Unit 6: Networks - Subjective Questions

A computer network is a collection of two or more computing devices connected together through communication media (wired or wireless) to share data, resources, and services.

Sharing data any time, anywhere:

• Connectivity: Networks link devices across rooms, buildings, cities, or the globe through the Internet.
• Remote access: Users can log in and retrieve files from any location using remote-access technologies and VPNs.
• Cloud storage: Data stored on network servers or the cloud can be accessed from multiple devices at any time.
• Mobility: Wireless networks (Wi-Fi, mobile data) allow access without physical cables.
• Real-time collaboration: Multiple users can work on shared documents simultaneously.

This 'any time, anywhere' capability improves productivity, supports remote work, and enables global communication.

Networks serve several important purposes in organizations:

• Resource sharing: Hardware such as printers, scanners, and storage devices can be shared among many users, reducing cost.
• Data sharing: Files, databases, and applications are accessible to authorized users from a central location.
• Communication: Enables email, instant messaging, video conferencing, and VoIP calls.
• Centralized management: Software, security policies, and backups can be managed from a central server.
• Cost reduction: Shared resources and centralized licensing lower operational expenses.
• Access to the Internet: A single connection can be shared across many devices.
• Data security and backup: Central storage allows controlled access and regular backups.

Overall, networks improve efficiency, collaboration, and reduce redundancy.

Networks are commonly classified by the area they cover:

• PAN (Personal Area Network): Smallest network, covering a few meters around a person. Example: Bluetooth connection between a phone and headset.
• LAN (Local Area Network): Covers a limited area such as a home, office, or building. Offers high speed and is privately owned. Example: office computers connected to a shared printer.
• MAN (Metropolitan Area Network): Spans a city or large campus, connecting multiple LANs. Example: a cable TV network or city-wide Wi-Fi.
• WAN (Wide Area Network): Covers large geographic areas such as countries or continents. Example: the Internet, the largest WAN.

Each type differs in size, speed, ownership, and cost, with LANs being fastest and WANs covering the greatest distance.

A Hybrid Network is a network that combines two or more different types of network topologies or network types to leverage the advantages of each while minimizing their disadvantages.

Key points:

• It integrates different structures (e.g., star and bus, or wired and wireless) into a single functioning network.
• Provides greater flexibility and scalability.
• Commonly used in large organizations where different departments have different needs.

Examples:

• A star-bus hybrid, where several star networks are connected along a central bus backbone.
• A star-ring hybrid, connecting star networks through a ring backbone.
• A network combining wired LAN and wireless Wi-Fi access.

Advantages: Reliable, flexible, scalable.
Disadvantages: Complex to design and more expensive to install and maintain.

Networks can be structured in two main ways:

Client-Server Network:

• A dedicated server provides resources and services to client computers.
• Centralized control of data, security, and management.
• More secure and scalable, suitable for large organizations.
• Higher cost due to dedicated server hardware and administration.

Peer-to-Peer (P2P) Network:

• All computers (peers) have equal status and can act as both client and server.
• No dedicated server; resources are shared directly among peers.
• Simple and inexpensive to set up, suitable for small networks.
• Weaker security and harder to manage as it grows.

The structure of a network defines how devices are organized and how they interact.

Key components:

• Node: Any device connected to the network (computer, printer, server, switch). Each node has a unique address.
• Server: A powerful computer that provides services, resources, or data to other computers. Types include file servers, print servers, web servers, and database servers.
• Client: A computer or device that requests and uses services from a server.
• Workstation: An individual computer used by an end user.

Structural models:

• Client-Server model: Centralized servers serve many clients.
• Peer-to-Peer model: All devices share resources equally.

The chosen structure affects performance, security, cost, and manageability of the network.

Network topology refers to the physical or logical arrangement of devices and connections in a network.

Bus Topology:

• All devices connect to a single central cable (the backbone).
• Data travels along the bus to all devices.

Advantages: Easy to install, uses less cable, inexpensive.
Disadvantages: Failure of the main cable brings down the whole network; performance drops with many devices; difficult to troubleshoot.

Star Topology:

• All devices connect to a central device (hub or switch).
• Data passes through the central device.

Advantages: Easy to add/remove devices; failure of one cable does not affect others; easy to troubleshoot.
Disadvantages: If the central hub fails, the whole network fails; requires more cable.

Ring Topology:

• Each device connects to exactly two neighboring devices, forming a closed loop.
• Data travels in one direction (or both in a dual ring) passing through each node.

Reliability: Failure of one node or cable can break the entire ring (unless dual-ring is used).
Cost: Moderate; uses limited cabling.

