1

Q. Explain the fundamentals of wireless communication technology.

Discuss the role of the electromagnetic spectrum in wireless
communication.

1. Fundamentals of Wireless Communication Technology

Wireless communication is the transfer of information between two or more devices
without using physical mediums like cables or wires. Instead, it uses electromagnetic
waves to transmit data through the air over distances ranging from a few meters to several
kilometers.
Key Characteristics:
 Medium: Uses the atmosphere or vacuum as the transmission medium.
 Transmission: Occurs through radio waves, microwaves, or infrared.

 Flexibility: Allows mobility and portability of devices.

 Accessibility: Facilitates quick deployment without infrastructure setup.
Types of Wireless Communication:
1. Radio Communication: Used in AM/FM radio, television.
2. Microwave Communication: Used in satellite and point-to-point communication.

3. Infrared Communication: Short-range communication like in remote controls.

4. Wi-Fi: Wireless LAN used in homes, campuses, enterprises.
5. Bluetooth/ZigBee: Used for personal area networks and IoT.
Advantages:
 Mobility: Users can move freely without losing connection.

 Ease of Installation: No need for physical infrastructure.

 Cost-Effective: Reduces cable and maintenance costs.
 Scalability: Can add new devices without rewiring.
Applications:
 Mobile telephony (2G/3G/4G/5G)

 Wi-Fi and Bluetooth networks

 Wireless sensor networks (WSNs)
 Satellite communications
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 Emergency and military communication systems

2. Role of the Electromagnetic Spectrum in Wireless Communication

The electromagnetic spectrum is the foundation of wireless communication. It

encompasses the range of all electromagnetic radiation frequencies. Different wireless
applications utilize different parts of this spectrum.

Definition:
The electromagnetic spectrum is a continuum of electromagnetic waves arranged
according to frequency or wavelength, ranging from low-frequency radio waves to high-
frequency gamma rays.

Frequency Ranges Used:

Band Frequency Range Common Applications

VLF/LF < 300 kHz Submarine communication

MF/HF 300 kHz – 30 MHz AM radio, maritime

VHF 30 – 300 MHz FM radio, TV broadcasting

UHF 300 MHz – 3 GHz Mobile phones, TV

SHF 3 – 30 GHz Wi-Fi, satellite, radar

EHF 30 – 300 GHz Experimental and military

Significance in Wireless Communication:

 Channel Allocation: Different services (TV, cellular, Wi-Fi) are assigned specific
frequencies to avoid interference.
 Signal Propagation: Higher frequencies generally offer higher data rates but shorter
ranges.
 Bandwidth Availability: Higher frequency bands have more bandwidth available,
crucial for modern applications like 5G.
Examples of Frequency Usage:

 2.4 GHz: Wi-Fi, Bluetooth, ZigBee

 5 GHz: Advanced Wi-Fi (802.11ac)
 868/915 MHz: Long-range low-power IoT (LoRa, Sigfox)
 900 MHz / 1800 MHz / 2100 MHz: Cellular communication
Challenges:
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 Spectrum Scarcity: Limited bandwidth leads to congestion.

 Interference: Overlapping frequencies can cause communication errors.
 Regulation: Spectrum usage is controlled by government bodies (e.g., TRAI in India,
FCC in the USA).

Here's a detailed 14-mark answer suitable for your BTech exam based on your syllabus:

Q2. What are the different radio propagation mechanisms in

wireless communication? Explain each briefly.

Introduction
Radio propagation refers to the behavior of radio waves as they travel from the
transmitter to the receiver through the atmosphere. In wireless communication,
understanding how these waves propagate is essential for designing efficient systems and
predicting signal performance.

Types of Radio Propagation Mechanisms

There are five major radio propagation mechanisms that affect how signals travel in real-
world environments:

1. Line-of-Sight (LOS) Propagation

Definition:
Line-of-sight propagation occurs when the transmitted signal travels in a straight,
unobstructed path from the transmitter to the receiver.
Characteristics:
 Common in outdoor environments or over short distances.
 Offers the best signal quality and strength.

 Used in microwave and satellite communications.

Example:
Communication between mobile towers and line-of-sight drones.

2. Reflection
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Definition:
Reflection occurs when radio waves strike large surfaces (e.g., buildings, walls) and bounce
back.
Characteristics:
 Reflected signals may take longer to reach the receiver.
 Can cause multipath interference if combined with direct signals.

 Affects indoor and urban communication.

Example:
Wi-Fi signals reflecting off furniture and walls in a room.

3. Diffraction
Definition:
Diffraction is the bending of radio waves around sharp edges or obstacles when the direct
path is blocked.
Characteristics:
 Enables communication even when obstacles block direct line-of-sight.

 More significant for lower frequency signals (longer wavelengths).

 Can cause signal loss or degradation.
Example:
A signal bending around a building or hill to reach a receiver.

4. Scattering
Definition:
Scattering occurs when the signal hits small objects (e.g., foliage, raindrops, dust particles)
and gets dispersed in multiple directions.
Characteristics:

 Causes signal weakening due to energy spreading.

 Common in urban and forested environments.
 Affects signal clarity and contributes to fading.
Example:
Scattering due to tree leaves or rough building surfaces.
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5. Multipath Propagation
Definition:
In multipath propagation, multiple copies of the transmitted signal arrive at the receiver
via different paths due to reflection, diffraction, or scattering.
Characteristics:
 Causes constructive or destructive interference, leading to fading.

 Leads to delay spread and inter-symbol interference in digital systems.

 Requires equalization or diversity techniques to mitigate.
Example:
A mobile phone receiving multiple signal paths in a city with high-rise buildings.

Visualization:
[Tx]----> (direct path) ----> [Rx]

\ ↘
\----> [Wall] → (reflected path) → [Rx]
\----> (diffraction around obstacle)
\----> (scattered by tree)

Q3. Differentiate between MANETs and WSNs. Provide their

key applications.

Introduction
Mobile Ad-hoc Networks (MANETs) and Wireless Sensor Networks (WSNs) are two
important types of wireless networks that operate without fixed infrastructure. Although
both share some similarities, they differ significantly in architecture, design goals, and
applications.

1. Definition

Aspect MANETs WSNs

Meaning A MANET is a self-configuring network A WSN is a network of spatially

of mobile devices connected by distributed autonomous sensor nodes
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Aspect MANETs WSNs

wireless links without fixed that monitor physical or environmental

infrastructure. conditions.

2. Primary Purpose

MANETs WSNs

Focused on providing communication Focused on collecting data from the

between mobile nodes in dynamic environment and transmitting it to a base
environments. station or sink.

3. Node Characteristics

MANETs WSNs

Nodes are typically mobile, with high Nodes are usually stationary, limited in
computation and communication capability processing power, memory, and energy
(e.g., smartphones, laptops). (e.g., tiny sensors).

4. Communication

MANETs WSNs

Peer-to-peer communication is common. Data flows from many sensors to one sink
Every node can act as a router. (many-to-one communication).

5. Topology

MANETs WSNs

Highly dynamic due to node Mostly static, though dynamic reconfiguration is possible
mobility. due to node failures.

6. Energy Consideration

MANETs WSNs

Energy constraints are less critical, as Energy efficiency is crucial, as sensor nodes are
devices may be recharged. battery-operated and hard to replace.
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7. Scalability

MANETs WSNs

Designed for small to medium-scale networks. Can be scaled to thousands of nodes.

8. Data Aggregation

MANETs WSNs

Not a primary concern. Data aggregation is vital to reduce redundancy and save energy.

9. Examples of Devices

MANETs WSNs

Mobile phones, laptops, PDAs. Temperature sensors, pressure sensors, motion detectors.

10. Routing Protocols

MANETs WSNs

Uses routing protocols like Routing focuses on energy efficiency and may include
AODV, DSR, OLSR. LEACH, Directed Diffusion.

Key Applications
Applications of MANETs:

1. Military battlefield communication

2. Emergency and disaster relief operations
3. Temporary event setups (e.g., concerts, exhibitions)
4. Vehicle-to-vehicle (V2V) communication
5. Remote area networking

Applications of WSNs:
1. Environmental monitoring (e.g., forest fire detection, pollution tracking)
2. Industrial automation and machinery health monitoring
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3. Smart agriculture (soil moisture, crop health)

4. Structural health monitoring (bridges, buildings)
5. Healthcare (patient vital signs monitoring)

Q4. Discuss the design challenges in Ad-hoc and Sensor Networks.

How do these challenges impact real-world applications?

Introduction
Ad-hoc Networks (like MANETs) and Wireless Sensor Networks (WSNs) are decentralized,
infrastructure-less networks that operate in dynamic and often harsh environments. Their
design must address numerous challenges to ensure efficiency, reliability, and
sustainability.

I. Design Challenges in Ad-hoc and Sensor Networks

1. Energy Constraints
Explanation:
 Nodes are typically powered by batteries.
 In WSNs, sensor nodes are often deployed in inaccessible areas where battery
replacement is not feasible.
Impact:
 Energy-efficient protocols and algorithms are required.

 Limits data transmission, sensing frequency, and computation.

2. Limited Hardware Capabilities

Explanation:
 Sensor nodes have limited memory, processing power, and communication range.

Impact:
 Complex algorithms and heavy data processing must be avoided.
 Trade-offs between performance and resource usage are necessary.
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3. Dynamic Topology
Explanation:

 Nodes in MANETs are mobile, leading to frequent changes in network topology.

Impact:
 Requires robust routing protocols that can quickly adapt to topology changes (e.g.,
AODV, DSR).
 Increases overhead and latency.

4. Scalability

Explanation:
 Networks can range from tens to thousands of nodes.
Impact:
 Protocols must perform efficiently as network size increases.
 Centralized approaches fail in large networks.

5. Data Aggregation and Fusion

Explanation:
 In WSNs, multiple nodes may sense the same data (redundancy).
 Data aggregation reduces data traffic and energy consumption.

Impact:
 Aggregation methods must be energy-aware and delay-tolerant.
 Poor aggregation can lead to information loss or delays.

6. Fault Tolerance and Reliability

Explanation:
 Nodes may fail due to battery depletion, hardware malfunction, or environmental
factors.
Impact:
 Systems must continue functioning despite node failures.
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 Redundant paths and nodes are needed, increasing complexity and cost.

7. Security and Privacy

Explanation:
 Wireless medium is vulnerable to eavesdropping, spoofing, jamming, and denial-
of-service attacks.
Impact:
 Security measures must be lightweight to suit resource-constrained nodes.
 Security overhead can reduce network lifespan and performance.

8. Quality of Service (QoS)

Explanation:
 Includes throughput, delay, packet loss, and jitter.
 Real-time applications (e.g., healthcare) require guaranteed QoS.
Impact:

 Hard to maintain QoS in dynamic, resource-limited networks.

