Chapter 2 : Data Communication and Networking : Computer Sci NEB Class 12

Unit 2: Data Communication and Networking

Concept of Network and Data Communication

Communication

Communication is the process of sharing information or messages between people or groups. It involves sending and receiving information through various methods such as speaking, writing, gestures, or electronic devices like phones and computers. Effective communication helps individuals convey their thoughts, feelings, and ideas, fostering understanding and collaboration among people.

A network is an interconnection of two or more computers or networking devices with the help of transmission media and protocols. Computer network brings communication (information exchange) faster, reliable, cheaper and secure.

Data Communication

The transferring of data from one computer to another computer is called data communication. It is also known as the exchange of information or data between devices or systems using various methods such as wired or wireless connections, signals, protocols, and devices like computers, smartphones, routers, and satellites.

2.1 Communication System, Basic Elements, and Model

Communication System

A communication system is a network of devices and processes that allows people to exchange information or messages. It includes various components such as transmitters, receivers, channels (like wires or airwaves), and protocols (rules for how data is transmitted and received). Communication systems enable individuals or groups to share data, ideas, or emotions over short or long distances, using different technologies like telephones, computers, radios, or the internet. They play a crucial role in facilitating connections and interactions between people, whether through spoken words, written text, or digital media.

Fig: Block Diagram of Communication System

A diagram shows a 'Source of information' sending a 'Message signal' to a 'Transmitter'. The 'Transmitter' sends a 'Transmitted signal' through a 'Channel'. The 'Channel' delivers a 'Received signal' to a 'Receiver'. The 'Receiver' produces an 'Estimate of message signal' for the 'User of information'.

Basic Elements of Communication (Components of Data Communication)

A communication system has five major components:

1. Sender: The person or entity initiating and encoding the message to be communicated. The sender device sends the message to the receiver and it can be a computer, workstation or any networking device.
2. Receiver: The intended recipient of the message who decodes and interprets the information. The receiver device receives the messages from the medium and it can be a computer, workstation or any networking device.
3. Message (Data): The message is the actual information or content being communicated between the sender and receiver. It is in the form of text, number, picture, audio, and video.
4. Medium (Transmission Medium): The method or channel used to transmit the message, such as speech, writing, or electronic devices. The transmission medium is the physical connection or path in which a message can travel from sender to receiver and vice versa. The medium can be wired or wireless.
5. Protocol: A protocol is the set of rules or guidelines governing the exchange of data, ensuring proper communication and understanding. Without a protocol, two devices can be connected but not be communicated.

2.2 Data Communication Elements and Mode

The elements of data communication are the same as the basic elements of communication listed above: Sender, Receiver, Message, Medium, and Protocol.

Modes of Communication (Transmission Mode)

Communication has three modes. Data communication can be classified into three types on the basis of the direction of communication flow. Communication mode defines the direction of data flow in the communication.

• Simplex: In simplex communication, data flows in one direction only, also known as unidirectional. One device is the sender, and the other is the receiver, but they cannot exchange roles. In this mode transmission is possible in only one direction similar to a one-way street. Examples include television broadcasts, radio transmissions, or one-way paging systems.

• Half-Duplex: In half-duplex communication, data can flow in both directions, but not simultaneously. Devices can take turns sending and receiving data, but they cannot do both at the same time. This mode is a communication mode where two devices can communicate with each other, but not simultaneously. Examples include walkie-talkies and some two-way radios.

• Full-Duplex: In full-duplex communication, data can flow in both directions simultaneously. Devices can send and receive data at the same time, enabling real-time two-way communication. This method allows data to be sent and received simultaneously, similar to a two-way road where traffic can flow in both directions at the same time. Examples include telephone conversations, video conferencing, mobile and telephone communication, and most internet connections.

Computer Network

A computer network is like a digital highway that connects computers and other devices, allowing them to communicate and share information with each other. A group of interconnected computers which can share data, software, and hardware and also communicate with other people is called a computer network. It enables devices to send and receive data, share resources like printers or files, and access the internet. Networks can be wired, using cables like Ethernet, or wireless, using technologies like Wi-Fi or Bluetooth. Computer networks are essential for businesses, schools, and homes, facilitating collaboration, communication, and access to resources and services.

