Computer Networks 2022

Group A

1. What is the difference between internet and intranet?

Ans: The primary difference between the internet and an intranet lies in their scope,
accessibility, and purpose. Here’s a detailed comparison:

Internet

1. Scope:

 Global network connecting millions of private, public, academic,

business, and government networks.

2. Accessibility:

 Publicly accessible to anyone with an internet connection.

 No restrictions on who can access the internet (though specific content
can be restricted by governments or service providers).

3. Purpose:

 Facilitates worldwide communication and access to information.

 Supports a wide array of services such as email, web browsing, social
media, online banking, and e-commerce.

4. Security:

 Generally less secure due to its open nature.

 Requires robust security measures like firewalls, encryption, and
antivirus software to protect data and privacy.

5. Content:

 Vast and diverse range of content from numerous sources.

 Includes websites, forums, social media platforms, online stores, and
more.

Intranet

1. Scope:
  Private network used within an organization (e.g., a corporation, school,
or government agency).

2. Accessibility:

 Restricted to authorized users within the organization.

 Access is typically controlled through login credentials and network
permissions.

3. Purpose:

 Facilitates internal communication, collaboration, and information

sharing within an organization.
 Often used for hosting internal applications, databases, and
collaboration tools like wikis and project management systems.

4. Security:

 More secure due to controlled access.

 Often protected by additional layers of security such as VPNs (Virtual
Private Networks) and internal firewalls.

5. Content:

 Content is specific to the organization’s needs and is typically created

and maintained by its employees.
 Includes internal documents, employee directories, project
management tools, and corporate policies.

Key Points of Comparison

 Accessibility: Internet is public; intranet is private and restricted.

 Scope: Internet is global; intranet is confined to an organization.
 Purpose: Internet provides a platform for global communication and services;
intranet supports internal organizational needs.
 Security: Internet has higher security risks; intranet has controlled access and
generally higher security within its scope.
 Content: Internet content is diverse and extensive; intranet content is tailored
to an organization's specific requirements.
2. What is flow control?

Ans: Flow control is a technique used in computer networks and data communication to
manage the rate at which data is transmitted between a sender and a receiver. Its primary
goal is to ensure that the sender does not overwhelm the receiver with too much data at
once, which can lead to data loss, congestion, or inefficient use of network resources. Flow
control is essential for maintaining data integrity and optimal performance in communication
systems.

3. What is the function of relays in a switch?

Ans: Relays play a crucial role in switches, particularly in electrical and networking
contexts. Here’s an explanation of their functions in both domains:

Electrical Switches

In electrical switches, relays are used to control high-power circuits with low-power
signals. Their primary functions include:

1. Isolation:

 Relays provide electrical isolation between the control circuit (low

voltage) and the load circuit (high voltage). This ensures that the
control side is protected from high voltages and currents.

2. Switching High Current Loads:

 Relays can switch high-current loads with a small control signal. This is
essential in applications where delicate control circuits need to manage
powerful devices, such as motors, lights, and heating elements.

3. Multiplexing:

 Relays can be used to control multiple circuits with a single relay. For
instance, one relay can switch between different power sources or
direct the current to multiple output circuits.

4. Automation and Safety:

 Relays are fundamental in automated systems. They allow the

automation of processes by controlling the flow of electricity based on
preset conditions. Additionally, they enhance safety by enabling
emergency shutdowns and isolating faulty sections of a circuit.

Networking Switches
In networking switches, relays, although not typically used in modern digital switches,
can have specific roles in certain types of network equipment. Their functions include:

1. Power Control:

 Relays can be used to manage power distribution within the switch,

turning on and off different components or entire sections of the
switch as needed.

2. Signal Routing:

 In some older or specialized networking equipment, relays might be

used to physically route signals between different network paths,
especially in hybrid systems that combine both electronic and
mechanical components.

3. Protection and Fault Isolation:

 Relays can be used for protecting network equipment by isolating

faulty sections. If a fault is detected, a relay can disconnect the affected
part to prevent damage to the rest of the system.

Modern Networking Context

In modern digital networking equipment, relays are largely replaced by solid-state

components such as transistors and integrated circuits. These components perform
similar functions but are faster, more reliable, and more efficient than mechanical
relays. However, the basic principles of controlling and routing electrical signals
remain relevant.

Summary

 Electrical Switches: Relays control high-power circuits with low-power

signals, provide isolation, manage high-current loads, enable multiplexing,
and enhance automation and safety.
 Networking Switches: Although less common in modern equipment, relays
can manage power control, signal routing, and fault isolation.

In both contexts, the fundamental role of a relay is to use a small control signal to
manage a larger electrical load or to switch between different circuits, thereby
enabling more complex control and automation in electrical and networking systems.
4. What is critical angle?

Ans : The critical angle is the minimum angle of incidence at which total internal reflection
occurs. When light is incident at this angle, it refracts along the boundary between the two
media and does not exit the original medium. The critical angle is a concept in optics that
pertains to the behavior of light as it passes from one medium to another, specifically when
light travels from a medium with a higher refractive index to one with a lower refractive
index.

