UNIT-1

Introduction to Ad-hoc Wireless Networks :

An ad hoc sensor network with internet connectivity refers to a network of wireless
sensors that can communicate with each other and also connect to the internet. This type of
network is typically used for various applications such as environmental monitoring, smart cities,
industrial automation, and healthcare.

In an ad hoc sensor network, each sensor node is equipped with a wireless communication module,
sensors to collect data, and processing capabilities. These nodes can communicate with each other
using wireless protocols such as Zigbee, Bluetooth, or Wi-Fi. They form a self-organizing network
where nodes can dynamically join or leave the network without relying on a centralized
infrastructure.

To enable internet connectivity, one or more sensor nodes in the network can be equipped with a
gateway device. The gateway acts as a bridge between the ad hoc sensor network and the internet.
It can connect to the internet using wired or wireless technologies such as Ethernet, 3G/4G, or
satellite communication. The gateway node can transmit the collected sensor data to the internet
and also receive commands or updates from the internet to control the sensor network.

The internet connectivity in an ad hoc sensor network opens up various possibilities. It allows remote
monitoring and control of the sensor network from anywhere in the world. The collected sensor
data can be transmitted to a central server or cloud platform for storage, analysis, and
visualization. This enables real-time monitoring, data-driven decision making, and integration
with other internet-based services or applications.

However, there are also challenges in implementing an ad hoc sensor network with internet
connectivity. These include power management to ensure long battery life for the sensor nodes,
security and privacy concerns, network scalability, and efficient routing algorithms to handle
dynamic network topologies.

Overall, an ad hoc sensor network with internet connectivity provides a flexible and scalable solution
for collecting and transmitting sensor data in various applications, enabling real-time monitoring
and control from anywhere in the world.
What is cellular network?
A cellular network is a telecommunications network that allows mobile devices to communicate with
each other and connect to the internet through a series of interconnected base stations. It is called a
"cellular" network because the coverage area is divided into smaller geographic areas called cells,
which are served by individual base stations.

Here's a simplified diagram illustrating a cellular network:

In this diagram, the mobile device communicates wirelessly with the nearest base station. The base
station acts as a link between the mobile device and the rest of the network. Multiple base stations
are strategically placed to cover different areas or cells, and they are connected to each other and
the internet to enable communication between mobile devices and other devices on the network.
 Mobile Device
|
|
+------------+
| Base Station |
+------------+
|
|
+------------+
| Base Station |
+------------+
|
|
+------------+
| Base Station | |
+------------+
Internet

What is the Ad-hoc network?

An ad hoc network is a decentralized type of network where devices communicate directly with each
other without the need for a central infrastructure such as base stations or access points. In an ad
hoc network, each device can act as a router, forwarding data to other devices in the network,
allowing for peer-to-peer communication.
Here's a simplified diagram illustrating an ad hoc network:

+----------
--+
| Device
A |
+----------
--+
| \
| \
| \
+----------
--+
| Device
B |
+----------
--+
| \
| \
| \
+----------
--+
| Device
C |
+----------
 -+

Difference between Cellular networks & Adhoc networks:

Feature Cellular Networks Ad Hoc Networks

Centralized infrastructure Decentralized; no fixed
Infrastructure (base stations) infrastructure
Network Peer-to-peer, self-
Formation Hierarchical architecture organizing
Wide coverage area
(global, regional, or Limited coverage area
Coverage local) (localized)
Scalability Highly scalable Limited scalability
Mobility Seamless handover
Support between cells Limited mobility support
Network Centralized network Distributed network
Control control control
High reliability due to Less reliable due to
Reliability infrastructure dynamic topology
Optimized for high- Limited bandwidth
Bandwidth bandwidth efficiency due to
Efficiency communication shared medium
Centralized security Distributed security
Security mechanisms mechanisms
High cost due to Lower cost due to no
Deployment infrastructure infrastructure
Cost development requirements
Mobile ad hoc networks
(MANETs), sensor
Examples 2G, 3G, 4G, 5G networks
Applications of Ad-hoc Wireless Networks:
Ad-hoc wireless networks, also known as mobile ad-hoc networks (MANETs), are decentralized
wireless networks that do not rely on any fixed infrastructure or centralized access points. Instead,
the nodes in an ad-hoc network directly communicate with each other to establish connections and
forward data packets. These networks are dynamic and self-configuring, making them suitable for
various applications where traditional infrastructure-based networks may not be practical or
available. Some of the applications of ad-hoc wireless networks include:
1. Emergency and Disaster Response: Ad-hoc networks are invaluable in disaster scenarios when
traditional communication infrastructure may be damaged or non-existent. Emergency responders
can quickly set up ad-hoc networks to coordinate their efforts, share real-time information, and
locate survivors.
2. Military Applications: Ad-hoc wireless networks are extensively used in military operations,
particularly in areas with limited or compromised communication infrastructure. Soldiers can form
dynamic networks on the battlefield to share critical data, coordinate movements, and maintain
situational awareness.
3. Sensor Networks: Ad-hoc networks are widely used in wireless sensor networks (WSNs), where
numerous sensor nodes collaborate to collect and relay data from various physical environments.
Examples include environmental monitoring, smart agriculture, and industrial automation.
4. Vehicular Ad-hoc Networks (VANETs): VANETs enable communication between vehicles and
with roadside infrastructure. These networks support applications such as traffic management,
collision avoidance, and real-time updates on road conditions.
5. Mobile Gaming and Entertainment: Ad-hoc networks are used to enable multiplayer gaming and
content sharing among mobile devices without requiring a centralized server.
6. Ad-hoc Internet Sharing: In situations where traditional internet access is unavailable, ad-hoc
networks can be used to share internet connectivity among devices, forming a local network.
7. Search and Rescue Operations: In remote or hazardous environments, ad-hoc networks can help
search and rescue teams to communicate, coordinate their efforts, and locate missing individuals.
8. Community Networks: Ad-hoc networks can empower communities in remote or underserved
areas to create their own communication networks without relying on traditional infrastructure.
9. Collaborative Work Environments: Ad-hoc networks can facilitate seamless communication and
data sharing among individuals in temporary workspaces or during collaborative projects.
10. Indoor Navigation: Ad-hoc networks can be used to create ad-hoc positioning systems, allowing
devices to determine their location accurately in indoor environments where GPS signals may be
weak or unavailable.
Overall, the flexibility and self-organizing nature of ad-hoc wireless networks make them a
valuable solution in various scenarios where traditional infrastructure-based networks are
impractical or challenging to implement. However, they also present challenges, such as routing
efficiency, security, and scalability, which need to be carefully addressed for successful
deployment in specific applications.
Issues in Ad hoc wireless networks :
The major issues that affect the design, deployment, and performance of an ad hoc wireless system
are as follows:
1. Medium Access Control (MAC)
2. Routing
3. Multicasting
4. Transport layer protocol
5. Quality of Service (QOS)
6. Self-organization
7. Security
8. Energy management
9. Addressing and service discovery
10. Deployment considerations
11. Scalability

1. Medium Access Scheme **

The primary responsibility of a Medium Access Control (MAC) protocol in adhoc wireless networks
is the distributed arbitration for the shared channel for transmission of packets. The major issues
to be considered in designing a MAC protocol for adhoc wireless networks are as follows:

 Distributed Operation: The ad hoc wireless networks need to operate in environments where no
centralized coordination is possible. The MAC protocol design should be fully distributed
involving minimum control overhead.

 Synchronization: The MAC protocol design should take into account the requirement of time
synchronization. Synchronization is mandatory for TDMA-based systems for management of
transmission and reception slots.

 Hidden Terminals: Hidden terminals are nodes that are hidden(or not reachable) from the sender
of a data transmission session, but are reachable to the receiver of the session.