Advantages of Computer Network

• Resource Sharing: Networks allow multiple users to share hardware (like printers) and software (such as applications) resources.
• Communication: Networks enable quick, faster, and cheaper exchange of messages, emails, and files between users, enhancing collaboration.
• Information Access: Networks provide access to vast amounts of data and online resources, aiding research and decision-making.
• Centralized Data Management / Control: Networks facilitate centralized storage and management of data, improving reliability and security.
• Cost Savings: By sharing resources, networks help reduce hardware, software, and maintenance costs.
• Improved Efficiency: Networks streamline workflows and automate tasks, boosting productivity and operational efficiency.
• Scalability: Networks can easily accommodate growth in users and devices without major disruptions.
• Flexibility: Networks support flexible work arrangements like remote access, enabling users to work from anywhere.
• Enhanced Security: Networks allow for the implementation of security measures to protect data from unauthorized access and cyber threats.
• Global Connectivity: Networks connect users across geographical boundaries, fostering international cooperation and business opportunities.
• Backup and recovery.
• Workgroup computing.
• Remote accessing facility.

Disadvantages of Computer Network

• Security Risks / Hacking: Networks can be vulnerable to hackers and viruses, risking the safety of sensitive information and leakage of private information.
• Dependency on Infrastructure: If network components fail, communication and access to data may be disrupted.
• Slowdowns: When many users use the network at once, it can slow down, making tasks take longer.
• Complexity: Setting up and fixing networks can be complicated and may need special skills or experience to set up.
• Privacy Concerns: Personal information sent over networks may be seen by unauthorized people.
• Costs: Creating and keeping up networks can be expensive, needing money for equipment and maintenance.
• Compatibility Problems: Devices or software may not work well together on a network, causing issues.
• Risk of Losing Data: If something goes wrong with the network, important data could be lost or damaged.
• Spread of virus.
• Software piracy.
• Needs skilled manpower to operate.

2.3 Define and Apply LAN and WAN

On the basis of Geographical area of a network, a computer network can be further classified into three types: LAN, MAN, and WAN.

Local Area Network (LAN)

A LAN (Local Area Network) is like a private neighborhood of connected devices, such as computers, printers, and servers, all within a limited geographical area like a home, office, school, or a building. It is a privately owned small-sized network. It allows these devices to communicate and share resources, such as files or internet connections, quickly and efficiently. LANs are typically owned, controlled, and managed by a single organization or individual, providing a secure and reliable network environment for local communication and collaboration. It ranges about 100 meters up to a few kilometers (2 or 3 kilometers).

Advantages of LAN:

• Devices can easily share printers, files, and more.
• Data moves quickly between connected devices. Data transmission speed is faster than MAN & WAN.
• Network connection is reliable.
• All files are stored in one place for easy access.
• Network is set up for efficiency.
• It is cheaper to establish and easier to manage and operate.

Disadvantages of LAN:

• LANs can be vulnerable to hacking and data breaches.
• Network failures can disrupt communication and operations.
• High traffic can slow down data transfer speeds.
• Setting up and managing LANs can be complicated.
• Network failures may result in loss of important data.
• It is limited only to a small area.
• It connects a small number of computers.
• Lack of backup provision.

Metropolitan Area Network (MAN)

A MAN (Metropolitan Area Network) is a network that covers a city or a large geographical area, connecting multiple LANs together. A MAN is larger than a LAN but smaller than a WAN. It allows organizations or individuals within a city to share resources, communicate, and access data over a wider area. It ranges up to 100 km. Examples include a cable TV network or an Internet Service Provider (ISP) in a city. MANs often use high-speed connections like fiber optics and wireless technologies to facilitate fast and reliable communication within a metropolitan area.

Advantages of MAN:

• MANs link multiple LANs across a city or metropolitan area, facilitating communication and data exchange over a larger geographical area.
• MANs provide high-speed connectivity, enabling faster transmission of data and information between different locations within the city.
• MANs allow for the sharing of resources such as printers, servers, and internet connections among users and organizations.
• It covers a larger area than LAN.
• It can connect dissimilar systems and networks.