5. What is piggybacking?

Ans: Piggybacking is a term used in networking and wireless communication to

describe two different concepts:

1. Networking (Data Communication)

In data communication, piggybacking refers to the technique of combining

acknowledgment of received data packets with the transmission of data packets. This
is used in bidirectional data communication to improve efficiency. Here’s how it
works:

Process
 Acknowledge and Send Data Together: Instead of sending a separate
acknowledgment packet for each received data packet, the acknowledgment
information is included (piggybacked) with the next outgoing data packet.
 Two-Way Communication: In a two-way communication link, both sides are often
sending and receiving data. By piggybacking acknowledgments onto outgoing data
packets, the number of packets sent over the network is reduced.
Benefits
 Reduced Overhead: Fewer packets mean less overhead, reducing the total amount
of data transmitted and improving network efficiency.
 Improved Efficiency: Combining data and acknowledgment packets helps to make
better use of available bandwidth.
Example
Consider two devices, A and B, communicating over a network:

 Device A sends a data packet to Device B.

 Device B receives the packet and prepares to send data back to Device A.
 Instead of sending an acknowledgment packet separately, Device B includes the
acknowledgment for the received packet within its outgoing data packet.

2. Wireless Communication (Wi-Fi)

In the context of wireless communication, particularly Wi-Fi, piggybacking has a
different connotation. It refers to the unauthorized access of someone else's wireless
network. Here’s a breakdown:

Process
 Unauthorized Access: An individual connects to a wireless network without
permission, typically because the network is unsecured or the password has been
obtained without the owner’s consent.
 Use of Resources: The unauthorized user utilizes the bandwidth and network
resources of the legitimate owner.
Implications
 Security Risks: The legitimate owner’s network and data may be exposed to security
risks, including data breaches or malware infections.
 Bandwidth Theft: The unauthorized user consumes bandwidth, potentially slowing
down the network for legitimate users.
 Legal and Ethical Issues: Piggybacking on someone else’s Wi-Fi without permission
is generally considered unethical and may be illegal in many regions.
Prevention
 Securing Networks: To prevent piggybacking, network owners can secure their Wi-Fi
networks using strong passwords, encryption methods like WPA3, and additional
security measures such as MAC address filtering.

Summary
 In Networking (Data Communication): Piggybacking refers to the technique of
combining acknowledgment information with outgoing data packets to improve
efficiency and reduce overhead.
 In Wireless Communication (Wi-Fi): Piggybacking refers to the unauthorized access
and use of someone else's wireless network, posing security risks and ethical
concerns.

Both concepts highlight different aspects of improving efficiency in data

communication and addressing security in wireless networks.

6. What is stuffing?

Ans: "Stuffing" refers to techniques used in data communication to ensure that

special bit patterns or sequences used for control purposes do not appear in the
actual data being transmitted. Here are two main types of stuffing:

1. Bit Stuffing

Bit stuffing is used in protocols where a specific bit pattern signifies the start or end
of a frame.
Process
 Purpose: Prevent confusion between data and control sequences.
 Mechanism: If a certain pattern (e.g., five consecutive '1's) appears in the data, an
extra '0' bit is inserted (stuffed) to break the pattern.
 Example: In HDLC (High-Level Data Link Control), a flag sequence of '01111110' is
used to mark frame boundaries. If the data contains five consecutive '1's, a '0' is
inserted after these '1's to prevent misinterpretation as a flag.

2. Byte Stuffing (Character Stuffing)

Byte stuffing is used when control characters are defined to mark frame boundaries
or for other control purposes.

Process
 Purpose: Ensure special control characters do not appear in the data stream.
 Mechanism: If a special control character appears in the data, a predefined escape
character is inserted before it.
 Example: In PPP (Point-to-Point Protocol), if a data byte matches a control character
(e.g., the flag character '01111110'), an escape character is added before the data
byte to differentiate it from the control character.

Summary

 Bit Stuffing: Inserting bits into the data to avoid patterns that could be mistaken for
control sequences.
 Byte Stuffing: Inserting escape characters into the data to prevent confusion with
control characters.

Both techniques help maintain data integrity and proper frame synchronization in
communication protocols.

Group B

7. Write down different steps of generating checksum.

Ans: Generating a checksum involves a series of steps designed to produce a small,

fixed-size value that represents a larger block of data. This value is used for error
detection. Here are the general steps for generating a checksum:

Steps for Generating a Checksum

1. Choose a Checksum Algorithm:

  Common algorithms include simple additive checksums, cyclic
redundancy checks (CRC), and cryptographic hash functions (e.g., MD5,
SHA-1).

2. Divide the Data:

 Split the data into equal-sized blocks if the algorithm requires it. The
size of each block depends on the algorithm (e.g., 8-bit, 16-bit, 32-bit).

3. Initialize the Checksum Value:

 Set an initial value for the checksum. This is often zero or a predefined
constant depending on the algorithm.