 Prioritization and scheduling mechanisms become necessary.

9. Localization and Deployment

Explanation:

 Many applications require knowledge of node locations (e.g., tracking,

environment mapping).
 Manual deployment is not practical for large-scale WSNs.
Impact:
 GPS is energy-consuming and costly.
 Localization algorithms must be lightweight and accurate.

10. Heterogeneity
Explanation:
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 Networks may consist of nodes with different capabilities (e.g., sensing,

processing).
Impact:
 Protocols must adapt to varied node roles and capacities.
 Complex coordination strategies are needed.

II. Impact on Real-World Applications

Application Area Impact of Design Challenges

Military Operations Security and mobility are crucial; any delay or failure can be
(MANETs) catastrophic.

Fault tolerance and quick deployment are essential; lack of

Disaster Management
infrastructure limits coordination.

Smart Agriculture Energy-efficient, long-term operation is vital; frequent

(WSNs) maintenance is impractical.

Reliable, real-time data with high QoS is critical; energy and

Health Monitoring
privacy are major concerns.

Environmental Nodes must survive in harsh conditions; long battery life and
Monitoring remote access are key.

Q1. What are the key issues in designing a MAC Protocol for Ad-hoc
Wireless Networks?

Introduction

The Medium Access Control (MAC) protocol is responsible for regulating how nodes in a
wireless network access the shared communication medium. In Ad-hoc Wireless
Networks, where there is no central control and nodes communicate peer-to-peer,
designing an efficient MAC protocol is challenging.
The goal of a MAC protocol in such networks is to ensure efficient, fair, and collision-free
access to the wireless medium while addressing mobility, energy constraints, and dynamic
topology.
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Key Design Issues in MAC Protocols for Ad-hoc Wireless Networks

1. Lack of Centralized Control

Issue:
 No fixed infrastructure or base stations exist to manage access to the medium.
Impact:
 Protocols must be distributed and self-organizing.
 Requires nodes to coordinate access autonomously.

2. Hidden Terminal Problem

Explanation:
 Occurs when two nodes (A and C) are out of each other’s range but both can
communicate with a common node B. When A and C transmit simultaneously, their
signals collide at B.
Impact:
 Causes data collisions and reduced throughput.

Solution Example:
 RTS/CTS mechanism (used in MACA/802.11) helps mitigate this.

3. Exposed Terminal Problem

Explanation:

 A node (say, B) is prevented from sending data to another node (C) because it
senses the medium is busy due to another nearby transmission (A to D), even
though the transmission would not cause interference.
Impact:

 Leads to under-utilization of the channel.

4. Mobility of Nodes
Issue:
 Nodes frequently change their location, leading to changes in topology.

Impact:
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 MAC protocols must adapt quickly to these changes.

 Connections can be broken or re-established often.

5. Limited Bandwidth and Shared Medium

Issue:
 Wireless spectrum is limited and must be shared by all nodes.
Impact:
 Efficient bandwidth utilization is critical.

 MAC protocols must minimize overhead.

6. Energy Efficiency
Issue:
 Nodes operate on limited battery power, especially in multi-hop scenarios.

Impact:
 MAC protocols must reduce energy consumption by minimizing idle listening,
collisions, retransmissions, and overhearing.
Examples:
 Duty-cycling and sleep scheduling in protocols like S-MAC.

7. Fairness

Issue:
 All nodes should have fair access to the medium.
Impact:
 MAC protocols should prevent starvation of certain nodes.
 Must avoid giving priority to specific nodes unless explicitly needed (QoS).

8. Throughput and Delay

Issue:
 Networks must support high throughput with minimal delay.
Impact:
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 MAC protocols should reduce control packet overhead and optimize channel
access.

9. Scalability
Issue:

 The number of nodes in ad-hoc networks can vary widely.

Impact:
 Protocols must perform well even as network size increases.

10. Support for QoS (Quality of Service)

Issue:
 Some applications (e.g., voice, video) require guaranteed delay, jitter, and
bandwidth.
Impact:
 MAC protocols must support prioritization and QoS differentiation.

11. Collision Avoidance

Issue:
 Wireless medium cannot detect collisions during transmission.
Impact:
 Protocols must avoid collisions rather than detect them.

 Use of techniques like Carrier Sense Multiple Access with Collision Avoidance
(CSMA/CA).

12. Synchronization
Issue:
 Some MAC protocols require time synchronization among nodes for slot-based
access.
Impact:
 Time synchronization is difficult and costly in ad-hoc networks.
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Q2. Differentiate between contention-based MAC and reservation-

based MAC protocols in Ad-hoc networks.

Introduction
In Ad-hoc wireless networks, the Medium Access Control (MAC) protocol is essential for
coordinating access to the shared communication medium. Based on how they manage
medium access, MAC protocols are broadly categorized into:
 Contention-Based MAC Protocols

 Reservation-Based MAC Protocols

These two types differ significantly in terms of how they allocate access, handle collisions,
and support quality of service.

I. Comparison Table

Aspect Contention-Based MAC Reservation-Based MAC

Nodes contend (compete) for the Nodes reserve the channel in

Access Method
channel advance

Collisions are likely; avoided using Collisions are prevented by

Collision Handling
techniques like CSMA/CA reserving slots or time

Channel Efficient under low traffic; poor Efficient under high traffic; may
Utilization under high traffic waste bandwidth under low traffic

Requires time synchronization

Synchronization No need for time synchronization
among nodes

Lower overhead (fewer control Higher overhead due to

Control Overhead
packets) reservation signaling

Quality of Service Easier to support QoS

Hard to guarantee QoS
(QoS) requirements (bandwidth, latency)

May be higher due to idle

Energy Can be lower with sleep
listening, collisions, and
Consumption scheduling during unused slots
retransmissions

Better suited for small to medium Better for large-scale networks

Scalability
networks with stable topology
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Aspect Contention-Based MAC Reservation-Based MAC

Best for dynamic environments Best for stable environments with

Suitability
with sporadic traffic predictable traffic

II. Contention-Based MAC Protocols

Working Principle:
 Nodes sense the medium before transmitting.
 If the medium is busy, they wait for a random backoff period.

 Common techniques: Carrier Sense Multiple Access with Collision Avoidance

(CSMA/CA), RTS/CTS.

Examples:
 IEEE 802.11 DCF (Distributed Coordination Function)
 MACA (Multiple Access with Collision Avoidance)
Advantages:
 Simple and decentralized.

 Adaptive to dynamic topologies.

Disadvantages:
 High collision probability in dense networks.
 No guaranteed bandwidth or QoS.

III. Reservation-Based MAC Protocols

Working Principle:
 Nodes reserve time slots or frequency bands in advance.
 Avoids collisions by ensuring only one node transmits in a slot.
Mechanisms:

 Time Division Multiple Access (TDMA)

 Frequency Division Multiple Access (FDMA)
 Code Division Multiple Access (CDMA)
Examples:
 FPRP (Floor Acquisition Multiple Access Protocol)
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 HRMA (Hop Reservation MAC)

Advantages:
 Prevents collisions entirely.

 Supports delay-sensitive and real-time applications.

Disadvantages:
 Complex to implement.
 Requires synchronization and centralized or distributed coordination.

IV. Real-World Applications

Contention-Based MAC Reservation-Based MAC

Disaster recovery communications Military tactical networks

Casual ad-hoc chatting or file sharing Industrial automation with real-time constraints

Unpredictable, bursty data traffic Multimedia streaming, VoIP in MANETs

Here’s a detailed 14-mark answer to your BTech exam question on multi-channel MAC
protocols, based on your uploaded syllabus:

Q3. What are Multi-Channel MAC Protocols? How do they work?

Introduction
In ad-hoc wireless networks, all nodes usually share a single wireless channel for
communication. However, this can lead to issues such as increased collisions, limited
throughput, and interference. To overcome these problems, multi-channel MAC protocols
have been developed.

Multi-channel MAC protocols use multiple frequency channels to allow parallel

transmissions, reduce contention, and improve network performance.

Definition
A Multi-Channel MAC (MMAC) Protocol is a type of medium access control protocol that
allows wireless nodes to utilize multiple frequency channels dynamically to improve
throughput, reduce interference, and enhance network performance in ad-hoc networks.
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Working Principle of Multi-Channel MAC Protocols

1. Channel Classification

 Control Channel: A dedicated channel used for control information exchange (e.g.,
channel negotiation, RTS/CTS).

 Data Channels: Channels used exclusively for data transmission.

2. Phases of Operation
1. Channel Negotiation:
o Nodes exchange control packets (e.g., RTS/CTS) over the common control
channel.
o They agree on a common data channel and time slot for communication.

2. Channel Switching:
o After negotiation, nodes switch to the selected data channel.
o Data is transmitted without interference from others on different channels.
3. Return to Control Channel:
o Once communication ends, nodes switch back to the control channel to
participate in new negotiations.

3. Synchronization (Optional but Recommended)

 Some protocols require time synchronization among nodes to avoid overlapping
transmissions.
 Time is often divided into beacon intervals or windows for negotiation and data
transfer.

Architecture Diagram (Textual)

+-----------------------------+

| Control Channel |
| (Used for RTS/CTS & Sync) |
+-----------------------------+
/ | \
/ | \
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+---------+ +---------+ +---------+

| Data Ch1| | Data Ch2| | Data Ch3|
+---------+ +---------+ +---------+

Advantages of Multi-Channel MAC Protocols

Advantage Explanation

Improved Throughput Parallel transmissions on different channels reduce congestion.

Reduced Collisions Fewer nodes contend on each channel.

Lower Delay Multiple channels reduce wait times for accessing the medium.

Better Scalability More effective in dense networks with many active nodes.

Challenges and Issues

Challenge Description

Channel Coordination Nodes must agree on which channel to use.

A node listening on a different channel might miss

Deafness Problem
communication attempts.

Hardware Constraints Requires multiple transceivers or fast channel switching.

Synchronization
Some protocols require tight time synchronization.
Overhead

Examples of Multi-Channel MAC Protocols

Protocol Key Idea

Uses a single transceiver and divides time into

MMAC
synchronization windows.

DS-MMAC Dynamic switching between data and control channels.

DCA (Dynamic Channel

Channels assigned dynamically based on usage.
Assignment)

MC-LMAC Combines TDMA with multi-channel access for scheduling.

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Use Cases / Applications

 Military ad-hoc networks (need for high throughput and low interference)

 Wireless mesh networks

 Disaster relief and emergency networks
 Multimedia and real-time applications (VoIP, video conferencing)

Here’s a detailed explanation of how Multi-Channel MAC Protocols improve performance

in Ad-hoc Wireless Networks, tailored for a 14-mark BTech exam question:

How Do Multi-Channel MAC Protocols Improve Performance?