Disadvantages of MAN:

• Setting up and maintaining MAN infrastructure can be expensive, especially across large metropolitan areas.
• MANs can be susceptible to disruptions like natural disasters or technical failures, leading to network outages and service interruptions.
• MANs may not cover every area within a city, leaving some regions with limited or no access to the network's benefits.
• It is complex to manage and provide security.
• Transmission speed is usually slower compared to LAN.

Wide Area Network (WAN)

A Wide Area Network (WAN) is a network that extends over a large geographical area such as states, countries, or even the world. It is also known as the internet. A WAN is quite a bigger network than the MAN. It is not limited to a single location, but it spans over a large geographical area through a telephone line, fiber optic cable, or satellite links. It ranges above 1000 km. It connects a larger number of computers than LAN and MAN.

Advantages of WAN:

• Wide coverage: WANs cover large geographical areas, allowing users to connect across cities, countries, or even continents.
• Global connectivity: WANs provide global connectivity, enabling users to access resources, services, and information from anywhere in the world.
• Centralized resources: WANs allow for the centralization of resources such as servers, databases, and applications, enhancing efficiency and productivity.
• It also connects dissimilar systems and networks.

Disadvantages of WAN:

• High costs: Setting up and maintaining WAN infrastructure, including leased lines and equipment, can be expensive.
• Security risks: WANs face security threats such as data breaches and malware attacks, especially when transmitting sensitive information over public networks. It provides less security.
• Lower speeds: WANs may have lower data transfer speeds compared to LANs due to longer distances. Transmission speed is usually slower.
• It is more complex to establish, manage and operate.

Comparison between LAN, MAN, and WAN

2.6 Network Architecture

Network architecture refers to the various services provided by the network and it also deals with how data is transmitted from one computer to others. On the basis of network architecture, computer networks can be classified into two types.

Peer-to-Peer Architecture

Peer-to-peer networks are computer networks that do not have a central server controlling the network. In this architecture, each node/workstation has the same capabilities and responsibilities. Each computer is called a peer, and these peers are connected to one another. No computer has control over another. Each computer functions as both client and a server. This type of network is not suitable for a large network where a client-server structure would be preferable. In a peer to peer architecture, all computers have equal authority to access data.

Advantages of Peer-to-Peer Network:

• Each computer can communicate and share its data and resources with all others (e.g., files or a printer).
• Users can control which files they wish to share or keep private.
• No cost in buying a server. Cheaper than client server.
• No need to pay a network technician (each user manages own file sharing permissions).
• Easier to set up with less specialist knowledge needed. Simple and easy to install.
• Overall set up cost is cheaper.
• Computer failure will only disrupt the files being shared from that computer.
• All nodes have equal right to access the resources.
• Suitable for small size network.

Disadvantages of Peer-to-Peer Network:

• Difficult to recover files as they are not backed up centrally. Each computer needs its backup system.
• Files and resources are more difficult to share.
• Files are potentially less secure when not centralized. Network security problem.
• Difficult to administrate the whole network as the system is not centralized.
• Performance may be slower due to each computer fulfilling more than one role. Very low performance for large size network.
• Security can be more expensive as each computer needs its anti-virus software.
• It is up to the user of each computer to ensure viruses are not introduced to the network.
• Having lots of users/computers on the network becomes problematic.
• No central backup and recovery mechanism.

Client-Server Architecture

Client-server networks are computer networks that use a dedicated computer (server) to store data, manage/provide resources and control user access. The server is more powerful than any other computer in the network. The server acts as a central point on the network upon which the other computers connect to. A computer that connects to the server is called a client. A client-server network is usually preferred over a peer-to-peer network for larger networks. In a client-server architecture, the server always provides its resources to the clients and the client always receives resources from the server.

Advantages of Client-Server Network:

• Generally, more secure than peer-to-peer networks. High security.
• One client computer crashing does not affect the other computers.
• Easier to recover files as backups can be controlled centrally by the network administrator.
• Files and resources are easier to share and control from the server. Centralized administration.
• Improved levels of security as files are centralized.
• It's easier to administrate the whole network using a server. Easy to manage the network.
• Faster performance as each computer is only fulfilling one role.
• Security is potentially cheaper and easier when done centrally.
• Individual users do not have to worry about backups or security.
• Larger networks can be created. Reliable architecture.