4. Process Each Block:

 For each block of data:

 Simple Additive Checksum: Add the value of each block to the
running total.
 CRC: Perform a series of bitwise operations (XOR, shift) on each
block with a polynomial divisor.
 Hash Functions: Process each block through a series of
transformations defined by the hash function.

5. Combine Intermediate Results:

 Depending on the algorithm, combine intermediate results to form the

final checksum value.
 For additive checksums, this is usually just the final sum.
 For CRC, it might involve a final XOR with a constant value.
 For hash functions, it involves finalizing the hash value based on
internal state.

6. Output the Checksum:

 Convert the resulting value to the appropriate format (binary,

hexadecimal, etc.) for storage or transmission.
 The final checksum value is then used as a concise representation of
the data for error checking.
Example: Simple Additive Checksum

1. Algorithm: Simple 8-bit additive checksum.

2. Data: "Hello" (ASCII values: 72, 101, 108, 108, 111).
3. Initialize: Set checksum to 0.
4. Process Each Block:
 Add each ASCII value to the checksum:
 checksum = 0 + 72 = 72
 checksum = 72 + 101 = 173
 checksum = 173 + 108 = 281
 checksum = 281 + 108 = 389
 checksum = 389 + 111 = 500

5. Combine: For an 8-bit checksum, wrap around using modulo 256 (since 8 bits
can represent values 0-255):
 checksum = 500 % 256 = 244

6. Output: The final checksum value is 244.

Example: CRC (Cyclic Redundancy Check)

1. Algorithm: CRC-8 with polynomial x^8 + x^2 + x + 1 (binary 100000111).

2. Data: "Hello" (binary values: 01001000 01100101 01101100 01101100 01101111).
3. Initialize: Set CRC to 0.
4. Process Each Block:
 Perform bitwise XOR and shifts according to the polynomial for each
bit of the data.
5. Combine: The result after processing all bits is the CRC value.
6. Output: Convert the final CRC value to a suitable format (usually
hexadecimal).

Checksum generation is essential for detecting data corruption and ensuring data
integrity in various applications, including network communication and file storage.

8. Explain different functions of data link layer.

Ans:
The Data Link Layer, which is the second layer in the OSI (Open Systems
Interconnection) model, is responsible for providing reliable communication between
directly connected nodes. It performs several key functions to ensure data integrity,
proper sequencing, and error control. Here are the primary functions of the Data Link
Layer:
1. Framing

 Definition: Framing is the process of dividing the stream of bits received from
the network layer into manageable data units called frames.
 Purpose: Frames make it easier to manage and process data and provide
structure for error detection and correction.
 Implementation: Each frame typically contains a header, payload, and trailer.

2. Physical Addressing

 Definition: The Data Link Layer adds physical addresses (also known as MAC
addresses) to frames.
 Purpose: Physical addresses ensure that frames are delivered to the correct
device on a local network segment.
 Implementation: The MAC address is included in the frame header and
identifies both the source and the destination.

3. Error Detection and Correction

 Definition: The Data Link Layer provides mechanisms to detect and correct
errors that may occur during the transmission of frames.
 Purpose: To ensure the integrity of the data being transferred.
 Implementation: Common methods include checksums, CRC (Cyclic
Redundancy Check), and parity bits. Error detection helps identify corrupted
frames, and correction mechanisms may request retransmission of corrupted
frames.

4. Flow Control

 Definition: Flow control is the process of managing the rate of data

transmission between two nodes to prevent a fast sender from overwhelming
a slow receiver.
 Purpose: To ensure that the receiver can handle all incoming frames without
data loss.
 Implementation: Techniques such as stop-and-wait and sliding window
protocols are used for flow control.

5. Access Control

 Definition: Access control determines which device has permission to use the
communication channel at any given time.
  Purpose: To prevent data collisions when multiple devices attempt to send
data simultaneously over the same medium.
 Implementation: Methods include Carrier Sense Multiple Access with
Collision Detection (CSMA/CD) for Ethernet and Carrier Sense Multiple Access
with Collision Avoidance (CSMA/CA) for Wi-Fi.

6. Frame Synchronization

 Definition: Frame synchronization ensures that the sender and receiver are in
agreement about the boundaries of each frame.
 Purpose: To allow the receiver to correctly identify the start and end of each
frame, ensuring that data is properly interpreted.
 Implementation: Techniques such as preamble sequences, start and end
delimiters, and unique bit patterns help achieve synchronization.

7. Multiplexing

 Definition: Multiplexing allows multiple logical data streams to be sent over a

single physical link.
 Purpose: To optimize the use of the physical medium and enable
simultaneous data transmissions from multiple sources.
 Implementation: Techniques such as Time Division Multiplexing (TDM) and
Frequency Division Multiplexing (FDM) are used.

Summary

The Data Link Layer provides critical services that ensure data is transmitted reliably
and efficiently across physical networks. These functions include framing, physical
addressing, error detection and correction, flow control, access control, frame
synchronization, and multiplexing. By performing these functions, the Data Link Layer
plays a vital role in enabling communication between directly connected nodes and
preparing data for transmission to higher layers of the OSI model.

