Chapter 2: Data Communication and Networking

2.13   Network Topologies: Bus, Ring and Star topology

Network topology is the arrangement or layout of devices and connections within a network, defining how they interact and exchange data.

Some common types of network topologies:

1)      Bus Topology: All devices are connected to a single central cable, known as the bus.

2)      Star Topology: All devices are connected to a central hub or switch.

3)      Ring Topology: Each device is connected to exactly two other devices, forming a circular data path.

4)      Mesh Topology: Devices are interconnected, with multiple pathways for data to travel between nodes.

5)      Tree Topology: A hierarchical structure with a root node and multiple levels of connected devices.

6)      Hybrid Topology: A combination of two or more different topologies to form a complete network.

Comparison Table: Bus, Ring, and Star Topology

Feature	Bus Topology	Ring Topology	Star Topology
Description	A network topology where all devices are connected to a single central cable (called the bus), which acts as the shared communication medium.	A network topology where devices are arranged in a closed-loop structure, with each device connected to exactly two others.	A network topology where all devices are connected to a central hub or switch, which manages communication.
Cost	Low (less cabling required).	Moderate (circular layout needs additional cabling).	High (requires more cables and a central hub).
Setup Complexity	Simple to set up.	Moderate due to sequential device connection.	Easy to install but needs a central device.
Scalability	Limited; adding devices can slow down performance.	Moderate; adding devices can affect the loop.	High; easy to add devices without disrupting the network.
Performance	Degrades with increased devices or heavy traffic.	Predictable, but slower in high-traffic scenarios.	High, as traffic is managed by the central hub.
Reliability	Failure in the main cable brings down the entire network.	Single failure can disrupt the entire network unless redundant paths are used.	Central hub failure disables the network, but individual failures do not.
Troubleshooting	Difficult to pinpoint issues in the main cable.	Moderate; failure in a single device impacts the loop.	Easy; issues are isolated to individual devices or the hub.
Data Transmission	Broadcast-based; all devices hear every message but only the intended recipient processes it.	Token-passing; a token circulates in the loop, granting devices permission to transmit.	Hub-based; data is sent to the central hub, which forwards it to the recipient.
Pros	- Cost-effective for small networks. - Easy to expand with T-connectors.	- Predictable data flow. - Suitable for consistent traffic.	- Easy to install and troubleshoot. - High performance and scalability.
Cons	- Main cable failure halts the network. - Performance degrades with traffic.	- Entire network fails if one device fails (without redundancy). - Troubleshooting is complex.	- Requires a central hub, increasing cost. - Hub failure disrupts the network.

 

Note:   Users prefer star topology because it offers several advantages:

1.       Scalability: Easy to add or remove nodes without affecting the entire network.

2.       Centralized Management: Simplifies network monitoring and management with a central hub.

3.       Reliability: Node failures do not disrupt the entire network.

4.       Flexibility: Supports various network media and configurations.

5.       Cost-Effectiveness: Generally lower installation and maintenance costs.

6.       Performance: Optimized for efficient data transfer.

These features make star topology a practical and efficient choice for many network designs.

ImpQ) Why is CAT 6 cable suitable for designing a LAN topology?

ANS:  

Category 6 (CAT 6) cables are widely used for designing Local Area Networks (LANs) because of the following features:

Ø  High-Speed Data Transfer: CAT 6 supports up to 1 Gbps over 100 meters and 10 Gbps over shorter distances, ideal for modern networks.

Ø  High Bandwidth: Offers a bandwidth of 250 MHz, ensuring smooth handling of large data and minimizing delays.

Ø  Reduced Interference: Better shielding and tighter twists reduce crosstalk, improving connection reliability.

Ø  Future-Proofing: Compatible with newer technologies and standards, making it a long-term investment.

Ø  Durable and Cost-Effective: Built for durability with higher-quality materials, offering a good balance of performance and cost.

2.7 Transmission Medium: Guided and Unguided

A transmission medium is a pathway that carries the information from the sender to the receiver. It can be either guided (wired) or unguided (wireless) as explained below:

1. Guided Media

Definition: Guided media refers to transmission that uses a physical pathway to direct signals from the sender to the receiver.

Key Characteristics:

• The signal is confined to a path/medium/channel.
• Usually more secure and less affected to interference and environmental factors like weather compared to unguided media.
• Suitable for short to medium distances.

Examples:

a. Twisted Pair Cable: Consists of pairs of insulated copper wires twisted together.