Disadvantages of Client-Server Network:

• Servers can be expensive to buy and maintain. More expensive to setup.
• A network technician will often be required.
• Trickier to set up with specialist knowledge needed.
• Server failure will probably disrupt all computers on the network. If the server fails, the whole network gets disturbed.
• Data traffic may lead to data collision.

Differences Between Peer-to-Peer and Client-Server Architecture

2.4 Transmission Medium

A transmission medium can be broadly defined as anything that can carry information from a source to a destination. Transmission media refers to the physical connection through which data are transmitted between sender and receiver devices. The transmission medium is usually free space, metallic cable, or fiber-optic cable. The information is usually a signal that is the result of a conversion of data from another form. They are classified as follows: Guided Media and Unguided Media.

Guided Media (Wired / Bounded Media)

Guided media refers to communication channels that use physical pathways to transmit data signals, such as copper wires, fiber-optic cables, or coaxial cables. Guided media is a physical link between devices that can send data through wires. These pathways guide the signals along a specific route, providing a reliable and secure means of communication for transmitting data over short or long distances.

• Twisted-Pair Cable: This is the oldest and still most common transmission media. It consists of pairs of insulated copper wires twisted together to reduce electromagnetic interference and crosstalk. Tighter the twisting cables, greater the transmission rate. It is used for both analog and digital transmission. It is available in different categories i.e. CAT 1, CAT 2, ..., CAT 6, CAT 7, etc. This cable is connected with the help of RJ45.

  There are two types: Unshielded Twisted Pair (UTP) which is the most common and cheaper, and Shielded Twisted Pair (STP) which is rarely used, more expensive, but can carry data signals for longer distances.

  Advantages: It is light, thin and more flexible. It is cheaper than other cables. It can transmit data at a higher bandwidth for short distance.

  Disadvantages: It cannot be used for long distance transmission. It is slowed for data transmission than other cables.

• Coaxial Cable (COAX): This cable consists of a copper wire conductor which is surrounded by an insulator over which there is a sleeve of copper which is then covered by protective plastic. It carries data signals at a faster speed than twisted pair cable. Coaxial cables are commonly used for cable television (CATV) distribution, internet connectivity, and networking applications due to their ability to carry high-frequency signals with low attenuation. This cable is connected with the help of a BNC Connector (Bayonet-Neill-Concelman).

  There are two types: Thin COAX (thinnest, 10 mbps, up to 200 meters) and Thick COAX (thickest, 10 mbps, up to 500 meters).

  Advantages: It provides faster data transmission. It can transmit data over a medium range distance. It is easy to install.

  Disadvantages: It is expensive to install. It is not appropriate for long-distance transmission. It is rarely used at present for a computer network.

• Fiber-Optic Cable: It is made up of a glass or plastic that transfers signals in the form of light. It consists of thin strands of glass or plastic fibers that transmit data using light pulses. Fiber optic cables are known for their high bandwidth, low attenuation, and immunity to electromagnetic interference. The main core glass is surrounded by a strong cladding with a lower index of refraction. It works on the principle of total internal reflection. This cable is connected with the help of an S-T connector (Straight Tip connector).

  Advantages: It provides the fastest data transmission. The speed is highest of all cables (Gbps, Tbps). It can be used for both short to long distance transmission. It provides error-free and highly secured transmission.

  Disadvantages: It is the most expensive and difficult to install. It is not preferred to use in hillside areas. Skilled manpower is required to install.

Unguided Media (Wireless / Unbounded Media)

Unguided media, also called wireless media, transport electromagnetic waves without using a physical conductor. It refers to the use of wireless media to transfer data. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them.

• Microwave System: Microwaves are a type of electromagnetic radiation with wavelengths longer than infrared light but shorter than radio waves. It uses very high-frequency radio signals to transmit data through the air. The transmitting and receiving antennas must be placed on tall buildings or towers, hills and mountain peaks in a line-of-sight path. For long-distance transmission, repeaters are used at different intervals.

• Satellite Communication: A satellite serves as a relay station for transmitting and receiving signals through space without the need for physical cables. It is the most common worldwide communication system at present. It uses a satellite as a repeater that orbits in space. The ground station has receivers and transmitters. The satellite amplifies the weak signal and transmits it back to the receiver.