Multi-channel MAC protocols significantly enhance the overall efficiency, capacity, and
reliability of wireless ad-hoc networks by overcoming the limitations of single-channel
communication. Here's how:

1. Increased Network Throughput

 Why it happens:
By using multiple data channels, different node pairs can communicate
simultaneously without interfering with each other.
 Example:
If 3 pairs of nodes use 3 separate data channels, all 3 can transmit data at the same
time, tripling the throughput compared to a single-channel MAC.
 Impact:
Boosts the data carrying capacity of the network, especially in high-traffic
scenarios.

2. Reduced Collisions and Interference

 Why it happens:
With multiple channels available, the probability of two nodes selecting the same
channel is lower.

 Impact:
o Fewer packet retransmissions.
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o Lower medium contention.

o Less energy wasted due to collision recovery.

3. Lower End-to-End Delay

 Why it happens:
Since multiple nodes can transmit simultaneously on different channels, waiting
time for channel access is reduced.
 Impact:
o Suitable for real-time and delay-sensitive applications (e.g., VoIP, video
streaming).
o Improves responsiveness of the network.

4. Better Scalability

 Why it happens:
Multi-channel systems distribute traffic across multiple channels, reducing load per
channel.

 Impact:
o Networks can support more nodes without degradation in performance.
o Performs well in dense or large-scale networks.

5. Improved Quality of Service (QoS)

 Why it happens:
Channels can be dedicated for different traffic types or priority levels.

 Impact:
o Guarantees for bandwidth, delay, and jitter.
o Makes multi-channel MAC suitable for multimedia applications.

6. Energy Efficiency (Indirect Improvement)

 Why it happens:
Fewer collisions and less idle listening result in reduced energy consumption.
 Impact:
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o Prolongs network lifetime, especially important in battery-powered nodes

(e.g., sensor networks).

7. Flexibility and Adaptivity

 Why it happens:
Some protocols dynamically assign channels based on real-time network conditions
(load, interference).
 Impact:

o Optimizes performance even under changing traffic and topology.

o Avoids congested or noisy channels.

Real-World Performance Gains

Metric Improvement with Multi-Channel MAC

Throughput Can increase 2x–5x compared to single-channel

Collision Rate Significantly reduced

Average Delay Reduced by parallel transmissions

Energy Consumption Lower due to fewer retransmissions

Packet Delivery Ratio Improved under high traffic

How Do Multi-Channel MAC Protocols Improve Performance?

Multi-channel MAC protocols significantly enhance the overall efficiency, capacity, and
reliability of wireless ad-hoc networks by overcoming the limitations of single-channel
communication. Here's how:

1. Increased Network Throughput

 Why it happens:
By using multiple data channels, different node pairs can communicate
simultaneously without interfering with each other.
 23

 Example:
If 3 pairs of nodes use 3 separate data channels, all 3 can transmit data at the same
time, tripling the throughput compared to a single-channel MAC.
 Impact:
Boosts the data carrying capacity of the network, especially in high-traffic
scenarios.

2. Reduced Collisions and Interference

 Why it happens:
With multiple channels available, the probability of two nodes selecting the same
channel is lower.
 Impact:
o Fewer packet retransmissions.

o Lower medium contention.

o Less energy wasted due to collision recovery.

3. Lower End-to-End Delay

 Why it happens:
Since multiple nodes can transmit simultaneously on different channels, waiting
time for channel access is reduced.
 Impact:

o Suitable for real-time and delay-sensitive applications (e.g., VoIP, video

streaming).

o Improves responsiveness of the network.

4. Better Scalability
 Why it happens:
Multi-channel systems distribute traffic across multiple channels, reducing load per
channel.
 Impact:
o Networks can support more nodes without degradation in performance.

o Performs well in dense or large-scale networks.

 24

5. Improved Quality of Service (QoS)

 Why it happens:
Channels can be dedicated for different traffic types or priority levels.
 Impact:
o Guarantees for bandwidth, delay, and jitter.

o Makes multi-channel MAC suitable for multimedia applications.

6. Energy Efficiency (Indirect Improvement)

 Why it happens:
Fewer collisions and less idle listening result in reduced energy consumption.
 Impact:

o Prolongs network lifetime, especially important in battery-powered nodes

(e.g., sensor networks).

7. Flexibility and Adaptivity

 Why it happens:
Some protocols dynamically assign channels based on real-time network conditions
(load, interference).
 Impact:
o Optimizes performance even under changing traffic and topology.
o Avoids congested or noisy channels.

Real-World Performance Gains

Metric Improvement with Multi-Channel MAC

Throughput Can increase 2x–5x compared to single-channel

Collision Rate Significantly reduced

Average Delay Reduced by parallel transmissions

Energy Consumption Lower due to fewer retransmissions

Packet Delivery Ratio Improved under high traffic

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Q: Discuss the IEEE 802.11 MAC Protocol. Explain how it handles

contention and ensures efficient communication.

1. Introduction to IEEE 802.11 MAC Protocol

The IEEE 802.11 standard is the basis for Wi-Fi networks, including infrastructure-based
and ad-hoc wireless networks. The MAC (Medium Access Control) layer in 802.11 is
responsible for coordinating access to the shared wireless medium.
In ad-hoc mode (also called IBSS – Independent Basic Service Set), each node
communicates directly with others without centralized access points.

2. MAC Access Mechanisms in IEEE 802.11

The IEEE 802.11 standard specifies two MAC access methods:

A. Distributed Coordination Function (DCF)

 Mandatory mechanism in all 802.11 implementations.

 Based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).

 Operates in a decentralized manner, suitable for ad-hoc networks.

B. Point Coordination Function (PCF)

 Optional mechanism.

 Requires a central coordinator (used in infrastructure mode, not in ad-hoc mode).

 Not applicable in most ad-hoc wireless scenarios.

✅ We'll focus on DCF, as it’s used in ad-hoc mode.

3. Working of IEEE 802.11 DCF

Step-by-Step Operation:
1. Carrier Sensing
 A node listens to the medium before transmitting.
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 If the medium is idle for a specific time (DIFS – DCF Interframe Space), the node
proceeds to transmit.
2. If Medium is Busy
 The node waits until the medium is idle for DIFS.
 Then, it chooses a random backoff time in units of slot time and counts it down.

 While counting, if medium becomes busy, it pauses the countdown and resumes
after the channel is idle again.
3. Collision Avoidance – RTS/CTS Mechanism
 Optional but used to avoid the hidden terminal problem.
 RTS (Request to Send) is sent to the receiver.
 Receiver replies with CTS (Clear to Send).

 Only then the sender transmits data.

 Other nearby nodes hearing RTS or CTS remain silent for the duration of
transmission.
4. Data Transmission and Acknowledgement
 Sender transmits the data.
 Receiver sends an ACK after a SIFS (Short Interframe Space).
 If no ACK is received, retransmission is attempted.

4. Contention Handling in IEEE 802.11

A. CSMA/CA with Backoff Algorithm
 If two nodes sense an idle channel at the same time, they choose random backoff
times.
 The node with the smaller backoff transmits first.
 This avoids collisions better than pure CSMA.

B. Binary Exponential Backoff (BEB)

 If collision occurs, the contention window (CW) is doubled.
 The node selects a new random backoff in a larger range.
 Reduces chance of repeated collisions.

5. Efficient Communication Features

 27

Feature Purpose Benefit

Avoids hidden terminal

RTS/CTS More reliable communication
collisions

ACK frames Confirms successful reception Reduces retransmission overhead

Interframe spaces Avoids collision between control

Prioritizes control/data traffic
(SIFS, DIFS) and data

Handles simultaneous access Reduces collisions and medium

Backoff timer
attempts contention

6. Drawbacks / Limitations
 Collision may still occur with control frames (RTS/CTS).
 Overhead of control packets can reduce efficiency for small data payloads.
 Not ideal for real-time QoS applications (solved in 802.11e with EDCA/HCCA).

7. Example of Timeline
Time ------------------>
Sender: RTS --- wait --- DATA ---------
Receiver: CTS ------ ACK ---------
Other nodes: NAV (Network Allocation Vector) silence

Q: Discuss the IEEE 802.11 MAC Protocol. Explain how it handles

contention and ensures efficient communication.

1. Introduction to IEEE 802.11 MAC Protocol

The IEEE 802.11 standard is the basis for Wi-Fi networks, including infrastructure-based
and ad-hoc wireless networks. The MAC (Medium Access Control) layer in 802.11 is
responsible for coordinating access to the shared wireless medium.
In ad-hoc mode (also called IBSS – Independent Basic Service Set), each node
communicates directly with others without centralized access points.
 28

2. MAC Access Mechanisms in IEEE 802.11

The IEEE 802.11 standard specifies two MAC access methods:

A. Distributed Coordination Function (DCF)

 Mandatory mechanism in all 802.11 implementations.
 Based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).
 Operates in a decentralized manner, suitable for ad-hoc networks.

B. Point Coordination Function (PCF)

 Optional mechanism.
 Requires a central coordinator (used in infrastructure mode, not in ad-hoc mode).
 Not applicable in most ad-hoc wireless scenarios.

✅ We'll focus on DCF, as it’s used in ad-hoc mode.

3. Working of IEEE 802.11 DCF

Step-by-Step Operation:
1. Carrier Sensing
 A node listens to the medium before transmitting.

 If the medium is idle for a specific time (DIFS – DCF Interframe Space), the node
proceeds to transmit.

2. If Medium is Busy
 The node waits until the medium is idle for DIFS.
 Then, it chooses a random backoff time in units of slot time and counts it down.
 While counting, if medium becomes busy, it pauses the countdown and resumes
after the channel is idle again.
3. Collision Avoidance – RTS/CTS Mechanism

 Optional but used to avoid the hidden terminal problem.

 RTS (Request to Send) is sent to the receiver.
 Receiver replies with CTS (Clear to Send).
 29

 Only then the sender transmits data.

 Other nearby nodes hearing RTS or CTS remain silent for the duration of
transmission.
4. Data Transmission and Acknowledgement
 Sender transmits the data.

 Receiver sends an ACK after a SIFS (Short Interframe Space).

 If no ACK is received, retransmission is attempted.

4. Contention Handling in IEEE 802.11

A. CSMA/CA with Backoff Algorithm

 If two nodes sense an idle channel at the same time, they choose random backoff
times.
 The node with the smaller backoff transmits first.
 This avoids collisions better than pure CSMA.
B. Binary Exponential Backoff (BEB)
 If collision occurs, the contention window (CW) is doubled.

