet
to the sender node through the determined strong path. The operation of SSA protocol is
shown in Fig. 2.2.10 (a).
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ww
w .Ea
Fig. 2.2.10 (a) Operation of SSA protocol

Consider that node-A wants to send a packet to node-H. As discussed in ABR, solid
lines represent strong links and the dotted lines represent weak links. Node-A broadcasts

syE
route request packet that can be received by node-B and node-D. Since the path between
node-A and node-B is weak, node-B does not forward route request packet further. But

ngi
node-D will forward the packet to its neighbours. This process continues until node-H
receives route request packet. On receiving route request packet through the path A-D-E-

nee
G-H, the node-H sends route reply message to node-A through the reverse path H-G-E-
D-A.

Route Maintenance rin

g
When any one of the link from the established path breaks and is identified by the end
nodes of the link, then the end nodes will send a Path Break Notification (PBN) packet to .ne
the sender node. The route maintenance phase is shown in Fig. 2.2.10 (b).
t

Fig. 2.2.10 (b) Route maintenance in SSA protocol

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If the link between node-E and node-G breaks, then the end nodes-E and node-G of the
link will send PBN packet to the sender node-A and the receiver node-H of the path
respectively. After receiving the PBN packet, the sender node initiates broadcasting route
request packet to establish a new path between nodes A and H.

2.2.2.7 Flow Oriented Routing Protocol

Flow Oriented Routing Protocol (FORP) is one of the reactive routing protocols. FORP
uses a prediction based mechanism called multi-hop handoff for providing solution to
path breaks in real-time packet flows. Unlike other on-demand routing protocols, FORP

ww
operates based on prediction mechanism to prevent the link breaks. In order to prevent
link breaks, FORP uses the following information.

 wMobility of a node

.Ea
Location of a node.
Based on the above information, each node maintains the following details of the path.
 syE
Link Expiry Time (LET)
 Route Expiry Time (RET).
ngi
Link Expiry Time - LET is the maximum lifetime of a link that can be determined by

nee
every node. LET can be calculated based on the positional information of the node,
moving direction and its transmission range.

rin
Route Expiry Time - The lowest LET of the wireless link of a path is assumed as RET.

Route Establishment g
When a node wants to send a packet to the receiver, it first checks its routing table to .ne
know the path details in order to identify the reachability of destination. If the routes are
not available, then the sender node broadcast a flow request packet. This packet includes
t
the ID of the sender, ID of the receiver and the sequence number. Each fresh transmission
will have highest sequence number than the previous transmission. The sequence number
is used to identify the freshness of the message.
On receiving flow request packet, every neighbour node forwards the packet if the
sequence number exists on the packet is higher than the old packet which had been
received by the node. Otherwise, the packet will be discarded.
Moreover, when a node receives a flow request packet, it attaches the ID of the node
and the LET value of the most recent link through which the packet has been traversed.
When a destination node receives a flow request packet with LET values of all links
through which the packet traversed, it can able to determine the RET value of newly
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received route. If the newly computed value of RET is better than the old one which is
currently being used by destination, then the newly received path will be stored in the
table. This new route will be used for further communication. The operation of FORP is
shown in Fig. 2.2.11.

ww
w .Ea
syE
Fig. 2.2.11 Route establishment of FORP

ngi
Consider that node-A sends a packet to node-F. Node A broadcasts flow request

nee
packet and the intermediate nodes B and G forwards the packet. Finally, node-F receives
two flow request packets, A-B-D-F and A-G-E-F, from different paths. After receiving the

rin
flow request packet, the destination node F will response with flow setup message to
sender node A.

Calculation of LET
g .ne
Let the transmission range of two nodes A and G be denoted as TA and TG and the
velocity of node A and node G be VA and VG respectively. Now, LET of the wireless link
t
between node A and node G can be computed as,
– (pq + rs) + (p2 + r2)TX2 – (ps – qr)2
LETAG =
p2 + q2
where
p = VA cos TA – VG cos TG
q = XA – X G
r = VA sin TA – VG sin TG
s = YA – YG

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Route Maintenance
Each destination can able to calculate RET of the path being used. Based on the RET
value, the node can able to find out at what time (critical time) the link break would
occur. Before the critical time exceeds, the destination node broadcast a flow-handoff
packet to the source node and the neighboring nodes which receive the flow-handoff
packet will forward the message as broadcasting flow request packet. Sender node may
receive many flow-handoff messages through different paths. Further, the source node
calculates RET values of all the paths and finds a better path to continue data
transmission.

ww
2.2.3 Hybrid Routing Protocols

w
1. Hybrid routing protocols combine the features of both proactive and reactive

.Ea
routing protocols.
2. In this protocol, the network is divided into zones. Each node uses node ID and

syE
zone ID during packet transmission.
3. Data transmission can be carried out to other zones using border nodes of a zone.