• Types: Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP).

• Applications: LANs, telephone systems, and Ethernet networks.

• Advantages: Low cost, easy to install.

• Disadvantages: Limited bandwidth, susceptible to interference.

b. Coaxial Cable: Has a central conductor, insulating layer, metallic shield, and outer jacket.

• Types: RG-6 (cable TV), RG-59 (CCTV), RG-11 (long-distance).

• Applications: Cable TV, broadband internet, and CCTV systems.

• Advantages: Higher bandwidth, better noise resistance.

• Disadvantages: Bulky, limited distance.

c. Fiber Optic Cable: Uses light pulses to transmit data through glass or plastic fibers.

• Types: Single-mode (long-distance) and multimode (short-distance).

• Applications: Telecommunications, internet backbones, and data centers.

• Advantages: Extremely high bandwidth, long-distance transmission.

• Disadvantages: Expensive, fragile, complex installation.

2. Unguided Media

Definition: Unguided media refers to wireless transmission where the signal travels through free space (air, vacuum, or water) without a physical conductor.

Key Characteristics:

• The signal is broadcast in all directions and can be intercepted easily.
• Usually less secure and more affected to interference and environmental factors like weather.
• Suitable for long distances or areas where laying physical cables is impractical.

Examples:

a. Radio Waves: Uses radio frequencies for communication.

• Applications: Wi-Fi, Bluetooth, and cellular networks.

• Advantages: Wide coverage, easy to set up.

• Disadvantages: Susceptible to interference, limited bandwidth.

b. Microwaves: Uses high-frequency waves for point-to-point communication.

• Applications: Satellite communication and long-distance links.

• Advantages: High bandwidth, suitable for remote areas.

• Disadvantages: Expensive, affected by weather.

c. Infrared: Uses infrared light for short-range communication.

• Applications: Remote controls and IR sensors.

• Advantages: Secure, low cost.

• Disadvantages: Limited range, line-of-sight required.

d. Satellite Communication: Uses satellites to relay signals over long distances.

• Applications: GPS, satellite TV, and global communication.

• Advantages: Wide coverage, suitable for remote areas.

• Disadvantages: High latency, expensive infrastructure.

Comparison Table:

Basis of Differentiation	Guided Media(bounded)	Unguided Media(unbounded)
Definition	Guided media refers to transmission that uses a physical pathway to direct signals from the sender to the receiver.	Unguided media refers to wireless transmission where the signal travels through free space (air, vacuum, or water) without a physical conductor.
Medium	Uses physical cables like wires or optical fibers to transmit signals	Uses free space (air, vacuum, or water) to transmit signals
Signal Direction	Confined to a specific path (through cables)	Broadcasts signals in all directions
Security	More secure as data stays within cables	Less secure since signals can be intercepted
Interference	Minimal interference due to shielding in cables	More prone to interference from weather, obstacles, and other signals
Examples	Twisted pair cables, coaxial cables, optical fiber	Radio waves, microwaves, infrared
Applications	Used in LANs, wired internet connections and high-speed internet.	Used in Wi-Fi, mobile networks, satellite communication and broadcasting.

2.9 Basic concept of networks Architecture: Client - Server and Peer - to -Peer

Networks can be broadly categorized into client-server and peer-to-peer (P2P) based on their architecture and how devices interact.

A client-server network is a type of network where one or more centralized computers (called servers) provide resources, services, or data to multiple other computers (called clients). The server manages and controls access to resources, while clients request and use those resources. Some examples are Web browsing, email, online banking, cloud storage, etc.

Advantages of client-server network architecture are as follows:

1)      Centralized Management: Easier to manage and secure data since everything is stored on the server.

2)      Scalability: Can handle a large number of clients by upgrading the server.

Disadvantages of peer-to-peer network architecture are as follows:

1)      Single Point of Failure: If the server goes down, the entire network is affected.

2)      Costly: Requires expensive hardware and maintenance for the server.

A peer-to-peer network is a decentralized network where all devices (called peers) are equal and can act as both clients and servers. Each device can share resources (like files or processing power) and access resources from other devices directly, without the need for a central server. Some examples are Torrenting, blockchain, P2P gaming, VoIP, etc.

Advantages of client-server network architecture are as follows:

1)      Cost-Effective: No need for a dedicated server, reducing costs.

2)      Decentralized: No single point of failure; if one peer goes down, others can still communicate.