9. Discuss the working of non-persistent CSMA.

Ans:
Non-persistent Carrier Sense Multiple Access (CSMA) is a network protocol used to
manage how data packets are transmitted over a shared communication medium,
such as Ethernet. The primary goal of non-persistent CSMA is to reduce the
likelihood of collisions (where two or more stations send data simultaneously) and to
maximize the efficiency of the network. Here's a detailed explanation of how non-
persistent CSMA works:
Working of Non-Persistent CSMA

1. Carrier Sensing:

 Before a station (node) attempts to transmit data, it first listens to the

communication medium to check if it is currently in use. This process is
known as carrier sensing.
 The station listens for a carrier signal to determine if another
transmission is in progress.

2. Idle Channel Check:

 If the channel is found to be idle (no carrier signal detected), the station
proceeds to transmit its data immediately.
 If the channel is busy (a carrier signal is detected), the station does not
attempt to transmit immediately.

3. Backoff Mechanism:

 Instead of continuously sensing the channel and retrying immediately,

the station waits for a random amount of time before trying again. This
waiting period is known as the backoff time.
 The random backoff time helps to reduce the probability of collisions
when multiple stations are waiting to transmit after a busy period.

4. Transmission:

 After the backoff period, the station senses the channel again:
 If the channel is still idle, the station transmits its data.
 If the channel is busy, the station repeats the backoff process.

5. Collision Detection (if applicable):

 While non-persistent CSMA does not include collision detection by

itself, it is often used in conjunction with CSMA/CD (Collision
Detection) in Ethernet networks.
 In such cases, if a collision is detected during transmission, the station
stops transmitting and initiates a random backoff period before
attempting to resend the data.

Advantages of Non-Persistent CSMA

  Reduced Channel Idle Time: Since stations wait a random amount of time
before retrying, there is a lower chance of collisions compared to persistent
CSMA, where stations retry immediately.
 Efficient Utilization: The random backoff mechanism helps in spreading out
the transmission attempts over time, leading to more efficient use of the
communication medium.

Disadvantages of Non-Persistent CSMA

 Increased Delay: The random backoff periods can introduce delays in data
transmission, especially in networks with high traffic loads.
 Less Aggressive: The non-persistent approach is less aggressive in utilizing
the available bandwidth compared to persistent methods, which may lead to
underutilization in low traffic scenarios.

Example Scenario

Consider a local area network (LAN) where multiple computers (stations) are
connected and using non-persistent CSMA to communicate:

1. Station A wants to send a data packet. It first listens to the channel.

 If the channel is idle, Station A transmits the packet immediately.

 If the channel is busy, Station A waits for a random period before
sensing the channel again.

2. Station B also wants to send a data packet. It senses the channel and finds it
busy because Station A is transmitting.

 Station B waits for a random backoff time.

3. After completing its transmission, Station A releases the channel. Station B

senses the channel again after its backoff period.

 If the channel is now idle, Station B transmits its packet.

By following this process, non-persistent CSMA helps manage access to the shared
communication medium, reducing the chances of collisions and improving overall
network efficiency, though with the trade-off of potentially increased delays.

10. Explain five classes of IP address.

Ans:
IP addresses are divided into several classes based on their bit patterns and the size
of their network and host portions. The five classes of IP addresses are Class A, Class
B, Class C, Class D, and Class E. Here's an explanation of each class:

1. Class A IP Addresses

 Range: 1.0.0.0 to 126.255.255.255

 First Octet: Starts with a value from 1 to 126 (binary: 0xxxxxxx)
 Network Bits: 8 bits (First octet)
 Host Bits: 24 bits (Remaining three octets)
 Usage: Reserved for very large networks due to their large number of host
addresses.
 Example: 10.0.0.0 (Private IP range), 126.255.255.255

2. Class B IP Addresses

 Range: 128.0.0.0 to 191.255.255.255

 First Octet: Starts with a value from 128 to 191 (binary: 10xxxxxx)
 Network Bits: 16 bits (First two octets)
 Host Bits: 16 bits (Last two octets)
 Usage: Suitable for medium-sized networks with moderate numbers of host
addresses.
 Example: 172.16.0.0 to 172.31.255.255 (Private IP range), 191.255.255.255

3. Class C IP Addresses

 Range: 192.0.0.0 to 223.255.255.255

 First Octet: Starts with a value from 192 to 223 (binary: 110xxxxx)
 Network Bits: 24 bits (First three octets)
 Host Bits: 8 bits (Last octet)
 Usage: Suitable for small-sized networks with fewer host addresses but more
network addresses compared to Class B.
 Example: 192.168.0.0 to 192.168.255.255 (Private IP range), 223.255.255.255

4. Class D IP Addresses (Multicast)

 Range: 224.0.0.0 to 239.255.255.255

 First Octet: Starts with a value from 224 to 239 (binary: 1110xxxx)
 Usage: Reserved for multicast groups, where data is sent to multiple
recipients simultaneously.
  Example: 224.0.0.1 (All systems on this subnet), 239.255.255.255 (Limited
broadcast)

5. Class E IP Addresses (Reserved)

 Range: 240.0.0.0 to 255.255.255.255

 First Octet: Starts with a value from 240 to 255 (binary: 1111xxxx)
 Usage: Reserved for experimental purposes and future use, not typically used
in regular network configurations.