Advantages ngi
 Requires less memory and processing power
nee
 Integrates reactive and proactive routing advantages.
rin
Disadvantage
 g
If the border nodes move away, then re-establishing a path takes long time
.ne
Hybrid Routing Protocols
Hybrid routing takes the advantages of both the proactive and reactive routing
t
protocols. In this routing protocol, nodes are grouped into zones.
Nodes which want to communicate within a particular region (zone) can act
proactively. In this case, each node maintains a routing table; whenever a node wants to
communicate within the region can looks at the routing table and find the path for the
intended recipient. Otherwise, each node uses reactive type of protocol for transmitting a
packet to the designated recipient. In this case, each node discovers a route using route
discovery mechanism.
Various routing protocols which use hybrid routing concept are as follows,
1. Core extraction distributed ad hoc routing protocol
2. Zone routing protocol
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3. Zone-based hierarchical link state routing protocol

2.2.3.1 Core Extraction Distributed Ad-hoc Routing Protocol

Core Extraction Distributed Ad-hoc Routing (CEDAR) protocol is one of the hybrid
routing protocols. It takes the advantages of proactive and reactive routing. It is also
called as partitioning protocol. In CEDAR, each network has partitions where dominating
nodes or core nodes are available. Other nodes are called as core members. The core
nodes form a set called Dominating Set (DS). In DS, each node is at most one hop away
from core node. All the core nodes are interconnected via virtual links called tunnels. A

ww
virtual link is a path between two core nodes of the network. CEDAR uses an algorithm
called core selection algorithm to select core nodes in the network.

w
Core Node Selection Procedure

.Ea
The selection of core nodes is done by using distributed algorithm. Initially, during the

syE
core extraction phase, a set of nodes is selected dynamically to form the core of the
network. Core nodes are taking responsibility to transmit packet over the network. In

ngi
order to perform routing efficiently, each core node collects the information of its
neighboring core nodes.

Core Broadcast Mechanism nee

rin
Core broadcast mechanism is used to determine a route in order to transmit a packet.
Each core node exchanges its information with neighboring core nodes and hence

g
creating virtual link between them. This process leads to efficient routing. When a core
node moves away, a new core selection phase will be initiated. .ne
Information regarding link state is propagated throughout the network using link state
propagation mechanism. The link state propagation mechanism uses two types of waves,
t
 Slow-moving increase-waves
 Fast-moving decrease-waves.
The increase-waves carry high bandwidth link information whereas decreasing-waves
carries reduction in the available total bandwidth.

Route Establishment
The route establishment of CEDAR uses two phases namely,
 Detection of core path
 Detection of QoS achievable path over core path.

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The path between source and destination core is known as core path. When a node
wants to transmit a packet, it starts broadcasting route request packet. All the
neighboring core nodes will receive the route request packet and will in turn forward the
same packet if the destination is not in its core member.
If the core node finds that intended destination is present in its core member, then the
core node sends a reply to the sender node.

Finding Core Path

The source core establishes a path with the destination core using shortest-highest-

ww
bandwidth links. Fig. 2.2.12 shows the operation of CEDAR protocol.

w .Ea
syE
ngi
nee
Fig. 2.2.12 Operation of CEDAR protocol

rin
Assume that node-A wants to communicate with node-G. As shown in Fig. 2.2.12, the

g
dominating nodes or core nodes are represented as double circles. In the given network
topology, node-C and node-E are the core nodes. When node-A broadcasts route request .ne
packet and intimates the ID of source and destination information to the core node, the
core node-C receives the information. If the core node-C possesses the information about
the dominator node of node-G, it does not broadcast the route request packet. Otherwise,
t
node-C rebroadcasts the packet.
Once the core path is set, then the availability of bandwidth on the path will be
checked. If the required bandwidth is found, then the path is established.

Route Maintenance
Route maintenance phase is used to repair the route when a path is broken. When a
link fails, the end nodes of the link will intimate it to the source node. The source node
will reestablish the path between source and destination. Link failure may occur in three
places as discussed below.