Disadvantages of peer-to-peer network architecture are as follows:

1)      Less Secure: Harder to manage security since each device is independent.

2)      Limited Scalability: Not suitable for large networks as it becomes difficult to manage.

Some key differences between Client-Server and Peer-to-Peer (P2P) network architectures:

Basis of Difference	Client-Server Network	Peer-to-Peer (P2P) Network
Definition	A centralized network where a server provides resources to multiple clients.	A decentralized network where all devices (peers) share resources directly.
Resource Management	Resources are stored and managed centrally on the server.	Resources are distributed across all peers.
Dependency	Clients depend on the server for resources and services.	No dependency on a central server; peers rely on each other.
Cost	Expensive due to the need for a dedicated server and maintenance.	Cost-effective as no dedicated server is required.
Scalability	Highly scalable; can handle many clients by upgrading the server.	Less scalable; performance decreases as the number of peers increases.
Security	More secure as the server controls access and data.	Less secure as each peer manages its own security.
Reliability	Single point of failure; if the server goes down, the network is affected.	No single point of failure; if one peer goes down, others can still communicate.
Examples	Web browsing (Google), email services (Gmail), online banking.	Torrenting (BitTorrent), blockchain (Bitcoin), P2P gaming (Minecraft LAN).
Use Case	Suitable for large networks with centralized control (e.g., businesses, organizations).	Suitable for small networks or file-sharing systems (e.g., home networks).

Client-Server Architecture:

Advantages:

1. Centralized Management: Easier to manage and update software and data, since everything is centralized on the server.

2. Scalability: Can handle a large number of clients by upgrading server capacity.

3. Security: Centralized control allows for better security management.

4. Data Consistency: Centralized database ensures consistent data across the network.

5. Maintenance: Easier to perform maintenance tasks like backups and updates.

Disadvantages:

1. Single Point of Failure: If the server goes down, the entire network or service may be disrupted.

2. Cost: Servers can be expensive to set up and maintain.

3. Performance Bottlenecks: Server overload can lead to performance issues if not properly scaled.

4. Dependency: Clients rely heavily on the server for services and data.

5. Complexity: Setting up and maintaining a client-server architecture can be complex and require specialized knowledge.

Peer-to-Peer (P2P) Architecture:

Advantages:

1. Distributed Resources: No single point of failure, as each peer contributes resources.

2. Scalability: Can scale easily as more peers join the network.

3. Cost-Effective: No need for expensive central servers.

4. Resilience: Network is more resilient to failures, as data and services are distributed.

5. Autonomy: Each peer can operate independently, sharing resources as needed.

Disadvantages:

1. Security: Decentralized nature can make it harder to enforce security policies.

2. Data Consistency: Maintaining consistent data across all peers can be challenging.

3. Management: Harder to manage and monitor, as there is no central authority.

4. Performance: Performance can vary depending on the peers’ resources and network connectivity.

5. Reliability: Peers may join and leave the network unpredictably, affecting availability and reliability.

Different Types of Cable:

Twisted Pair Cable:

Twisted pair cable is a type of electrical cable that consists of two conductors that are twisted together. The twisting of the conductors helps to reduce crosstalk and electromagnetic interference, which can cause signal degradation.

Features of twisted pair cable include:

1. Conductors: Twisted pair cable has two conductors, typically made of copper, that carry the signal.
2. Insulation: Each conductor is surrounded by an insulating layer, typically made of polyethylene or polypropylene, which prevents the signal from leaking out of the cable.
3. Twisting: The two conductors are twisted together, which helps to reduce crosstalk and electromagnetic interference.
4. Jacket: The cable is coated with a protective layer, typically made of polyethylene or polypropylene, which protects the cable from physical damage and environmental factors.

Advantages of twisted pair cable are as follows:

1. Cost-effective: Twisted pair cable is relatively inexpensive to produce and install.
2. Easy to install: Twisted pair cable is easy to install and can be used in a variety of environments.
3. Suitable for low-speed data transmission: Twisted pair cable is suitable for transmitting low-speed data, such as telephone signals or low-speed computer data.

Disadvantages of twisted pair cable are as follows:

1. Limited bandwidth: Twisted pair cable has a limited bandwidth, making it less suitable for transmitting high-speed data.
2. Susceptible to signal degradation: Twisted pair cable is susceptible to signal degradation over long distances, which can result in a loss of signal quality.
3. Limited range: Twisted pair cable has a limited range, and the signal can degrade over long distances.
4. Requires specialized connectors: Twisted pair cable requires specialized connectors, which can be expensive and difficult to install.