 Exposed terminals: Exposed terminals, the nodes that are in the transmission range of the sender
of an on-going session, are prevented from making a transmission.

 Throughput: The MAC protocol employed in adhoc wireless networks should attempt to
maximize the throughput of the system.

 The important considerations for throughput enhancement are

o Minimizing the occurrence of collisions.

o Maximizing channel utilization and

o Minimizing control overhead.

 Access delay: The average delay that any packet experiences to get transmitted. The MAC
protocol should attempt to minimize the delay.

 Fairness: Fairness refers to the ability of the MAC protocol to provide an equal share or weighted
share of the bandwidth to all competing nodes. Fairness can be either node-based or flow-based.

2. Routing **

The responsibilities of a routing protocol include exchanging the route information; finding a feasible
path to a destination. The major challenges that a routing protocol faces are as follows:

 Mobility:
The Mobility of nodes results in frequent path breaks, packet collisions, transient loops, stale routing
information, and difficulty in resource reservation.

 Bandwidth constraint:
Since the channel is shared by all nodes in the broadcast region, the bandwidth available per wireless
link depends on the number of nodes & traffic they handle.

 Error-prone and shared channel:

The Bit Error Rate (BER) in a wireless channel is very high [ 10-5 to 10 -3 ] compared to that in its
wired counterparts [ 10-12 to 10-9 ].

The major requirements of a routing protocol in adhoc wireless networks are the following.

a. Minimum route acquisition delay:

The route acquisition delay for a node that does not have a route to a particular destination node
should be as minimal as possible.

The delay may vary with the size of the network and the network load.

b. Quick route reconfiguration:

The unpredictable changes in the topology of the network require that the routing protocol be able to
quickly perform route reconfiguration in order to handle path breaks and subsequent packet losses.

c. Loop-free routing:

This is a fundamental requirement to avoid unnecessary wastage of network bandwidth .In adhoc
wireless networks, due to the random movement of nodes, transient loops may form in the route
thus established. A routing protocol should detect such transient routing loops & take corrective
actions.

3. Multicasting **

It plays important role in emergency search & rescue operations & in military communication. Use of
single- link connectivity among the nodes in a multicast group results in a tree-shaped multicast
routing topology. Such a tree-shaped topology provides high multicast efficiency, with low packet
delivery ratio due to the frequency tree breaks. The major issues in designing multicast routing
protocols are as follows:

 Robustness: The multicast routing protocol must be able to recover & reconfigure quickly from
potential mobility-induced link breaks thus making it suitable for use in high dynamic
environments.

 Efficiency: A multicast protocol should make a minimum number of transmissions to deliver a

data packet to all the group members.

 Control overhead: The scarce bandwidth availability in ad hoc wireless networks demands
minimal control overhead for the multicast session.

 Quality of Service: QoS support is essential in multicast routing because, in most cases, the data
transferred in a multicast session is time-sensitive.

 Scalability: The multicast routing protocol should be able to scale for a network with a large
 number of node

 Security: Authentication of session members and prevention of non-members from gaining

unauthorized information play a major role in military communications

4.Transport Layer Protocol**

The main objectives of the transport layer protocols include:

Setting up & maintaining end-to-end connections,

Reliable end-to-end delivery of packets,

Flow control &

Congestion control.

Examples of some transport layers protocols are,

a. UDP (User Datagram Protocol) :

It is an unreliable connectionless transport layer protocol.

It neither performs flow control & congestion control.

It do not take into account the current network status such as congestion at the intermediate links,
the rate of collision, or other similar factors affecting the network throughput.

b. TCP (Transmission Control Protocol):

It is a reliable connection-oriented transport layer protocol.

It performs flow control & congestion control.

5.Quality of Service Provisioning (QoS) **

QoS is the performance level of services offered by a service provider or a network to the user.

QoS provisioning often requires ,

o Negotiation between host & the network.

o Resource reservation schemes.

o Priority scheduling &

o Call admission control.