• Infrared Technology: Infrared (IR) is a type of electromagnetic radiation with wavelengths longer than visible light but shorter than microwaves. It can be used for short-distance transmission. It is mainly used in wireless remote control, wireless LAN, wireless mouse and keyboard, bluetooth, etc. They cannot penetrate walls or any solid objects.

• Radio wave: Radio waves are a type of electromagnetic radiation used for wireless communication. They transmit information through the air, allowing devices like radios, cell phones, and Wi-Fi routers to communicate without the need for physical connections.

• Bluetooth: Bluetooth is a short-range wireless technology that is used for exchanging data between fixed and mobile devices over short distances (up to 10m to 20m). It relies on radiofrequency and does not require line of sight.

• Wi-Fi: Wi-Fi is a wireless networking technology that uses radio waves to provide wireless high-speed internet access. It uses high band frequencies such as 2.4 GHz up to 5 GHz.

2.5 Terminologies for Transmission Impairments

Transmission impairments are disruptions or distortions that occur during the transmission of data signals over a communication channel. These impairments can be caused by various factors and can degrade the quality and integrity of the transmitted signals, leading to errors, loss of information, and reduced performance in communication systems.

• Jitter: Jitter refers to the variation in the arrival times of data packets transmitted over a network. It is a fluctuation in delay as packets are being transferred. It can result in inconsistent delays, affecting the smoothness and reliability of real-time communication applications such as voice over IP (VoIP) or video streaming.
• Echo and Singing: Echo is a sound that is a copy of another sound produced when sound waves bounce on the surface. Echo and singing are phenomena that occur in telecommunications due to signal reflections within the communication channel.
• Crosstalk: Crosstalk is the unwanted interference between adjacent communication channels, resulting in the leakage of signals from one channel to another. It is a form of interference in which a signal in one cable is mixed with another cable. It can lead to data errors and decreased signal quality.
• Distortion: Distortion refers to the alteration or deformation of a signal as it travels through a communication channel. It is a change in the form or shape of a signal that can cause an unclear reception. It can result from various factors such as noise, interference, or limitations in the transmission medium.
• Noise: Noise refers to unwanted or random signals that interfere with the transmission and reception of data. It is the mix-up of different unwanted signals or frequencies while communicating messages. It can degrade the quality of the signal, leading to errors.
• Bandwidth: Bandwidth refers to the capacity or range of frequencies available for transmitting data over a communication channel. It refers to the speed of the internet. It determines the amount of data that can be transmitted in a given amount of time, typically measured in bits per second (bps). A higher bandwidth allows for faster data transmission.

2.8 Network Topologies, Devices, and Tools

Network Topology

Network topology refers to the layout or structure of a computer network, including how devices are connected and the paths data follows. The physical and logical arrangement of nodes on a network is called network topology. It describes how computers, printers, and other devices are arranged and linked together. Nodes usually include routers, computers, switch, software, etc.

Types of Network Topology

• Bus Topology: Bus topology is a type of network setup where all devices are connected to a single main cable, called a bus or trunk. Coaxial cable is used in this topology. Data travels along this cable, and all devices on the network receive the data. Terminators are used at both ends of the trunk to absorb the signal. If the main cable breaks, the entire network can be affected.

  Advantages: Simplicity (Easy to set up), Cost-Effective (Cheaper and easier to implement), Scalability (Easy to expand by adding devices).

  Disadvantages: Single Point of Failure (Entire network can fail if the main cable is damaged), Limited Bandwidth (Shared among all devices), Data Collisions, Difficulty in Identifying Faults.

• Ring Topology: In this ring topology, each device is connected to exactly two other devices, forming a circular pathway. Data travels in one direction around the ring (clockwise or anti-clockwise). While it offers balanced traffic flow, disruptions to any single connection can potentially disrupt the entire network.

  Advantages: Balanced Traffic, Simple Setup, Efficient Communication (Each device has equal priority to communicate).

  Disadvantages: Vulnerability to Ring Breakage (If one connection fails, the entire network can be affected), Limited Scalability (Adding/removing devices can be difficult), Slower Performance as network grows.