 The node selects a new random backoff in a larger range.

 Reduces chance of repeated collisions.

5. Efficient Communication Features

Feature Purpose Benefit

Avoids hidden terminal

RTS/CTS More reliable communication
collisions

ACK frames Confirms successful reception Reduces retransmission overhead

Interframe spaces Avoids collision between control

Prioritizes control/data traffic
(SIFS, DIFS) and data

Handles simultaneous access Reduces collisions and medium

Backoff timer
attempts contention

6. Drawbacks / Limitations
 30

 Collision may still occur with control frames (RTS/CTS).

 Overhead of control packets can reduce efficiency for small data payloads.
 Not ideal for real-time QoS applications (solved in 802.11e with EDCA/HCCA).

7. Example of Timeline
Time ------------------>
Sender: RTS --- wait --- DATA ---------
Receiver: CTS ------ ACK ---------

Other nodes: NAV (Network Allocation Vector) silence

Key Issues in Designing Routing and Transport Layer

Protocols for Ad Hoc Networks
Introduction
Ad hoc networks are decentralized, infrastructure-less wireless networks where nodes
communicate directly or via intermediate nodes. Due to their unique characteristics like
node mobility, limited resources, and dynamic topology, designing efficient routing and
transport layer protocols presents several challenges.

1. Key Issues in Designing Routing Layer Protocols

Routing in ad hoc networks is responsible for discovering and maintaining routes between
nodes in a dynamic and resource-constrained environment.
a) Dynamic Topology and Mobility

 Nodes move arbitrarily, causing frequent and unpredictable changes in network

topology.

 Routing protocols must quickly adapt to broken or new links.

 Example: In Dynamic Source Routing (DSR), route cache updates and frequent
route discoveries handle topology changes.
b) Limited Bandwidth and Wireless Link Constraints
 Wireless channels have lower capacity and are prone to interference, fading, and
noise.
 Routing protocols must minimize control message overhead to conserve
bandwidth.
 31

 Example: Flooding route requests in reactive protocols like Ad hoc On-demand

Distance Vector (AODV) is controlled to reduce bandwidth consumption.
c) Energy Constraints
 Nodes are battery-powered with limited energy.
 Routing protocols should be energy-aware to prolong node and network lifetime.

 Example: Protocols may use metrics such as minimum energy routes or avoid
nodes with low battery.
d) Scalability
 Protocols must function efficiently as the number of nodes increases.
 Excessive control messaging or route maintenance overhead can degrade
performance.
 Example: Hierarchical routing protocols cluster nodes to improve scalability.
e) Multi-hop Communication

 Data packets often traverse multiple wireless hops.

 Routing must find reliable multi-hop paths that cope with node mobility and link
variability.
 Example: DSR uses source routing to embed entire paths, simplifying intermediate
node processing.
f) Security
 Open wireless medium is vulnerable to attacks such as spoofing, blackhole, or
wormhole attacks.
 Routing protocols must ensure data integrity and authenticate nodes.
 Example: Secure routing protocols add cryptographic methods for route
verification.

2. Key Issues in Designing Transport Layer Protocols

The transport layer ensures reliable end-to-end data delivery. In ad hoc networks, it must
handle wireless-specific issues.
a) Loss Differentiation
 Packet loss can be due to congestion or wireless link errors and mobility-related
route breaks.
 32

 Standard TCP interprets all losses as congestion, causing unnecessary rate

reduction.
 Example: TCP variants like TCP-ELFN provide explicit loss notifications to distinguish
causes.
b) Congestion Control
 Wireless bandwidth is limited and variable; congestion control must adapt
accordingly.
 Overly aggressive congestion window reductions hurt throughput.

 Example: Modified TCP schemes adjust window sizes based on wireless error rates.
c) End-to-End Reliability
 Ensuring data delivery over multi-hop wireless routes prone to failures is complex.
 Retransmission mechanisms should be efficient and minimize energy consumption.
 Example: Hybrid protocols combine end-to-end and hop-by-hop acknowledgments.

d) Connection Establishment and Maintenance

 Frequent route breaks cause connection disruptions.
 Transport protocols must detect and recover from route failures quickly.
 Example: TCP-F modifies connection management to handle intermittent
connectivity.
e) Energy Efficiency
 Excessive retransmissions or acknowledgments drain node batteries.

 Transport protocols should minimize overhead while maintaining reliability.

Explanation with Examples

Example 1: Routing Protocol – DSR (Dynamic Source Routing)
 How it addresses key issues:

o Reactive route discovery reduces overhead during idle periods (scalability,

bandwidth).
o Route caches speed up route lookup (efficiency).
o Source routing simplifies intermediate nodes’ work but increases packet
header size (trade-off).
 Challenges:
 33

o Frequent route breakages lead to repeated route discoveries (dynamic

topology).
o Larger headers cause overhead in longer routes (bandwidth).
Example 2: Transport Protocol – TCP over Ad Hoc Networks
 Problem:

o TCP interprets wireless losses as congestion, reducing throughput

unnecessarily.
o Route failures cause connection timeouts.
 Solutions:
o TCP-ELFN (Explicit Link Failure Notification): Network layer notifies TCP
about route breaks, pausing transmissions instead of congestion control.
o TCP-F: Adjusts retransmission behavior to handle intermittent connectivity
better.

Example
Layer Key Issues Explanation
Protocol/Concept

Dynamic topology, bandwidth Reactive routing, route

Routing limits, energy, scalability, DSR, AODV caching, controlled
security flooding

Loss differentiation, Modified TCP variants for

Transport congestion control, connection TCP-ELFN, TCP-F wireless errors and route
maintenance breaks

Difference Between Proactive, Reactive, and Hybrid

Routing Protocols in Ad Hoc Networks
Ad hoc networks use various routing approaches to handle dynamic topology and resource
constraints. The three main categories are Proactive, Reactive, and Hybrid routing
protocols. Each has distinct characteristics, advantages, and disadvantages.
 34

Feature Proactive Routing Reactive Routing Hybrid Routing

Combines proactive and

Maintains up-to-date Discovers routes only
reactive approaches,
Routing routing tables for all when needed, on-
maintaining routes
Information nodes periodically, demand, by initiating
proactively within local
Maintenance regardless of route discovery
zones and reactively for
communication need. processes.
distant nodes.

Routes are available

Route discovery occurs Uses proactive routing
immediately when
Route only when data needs within a local area and
needed, as they are
Discovery to be sent and no reactive routing beyond
pre-computed and
route is known. that area.
stored.

High, due to periodic Moderate overhead,

Low control overhead
updates and balancing periodic
Control during idle times;
maintenance of updates in zones and
Overhead higher during route
routing tables, even if reactive discovery
discovery floods.
routes are not used. elsewhere.

Low latency since Higher latency due to Moderate latency, with

Latency in
routes are pre- route discovery delay quick local communication
Data
established before before data can be and delayed distant
Transmission
data transmission. sent. communication.

Poor scalability in large Better scalability for

Better scalability by
or highly dynamic large, sparse networks
Scalability limiting proactive updates
networks due to with less frequent
to smaller zones.
overhead. communication.

DSDV (Destination-
AODV (Ad hoc On-
Sequenced Distance ZRP (Zone Routing
Demand Distance
Examples Vector), OLSR Protocol), HARP (Hybrid
Vector), DSR (Dynamic
(Optimized Link State Ad hoc Routing Protocol)
Source Routing)
Routing)

Suitable for highly

Suitable for networks Suitable for moderate to
dynamic or large
Suitability with low mobility and large networks balancing
networks where traffic
small to medium size. overhead and latency.
is sporadic.

Explanation
Proactive Routing Protocols
 35

 Maintain routes to every node at all times via periodic route updates.
 Advantages: Immediate route availability, low delay.
 Disadvantages: High control overhead, consumes bandwidth and energy even if no
data is sent.
Reactive Routing Protocols

 Create routes only when needed by flooding route requests.

 Advantages: Reduced control overhead when network traffic is low.
 Disadvantages: Delay in route discovery, overhead spikes during discovery.
Hybrid Routing Protocols
 Combine the strengths of proactive and reactive routing.

 Proactively maintain routes within a local zone for low latency communication.
 Use reactive discovery for nodes outside the local zone to reduce overhead.
 Strive for a balance between latency and control overhead.

Here's a detailed and structured 14-mark BTech-style answer explaining the AODV (Ad hoc
On-Demand Distance Vector Routing) protocol with an example scenario, suitable for your
exam on Ad Hoc and Wireless Sensor Networks.

AODV (Ad hoc On-Demand Distance Vector) Routing Protocol

Introduction
AODV is a reactive routing protocol used in mobile ad hoc networks (MANETs). It creates
routes only when needed by the source node, reducing control overhead. AODV uses
Route Request (RREQ) and Route Reply (RREP) messages to discover and establish paths.

Key Features of AODV

 Reactive: Routes are created only when required.

 Uses Sequence Numbers: To avoid routing loops and ensure fresh routes.
 Maintains Routing Table: Each node maintains a routing table with next-hop
information.
 Route Maintenance: Uses Route Error (RERR) messages for broken links.
 36

AODV Routing Process (Step-by-Step)

Scenario:
Assume the ad hoc network has the following nodes:

S (Source) → A → B → C → D (Destination)
The source node S wants to send data to D, but it does not have a route to D.

Step 1: Route Request (RREQ) Broadcast

 Node S initiates a RREQ broadcast to discover a route to D.

 The RREQ includes:

o Source ID (S)
o Destination ID (D)
o Source Sequence Number
o Broadcast ID (unique for each request)

o Hop Count (initialized to 0)

 Each intermediate node:
o Increments hop count.
o Stores reverse path to the source (used for sending RREP back).
o Forwards RREQ further if it hasn't seen this RREQ before.

Example Flow:
S → RREQ → A → RREQ → B → RREQ → C → RREQ → D

Step 2: Route Reply (RREP)

 When node D receives the RREQ:

o It sends a Route Reply (RREP) back to S using the reverse path.

o RREP contains:
 Destination Sequence Number
 Hop Count
 Source and Destination Addresses
Example Flow:
 37

D → RREP → C → RREP → B → RREP → A → RREP → S

 Each node along the reverse path:
o Updates its routing table with the next hop to reach D.

o Forwards the RREP to the next node toward S.

Step 3: Data Transmission

 Once S receives the RREP, it starts sending data packets to D via the established
route:
S→A→B→C→D

Step 4: Route Maintenance (Using RERR)

 If a link breaks (e.g., between B and C), the upstream node (B) detects it.
 Node B sends a Route Error (RERR) message back to S.
 All nodes that used the broken link invalidate the route and remove it from their
routing tables.
 If S still needs to send data, it initiates a new RREQ.