Summary

 Class A: Large networks, few network bits, many host bits.

 Class B: Medium-sized networks, moderate network and host bits.
 Class C: Small networks, more network bits, fewer host bits.
 Class D: Multicast addresses for sending data to multiple recipients.
 Class E: Reserved for experimental and future use.

Understanding IP address classes is crucial for network administrators to effectively

manage IP addressing and subnetting within their networks. Note that with the
introduction of CIDR (Classless Inter-Domain Routing), the strict boundaries between
classes have become less significant, and variable-length subnet masks are
commonly used to optimize address allocation.

11. Explain different elements of a protocol.

Ans:
A protocol is a set of rules and conventions that govern how data is transmitted and
received in a network or communication system. Several elements make up a
protocol, each serving a specific purpose to ensure reliable and efficient
communication. Here are the key elements of a protocol:

1. Syntax

 Definition: Syntax refers to the format and structure of the data packets or
messages exchanged between devices in a communication system.
 Purpose: Ensures that the data transmitted adheres to a specific format that
both the sender and receiver can understand.
 Example: In HTTP (Hypertext Transfer Protocol), the syntax includes methods
like GET, POST, and headers like Content-Type.

2. Semantics
  Definition: Semantics defines the meaning of the data packets or messages
exchanged within the protocol.
 Purpose: Ensures that the data exchanged has the intended interpretation by
both the sender and receiver.
 Example: In HTTP, a GET request semantics indicate that the client is
requesting data from the server.

3. Timing

 Definition: Timing refers to the timing and sequencing of events within the
communication process, including when data is transmitted and how long
devices wait for responses.
 Purpose: Ensures that data is transmitted and processed in an orderly
manner, minimizing delays and optimizing performance.
 Example: In TCP (Transmission Control Protocol), timing mechanisms include
timeouts for retransmissions and acknowledgments to ensure reliable data
delivery.

4. Flow Control

 Definition: Flow control manages the rate of data transmission between

devices to prevent overwhelming the receiving device with too much data.
 Purpose: Prevents data loss and congestion by regulating the flow of data
based on the receiver's ability to process it.
 Example: In TCP, flow control is implemented using window size and
acknowledgment mechanisms.

5. Error Control

 Definition: Error control mechanisms detect and correct errors that may occur
during data transmission, ensuring data integrity.
 Purpose: Minimizes the impact of data corruption or loss, maintaining the
accuracy and reliability of transmitted data.
 Example: In TCP, error control includes checksums, acknowledgment and
retransmission mechanisms, and sequence numbers.

6. Security

 Definition: Security features within a protocol protect data from unauthorized

access, interception, or modification.
 Purpose: Ensures the confidentiality, integrity, and authenticity of data
exchanged between devices.
  Example: In HTTPS (Hypertext Transfer Protocol Secure), security features
include encryption (SSL/TLS) and authentication mechanisms.

7. Addressing and Routing

 Definition: Addressing and routing elements specify how devices are

addressed within a network and how data is routed from source to
destination.
 Purpose: Enables devices to identify each other and determine the best path
for data transmission.
 Example: In IP (Internet Protocol), addressing involves assigning unique IP
addresses to devices, while routing protocols determine the optimal paths for
data packets.

8. Session Management

 Definition: Session management elements establish, maintain, and terminate

communication sessions between devices.
 Purpose: Ensures that data exchanges are organized into meaningful sessions,
allowing devices to manage state and handle communication in a structured
manner.
 Example: In TCP/IP, session management includes establishing connections
(TCP handshake) and closing connections (TCP teardown).

Summary

Each element of a protocol plays a crucial role in defining how data is communicated
within a network or communication system. By addressing syntax, semantics, timing,
flow control, error control, security, addressing and routing, and session
management, protocols enable devices to exchange data reliably, efficiently, and
securely, forming the backbone of modern communication systems.

12. Explain different features of circuit switching technology.

Ans:
Circuit switching is a communication method that establishes a dedicated
communication path between two nodes in a network before transmitting data. This
path remains active for the duration of the communication session. Here are the
different features of circuit switching technology:

1. Dedicated Communication Path

  Definition: Circuit switching establishes a dedicated path (circuit) between the
sender and receiver for the duration of a communication session.
 Feature: Ensures exclusive use of resources during the session, providing
consistent bandwidth and low latency for data transmission.
 Example: Traditional telephone networks use circuit switching to establish
dedicated voice channels for phone calls.

2. Connection Establishment

 Definition: Before data transmission begins, circuit switching protocols

establish a connection by signaling between the sender and receiver.
 Feature: Ensures that resources are allocated and reserved along the
communication path, including bandwidth and buffer space.
 Example: In PSTN (Public Switched Telephone Network), the signaling process
includes call setup, channel allocation, and connection confirmation.