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Case 1 - Link break may occur near the destination node. In this case, the time taken to
intimate the link breakage to the source node will take long time. During this time, the
packets received by the end node from the source node will be dropped at end node.
Case 2 - Link break may occur near the source node. In this case, the time taken to
intimate the link breakage to the source node will take less time. During this time, the
packets received by the end node are less and hence the packet loss is highly reduced.
Case 3 - Link break may occur in the middle of the path. Then the time taken to
intimate the link breakage to the source node is considerably average.
When a link break occurs, the end node (after which the link break occurred) will

ww
identify the link breakage and will send a notification of failure packet to the sender node.
The sender node begins to find a new path from it to the intended destination. The above

w
mentioned end node rejects every received packet until it finds a new path to the

.Ea
destination. Meanwhile, when the source receives the notification message, it stops the

syE
current data transmission and tries to find a new path to the destination. If the new route
is found by the sender or the particular end node, then a new path is established from the
source to the destination.
ngi
In the above given network topology, if the link break occurs between nodes C and E,

nee
then node-C will intimate the link breakage to node-A. Node-A will re-establish the core
path between the source and destination.

2.2.3.2 Zone Routing Protocol rin

g
Zone Routing Protocol (ZRP) is one of the hybrid routing protocols which uses the
advantages of both proactive and reactive routing protocols. In this protocol, each node .ne
acts proactively within a n-hop neighborhood of each node in the network. The route
discovery phase of reactive routing protocol is used by every node when the destination
t
node is beyond the sender's zone. The nodes which are on the edges of the zone are called
border nodes. ZRP uses two protocols for packet transmission are discussed below,
 Intra-zone routing protocol
 Inter-zone routing protocol
Intra-zone routing protocol (IARP) is used when the nodes use proactive routing. The
Inter-zone Routing Protocol (IERP) can be used by the node when it uses reactive routing.
The zone can be n = 1 – hop neighborhood and n = 2 - hop neighborhood. Fig. 2.2.13
depicts the routing zone of node - A.

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ww
w .Ea
syE
Fig. 2.2.13 Zone radius with respect to node A

The zone consists of all nodes within a certain number of n-hops, called the zone

ngi
radius (r), away from the node. If the node forms with the nodes 1-hop away or 2-hops

nee
away, then the zone radius is r = 1 or r = 2 respectively. In the above Fig. 2.2.13, the zone
radius for node-A is shown.

Packet Transmission rin

g
When a node needs to route a packet, it first checks to see whether the destination

.ne
node is within its zone or not. If it is within the zone, then the sender node identifies the
path to reach the destination from its routing table and send the packet directly to the
destination. Else, the sender node has to initiate route discover phase to establish a path
from the source to destination. To achieve this, the sender node uses DSR reactive routing
t
protocol.
In order to reduce number of packets flooding on the network, in ZRP, the sender
node sends the route request node to the border nodes. This process is called border-
casting. When the border nodes receive the route request packet, they repeat the process
for their own zones to discover a path to the intended destination. Thus the path between
sender and receiver nodes is established. For example, in the given topology, if node-A
wants to send a packet to node-P, then node-A sends the request packet to node-C
(border node), which will in turn find a path to node-P. After establishing a path between
node-A and node-P, data transmission will be carried out.

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2.2.3.3 Zone-based Hierarchical Link State Routing Protocol

Zone-based Hierarchical Link State (ZHLS) routing protocol operates based on hybrid
routing protocol. This protocol uses the positional information of each node to create non-
overlapping zones. Network is divided into zones and unique ID is assigned to each
zone. Each node in the zone is identified using node ID. In order to route a packet, each
node uses node ID and zone ID. The positional information of each node is identified
based on its zone ID. The location or positional information of each node can be
determined using GPS.