Diagram (Text Representation)

Route Discovery (RREQ):

S --RREQ--> A --RREQ--> B --RREQ--> C --RREQ--> D

Route Reply (RREP):

D --RREP--> C --RREP--> B --RREP--> A --RREP--> S

Data Transmission:

S --> A --> B --> C --> D

 38

Advantages of AODV
 Reduces unnecessary overhead by creating routes on-demand.
 Avoids routing loops using sequence numbers.

 Adapts well to dynamic topology.

Limitations
 Initial route discovery causes latency.
 RREQ flooding may cause temporary congestion.

 Frequent route discoveries in highly mobile environments may lead to overhead.

Here's a detailed, structured answer suitable for a 14-mark BTech

exam question on the topic “Challenges in Implementing TCP over
Ad Hoc Wireless Networks”, based on your Ad Hoc and Wireless
Sensor Networks syllabus.

Challenges in Implementing TCP over Ad Hoc Wireless Networks

Introduction
TCP (Transmission Control Protocol) is the dominant transport layer protocol designed for
reliable, connection-oriented communication in wired networks. However, in ad hoc
wireless networks, TCP faces significant performance degradation due to assumptions
made in its design (e.g., congestion is the main reason for packet loss).
Ad hoc networks have unique characteristics such as dynamic topology, wireless medium,
and multi-hop communication, which introduce several challenges in using standard TCP.

Key Challenges in TCP Implementation in Ad Hoc Wireless Networks

1. Misinterpretation of Packet Loss

 Cause:
o In TCP, any packet loss is interpreted as a sign of network congestion.
o But in ad hoc networks, losses often occur due to:
 Wireless channel errors
 Route failures
 39

 Link breakages due to mobility

 Effect:
o TCP triggers congestion control mechanisms (like window size reduction),
leading to unnecessary throughput degradation.
 Example:

o If a route breaks, TCP assumes congestion and reduces its sending rate
unnecessarily.

2. Frequent Route Failures Due to Mobility

 Cause:
o Nodes move frequently, breaking established routes.

 Effect:
o Causes long delays in packet delivery or packet drops.
o TCP cannot differentiate between delay due to route discovery and
congestion.
 Result:
o TCP timeouts and retransmissions increase, reducing efficiency.

3. Hidden and Exposed Terminal Problems

 Cause:
o In wireless multi-hop networks, hidden terminals cause collisions.
o Exposed terminals unnecessarily defer transmissions.
 Effect:

o Increases packet loss or delay.

o TCP again misinterprets these issues as congestion.

4. Unreliable MAC Layer

 Cause:

o MAC layer retransmissions are limited.

o It may fail to recover from wireless errors.
 40

 Effect:
o Packet losses bubble up to TCP, which reacts by reducing the congestion
window.

5. Path Asymmetry

 Cause:
o Forward and reverse paths in multi-hop ad hoc networks may have different
qualities (bandwidth, delay).
 Effect:
o TCP acknowledgements (ACKs) may get delayed or lost.
o Leads to incorrect round-trip time (RTT) estimation and poor congestion
control.

6. Network Partitioning
 Cause:
o Node mobility or power failure can lead to temporary disconnection of the
network.
 Effect:
o TCP interprets the inability to send or receive packets as severe congestion,
activating back-off algorithms and timeouts.

7. Shared Medium and Contention

 Cause:
o In wireless networks, nodes share the medium for transmission.
 Effect:
o TCP flows contend for bandwidth, causing collisions and delays.

o Leads to performance degradation when multiple flows exist.

8. Lack of Cross-layer Awareness

 Cause:
o TCP operates independently of lower layers (routing, MAC).
 41

 Effect:
o Cannot utilize information like link breaks or route re-establishments.
 Solution Approach:

o Cross-layer designs or feedback-based TCP variants (e.g., TCP-F, TCP-ELFN).

Summary Table

TCP Misinterpretation /
Challenge Cause
Problem

Packet loss due to Treated as congestion →

Wireless errors and route failures
mobility/errors reduces rate

Timeouts and
Route failures Node mobility
retransmissions

Hidden terminal
Wireless interference Packet collisions → loss
problem

RTT errors → performance

Path asymmetry Uneven link quality
drop

Disconnections due to node Back-off and delayed

Network partitioning
movement or power loss recovery

MAC unreliability Limited retransmissions Loss bubbles up to TCP

Delays and increased

Medium contention Shared channel among nodes
collisions

Solutions and Enhancements (Brief Mention)

To overcome these issues, various enhancements to TCP have been proposed:

 TCP-ELFN (Explicit Link Failure Notification): Pauses transmission on route failure.
 TCP-F (Feedback-based TCP): Uses feedback from intermediate nodes.
 ATCP (Ad hoc TCP): Uses cross-layer feedback for more intelligent congestion
handling.
 Split TCP: Splits connections at intermediate nodes to isolate mobility effects.
 42

Here’s a detailed and structured 14-mark BTech-level answer explaining the working of the
DSR (Dynamic Source Routing) protocol and how it differs from AODV (Ad hoc On-demand
Distance Vector). This answer is aligned with your Ad Hoc and Wireless Sensor Networks
syllabus and suitable for your exam preparation.

Dynamic Source Routing (DSR) Protocol – Working

Introduction
DSR is a reactive (on-demand) routing protocol designed for multi-hop wireless ad hoc
networks. It is based on source routing, meaning the entire path from the source to the
destination is included in the packet header.

Key Components of DSR

1. Route Discovery
2. Route Maintenance

🔶 1. Route Discovery in DSR

 Initiated when a source node needs a route to a destination and does not have a
cached route.
 The source broadcasts a Route Request (RREQ) to all neighbors.

 The RREQ contains:

o Source ID
o Destination ID
o A route record (initially empty) to store the list of traversed nodes
Process:

1. Each intermediate node appends its ID to the route record and forwards the RREQ.
2. If a node has a route to the destination in its cache, it may reply with a Route Reply
(RREP).
3. When the RREQ reaches the destination (or a node with a valid route), a Route
Reply (RREP) is sent back to the source using the reverse route recorded.

🔶 2. Route Maintenance in DSR

 43

 Used to detect and repair broken links during data transmission.

 When a link break is detected (via link-layer feedback or missing ACKs), a Route
Error (RERR) is sent to the source.
 The source then:
o Removes the broken link from its route cache

o Tries an alternate cached route or re-initiates route discovery

🔁 Example of DSR Working

Scenario:
Nodes: S → A → B → C → D
1. S needs to send data to D and starts route discovery.

2. RREQ:
3. S → A → B → C → D
4. Route record accumulates: [S, A, B, C, D]
5. D receives RREQ and sends RREP back along [D, C, B, A, S].
6. S now sends data with the entire path [S, A, B, C, D] in the header of each data
packet.

✅ Advantages of DSR
 No periodic messages: Reduces bandwidth and energy usage.
 Multiple routes caching: Reduces the need for frequent route discoveries.
 Loop-free: Source routing inherently avoids routing loops.

❌ Disadvantages of DSR
 Header overhead: Entire route in packet headers increases size, especially for long
paths.

 Scalability issues: Not efficient for large networks.

 Stale route cache: Cached routes may become invalid due to mobility.

🆚 Difference Between DSR and AODV

 44

DSR (Dynamic Source AODV (Ad hoc On-Demand

Feature
Routing) Distance Vector)

Source routing (entire route Hop-by-hop routing (next-hop info

Routing Technique
in packet) in table)

Routes stored in route cache

Route Storage Routing tables with next-hop info
at each node

Broadcasts RREQ and Broadcasts RREQ and replies with

Route Discovery
accumulates path RREP

Packet Header High – carries full route in Low – only destination and next
Overhead packet header hop info

Intermediate Node Can reply from cache if valid Replies only if it is the destination
Reply route exists or has a fresh route

Uses sequence numbers to prevent

Loop Prevention Achieved using source route
loops

Sends RERR and removes

Route Maintenance Sends RERR, updates routing tables
route from cache

Performance in Large Less efficient (due to header

More scalable than DSR
Networks size)

Protocol Type Reactive Reactive

✅ Summary
 DSR is a source-routing based reactive protocol where each packet carries the full
path.
 It uses route cache and has no periodic overhead, making it efficient for small, low-
mobility networks.
 Compared to AODV, DSR has more header overhead but better route caching.
AODV, on the other hand, is more scalable and efficient in larger and more dynamic
networks.

Here’s a detailed 14-mark BTech-level answer explaining the architecture of a Wireless

Sensor Network (WSN), complete with a diagram and a breakdown of key components
and their roles — as per your Ad Hoc and Wireless Sensor Networks syllabus.
 45

✅ Architecture of a Wireless Sensor Network (WSN)

Introduction
A Wireless Sensor Network (WSN) is a collection of spatially distributed autonomous
sensor nodes that monitor physical or environmental conditions like temperature,
humidity, sound, pressure, etc., and cooperatively pass the data through the network to a
central location called the base station or sink.

🔷 Diagram: Architecture of a WSN

Here’s a labeled representation of a typical WSN architecture:
+-------------------+

| Base Station |
| (Sink / Gateway) |
+-------------------+
↑
Aggregated Data

↑
------------------------
| |
+-------------+ +-------------+
| Cluster Head| | Cluster Head|

+-------------+ +-------------+
↑ ↑ ↑ ↑
/ \ / \
Sensor Sensor Sensor Sensor
Node Node Node Node

🔷 Key Components and Their Roles

1. Sensor Nodes
 Definition: Small devices equipped with sensors, a processor, memory, power
supply, and wireless transceiver.
 46

 Function:
o Sense environmental data (e.g., temperature, light).
o Process sensed data (data filtering or compression).

o Transmit data to neighboring nodes or cluster heads.

 Role: Primary data collection unit of the WSN.

2. Cluster Heads (Optional but Common)

 Definition: Special sensor nodes elected to coordinate communication within a
cluster.
 Function:

o Aggregate data from member sensor nodes.

o Perform data fusion or filtering.
o Transmit summarized data to the base station.
 Role: Local coordinator and data aggregator to reduce communication overhead.

3. Base Station (Sink Node or Gateway)

 Definition: A powerful node (often connected to a wired network or cloud) that
collects data from sensor nodes or cluster heads.
 Function:
o Acts as a gateway between WSN and end-users or the internet.
o May perform additional data processing or visualization.

o Sends commands/configurations to sensor nodes.

 Role: Central data collection and control point.

4. Power Source (Battery / Energy Harvester)

 Definition: Provides energy to sensor nodes.