 QoS parameters :

Applications Corresponding QoS parameter

1. Multimedia application 1. Bandwidth & Delay.

2. Military application 2. Security & Reliability.

3. Defense application 3. Finding trustworthy

intermediate hosts & routing

4. Emergency search and rescue operations 4.Availability.

5. Hybrid wireless network 5. Maximum available

link life, delay, bandwidth

6. Communication among the nodes in 6. Minimum energy

consumption,

6.Self-Organization **

• One very important property that an ad hoc wireless network should exhibit is organizing &
maintaining the network by itself.

• The major activities that an ad hoc wireless network is required to perform for self-organization are,

 Neighbour discovery.

 Topology organization &

 Topology reorganization (updating topology information)

7.Security**

1) Security is an important issue in ad hoc wireless network as the information can be hacked.

2) Attacks against network are of 2 types :

I. Passive attack → Made by malicious node to obtain information transacted in the network without
disrupting the operation.

II. Active attack → They disrupt the operation of network. Further active attacks are of 2 types :

o External attack: The active attacks that are executed by nodes outside the network.

o Internal attack: The active attacks that are performed by nodes belonging to the same network.

9. Energy Management **

Energy management is defined as the process of managing the sources & consumers of energy in a
node or in the network for enhancing the lifetime of a network.

Features of energy management are :

→Shaping the energy discharge pattern of a node’s battery to enhance battery life.

→Finding routes that consumes minimum energy.

→Using distributed scheduling schemes to improve battery life.

→Handling the processor & interface devices to minimize power consumption.

Energy management can be classified into the following categories :

a. Transmission power management:

The power consumed by the Radio Frequency (RF) module of a mobile node is determined by several
factors such as

The state of operation.

The transmission power and

The technology used for the RF circuitry.

The state of operation refers to transmit, receive, and sleep modes of the operation.

The transmission power is determined by

Reach ability requirement of the network.

Routing protocol and

MAC protocol employed.

b. Battery energy management:

The battery management is aimed at extending the battery life of a node by taking advantage of its
chemical properties, discharge patterns, and by the selection of a battery from a set of batteries
that is available for redundancy.

c. Processor power management:

The clock speed and the number of instructions executed per unit time are some of the processor
parameters that affect power consumption.

The CPU can be put into different power saving modes during low processing load conditions.

The CPU power can be completely turned off if the machines is idle for a long time. In such a
cases, interrupts can be used to turn on the CPU upon detection of user interaction or other events.

d. Devices power management:

Intelligent device management can reduce power consumption of a mobile node significantly.

This can be done by the operating system( OS) by selectively powering down interface devices that
are not used or by putting devices into different power saving modes, depending on their usage.

9. Addressing and service discovery **

Addressing & service discovery assume significance in ad hoc wireless network due to the absence
 of any centralised coordinator.

An address that is globally unique in the connected part of the ad hoc wireless network is required
for a node in order to participate in communication.

Auto-configuration of addresses is required to allocate non-duplicate addresses to the nodes.

10. Deployment Considerations **

The deployment of a commercial ad hoc wireless network has the following benefits when compared
to wired networks

a) Low cost of deployment:

The use of multi-hop wireless relaying eliminates the requirement of cables & maintenance in
deployment of communication infrastructure.

The cost involved is much lower than that of wired networks.

b) Incremental deployment:

Deployment can be performed incrementally over geographical regions of the city.

The deployed part of the network starts functioning immediately after the minimum configuration
is done.

c) Short deployment time:

Compared to wired networks, the deployment time is considerably less due to the absence of any
wired links.

d) Reconfigurability:

The cost involved in reconfiguring a wired network covering a Metropolitan Area Network(MAN) is
very high compared to that of an ad hoc wireless network covering the same service area

11.Scalability**

Scalability is the ability of the routing protocol to scale well in a network with a large number of
nodes.

It requires minimization of control overhead & adaptation of the routing protocol to the network
size.