Differences between STP and UTP:

Feature	STP	UTP
Shielding	Has an additional layer of shielding	Does not have an additional layer of shielding
Bandwidth	Higher bandwidth	Lower bandwidth
Cost	More expensive	Less expensive
Range	Longer range	Shorter range

Note: 

Cat 6 cable, also known as Category 6 cable, is a type of twisted pair cable that is designed for high-speed data transmission. It is commonly used in Ethernet networks and other high-speed data communication systems.

Coaxial Cable:

Coaxial cable is a type of electrical cable that has a central conductor, an insulating layer, a metallic shield, and an outer jacket.

Features of coaxial cable include:

1. Central conductor: The central conductor carries the signal.
2. Insulating layer: The insulating layer prevents the signal from leaking out of the cable.
3. Metallic shield: The metallic shield provides additional protection against signal loss and interference.
4. Outer jacket: The outer jacket protects the cable from physical damage and environmental factors.

Advantages of coaxial cable are as follows:

1. High bandwidth: Coaxial cable can transmit high-frequency signals.
2. Low signal loss: Coaxial cable has low signal loss, making it suitable for long-distance transmission.
3. Resistance to interference: The metallic shield provides protection against electromagnetic interference.
4. Cost-effective: Coaxial cable is relatively inexpensive to produce and install.

Disadvantages of coaxial cable are as follows:

1. Limited bandwidth: Coaxial cable has a limited bandwidth, making it less suitable for transmitting high-speed data.
2. Susceptible to signal degradation: Coaxial cable is susceptible to signal degradation over long distances.
3. Limited range: Coaxial cable has a limited range, and the signal can degrade over long distances.
4. Requires specialized connectors: Coaxial cable requires specialized connectors, which can be expensive and difficult to install.

Fiber Optic Cable:

Fiber optic cable is a type of communication cable that uses light to transmit data. It has a core made of glass or plastic, surrounded by a cladding layer that reflects the light back into the core. The cable is then coated with a protective layer to prevent damage.

Features of fiber optic cable include:

1. Core: The core is the central part of the cable, made of glass or plastic, and it carries the light signal.
2. Cladding: The cladding is a layer surrounding the core, made of a material with a lower refractive index than the core, which reflects the light back into the core.
3. Coating: The coating is a protective layer that surrounds the cladding, made of a material such as polyethylene or polypropylene, which protects the cable from physical damage and environmental factors.
4. Jacket: The jacket is an outer layer that protects the cable from physical damage and environmental factors.

Advantages of fiber optic cable are as folllows:

1. High bandwidth: It can transmit more data at a faster rate.
2. Low signal loss: The signal can travel long distances without degradation.
3. Resistance to electromagnetic interference: It is immune to electromagnetic interference.
4. Security: It is difficult to tap, making it a secure option for transmitting sensitive data.

Disadvantages of fiber optic cable are as follows:

1. High cost: It is more expensive to produce and install than copper cables.
2. Fragility: It is fragile and can be easily damaged if not handled properly.
3. Limited range: The signal can degrade over long distances.
4. Requires specialized equipment: It requires specialized equipment to install and maintain, which can be expensive.

2.10 Some Basic Terms and Tool Used in Computer Network: IP Address, Sub Net Mask and Gateway, MAC address, Internet, Intranet.

1.    IP Address: An IP address is a unique number assigned to every device connected to a computer network. It helps identify and locate the device on the network.

2.    Subnet Mask: A subnet mask is a number that helps divide a network into smaller sub-networks or subnets. It determines which part of the IP address represents the network and which part represents the device.

3.    Gateway: A gateway is a device that acts as a bridge between two different networks. It allows devices on one network to communicate with devices on another network.

4.    MAC Address: A Media Access Control (MAC) address is a unique identifier assigned to a network interface controller (NIC) in a device. It helps identify the device on a local network. For example: 00:1A:2B:3C:4D:5E

5.    Internet: The internet is a global network of interconnected computer networks. It allows devices from different networks to communicate with each other.

6.    Intranet: An intranet is a private network within an organization. It allows employees to share information and resources within the organization.

IP Address:

An IP address is a unique number assigned to every device connected to a computer network. It helps identify and locate the device on the network. It allows devices to communicate with each other over a network or the internet.  Example of IP Address Usage: 

a) Public IP: 203.0.113.1 (used by a home router to access the internet)

b) Private IP: 192.168.1.10 (used by a laptop inside a home network).