 Function:
o Power the sensing, processing, and communication modules.
o May include energy harvesting (solar, vibration) in some WSNs.
 Role: Enables autonomous operation of sensor nodes, often a limiting factor.
 47

5. Communication Medium
 Definition: Wireless link over which sensor nodes communicate (e.g., IEEE 802.15.4,
ZigBee, LoRa).
 Function:

o Enable multi-hop or direct transmission of data.

 Role: Supports data transfer across nodes and to the base station.

6. Processing Unit (Microcontroller)

 Definition: Onboard computer that processes sensed data.

 Function:
o Execute routing and sensing algorithms.
o Control power management.
 Role: Intelligence center of the sensor node.

7. Memory
 Definition: Stores programs and sensor readings.
 Function:
o Temporarily or permanently hold collected data.
 Role: Supports local decision-making and buffering.

🔶 Summary of Roles

Component Role

Sensor Node Sensing and local data processing

Cluster Head Aggregation and transmission to base station

Base Station Central control and data sink

Power Source Energy supply for sensor node operation

Communication Medium Wireless transmission support

 48

Component Role

Processing Unit Logic and control of sensor node

Memory Program and data storage

Here’s a detailed BTech-level answer (for a 14-mark exam) to the question:

What are the Key Hardware and Software Components of a Sensor Node in a Wireless
Sensor Network (WSN)?

✅ Introduction
A sensor node is the fundamental building block of a Wireless Sensor Network (WSN). It is
a small, low-power embedded system capable of sensing, computing, and communicating.
Each sensor node is composed of hardware and software components that allow it to
monitor physical phenomena, process data, and transmit the results.

🔷 Key Hardware Components of a Sensor Node

1. Sensing Unit (Sensor)
 Function: Detects physical phenomena (e.g., temperature, humidity, motion, light,
gas).
 Examples:
o DHT11 (temperature & humidity)

o MQ-135 (gas sensor)

o LDR (light sensor)
 Output: Analog or digital signal representing the sensed parameter.

2. Analog-to-Digital Converter (ADC)

 Function: Converts the analog signals from the sensors into digital form so that the
microcontroller can process it.
 Importance: Acts as an interface between analog sensors and digital processor.

3. Processing Unit (Microcontroller / Microprocessor)

 Function:
 49

o Processes sensor data

o Executes routing protocols
o Controls peripherals and power usage

 Examples:
o Microcontroller units (MCUs): Atmega328, MSP430, ARM Cortex-M
o Microprocessors: Raspberry Pi (in high-end sensor nodes)
 Role: Brain of the sensor node.

4. Memory Unit
 Types:
o Program Memory (ROM/Flash) – Stores the firmware.
o Data Memory (RAM) – Used for runtime operations and buffering sensor
data.
 Function: Temporary and permanent storage for code and data.
 Example: 32 KB Flash and 2 KB SRAM in Atmega328.

5. Communication Unit (Transceiver)

 Function: Transmits and receives data wirelessly from/to other sensor nodes or the
base station.
 Examples:
o ZigBee (IEEE 802.15.4), LoRa, Wi-Fi, Bluetooth

 Module Examples:
o CC2420, nRF24L01, ESP8266 (Wi-Fi), RFM95 (LoRa)

6. Power Supply Unit

 Function: Supplies energy to the node components.

 Sources:
o Batteries (AA, Li-ion)
o Energy harvesting (solar cells, vibration)
 Importance: Determines node lifespan and energy efficiency.
 50

7. Optional Components
 GPS Module: For location-aware sensing

 Actuators: For control applications (e.g., turning on a pump)

 External Interface: USB, UART for programming and debugging

🔶 Key Software Components of a Sensor Node

1. Operating System / Runtime Environment
 Function: Provides services for scheduling, resource management, and hardware
abstraction.
 Examples:

o TinyOS: Lightweight OS for embedded WSN

o Contiki OS: Supports IPv6 and multi-threading
o RIOT OS, FreeRTOS

2. Network Protocol Stack

 Layers and Functions:

o Application Layer: Sensing logic and commands
o Transport Layer: Reliable communication (e.g., UDP, TCP variants)
o Network Layer: Routing protocols like AODV, DSR
o Data Link Layer: MAC protocols (CSMA/CA, TDMA)

o Physical Layer: Modulation, signal transmission

3. Sensor Drivers
 Function: Interfaces between OS and physical sensor hardware.
 Purpose: Convert sensor input into usable data for applications.

4. Middleware / Services
 Function: Provides services like time synchronization, localization, data
aggregation, etc.
 51

5. Application Software
 Function: Executes the node's sensing tasks, data processing, and communication
logic.
 Examples: Environment monitoring, intruder detection, fire alert system

✅ Summary Table

Component Type Function

Sensor Hardware Sense physical parameters

ADC Hardware Convert analog data to digital

Microcontroller Hardware Process data and control node

Memory Hardware Store program and runtime data

Transceiver Hardware Wireless communication

Power Supply Hardware Provide energy

OS (e.g., TinyOS) Software System-level task management

Network Protocols Software Communication and routing

Sensor Drivers Software Interface sensor hardware with applications

Application Logic Software Perform specific sensing and reporting tasks

To calculate the total data transmitted per minute in megabytes (MB) by a Wireless Sensor
Network (WSN) with the given parameters:

📌 Given:
 Number of sensor nodes = 100
 Packets transmitted per second per node = 10 packets

 Size of each packet = 100 bytes

 Time = 1 minute = 60 seconds
 52

✅ Step-by-step Calculation:
1. Packets transmitted per second (by all nodes):
100 nodes×10 packets/sec=1000 packets/sec100 \text{ nodes} \times 10 \text{
packets/sec} = 1000 \text{ packets/sec}
2. Packets transmitted per minute:
1000 packets/sec×60 sec=60,000 packets/min1000 \text{ packets/sec} \times 60 \text{
sec} = 60,000 \text{ packets/min}

3. Total data per minute in bytes:

60,000 packets×100 bytes/packet=6,000,000 bytes60,000 \text{ packets} \times 100 \text{
bytes/packet} = 6,000,000 \text{ bytes}
4. Convert bytes to megabytes (MB):
 1 MB=1,048,576 bytes1 \text{ MB} = 1,048,576 \text{ bytes} (binary MB)
 Alternatively, use decimal MB if preferred: 1 MB=1,000,000 bytes1 \text{ MB} =
1,000,000 \text{ bytes}

➤ Using decimal MB (common for network data):

6,000,0001,000,000=6 MB per minute\frac{6,000,000}{1,000,000} = \boxed{6 \text{ MB
per minute}}

➤ Using binary MB (as used in memory/storage):

6,000,0001,048,576≈5.72 MB per minute\frac{6,000,000}{1,048,576} \approx \boxed{5.72
\text{ MB per minute}}

✅ Final Answer:
 Total data transmitted per minute = 6 MB (decimal)
 Or ≈ 5.72 MB (binary)

Here is a detailed BTech-level answer (14 marks) for your Ad Hoc and Wireless Sensor
Networks exam, discussing the MAC (Medium Access Control) layer protocols used in
Wireless Sensor Networks (WSNs) and a comparison between TDMA, FDMA, and CSMA-
based protocols.

✅ MAC Layer Protocols in Wireless Sensor Networks (WSNs)

🔷 Introduction
 53

The MAC layer in WSNs is responsible for coordinating access to the shared wireless
communication channel. It plays a critical role in:
 Minimizing energy consumption
 Avoiding collisions
 Providing fairness

 Supporting scalability
Due to the energy-constrained nature of WSNs, MAC protocols are designed to be energy-
efficient while ensuring reliable communication.

🔷 Types of MAC Protocols in WSNs

1. Contention-Based Protocols
 Based on random access techniques

 Example: CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

 Nodes contend for the medium
 Advantages: Simple, no synchronization
 Disadvantages: Collisions, idle listening, overhearing
2. Schedule-Based Protocols

 Use a predefined schedule for communication

 Examples: TDMA (Time Division Multiple Access), FDMA (Frequency Division
Multiple Access)
 Reduce collisions and idle listening
 Advantages: Energy efficient
 Disadvantages: Need synchronization, overhead in maintaining schedules

✅ Comparison: TDMA vs FDMA vs CSMA-Based MAC Protocols

Feature TDMA FDMA CSMA

Time Division Multiple Frequency Division Carrier Sense Multiple

Full Form
Access Multiple Access Access

Channel divided into Channel divided into Sense channel before

Access Mechanism
time slots frequency bands transmission
 54

Feature TDMA FDMA CSMA

Required (for
Required (to align
Synchronization frequency Not required
time slots)
coordination)

High (no idle listening Low (idle listening &

Energy Efficiency High (no contention)
or collision) collision)

Bandwidth Efficient if nodes are Less efficient (fixed Efficient under low
Utilization active freq per node) traffic

Limited (needs slot Poor (limited Good (no global

Scalability
assignment) frequency bands) coordination)

Predictable but can be Low delay (if freq Variable, can be high
Delay
high available) under load

None (slots are None (frequencies are Possible (if two nodes
Collision Possibility
exclusive) exclusive) transmit at once)

Implementation High (needs Medium (requires

Low
Complexity synchronization) filters, freq tuning)

Used in specialized
Examples in WSNs SMACS, TRAMA S-MAC, B-MAC, T-MAC
systems

🔷 Detailed Explanation

🔹 TDMA-Based MAC Protocols

 Each node is assigned a specific time slot for communication.
 No two nodes transmit in the same slot ⇒ no collision.
 Example Protocols: TRAMA, LEACH-TDMA
 Energy Saving: Nodes sleep when it's not their time slot.

🔹 FDMA-Based MAC Protocols

 Assigns separate frequency bands to each node or link.

 Used when hardware supports multiple frequency operation.

 Less common in WSNs due to cost and complexity.
 Not scalable as frequency bands are limited.

🔹 CSMA-Based MAC Protocols

 55

 Nodes sense the channel before transmission.

 If the channel is idle ⇒ transmit; else wait.
 Example Protocols: S-MAC, T-MAC, B-MAC

 Includes features like duty cycling to save energy.

🔷 When to Use Which Protocol?

Scenario Suitable MAC Protocol

High traffic, tight scheduling TDMA

Low traffic, simple deployment CSMA

Multiple channels available FDMA

Energy is a critical constraint TDMA or hybrid

Dynamic topology CSMA

✅ Conclusion
 TDMA and FDMA are energy-efficient but require synchronization and are complex
to implement.

 CSMA-based protocols are simple and scalable but less energy-efficient due to
collisions and idle listening.
 The choice of MAC protocol depends on the application requirements, energy
constraints, and network conditions.

Here’s a detailed BTech-level (14-mark) answer discussing the different types of security
attacks in Ad Hoc and Wireless Sensor Networks (WSNs) and how these attacks can be
mitigated — aligned with your exam syllabus on Ad Hoc and Wireless Networks.