• Star Topology: In a star topology, each computer is connected to a central device such as a hub or switch. Twisted-pair cable is commonly used. When one node wants to communicate with another, it sends data to the central hub, which then forwards the data to the intended recipient. If the hub fails, the entire network may become inaccessible.

  Advantages: Easy to Set Up, Simple to Manage, Scalability (Easier to add or remove a computer), Isolation of Devices (Failure in one computer doesn't affect the entire network), Centralized Control, Better Performance.

  Disadvantages: Dependency on Central Hub (Single Point of Failure), Costly (Requires more cables), Performance Bottleneck (Hub can get slow), more expensive than bus topology because of the cost of the hub/switch.

• Mesh Topology: Mesh topology is a network configuration where each device is connected to every other device in the network, creating multiple paths for data transmission. This redundancy ensures robustness and fault tolerance, as data can be rerouted if one connection fails.

  Advantages: High Reliability, Scalability, Flexibility (dynamic routing).

  Disadvantages: Cost (requires more cabling), Complexity (difficult to manage and configure).

• Tree Topology: Tree topology is a topology that seems like a hierarchical model in a tree structure. If the server node is affected, its child node is also affected.

• Hybrid Topology: Hybrid topology is a type of network topology in which two or more different topologies are integrated or combined to lay out a network.

Basic Networking Devices

• NIC (Network Interface Card): It is a device that connects the computers and Network cable. It coordinates the transfer of information between the computer and the network. Each NIC is assigned with a unique MAC address.
• Modem (Modulator-Demodulator): A modem is a hardware which connects a computer to a broadband network or wireless router. It converts digital data from a network into analog signals for transmission over telephone lines and vice-versa. The process of translating a digital signal into an analog signal is called modulation, and the reverse is demodulation.
• Hub: A basic networking device that connects multiple devices in a network, but unlike a switch, it broadcasts data to all devices connected to it. Hubs are less efficient than switches. It works at the physical layer.
• Switch: Connects devices within a single network, such as computers, printers, and servers. Switches are intelligent hubs that forward data packets to their intended destination within the same network based on MAC addresses, creating a direct connection between sender and receiver.
• Router: Directs data packets between different networks by determining the best path for them to reach their destination. Routers are essential for connecting multiple networks together, such as connecting a home network to the internet.
• Bridge: The bridge is used to connect two different network segments that use the same communication protocol. A bridge is more intelligent than a hub as it examines the destination address of each packet and only passes through those that need to get from one segment to the other.
• Gateway: A gateway is a network node used in telecommunications that connects two different networks using different network architectures or incompatible transport protocols. It acts as a translator between networks.
• Access Point (AP): Enables wireless devices to connect to a wired network. Access points are used in wireless networks to provide Wi-Fi connectivity.

2.7 Basic Terms and Tools Used in Computer Network

Basic Terms

• IP Address: An IP (Internet Protocol) address is a numerical label assigned to each device connected to a computer network. It serves two main purposes: identifying the host or network interface and providing the location of a device in the network.
  • IPv4 Address: Consists of four sets of numbers separated by periods (e.g., 192.168.1.1). IPv4 has 2^32 addresses.
  • IPv6 Address: Uses hexadecimal notation with longer addresses to accommodate the growing number of devices (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). IPv6 has 2^128 addresses.
• MAC Address: A MAC (Media Access Control) address is a 12-digit hexadecimal number assigned to each device's Network Interface Card (NIC) for communication at the data link layer. It is a unique identifier usually assigned by the manufacturer.
• Subnet Mask: A subnet mask is a 32-bit number used in IPv4 networking to divide an IP address into network and host portions. It determines which part of the IP address represents the network and which part represents the host.
• Gateway: This is like the door to the outside world for your local network. It's usually a router that helps your devices talk to devices on other networks, like the internet.
• Intranet: An intranet is a private network that functions similarly to the internet but is accessible only to authorized users within an organization (e.g., employees). It is used for sharing company documents, tools, and internal communication.
• Extranet: An extranet is a controlled private network that allows organizations to extend specific parts of their internal network to authorized external users or partners, such as clients, suppliers, or business partners.