3. Fixed Bandwidth Allocation

 Definition: Circuit switching allocates a fixed amount of bandwidth for the

duration of the communication session, regardless of whether data is actively
transmitted.
 Feature: Guarantees a predictable and constant data rate, suitable for
applications requiring continuous and consistent data transfer rates.
 Example: In a leased line connection, the entire bandwidth of the line is
dedicated to the connection, even if data is not actively transmitted.

4. Circuit Reservation

 Definition: Circuit switching reserves resources (such as channels or time

slots) along the communication path exclusively for the established circuit.
 Feature: Prevents other users from accessing the reserved resources, ensuring
that the allocated bandwidth is available for the active communication
session.
 Example: In ISDN (Integrated Services Digital Network), channels are reserved
for voice or data connections once a circuit is established.

5. Connection-oriented Communication

 Definition: Circuit switching follows a connection-oriented communication

model, where data is sent in sequence along the established circuit.
 Feature: Supports reliable, ordered, and in-sequence data transmission,
similar to a point-to-point communication link.
  Example: TCP (Transmission Control Protocol) in computer networks
establishes a connection-oriented circuit for reliable data delivery.

6. Resource Efficiency

 Definition: Circuit switching optimizes resource utilization by allocating

resources only when a connection is established and releasing them when the
connection terminates.
 Feature: Enhances efficiency by reducing idle time and ensuring that
resources are available for active connections.
 Example: In packet-switched networks, circuit switching is less efficient than
packet switching for bursty data traffic but can be more efficient for
continuous data streams.

7. Suitable for Constant Bit Rate (CBR) Traffic

 Definition: Circuit switching is well-suited for applications with constant and

predictable data transmission requirements, such as voice and video streams.
 Feature: Provides a stable and consistent data path with low jitter and
minimal latency variations, ideal for real-time communication.
 Example: Circuit switching is commonly used in legacy telecommunication
networks for voice calls, where a consistent bit rate is necessary.

Summary

Circuit switching technology offers several features, including dedicated

communication paths, connection establishment, fixed bandwidth allocation, circuit
reservation, connection-oriented communication, resource efficiency, and suitability
for constant bit rate traffic. While it provides stable and predictable data
transmission, it may not be as flexible or scalable as packet switching for handling
bursty and variable traffic patterns.

Group C
13. Explain different types of non-guided media used in data transmission.

Ans:
Non-guided media, also known as unguided or wireless media, refers to
communication channels that do not require physical paths or cables for data
transmission. These media rely on electromagnetic waves to carry data signals. Here
are the different types of non-guided media used in data transmission:

1. Radio Waves
  Frequency Range: Typically used in the frequency range of 3 kHz to 300 GHz.
 Characteristics:
 Omnidirectional propagation: Radio waves travel in all directions from
the transmitter, allowing for wide coverage.
 Penetration: Radio waves can penetrate obstacles like walls to some
extent, depending on the frequency.
 Susceptibility to interference: Susceptible to interference from other
devices operating in the same frequency range.
 Applications: Wi-Fi, Bluetooth, RFID, AM/FM radio, satellite communication.

2. Microwaves

 Frequency Range: Generally used in the frequency range of 1 GHz to 300

GHz.
 Characteristics:
 Line-of-sight propagation: Microwaves travel in straight lines and
require a clear line of sight between the transmitter and receiver.
 High bandwidth: Capable of carrying large amounts of data, suitable for
high-speed communication links.
 Short-range: Limited range due to absorption and scattering by
atmospheric elements.
 Applications: Microwave communication links for point-to-point
communication, satellite communication, radar systems.

3. Infrared (IR) Waves

 Frequency Range: Infrared waves have frequencies ranging from about 300
GHz to 430 THz.
 Characteristics:
 Short-range communication: Limited to short distances as infrared
waves do not penetrate obstacles well and are affected by ambient
light.
 Line-of-sight propagation: Requires direct line of sight between the
transmitter and receiver.
 Low interference: Less susceptible to interference compared to radio
waves.
 Applications: Infrared remote controls, short-range communication in
consumer electronics (e.g., IrDA for data transfer between devices).
4. Light Waves (Visible and Ultraviolet)

 Frequency Range: Visible light has frequencies ranging from about 430 THz
to 750 THz. Ultraviolet (UV) light has higher frequencies beyond the visible
range.
 Characteristics:
 Short-range communication: Limited to relatively short distances due
to absorption and scattering in the atmosphere.
 Line-of-sight propagation: Requires direct line of sight between
transmitter and receiver.
 Low interference: Less susceptible to interference compared to radio
waves.
 Applications: Optical communication using visible light (e.g., optical fiber
communication, Li-Fi), UV communication in specialized applications.