Types of IP Addresses

1. IPv4 (Internet Protocol Version 4):

Ø  32-bit address.

Ø  Format: Four octets separated by dots (e.g., 192.168.1.1).

Ø  Supports about 4.3 billion unique addresses.

Ø  IPv4 is divided into classes to support different network sizes:

a)       Class A: Range: 0.0.0.0 to 127.255.255.255 / Default subnet mask: 255.0.0.0

b)      Class B: Range: 128.0.0.0 to 191.255.255.255 / Default subnet mask: 255.255.0.0

c)       Class C: Range: 192.0.0.0 to 223.255.255.255 / Default subnet mask: 255.255.255.0

d)      Class D: Range: 224.0.0.0 to 239.255.255.255

e)      Class E: Range: 240.0.0.0 to 255.255.255.255

2. IPv6 (Internet Protocol Version 6):

Ø  128-bit address.

Ø  Format: Eight groups of hexadecimal numbers separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).

Ø  Supports vastly more addresses to accommodate future needs.

Class C IP address: (V.v.Imp)

A Class C IP address is a type of IP address used in IPv4 addressing to identify a network of devices on small to medium-sized local networks. Key Characteristics of Class C IP address are as follows:

Ø  Range: The first octet (first 8 bits) of a Class C IP address ranges from 192 to 223.

Ø  Structure:

The first three octets (24 bits) represent the network portion.

The last one octet (8 bits) represents the host portion.

Ø  Subnet Mask: The default subnet mask for Class C is 255.255.255.0.

Ø  Host Capacity: Each Class C network can support up to 254 hosts 

Ø  Example: 192.168.1.10 is a Class C IP address where:

192.168.1 is the network portion.

10 is the host portion.

To implement a Class C IP address in a LAN, you need to follow these steps:

Steps to Implement a Class C IP Address in a LAN:

1. Obtain a Class C IP Address

• Use private Class C IP ranges (e.g., 192.168.0.0 – 192.168.255.255) for internal networks.
• If setting up a public network, obtain a Class C IP address range from your Internet Service Provider (ISP).

2. Configure the Router

• Set the router's LAN IP address (gateway) within the Class C range. For example:
  • Gateway IP: 192.168.1.1
  • Subnet Mask: 255.255.255.0
• This gateway IP serves as the default route for all devices in the LAN.

3. Assign IP Addresses to Devices

• Assign each device a unique Class C IP address within the network range.
• Example:
  • Device 1: 192.168.1.2
  • Device 2: 192.168.1.3
  • Device 3: 192.168.1.4

4. Configure the Subnet Mask

• Set the subnet mask to 255.255.255.0 for a standard Class C network.
• This subnet mask divides the IP address into network and host portions.

5. Set Up DNS (Domain Name System)

• Configure the router or devices with a DNS server address (e.g., your ISP’s DNS or public DNS like Google’s 8.8.8.8).
• This allows devices to resolve domain names into IP addresses for internet access.

6. Test the Network

• Use commands like ping to check connectivity between devices and the router:
  • Example: ping 192.168.1.1 (router’s IP).
• Test internet access if applicable.

Note: 

Class C IP addresses are not used for public IP addresses, and they are not routable on the internet. They are used only for private networks.

2.12 Network Connecting Devices: NIC, Modem, router, switch

1.    Network Interface Card (NIC): A NIC is a hardware component that allows a device to connect to a network. It provides the physical connection between the device and the network.

2.    Modem: A modem is a device that modulates and demodulates digital signals. It allows a device to connect to the internet via a dial-up, DSL, or cable connection.

3.    Router: A router is a device that connect multiple networks and forwards data packets between different networks based on their destination address. It forwards data packets between networks based on their destination IP addresses. 

4.    Switch: A switch is a device that connects multiple devices on a local network. It uses MAC addresses to forward data packets to the correct device on the network.

2.6 Concept of LAN and WAN

Local Area Network (LAN): A LAN is a network that covers a small geographic area, such as a home, office, or school. It is typically connected using Ethernet cables or Wi-Fi.

Wide Area Network (WAN): A WAN is a network that covers a large geographic area, such as a city, country, or even the entire world. It is typically connected using telephone lines, satellite links, or fiber optic cables.