✅ Security Attacks in Ad Hoc and Wireless Sensor Networks

🔷 Introduction
Ad hoc and wireless sensor networks are decentralized, infrastructure-less, and resource-
constrained, making them highly vulnerable to security attacks. Attacks can occur at any
layer of the network and may target confidentiality, integrity, availability, and
authentication.
 56

🔶 Classification of Security Attacks

Security attacks in wireless networks can be broadly classified as:
1. Passive Attacks

2. Active Attacks

🔹 1. Passive Attacks
These attacks involve eavesdropping or monitoring of data transmissions without
modifying the data.
a. Eavesdropping
 The attacker silently listens to wireless communication to steal sensitive
information.
 Target: Confidentiality

 Mitigation:
o Encryption (e.g., AES, ECC)
o Secure key management
b. Traffic Analysis
 Attacker observes communication patterns to infer network topology or detect
critical nodes.
 Mitigation:

o Dummy traffic generation

o Random routing techniques

🔹 2. Active Attacks
These involve modification, fabrication, or disruption of communication.
a. Sybil Attack

 A single node presents multiple fake identities to disrupt routing, voting, or data
aggregation.

 Mitigation:
o Identity verification using certificates or physical location
 57

o Trust-based mechanisms
b. Wormhole Attack
 Two malicious nodes establish a tunnel between distant parts of the network,
misleading routing protocols.
 Mitigation:

o Packet leashes (geographic/temporal)

o Distance and hop-count checking
c. Blackhole Attack
 A malicious node advertises itself as having the shortest route to the destination
and then drops all packets.
 Mitigation:

o Route validation techniques

o Multiple route replies
o Trust-based AODV enhancements
d. Sinkhole Attack
 Attacker attracts traffic by advertising a high-quality route and then drops or
manipulates the data.
 Mitigation:

o Use of geographic routing

o Monitoring node behavior
e. Hello Flood Attack
 An attacker sends HELLO packets with high power to convince all nodes it is a
neighbor.
 Nodes try to route through it and fail.
 Mitigation:

o Bidirectional link verification

o Signal strength check
f. Denial of Service (DoS)
 Flooding the network with traffic or jamming the channel to make services
unavailable.
 Mitigation:
 58

o Rate-limiting techniques
o Use of secure MAC protocols
o Spread spectrum or frequency hopping

g. Replay Attack
 Attacker replays old packets to create confusion or rerun an old session.
 Mitigation:
o Timestamping and nonces
o Session token validation

h. Selective Forwarding
 Malicious node forwards only certain packets while dropping others.
 Mitigation:
o Watchdog mechanisms
o Multipath routing

🔷 Summary Table of Attacks and Countermeasures

Attack Type Effect Mitigation

Eavesdropping Passive Data confidentiality breach Encryption, key management

Traffic Analysis Passive Network inference Dummy traffic, random routing

Trusted certification, location

Sybil Attack Active Identity spoofing
checks

Packet leashes, hop-count

Wormhole Attack Active Route disruption
verification

Blackhole Attack Active Packet dropping Multipath routing, trust metrics

Attracting and dropping Behavior monitoring, secure

Sinkhole Attack Active
data routing

Hello Flood Attack Active Routing confusion Verify link bidirectionality

Network service
DoS / Jamming Active Rate control, frequency hopping
unavailability

Replay Attack Active Reuse of old packets Timestamps, sequence numbers

 59

Attack Type Effect Mitigation

Selective
Active Partial data loss Watchdog nodes, redundancy
Forwarding

Here is a detailed BTech-level answer (14-mark format) on Intrusion Detection Systems

(IDS) in Ad Hoc Networks, including their functionality, working, and types — aligned with
your Ad Hoc and Wireless Sensor Networks syllabus.

✅ Intrusion Detection Systems (IDS) in Ad Hoc Networks

🔷 1. Introduction
An Intrusion Detection System (IDS) is a security mechanism designed to monitor, detect,
and respond to unauthorized or malicious activity within a network. In Ad Hoc Networks,
which are dynamic, decentralized, and infrastructure-less, IDS plays a critical role due to
the lack of centralized control and the vulnerability to attacks like blackhole, wormhole,
DoS, etc.

🔷 2. Why IDS in Ad Hoc Networks?

 Traditional security measures like firewalls are not applicable.
 Nodes can join/leave dynamically ⇒ need for distributed and adaptive security.
 Routing protocols can be easily exploited by malicious nodes.
 Physical access to nodes ⇒ risk of compromise.

🔷 3. Goals of IDS in Ad Hoc Networks

 Detect malicious behaviors like dropping packets, spoofing, and false routing.
 Trigger alerts or countermeasures.
 Maintain network performance and trustworthiness.
 Ensure availability, confidentiality, and integrity.

✅ 4. Architecture of IDS in Ad Hoc Networks

IDS in Ad Hoc networks usually consists of the following components:
 60

Component Description

Monitoring Agent Observes activities like packet transmission, routing behavior, etc.

Analysis Engine Analyzes data to detect anomalies or signature-based attacks

Response System Triggers alarms, alerts nodes, or initiates preventive actions

Knowledge Base Stores signatures, normal behavior patterns, and known attack profiles

🔷 5. Types of IDS in Ad Hoc Networks

🔹 A. Based on Detection Method

Type Description

Signature-Based Detects intrusions by matching behavior against known attack

IDS signatures

Detects deviations from normal behavior (e.g., abnormal routing

Anomaly-Based IDS
pattern)

Specification-Based Uses pre-defined rules/policies to detect deviations

🔹 B. Based on Deployment

Type Description

Standalone IDS Each node independently detects intrusions

Distributed IDS Nodes collaborate and share intrusion-related information

Cooperative IDS Nodes vote or agree on intrusions and take collective action

Hierarchical IDS Used in clustered networks; cluster heads perform detection

🔹 C. Based on Layer of Detection

Layer Example Intrusions

Application Layer Malware behavior, unauthorized access

Transport Layer Session hijacking, SYN flooding

Network Layer Routing attacks (blackhole, wormhole)

 61

Layer Example Intrusions

MAC Layer Collision attacks, jamming

🔷 6. Working of an IDS (Example: Watchdog + Pathrater)

Scenario: Detecting Blackhole Attack in an Ad Hoc Network
1. Watchdog Mechanism
o Each node monitors its neighbor to ensure it forwards packets correctly.
o If a node does not forward, it is marked as suspicious.

2. Pathrater
o Maintains ratings for each node based on past behavior.
o Selects routing paths that avoid low-rated (possibly malicious) nodes.
3. Alerting System
o If threshold is exceeded, alarm is raised.

o Node may be isolated from network communication.

✅ 7. Challenges in IDS for Ad Hoc Networks

Challenge Description

Lack of Central
Detection must be fully distributed
Authority

Dynamic Topology Nodes move ⇒ behavior varies over time

Resource Constraints Nodes have limited power, memory, CPU

False Positives Legitimate behavior may appear anomalous

Multiple malicious nodes working together can mislead detection

Colluding Attackers
mechanisms

🔷 8. Countermeasures and Improvements

 Use of reputation and trust models to evaluate node behavior
 Lightweight machine learning for anomaly detection
 Cross-layer IDS that consider parameters from multiple protocol layers
 62

 Mobile agent-based IDS to traverse network and collect security data

✅ How TESLA Ensures Secure Broadcast Authentication

1. Introduction
TESLA is a lightweight, efficient protocol designed to provide authenticated broadcast in
resource-constrained environments like wireless sensor networks and ad hoc networks. It
addresses the challenge that traditional public-key-based authentication is too expensive
for these networks.

2. Key Idea of TESLA

TESLA provides asymmetric authentication using symmetric cryptographic primitives by
introducing the concept of delayed key disclosure and time synchronization.

3. Core Components

Component Description

Key Chain A sequence of secret keys generated using a one-way function.

Time Synchronization Loose synchronization between sender and receivers.

Delayed Key Keys are revealed after a delay to authenticate previous

Disclosure messages.

4. How TESLA Works

Step 1: Key Chain Generation

5. The sender creates a key chain K0,K1,...,KnK_0, K_1, ..., K_nK0,K1,...,Kn where
each key is generated by applying a one-way function FFF:

Ki=F(Ki+1)K_i = F(K_{i+1})Ki=F(Ki+1)

6. The last key KnK_nKn is chosen randomly, and earlier keys are derived backward by
applying FFF.
7. Because FFF is one-way, it’s computationally infeasible to find Ki+1K_{i+1}Ki+1
from KiK_iKi.
8.
 63

Step 2: Sending Messages with MAC

 Time is divided into intervals (epochs).
 In each interval iii, the sender uses key KiK_iKi to compute a Message
Authentication Code (MAC) for all messages sent during that interval.
 However, the key KiK_iKi is not revealed immediately.

Step 3: Delayed Key Disclosure

 After a fixed delay ddd intervals, the sender discloses key KiK_iKi to the receivers.
 Upon receiving KiK_iKi, receivers can:
o Verify KiK_iKi by applying FFF repeatedly until it matches a previously
known anchor K0K_0K0.

o Use KiK_iKi to verify the MAC of messages sent during interval iii.

Step 4: Authentication and Security

 Since keys are disclosed only after the messages are received, attackers cannot
forge MACs in real-time.
 The receivers buffer messages until key disclosure.
 Loose time synchronization ensures the receiver knows when to expect the key.

 TESLA relies on the one-way property of FFF to prevent attackers from predicting
future keys.

5. Advantages of TESLA

Advantage Explanation

Efficient Uses symmetric key cryptography (fast and lightweight)

Loss Tolerant Works even if some packets or keys are lost

Scalable Suitable for large broadcast groups

Asymmetric Security Provides broadcast authentication without public key ops

6. Limitations
 Requires loose time synchronization.
 64

 Requires buffering of packets until key disclosure.

 Introduces authentication delay due to key disclosure.

7. Summary

Step Action

Key Chain Creation Generate keys with one-way function

Message Transmission Send messages with MAC using key KiK_iKi

Key Disclosure Reveal key KiK_iKi after delay

Verification Receiver verifies key and MAC

Here’s a detailed BTech-level answer on Secure Routing Protocols in Ad Hoc Networks,

explaining their need, types, working principles, and examples — aligned with your Ad
Hoc and Wireless Sensor Networks syllabus.

✅ Secure Routing Protocols in Ad Hoc Networks

🔷 1. Introduction
Routing in Ad Hoc Networks is challenging due to:
 Dynamic topology,
 Lack of centralized infrastructure,
 Vulnerability to various attacks such as blackhole, wormhole, Sybil, and routing
table poisoning.