AD HOC WIRELESS INTERNET

Ad hoc wireless internet extends the services of the internet to the end users over an ad hoc
wireless network.

Some of the applications of ad hoc wireless internet are:

Wireless mesh network.

Provisioning of temporary internet services to major conference venues.

Sports venues.
 Temporary military settlements.

Battlefields &

Broadband internet services in rural regions.

The major issues to be considered for a successful ad hoc wireless internet are the following:

Gateway:

They are the entry points to the wired internet.

Generally owned & operated by a service provider.

They perform following tasks,

- Keeping track of end users. - Bandwidth management.

- Load balancing.

- Traffic shaping.

- Packet filtering.

- Width fairness &

- Address, service & location discovery.

 Ad hoc wireless internet, also known as mobile ad hoc networks (MANETs),
refers to a type of wireless network where devices can communicate with each other without
relying on a centralized infrastructure. In an ad hoc wireless internet, devices such as laptops,
smartphones, or IoT devices can form a network on the fly and share data directly with each other.
Here are some key points about ad hoc wireless internet:
1. Decentralized Network: Ad hoc wireless internet does not rely on fixed infrastructure such as
routers or access points. Instead, devices connect directly to each other to form a self-configuring
network. Each device can act as a node, forwarding data to other devices within its communication
range.

2. Dynamic Topology: The network topology in ad hoc wireless internet is dynamic and can change
frequently. Nodes can join or leave the network, and the movement of devices can cause the
network topology to change rapidly. This dynamic nature poses challenges in maintaining stable
communication paths.

3. Routing Protocols: Ad hoc wireless internet uses routing protocols that enable devices to discover
and maintain routes to reach other devices in the network. These protocols determine the best
paths for data transmission, considering factors like distance, link quality, and available resources.

4. Limited Range: The range of communication in ad hoc wireless internet is limited to the
transmission capabilities of the devices involved. Devices need to be within each other's radio
range to establish direct communication. To extend the network coverage, nodes can act as relays,
forwarding data to distant nodes.

5. Applications: Ad hoc wireless internet can be used in various scenarios where traditional
infrastructure-based networks are unavailable or impractical. Examples include disaster recovery
operations, military deployments, remote areas, and temporary events where network connectivity
needs to be established quickly.

6. Security Challenges: Ad hoc wireless internet faces security challenges due to its open and
dynamic nature. The lack of a centralized authority makes it difficult to enforce security policies
and authentication mechanisms. Ensuring data confidentiality, integrity, and preventing
unauthorized access are significant concerns.

7. Quality of Service: Providing consistent quality of service in ad hoc wireless internet can be
challenging due to the dynamic nature of the network and limited resources. Managing bandwidth,
 prioritizing traffic, and maintaining QoS parameters for different applications require efficient
resource allocation and routing strategies.

Ad hoc wireless internet offers flexibility and connectivity in situations where traditional
infrastructure is unavailable or impractical. While it presents unique challenges, ongoing research
and advancements in routing protocols, security mechanisms, and resource management aim to
improve the performance and reliability of ad hoc wireless networks.

Mobile Adhoc Network (MANET)