       Comparison between LAN and WAN are as follows:

1.    Geographic Coverage: LAN covers a small geographic area, such as a home, office, or school. WAN covers a large geographic area, such as a city, country, or even the entire world.

2.    Speed: LAN typically has higher data transfer speeds than WAN. This is because LAN is typically connected using high-speed Ethernet cables or Wi-Fi, while WAN is typically connected using slower telephone lines or satellite links.

3.    Cost: LAN is typically less expensive to set up and maintain than WAN. This is because LAN is typically connected using less expensive Ethernet cables or Wi-Fi, while WAN is typically connected using more expensive telephone lines, satellite links, or fiber optic cables.

4.    Connectivity: LAN is typically connected using Ethernet cables or Wi-Fi, while WAN is typically connected using telephone lines, satellite links, or fiber optic cables.

5.    Security: LAN is typically more secure than WAN, as it is easier to control access to a smaller network. This is because LAN is typically connected using a single, secure connection, while WAN is typically connected using multiple, less secure connections.

Wireless Network System (Wi-Fi):

Ø  Wi-Fi is a technology that allows devices to connect to a network wirelessly.

Ø  It uses radio waves to transmit data between devices, such as laptops, smartphones, and tablets.

Ø  Wi-Fi is commonly used in homes, offices, and public places, such as coffee shops and airports, to provide internet access to multiple devices.

Ø  Wi-Fi networks can be either public or private, and they can be secured or unsecured.

Ø  A secured Wi-Fi network requires a password to access, while an unsecured network is open to anyone within range.

Ø  Wi-Fi operates on two frequency bands: 2.4 GHz and 5 GHz.

Ø  The 2.4 GHz band is more widely used and has a longer range, but it is also more prone to interference from other devices.

Ø  The 5 GHz band has a shorter range but is less prone to interference and can provide faster data transfer speeds.

Devices and equipment necessary for a Wi-Fi network are as follows:

1.    Wireless Router: A device that connects to the internet and broadcasts a wireless signal to which other devices can connect.

2.    Wireless Adapter: A device that allows a computer or other device to connect to a Wi-Fi network.

3.    Access Point: A device that extends the range of a Wi-Fi network by providing additional wireless coverage.

4.    Network Interface Card (NIC): A hardware component that allows a device to connect to a network.

5.    Ethernet Cable: A type of cable that is used to connect devices to a network.

6.    Power Adapter: A device used to power the wireless router, access point, and other devices that require power to operate.

2.14 Basic Concept OSI Reference Model

The Open Systems Interconnection (OSI) model is a conceptual framework that describes how data travels across a network. It divides the complex process of network communication into seven distinct layers, each with a specific function.

Here's a breakdown of each layer, starting from the bottom (where the physical transmission of data occurs) and moving upwards to the applications we use:

1. Physical Layer: Deals with the physical transmission of raw data (bits) over a medium (cables, wireless signals, etc.). Examples: Cables, connectors, network interface cards (NICs), wireless signals.

2. Data Link Layer: Responsible for reliable communication between two directly connected devices. It packages data into frames, handles error detection, and controls access to the physical medium. Examples: Ethernet, Wi-Fi, MAC addresses.

3. Network Layer: Handles routing of data packets across networks. It determines the best path for data to travel and manages logical addressing (IP addresses). Examples: IP (Internet Protocol), routers.

4. Transport Layer: Ensures reliable end-to-end delivery of data between applications. It handles segmentation, reassembly, and flow control. Examples: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

5. Session Layer: Establishes, manages, and terminates connections (sessions) between applications. It handles authentication and authorization. Examples: Not as commonly used in modern networks.

6. Presentation Layer: Deals with data formatting, encryption, and decryption. It ensures that data is presented in a way that applications can understand. Examples: Encryption protocols (SSL/TLS), data compression.

7. Application Layer: Provides network services to applications. This is the layer that users interact with directly. Examples: Web browsers (HTTP), email clients (SMTP), file transfer (FTP).

Summary of the Email Example in OSI Model:

Physical Layer: Cables or Wi-Fi transmitting the email data

Data Link Layer: Your router or switch ensuring the data reaches the next device.

Network Layer: Internet routers finding the best path to the email server.

Transport Layer: TCP ensuring reliable delivery of the email.

Session Layer: The connection between your email client and the server.

Presentation Layer: Encryption securing the email content.

Application Layer: Your email client and SMTP protocol sending the email.