Route Establishment

ww
Every node maintains its zone information. The connectivity of nodes which are
present beyond the zone also maintained at each node. Using positional information, each
w .Ea
node determines its zone ID by mapping its node ID. ZHLS follows proactive routing
inside the zone and reactive routing outside the zone. Fig. 2.2.14 shows a network

syE
topology with different zones.

ngi
nee
rin
g .ne
t
Fig. 2.2.14 Network topology with different zones for ZHLS

Two types of Link State Packets (LSPs) are maintained. They are,
 Node LSP
 Zone LSP.
Node LSP carries a list of neighbors connected with it whereas zone LSP carries a list
of its connected zones. Each node propagates link state details to every other node
present within the zone in such a way each node maintains the node ID of all the nodes in
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its zone and maintains node-level topology. The node LSPs contain the zone IDs of the
neighboring zones which is shown in Table 2.2.3 (a).
Source Node LSP
A B, C and zone A

B A,D and zone E

C A, D and zone I

D B,C and zone C

Table 2.2.3 (a) Node LSP in zone B

ww
Each node can receive the link state information of other nodes present outside of the

w
zone through border nodes. Hence every node can able to know the connectivity with the

.Ea
nodes beyond its zone. Every node generates zone link state packet and circulate this
packet to entire network through border nodes. Table 2.2.3 (b) shows the zone link state
packet.
syE
Source Zone Zone LSP
A
ngi B

C
nee
A,C,E and I

D - rin
E

F
B

-
g .ne
G

H
-

-
t
I B

Table 2.2.3 (b) Zone LSP

Packet Transmission
When a source node wants to transmit a packet to destination, it first checks whether
the destination is present in its zone or not. If the destination is present in its zone, then
intra-zone routing protocol is used. If the destination is present outside of the zone, then
the source node initiates location request packet and forwards to border nodes. The
border nodes which receive the message will check its routing table and determine

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whether the destination belongs to its zone or not. If so, the border node sends location
response packet to the sender node. Else, it forwards the request packet.

Route Maintenance
In ZHLS, communication between the nodes will be carried out through border nodes.
So, border nodes are the key elements of ZHLS. If the border nodes move away, then the
established path will break. However, this route failure can be managed by other border
nodes with little delay.

2.3 Advantages and Disadvantages of Ad hoc Wireless Routing Protocols

ww
2.3.1 Proactive (Table Driven) Routing Protocols

DSDV w
Name of the Protocol

.Ea
Advantages
Route establishment requires
less time.
Disadvantages
Periodic beaconing increases
network overhead.

syE Not suitable for highly dynamic

environment.

ngi
Best path is maintained in the Inefficient due to periodic update
routing table.
nee mechanism.

Exchange of routing table

rin
consumes high bandwidth.

g
Each node has to maintain routing
table separately.
.ne
WRP Route establishment requires
less time.
Multiple table maintenance
requires larger memory. t
Faster convergence. Requires high processing power.

Tables can be obtained with

fewer information.

CGSR Better bandwidth utilization is Length of each path is high.

possible.

Implementing priority Instability of links due to high

scheduling schemes are easier. mobility.

Table 2.3.1 Advantages and disadvantages of various table driven routing protocols

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2.3.2 Reactive (On-Demand) Routing Protocols

Name of the Protocol Advantages Disadvantages
When there are no symmetric links, Failed link cannot be repaired.
then source will initiate route
discovery.

Periodic flooding is not required. Connection establishment is

DSR higher.

Reduces control overhead. Performance will be degraded

due to high mobility

ww Saves bandwidth. Routing overhead is heavy.

w .Ea
Most recent route is identified using
destination sequence number.

Periodic flooding is not required.

Large network leads to
maximizing delay in finding
path.

AODV
syE
Least congested route is established
rather than finding shortest route.
Asymmetric links cannot be

ngi
used.

Since source initiated protocol, In large networks, control

connection establishment takes little
delay. nee overhead may be heavy due to
multiple route reply packets.

Less overhead in small networks.

rin
Stable links are preferred.
g
The established stable path may

.ne
be longer than the shortest path.

ABR Fewer path breaks due to stable

links.
Route cache is not used.
t
More power consumption due
to beacon broadcast.

Uses stable routes. In case of link failure,

identifying a new path does not
follows link stability principle.

Link stability can be classified using Path establishment takes long

SSA beacon count. time.

More power consumption.

During path establishment,

shortest path may be omitted
due to longer stable path.

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Path break can be reduced by Requirement of time

calculating LET and RET. synchronization leads high
FORP control overhead.

Proactive routing performs well in Positional information of nodes

high dynamic topologies. depends on GPS.

Table 2.3.2 Advantages and disadvantages of various on-demand routing protocols

2.3.3 Hybrid Routing Protocol

Name of the Protocol Advantages Disadvantages

ww QoS and routing can be

performed effectively.
If core nodes move away,
performance will be highly

w .Ea Increase and decrease waves are

degraded.