Differences between Internet, Intranet, and Extranet

Network Tools

• Packet Tracer: Packet Tracer is a visual simulation program developed by the Cisco Network Academy. It simulates a Cisco network without a physical network. Its drag and drop interface is easy to use. It can be used to monitor packet transfer, data transfer and more in real-time topology.
• Remote login: Remote login, also known as remote access, is the ability to access the data stored on a computer from a remote location. It enables you to open, edit, and save files located on your device from anywhere in the world.

Protocols

A protocol is a set of rules and conventions that govern how data is transmitted and received over a network. It defines the format, sequence, error handling, and other aspects of communication between devices. Protocols are the set of rules that control and coordinate the transmission of messages over the network.

Commonly used Protocols:

• TCP (Transmission Control Protocol): Provides reliable, connection-oriented communication. It is responsible for dividing the data packets into smaller pieces. TCP ensures that data packets are delivered in the correct order and without errors.
• IP (Internet Protocol): Defines the addressing scheme and routing of data packets across networks. IP is responsible for providing the route to the data while transferring through different medium or channels.
• HTTP (Hypertext Transfer Protocol): Used for transmitting hypertext documents (web pages) over the internet. It is responsible for displaying web contents (text, images, audio, video).
• HTTPS (Hypertext Transfer Protocol Secure): A secure version of HTTP that encrypts data transmitted between a web browser and a web server.
• FTP (File Transfer Protocol): Used for transferring files (uploading or downloading) between a client and a server on a network.
• SMTP (Simple Mail Transfer Protocol): Used for sending email messages between servers over the internet.
• POP (Post Office Protocol): Used by email clients to retrieve email messages from a server.

2.9 OSI Reference Model and Internet Protocol Addressing

Open Systems Interconnection (OSI) Model

The OSI (Open Systems Interconnection) model is a framework that defines the communication functions of a network system through seven layers. The OSI model is a concept that describes how data communications should take place. It divides the process into a seven-group called layers (Open System Inter-connection). Each layer handles specific tasks to facilitate interoperability between network devices. It serves as a blueprint for designing and understanding network architectures.

The 7 Layers of the OSI Model

1. Physical Layer (Layer 1): This layer deals with the physical connection between devices. It is concerned with transmitting raw bits over a communication medium. It defines specifications for the transmission media, electrical signaling, connectors, and data encoding. It transmits the binary data (bits) as electrical or optical signals.
2. Data Link Layer (Layer 2): This layer is responsible for framing data into packets (frames), detecting and correcting errors that may occur during transmission, and controlling access to the physical medium (using MAC addresses). It ensures reliable point-to-point communication.
3. Network Layer (Layer 3): The network layer is responsible for the source to destination delivery of a packet across multiple networks. It handles logical addressing (IP addresses), routing, and forwarding of data packets. It determines the best path for data to travel from the source to the destination.
4. Transport Layer (Layer 4): The transport layer provides end-to-end communication between devices and ensures reliable data delivery. It is responsible for the source to destination (end-to-end) delivery of the entire message. It segments data into smaller packets, establishes connections, manages flow control, and reassembles packets at the receiving end. Common protocols include TCP and UDP.
5. Session Layer (Layer 5): The session layer is responsible for establishing, maintaining, managing, and terminating communication sessions between applications. It facilitates dialogue control and synchronization between devices.
6. Presentation Layer (Layer 6): The presentation layer is responsible for data translation, encryption, and compression, ensuring that data is presented in a format that the application layer can understand. Data is compressed for transmission and uncompressed when received.
7. Application Layer (Layer 7): The application layer provides network services directly to end-users and applications. It serves as the interface between the user and the network. It includes protocols such as HTTP, FTP, SMTP, and DNS for various applications and services.

Internet Protocol Addressing

Internet Protocol (IP) addressing is a core component of the network layer. As defined earlier, an IP address is a unique numerical label assigned to each device on a network that uses the Internet Protocol for communication. It is responsible for the logical addressing of devices and the delivery of packets to their intended destinations.

• IPv4: The fourth version of the Internet Protocol, using a 32-bit address space, which allows for 4.3 billion unique addresses. It is written in dot-decimal notation (e.g., 172.16.254.1).
• IPv6: The most recent version of the Internet Protocol, using a 128-bit address space, which provides a vastly larger number of unique addresses. It is written in hexadecimal notation and is designed to replace IPv4.