o A MANET consists of a number of mobile devices that come together to form a network as
needed, without any support from any existing internet infrastructure or any other kind of fixed
stations.
o A MANET can be defined as an autonomous system of nodes or MSs(also serving as routers)
connected by wireless links, the union of which forms a communication network modeled in the
form of an arbitrary communication graph.
o This is in contrast to the well-known single hop cellular network model that supports the needs of
wireless communication between two mobile nodes relies on the wired backbone and fixed base
stations.
o In a MANET, no such infrastructure exists and network topology may be changed dynamically in
an unpredictable manner since nodes are free to move and each node has limiting transmitting
power, restricting access to the node only in the neighboring range.
o MANETs are basically peer-to-peer, multi-hop wireless networks in which information packets
are transmitted in a store and forward manner from a source to an arbitrary destination, via
intermediate nodes as given in the figure:
o As nodes move, the connectivity may change based on relative locations of other nodes. The
resulting change in the network topology known at the local level must be passed on to other
nodes so that old topology information can be updated.
o For example, as MS2 in the figure changes its point of attachment from MS3 to MS4, other nodes
that are part of the network should use this new route to forward packets to MS2. In the figure, we
assume that it is not possible to have all nodes within each other's radio range. In case all nodes
are closed by within each other's radio range, there are no routing issues to be addressed.
o In figures raise another issue, that of symmetric and asymmetric (bidirectional) and asymmetric
(unidirectional) links. Consider symmetric links with associative radio range; for example, if MS1
is within radio range of MS3, then MS3 is also within radio range of MS1. The communication
links are symmetric. This assumption is not always valid because of differences in transmitting
power levels and the terrain. Routing in asymmetric networks is relatively hard task. In certain
cases, it is possible to find routes that exclude asymmetric links, since it is cumbersome to find the
return path. The issue of efficient is one of the several challenges encountered in a MANET.
o The other issue is varying the mobility patterns of different nodes. Some other nodes are highly
mobile, while others are primarily stationary. It is difficult to predict a node's movement and
direction of movement and numerous studies have been performed to evaluate their performance
using different simulators.

Characteristics of MANET

Some characteristics of adhoc network are as follows:

o Dynamic topologies: nodes are free to move arbitrarily; thus the network topology may be
changed randomly and unpredictably and primarily consists of bidirectional links. In some cases
where the transmission power of two nodes is different, a unidirectional link may exist.
o Bandwidth-constrained and variable capacity links: wireless links continue to have
significantly lower capacity than infrastructure networks.
o Energy-constrained operation: some or all of the MSs in a MANET may rely on batteries or
other exhaustible means for their energy. For these nodes or devices, the most important system
design optimization criteria may be energy conservation.
o Limited physical security: MANETs are generally more prone to physical security threats than
wire line networks. The increased possibility of eavesdropping, spoofing, and denial of services
(DoS) attacks should be considered carefully. To reduce security threats, many existing link
security techniques are often applied within wireless networks.

Applications of MANET

Some specific applications of ad hoc networks include industrial and commercial applications
involving cooperative mobile data exchange. There are many existing and future military
networking requirements for robust, IP-compliant data services within mobile wireless
communication networks, with many of these networks consist of highly dynamic autonomous
topology segments. Advanced features of Mobile ad hoc networks, including data rates compatible
with multimedia applications global roaming capability, and coordination with other network
structures are enabling new applications.

o Defense applications: Many defense applications require on the fly communications set-up, and
ad hoc/sensor networks are excellent candidates for use in battlefield management.
o Crisis management applications: These arise, for example, as a result of natural disasters in
which the entire communication infrastructure is in disarray. Restoring communications quickly is
essential.
o Telemedicine: The paramedic assisting the victim of a traffic accident in a remote location must
access medical records (e.g. X-rays) and may need video conference assistance from a surgeon for
an emergency intervention. In fact, the paramedic may need to instantaneously relay back to the
hospital the victim's X-rays and other diagnostic tests from the site of the accident.
o Tele-geoprocessing application: The combination of GPS, GIS (Geographical Information
Systems), and high-capacity wireless mobile systems enables a new type of application referred to
as tele- geo processing.
o Virtual Navigation: A remote database contains the graphical representation of building, streets,
and physical characteristics of a large metropolis. They may also "virtually" see the internal layout
of buildings, including an emergency rescue plan, or find possible points of interest.
o Education via the internet: Educational opportunities available on the internet or remote areas
because of the economic infeasibility of providing expensive last-mile wire line internet access in
these areas to all subscribers.
o Vehicular area network: This a growing and very useful application of adhoc network in
providing emergency services and other information. This is equally effective in both urban and
rural setup. The basic and exchange necessary data that is beneficial in a given situation.