5. Terahertz Waves

 Frequency Range: Terahertz waves have frequencies ranging from about 300
GHz to 3 THz.
 Characteristics:
 Emerging technology: Still in the research and development phase for
practical communication applications.
 High bandwidth potential: Capable of carrying very high data rates,
promising for future high-speed wireless communication.
 Limited range: Similar limitations to microwaves in terms of range and
line-of-sight requirements.
 Applications: Potential applications in high-speed wireless communication,
imaging, and sensing.

Summary

Non-guided media for data transmission include radio waves, microwaves, infrared
waves, light waves (visible and ultraviolet), and terahertz waves. Each type has unique
characteristics, advantages, and limitations, making them suitable for different
communication applications based on factors such as range, bandwidth, interference
susceptibility, and line-of-sight requirements.

14. Explain CRC with the help of an example.

Ans:
CRC (Cyclic Redundancy Check) is an error-detecting code commonly used in
communication networks to detect errors in transmitted data. It works by generating
a checksum based on the data bits and appending it to the transmitted message. The
receiver then recalculates the checksum based on the received data and compares it
with the checksum sent by the sender. If the calculated checksums match, the data is
assumed to be error-free. Here's an explanation of CRC with an example:

Example of CRC Calculation

Let's take a simple example where we want to transmit the 8-bit data sequence
"11011010" using CRC. We'll use a CRC polynomial of 𝑥3+𝑥2+1x3+x2+1, which
translates to the binary representation "1101" (since each term in the polynomial
corresponds to a bit position in the binary representation).

Step 1: Data and Polynomial Representation

 Data: 11011010
 Polynomial: 1101
Step 2: Appending Zeroes

 We append three zeroes (the degree of the polynomial minus one) to the data to
form the augmented data.
 Augmented Data: 11011010000
Step 3: CRC Calculation

 Perform a bitwise XOR operation between the augmented data and the polynomial.
 Divide the result by the polynomial (1101), ignoring the quotient and keeping the
remainder as the CRC code.
scss
Copy code
11011010000 (Augmented Data) XOR 1101 (Polynomial) ---------------- 100011 (Remainder/CRC)
Step 4: CRC Appended to Data

 Append the CRC (100011) to the original data to form the transmitted message.
 Transmitted Message: 11011010100011

CRC Check at the Receiver

At the receiver's end, the transmitted message "11011010100011" is received. The

receiver performs the same CRC calculation using the received data and the
polynomial. If the calculated CRC matches the CRC sent by the sender, the data is
considered error-free.
Step 1: Received Data

 Received Data: 11011010100011

Step 2: CRC Calculation

 Perform a bitwise XOR operation between the received data and the polynomial.
 Divide the result by the polynomial (1101), ignoring the quotient and keeping the
remainder as the calculated CRC code.
scss
Copy code
11011010100011 (Received Data) XOR 1101 (Polynomial) ------------------- 100011 (Calculated CRC)
Step 3: CRC Comparison

 Compare the calculated CRC (100011) with the CRC sent by the sender.
 If they match, the data is error-free. If not, an error is detected.

In this example, the calculated CRC matches the CRC sent by the sender (100011),
indicating that the data transmission was successful without errors.

CRC is widely used due to its simplicity and effectiveness in detecting common types
of errors, such as single-bit errors and burst errors, making it a valuable tool in
ensuring data integrity in communication networks.

15. Explain different layers of TCP/IP reference models.

Ans:
The TCP/IP (Transmission Control Protocol/Internet Protocol) reference model is a
conceptual framework that defines the protocols and standards used for
communication over the Internet. It consists of four layers, each responsible for
specific functions related to data transmission. Here are the different layers of the
TCP/IP reference model:

1. Application Layer

 Function: The Application Layer is responsible for providing network services

directly to end-users or applications. It enables communication and data
exchange between software applications running on different devices.
 Protocols: HTTP, HTTPS, FTP, SMTP, POP3, IMAP, DNS, SNMP, Telnet, SSH.
 Functions:
 Data formatting and syntax conversion.
 User authentication and authorization.
 File transfer and remote access.
 Email communication.
  Domain name resolution.
 Web browsing and content delivery.

2. Transport Layer

 Function: The Transport Layer ensures reliable end-to-end communication

between devices. It manages data segmentation, error detection, flow control,
and data integrity during transmission.
 Protocols: TCP (Transmission Control Protocol), UDP (User Datagram
Protocol).
 Functions:
 Segmentation and reassembly of data packets.
 Error detection and retransmission (TCP).
 Flow control and congestion avoidance.
 Connection establishment, maintenance, and termination (TCP).
 Reliable data delivery with acknowledgments and sequencing (TCP).
 Unreliable, connectionless communication (UDP).

3. Internet Layer

 Function: The Internet Layer facilitates packet routing and forwarding across
interconnected networks. It manages IP addressing, packet fragmentation, and
routing decisions to ensure data delivery between source and destination
devices.
 Protocols: IP (Internet Protocol), ICMP (Internet Control Message Protocol),
ARP (Address Resolution Protocol), RARP (Reverse Address Resolution
Protocol).
 Functions:
 IP addressing and packet encapsulation.
 Packet routing and forwarding based on destination IP addresses.
 Fragmentation and reassembly of large packets.
 Network layer diagnostics and error reporting (ICMP).
 Address resolution between IP and MAC addresses (ARP, RARP).