2.8 Transmission impairments terminology (Jitter, Singing, Echo, Crosstalk, Distortion, Noise, Bandwidth, Number of receivers)

1.       key transmission impairments you'll encounter in networking and telecommunications:

1. Jitter: Tiny variations in the timing of data packets as they travel across a network. Think of it like a slight stutter in a conversation.

2. Singing: A high-pitched tone or howl that occurs when feedback happens in an audio system. This often happens when a microphone picks up sound from a speaker.

3. Echo: When a signal is reflected back to its source, creating a delayed copy of the original sound or data.

4. Crosstalk: Interference between signals in adjacent communication channels. Imagine hearing snippets of another phone conversation on your own line.

5. Distortion: Any change to the shape or form of a signal during transmission. This can be due to various factors like equipment limitations or signal reduction.

6. Noise: Unwanted electrical or electromagnetic energy that interferes with the signal. This can be from sources like power lines, radio waves, or even thermal activity in devices.

7. Bandwidth: The range of frequencies that a communication channel can effectively transmit. Think of it as the width of a pipe through which data flows.

8. Number of Receivers: The quantity of devices designed to receive a transmitted signal.

      2.5 Simplex, Half duplex and Full duplex communication mode

Mode of communication refers to the way data is transmitted between devices in a network or communication system. It determines the direction and timing of data flow. There are three primary modes of communication as follows:

1) Simplex: One-way communication where one device sends and the other receives. Example: Radio broadcasting, where stations transmit to receivers without direct communication.

2) Half duplex: Two-way communication where devices can send and receive, but not simultaneously. Example: Walkie-talkies, where users can talk and listen, but not at the same time.

3) Full duplex: Two-way communication where devices can send and receive simultaneously. Example: Telephone calls, where both parties can speak and listen simultaneously.

Comparison of Simplex, Half Duplex, and Full Duplex:

Feature	Simplex	Half Duplex	Full Duplex
Direction of Data	One-way only.	Two-way, but not at the same time.	Two-way simultaneously.
Example	TV broadcasting.	Walkie-talkies.	Telephone calls.
Advantages	Simple and cost-effective.	Allows two-way communication.	Fast and efficient.
Disadvantages	No two-way communication.	Slower than full duplex.	Requires more complex hardware.

2.1 Basic elements of Communication System: 

2.2 Concept of Communication System

2.3 Block Diagram of communication System /Model

2.4 Elements of Data Communication/Transmission

A communication system is a collection of hardware, software, and protocols designed to reliably and efficiently transfer information from one point (the source) to another (the destination). 

1)    Information Source: This is where the message originates. It could be:

a)     A person speaking (sound)

b)    A computer (data)

c)     A camera (images/video)

d)    A sensor (temperature, pressure, etc.)

2)    Input Transducer: Converts the information from the source into an electrical signal. Examples:

a)     Microphone (sound to electrical)

b)     Camera (light to electrical)

3)    Transmitter: Processes the electrical signal to make it suitable for transmission. This often involves:

a)     Modulation: Encoding the information onto a carrier wave (think of it like putting your message in an envelope for easier delivery).

b)    Amplification: Increasing the signal strength for better travel.

4)    Channel: The medium through which the signal travels. This could be:

a)     Air (radio waves, Wi-Fi)

b)    Wires (telephone lines, cables)

c)     Optical Fiber (light signals)

d)    Space (satellite communication)

5)    Receiver: Receives the transmitted signal and performs the reverse of the transmitter's job:

a)     Demodulation: Extracts the original information from the carrier wave.

b)    Filtering: Removes noise or interference.

c)     Amplification: Further boost the signal.

6)    Output Transducer: Converts the electrical signal back into a form understandable by the destination:

a)     Speaker (electrical to sound)

b)    Computer screen (digital to visual)

c)     Printer (digital to text/image)

7)    Destination: The intended recipient (a person or thing that receives) of the message. This could be:

a.     A person listening

b.     A computer receiving data

c.     A storage device

2.11 Network Tool: Packet tracer, Remote Login

Packet Tracer: A network simulation software developed by Cisco that allows users to design, configure, and troubleshoot network devices in a virtual environment. It is widely used for learning and practicing networking concepts.

Remote Login: A method that enables users to access a computer or network device from a remote location over a network using protocols such as Telnet, SSH (Secure Shell), RDP (Remote Desktop Protocol), or VNC (Virtual Network Computing). It is commonly used for remote administration and troubleshooting.