Core node update mechanism

CEDAR
syE used in finding stable high-
bandwidth and unstable low-
bandwidth information.
leads to high control overhead.

ngi
Communication through core
nodes provides reliable
communication. nee
Control overhead is highly
rin
If the destination is not in the

ZRP
reduced due to proactive and
reactive routing.
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zone, then the message cannot

.ne
be received by the destination
with less delay.
Border-casting takes less time to
transmit a packet.

Less bandwidth is consumed.

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Requires less memory. High network overhead due to
zone-level topology.

Established path may be non-

ZHLS
optimal.
Robustness.
Requires geographical
information.

Table 2.3.3 Advantages and disadvantages of various hybrid routing protocols

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Ad hoc and Wireless Sensor Networks 2 - 37 Routing in Ad hoc Networks

2.4 Two Marks Questions with Answers

Part - A
Q.1 What do you mean by routing ?
Ans. : Routing is a process of establishing a path between the sender and receiver
nodes for transmitting the packet along the path.
Q.2 What are the design constraints of a routing protocol ?
Ans. : The design constraints of a routing protocol are,
 Node mobility
 Highly dynamic topology

ww


No infrastructure for centralized administration
Bandwidth constrained


wEnergy constrained

.Ea
Establishing end-to-end path.

syE
Q.3 What are the types of ad hoc routing protocols ?
Ans. : Ad hoc routing protocols can be broadly classified into three categories :

 ngi
Proactive or table driven routing protocols
Reactive or on-demand routing protocols
 Hybrid routing protocols.
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Q.4 What do you mean by proactive routing protocols ?
rin
Ans. : Proactive routing protocols are also called as table-driven routing protocols in

g
which each node maintains a routing table. Routing table contains up-to-date routing
information of the entire network.
.ne
Q.5 List the advantages and disadvantages of proactive routing protocols.
Ans. : Advantage
 Minimum time is required to find out a route for data transmission.
t
Disadvantages
 Due to the frequent change of network topology, the exchange of up-to-date
information has to be done periodically.
 Network overload is high.
 Bandwidth consumption is high in large networks.
 This type of protocol is not suited for large networks.
Q.6 Define reactive routing protocols.
Ans. : Reactive routing protocols are also called as on-demand routing protocols. In
this type of routing protocols, each node determines the routing path whenever it is
ready for transmitting data to other node in the network.
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Ad hoc and Wireless Sensor Networks 2 - 38 Routing in Ad hoc Networks

Q.7 List the advantages and disadvantages of reactive routing protocols.

Ans. : Advantages
 Needs to broadcast less control messages for discovering route when required
 Network overhead is low
 Suitable for large networks
 Bandwidth wastage is low.
Disadvantage
 Time taken to discover a route is non-predictable.
Q.8 What is hybrid routing protocols ?

ww
Ans. : Hybrid routing protocols combine the features of both proactive and reactive
routing protocols. In this protocol, the network is divided into zones.

w .Ea
Q.9 Define wireless routing protocol.
Ans. : Wireless Routing Protocol (WRP) is one of the proactive routing protocols in ad
hoc wireless networks.
Q.10 What is routing table ? syE
ngi
Ans. : It contains the shortest distance and the up-to-date information of all
destinations. In order to determine the shortest path, each node maintains the ID of
destination node, next hop, distance (cost) and predecessor node.
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2.5 Long Answered Questions
rin
Part - B
g
Q.1 How table-driven routing protocols for ad hoc networks work ? (Refer section 2.3.1) .ne
Q.2 Write down the difference between proactive and reactive routing. (Refer section 2.3)
Q.3 Discuss the various major issues in designing routing protocols for Ad hoc networks.
(Refer section 2.1)
t
Q.4 Explain in detail about the types of Ad hoc routing protocols. (Refer section 2.1)
Q.5 Discuss the steps involved for maintaining a routing table in DSDV. (Refer section 2.3)
Q.6 Write short note on wireless routing protocol. (Refer section 2.1)
Q.7 Explain in detail the various algorithms of reactive routing protocols. (Refer section 2.3)
Q.8 Write in detail the various algorithms of hybrid routing protocols. (Refer section 2.2.3)
Q.9 List out the advantages and disadvantages of various table driven routing protocols.
(Refer section 2.3.1)
Q.10 Discuss the advantages and disadvantages of various on-demand routing protocols.
(Refer section 2.3.2)

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