4. Link Layer (Network Access Layer)

  Function: The Link Layer establishes and maintains communication between
directly connected devices on the same physical network. It handles hardware
addressing, framing, error detection, and media access control.
 Protocols: Ethernet, Wi-Fi (IEEE 802.11), PPP (Point-to-Point Protocol), HDLC
(High-Level Data Link Control), ARP (Address Resolution Protocol).
 Functions:
 Media access control and data framing.
 Physical addressing (MAC addresses).
 Error detection and correction at the link level.
 Flow control and error recovery.
 Link establishment and termination.
 Address resolution between IP and MAC addresses (ARP).

Summary

The TCP/IP reference model comprises the Application Layer, Transport Layer,
Internet Layer, and Link Layer. Each layer performs specific functions, including
application-level services, reliable data transmission, packet routing, and network
access control. Together, these layers enable efficient and standardized
communication across interconnected networks, forming the backbone of the
modern Internet.

16. Explain the operation of HDLC.

Ans:
HDLC (High-Level Data Link Control) is a bit-oriented data link layer protocol used
for reliable and efficient communication between network devices. It is widely used in
point-to-point and multi-point communication links, particularly in synchronous data
transmission environments. HDLC defines how data frames are formatted,
transmitted, and acknowledged between sender and receiver. Here's an explanation
of the operation of HDLC:

Frame Structure

HDLC frames consist of several fields that serve different purposes in the
communication process:

1. Flag Sequence: Marks the beginning and end of an HDLC frame. The flag
sequence is typically the pattern "01111110" (7 bits of '1' surrounded by '0's).
 2. Address Field: Specifies the destination or source address of the frame. In
point-to-point connections, the address field is often omitted.

3. Control Field: Contains control information such as frame type (data,

acknowledgment, control), sequence numbers for error detection and flow
control, and control bits indicating the frame's purpose.

4. Information Field: Carries the actual data payload being transmitted.

5. Frame Check Sequence (FCS): A checksum or CRC value computed over the
frame's data to detect errors during transmission.

6. Flag Sequence: Marks the end of the frame, similar to the start flag sequence.

Operation Steps

The operation of HDLC involves several key steps during frame transmission and
reception:

1. Frame Transmission:

 The sender encapsulates the data to be transmitted into an HDLC

frame.
 The frame begins with the flag sequence, followed by the address field
(optional in point-to-point links), control field, information field, FCS,
and ends with the flag sequence.

2. Frame Reception:

 The receiver monitors the communication channel for incoming frames.

 Upon detecting the start flag sequence, the receiver begins capturing
and processing the incoming frame.

3. Address and Control Field Processing:

 If an address field is present, the receiver checks if the frame is

addressed to its own address. Otherwise, it processes the frame based
on the control information.
 Control bits in the control field specify the type of frame (data,
acknowledgment, control) and additional control functions such as
sequence numbering for error detection and flow control.
 4. Data Extraction:

 Upon successful address and control field processing, the receiver

extracts the data from the information field of the frame.
 The data payload is then delivered to the higher-layer protocol or
application for further processing.

5. Error Detection:

 The receiver computes the FCS (checksum or CRC) over the received
frame's data and compares it to the FCS value included in the frame.
 If the computed FCS matches the received FCS, the frame is considered
error-free. Otherwise, it indicates a transmission error, and the frame
may be discarded or retransmitted based on the protocol's error
handling mechanism.

6. Acknowledgment:

 Depending on the frame type and protocol configuration, the receiver

sends acknowledgment frames (ACK) to confirm successful reception of
data frames or control frames.

Control Functions

HDLC supports several control functions to ensure reliable and efficient

communication:

 Acknowledgment and Retransmission: Using ACK and NAK (negative

acknowledgment) frames to confirm data reception and request
retransmission if needed.
 Flow Control: Using control bits (e.g., sequence numbers, window sizes) to
manage data flow and prevent buffer overflow.
 Error Detection and Correction: Using CRC or checksum in the FCS field to
detect transmission errors and optionally request retransmission.
 Link Establishment and Termination: Using special control frames (SABM,
DISC) to establish, maintain, and terminate the link between devices.

Variants of HDLC

HDLC has several variants, including:

  Normal (N)-mode HDLC: Point-to-point communication with one sender
and one receiver.
 Asynchronous Balanced (AB)-mode HDLC: Supports multi-point
communication with multiple senders and receivers.
 Asynchronous Response (AR)-mode HDLC: Combines aspects of N-mode
and AB-mode for specific applications.

Each variant defines specific rules and procedures for addressing, framing, and
control functions based on the communication topology and requirements.

Summary

HDLC operates by framing data into structured frames with control information,
using flag sequences to mark frame boundaries, addressing and control fields to
manage communication, and error detection mechanisms for data integrity. Its
control functions enable reliable data transmission, flow control, error detection, and
link management, making it a versatile and widely used protocol in networking
environments.