Traditional routing protocols (like AODV, DSR) do not provide built-in security, so secure
routing protocols have been developed to protect routing information and ensure
trustworthy communication.

🔷 2. Why Secure Routing?

Without security:
 Malicious nodes can disrupt routing,
 Data packets can be dropped, misrouted, or altered,
 Network can suffer from Denial of Service (DoS),
 65

 The overall network performance and reliability deteriorate.

Secure routing protocols aim to detect, prevent, and mitigate routing attacks while
ensuring:
 Authentication of nodes,
 Integrity of routing messages,

 Confidentiality of routing information (in some protocols),

 Availability of routes.

🔷 3. Key Features of Secure Routing Protocols

Feature Description

Authentication Verify the identity of nodes and routing info

Data Integrity Ensure messages are not altered during transit

Non-repudiation Prevent nodes from denying their participation

Confidentiality Protect routing information from eavesdropping

Availability Protect routing from DoS and blackhole attacks

🔷 4. Classification of Secure Routing Protocols

A. Cryptographic Approaches
 Use digital signatures, hash chains, and encryption to protect routing messages.
 Example: ARAN (Authenticated Routing for Ad hoc Networks)
B. Trust-based Approaches

 Use trust metrics and reputation to select trustworthy nodes for routing.
 Example: CONFIDANT Protocol
C. Intrusion Detection Based Approaches
 Combine routing with IDS to detect malicious activities during routing.
 Example: IDS-enhanced versions of AODV, DSR

🔷 5. Working of Some Popular Secure Routing Protocols

1. ARAN (Authenticated Routing for Ad Hoc Networks)
 66

 Uses public key cryptography for node authentication.

 Nodes obtain certificates from a trusted authority (before deployment).
 Route discovery includes:

o Source broadcasts a signed route request (RREQ).

o Intermediate nodes verify signatures before forwarding.
o Destination sends back a signed route reply (RREP).
 Ensures message integrity and authentication.
 Prevents:

o Unauthorized participation,
o Modification or fabrication of routing messages.

2. SAODV (Secure AODV)

 Extends AODV by adding digital signatures and hash chains.

 Protects against:
o Modification of hop counts (using hash chains),
o Forgery of routing messages (using signatures).
 Provides authentication of routing messages while maintaining AODV’s reactive
nature.

3. CONFIDANT Protocol

 Uses trust and reputation to detect misbehaving nodes.

 Nodes monitor neighbors and report misbehavior.
 Isolation of malicious nodes by avoiding them during routing.
 Focuses on self-policing without requiring centralized authority.

🔷 6. General Steps in Secure Routing

1. Route Discovery:
o Secure broadcast of route requests with cryptographic protection.
2. Route Reply:
 67

o Authenticated replies from destination or intermediate nodes.

3. Route Maintenance:
o Monitor routes for anomalies or attacks.

o Rekey or reroute when malicious activity detected.

4. Attack Detection and Response:
o Use IDS or trust models to detect attacks.
o Isolate malicious nodes.

✅ 7. Summary Table

Protocol Approach Security Features Limitations

High computation, needs

ARAN Cryptographic Authentication, integrity via PKI
trusted CA

Hop count protection, message

SAODV Cryptographic Computational overhead
authentication

Trust evaluation, reputation- Trust establishment

CONFIDANT Trust-based
based routing complexity

IDS- Intrusion detection integrated Detection accuracy,

IDS + Routing
Enhanced with routing resource usage

Here’s a detailed BTech-level comparison between Wireless Ad Hoc Networks (WANETs)

and Wireless Sensor Networks (WSNs) — perfect for your exam:

✅ Differences between Wireless Ad Hoc Networks and Wireless Sensor Networks

Wireless Ad Hoc Network

Aspect Wireless Sensor Network (WSN)
(WANET)

A self-configuring network of
A network of spatially distributed
mobile nodes connected
Definition sensor nodes that monitor
wirelessly without fixed
physical/environmental conditions.
infrastructure.
 68

Wireless Ad Hoc Network

Aspect Wireless Sensor Network (WSN)
(WANET)

Enable peer-to-peer Collect and transmit sensor data

Primary Purpose communication between (temperature, pressure, etc.) to a base
mobile devices. station or sink node.

Nodes are usually mobile, Nodes are mostly static or low

Node
capable of acting as routers and mobility, resource-constrained (low
Characteristics
hosts. power, memory).

Network Dynamic topology due to node Generally static topology; nodes are
Topology mobility. often fixed in location.

Nodes perform routing, data

Node Nodes mainly sense data, process it
forwarding, and application
Functionality minimally, and forward it.
tasks.

Energy Moderate energy constraints Highly energy-constrained; battery life

Constraints (depending on devices). is critical.

Peer-to-peer or multi-hop
Communication Mostly many-to-one (sensor nodes to
communication among all
Patterns sink/base station).
nodes.

Use ad hoc routing protocols Use specialized energy-efficient

Routing Protocols
like AODV, DSR, OLSR. routing (data-centric, hierarchical).

Security Focus on node authentication, Focus on data confidentiality,

Concerns secure routing. integrity, and node compromise.

Military communication,
Deployment Environmental monitoring, health
disaster recovery, mobile
Scenarios care, industrial automation.
conferencing.

Moderate scalability; number of

Typically large-scale deployments
Scalability nodes is limited by routing
(hundreds or thousands of nodes).
complexity.

Data
Higher data rates to support Low data rates focused on periodic
Transmission
diverse applications. sensor readings.
Rate

Summary
 69

Wireless Ad Hoc Networks Wireless Sensor Networks

Mobile, peer-to-peer communication Mostly static, sensor data collection

Nodes act as routers and hosts Nodes are mainly sensing devices

Focus on connectivity and routing Focus on energy efficiency and data aggregation

Here’s a detailed BTech-level explanation of MAC protocols used in Wireless Sensor

Networks (WSNs), including types, working principles, and examples:

✅ MAC Protocols Used in Wireless Sensor Networks (WSNs)

1. Introduction
The Medium Access Control (MAC) layer in WSNs manages how sensor nodes access the
shared wireless medium. It plays a crucial role in:
 Saving energy (very important in WSNs),
 Avoiding collisions,
 Increasing throughput and fairness,

 Reducing latency.
Due to the resource constraints (battery, processing power) in sensor nodes, WSN MAC
protocols are designed differently from traditional wireless networks.

2. Types of MAC Protocols in WSNs

WSN MAC protocols can be broadly classified into three categories:

Type Description Examples

1. Contention- Nodes compete to access the medium; CSMA/CA (like IEEE 802.11), S-
based no fixed schedule. MAC, T-MAC

2. Schedule- Medium access is scheduled to avoid

TDMA, FDMA, CDMA
based collisions.

3. Hybrid Combine contention and schedule- Z-MAC, IEEE 802.15.4 (Beacon

Protocols based approaches. mode)
 70

3. Contention-Based MAC Protocols

Characteristics:
 Nodes use carrier sensing before transmission (CSMA/CA).

 Low latency and adaptive to traffic changes.

 Energy wasted in idle listening, collisions, and overhearing.
Example Protocols:
 S-MAC (Sensor-MAC):
o Uses periodic sleep and listen cycles to save energy.

o Nodes synchronize schedules with neighbors.

o Uses RTS/CTS to reduce collisions.
 T-MAC (Timeout-MAC):
o Improves S-MAC by dynamically adjusting sleep times based on traffic.
o If no activity is detected for a timeout period, node sleeps.

4. Schedule-Based MAC Protocols

Characteristics:
 Time divided into slots, nodes transmit in assigned slots.
 Avoids collisions and overhearing.

 Highly energy-efficient but requires strict synchronization.

 Can cause higher latency if slot is missed.
Examples:
 TDMA (Time Division Multiple Access):
o Each node assigned specific time slots.

o Energy efficient, collision-free.

o Needs global synchronization.
 FDMA (Frequency Division Multiple Access):
o Nodes assigned different frequency bands.
o Less common due to hardware complexity.
 CDMA (Code Division Multiple Access):
 71

o Uses unique spreading codes per node.

o Complex, less energy efficient for sensor nodes.

5. Hybrid MAC Protocols

Characteristics:
 Combine strengths of contention and schedule-based protocols.
 Adaptive to traffic conditions.
Examples:

 Z-MAC (Zebra MAC):

o Uses TDMA during high contention.
o Uses CSMA during low contention.
o Improves channel utilization and energy efficiency.
 IEEE 802.15.4 (Beacon-enabled mode):

o Uses superframes with active and inactive periods.

o Supports contention and contention-free periods.

6. Summary Table

Protocol Type Advantages Disadvantages Example

Contention- Simple, flexible, low Energy wasted in collisions, idle

S-MAC, T-MAC
based latency listening

Schedule- Collision-free, energy Requires synchronization, less TDMA, FDMA,

based efficient flexible CDMA

Adaptive to traffic, Z-MAC, IEEE

Hybrid Complexity
balanced 802.15.4

7. Conclusion
Choosing the right MAC protocol in WSN depends on the application needs:

 For low traffic and energy efficiency, schedule-based or hybrid protocols are
preferred.
 For variable or bursty traffic, contention-based protocols offer flexibility.
 72

Here’s a clear, detailed comparison between Wireless Ad Hoc Networks (WANETs) and
Wireless Sensor Networks (WSNs) for your BTech syllabus:

Difference Between Wireless Ad Hoc Network and Wireless Sensor Network

Wireless Ad Hoc Network

Aspect Wireless Sensor Network (WSN)
(WANET)

Enable communication between

Monitor physical/environmental
Purpose mobile nodes without
conditions via sensors.
infrastructure.

Nodes are usually mobile and Nodes are mostly static or have very
Node Mobility
can move freely. limited mobility.

Nodes have more processing

Nodes are resource-constrained
Node Capabilities power, memory, and energy
(limited energy, memory, processing).
resources.

Dynamic topology changes

Mostly static or slowly changing
Topology frequently due to node
topology.
movement.

Communication Peer-to-peer communication Many-to-one (sensor nodes to

Pattern among nodes. sink/base station) communication.

Uses routing protocols like

Uses energy-efficient, data-centric
Routing Protocols AODV, DSR to find paths
routing protocols.
dynamically.

Energy Highly energy-constrained, with focus

Moderate energy constraints.
Constraints on battery conservation.

Can handle varied types and Mostly periodic sensor data with low
Data Traffic
volumes of data. data rate.

Focus on secure routing and Focus on data confidentiality,

Security Concerns
authentication. integrity, and node compromise.

Deployment Military, disaster recovery, Environmental monitoring,

Scenarios mobile communication. healthcare, industrial automation.

Moderate scale, typically fewer Large scale, often hundreds or

Scale
nodes. thousands of nodes.
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