Mesh Topology:

• Every device is connected to every other device with dedicated links.
• For nodes, the number of links required is .

Reliability: Very high; multiple paths mean failure of one link does not stop communication.
Cost: Very high due to large amount of cabling and ports.

In a full mesh topology, every node connects directly to every other node.

Derivation:

• Consider nodes. Each node must connect to the other nodes.
• Total connection ends .
• Since each cable is shared between two nodes, it is counted twice, so divide by 2.

Thus the number of cables is:

Number of I/O ports per node , and total ports .

Calculation for :

So 28 cables are required to connect 8 nodes in a full mesh topology.

A network protocol is a set of rules and standards that govern how data is transmitted, formatted, and received across a network. Both communicating devices must follow the same protocol to understand each other.

Why protocols are essential:

• Common language: They ensure devices from different manufacturers can communicate.
• Data formatting: Define how data is packaged into packets.
• Addressing: Specify how source and destination are identified.
• Error control: Detect and correct transmission errors.
• Flow control: Manage the rate of data transfer to prevent overload.
• Sequencing: Ensure packets are reassembled in the correct order.

Examples: TCP/IP, HTTP, HTTPS, FTP, SMTP, and DNS.

Without protocols, reliable and orderly communication between devices would be impossible.

TCP/IP (Transmission Control Protocol / Internet Protocol) is the fundamental suite of protocols that governs communication over the Internet.

Role of IP (Internet Protocol):

• Responsible for addressing and routing packets from source to destination.
• Assigns unique IP addresses to devices.
• Breaks data into packets and determines the best path (routing).
• Connectionless and does not guarantee delivery.

Role of TCP (Transmission Control Protocol):

• Provides reliable, connection-oriented communication.
• Establishes a connection using a three-way handshake.
• Ensures packets arrive in order and without errors through acknowledgments and retransmission.
• Handles flow control and error checking.

Together: IP delivers packets to the correct address, while TCP ensures they arrive reliably and in the correct order. This combination makes the Internet dependable.

Application-layer protocols enable specific services for users:

• HTTP (HyperText Transfer Protocol): Used to transfer web pages between web servers and browsers. HTTPS is its secure, encrypted version using SSL/TLS.
• FTP (File Transfer Protocol): Used for uploading and downloading files between a client and a server. Supports large file transfers.
• SMTP (Simple Mail Transfer Protocol): Used for sending email between mail servers.
• POP3 / IMAP: Used for receiving/retrieving email from a server.
• DNS (Domain Name System): Translates human-readable domain names (e.g., www.example.com) into IP addresses.
• DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP addresses to devices on a network.

Each protocol serves a distinct purpose in enabling network-based services.

Network media are the physical or wireless channels through which data travels. They are classified into two broad categories:

1. Guided (Wired) Media:

• Twisted Pair Cable: Two insulated copper wires twisted together. Types: UTP and STP. Cheap and common in LANs (Ethernet).
• Coaxial Cable: A central copper conductor surrounded by insulation and shielding. Used in cable TV and older networks; higher bandwidth than twisted pair.
• Fiber Optic Cable: Transmits data as light through glass/plastic fibers. Offers very high speed, large bandwidth, long distance, and immunity to interference.

2. Unguided (Wireless) Media:

• Radio waves: Used in Wi-Fi and mobile networks.
• Microwaves: Point-to-point communication using directional antennas.
• Infrared: Short-range communication (e.g., remote controls).
• Satellite: Long-distance global communication.

The choice depends on speed, distance, cost, and interference requirements.

The three main guided media differ in performance and cost:

Summary:

• Twisted pair is cheapest and widely used in LANs.
• Coaxial offers better shielding and bandwidth.
• Fiber optic is the fastest, most reliable, and best for long distances but is the most expensive.

Network hardware consists of the physical devices that connect and manage data flow in a network:

• Network Interface Card (NIC): Hardware that connects a computer to the network; each has a unique MAC address.
• Hub: A basic device that broadcasts incoming data to all connected devices (works at the physical layer). Inefficient due to collisions.
• Switch: An intelligent device that forwards data only to the intended recipient using MAC addresses, reducing collisions.
• Router: Connects different networks and routes data packets between them using IP addresses; commonly connects a LAN to the Internet.
• Modem: Converts digital signals to analog (modulation) and back (demodulation) for transmission over telephone/cable lines.
• Bridge: Connects and filters traffic between two network segments.
• Gateway: Connects networks using different protocols.
• Access Point: Provides wireless connectivity to a wired network.

Each device plays a specific role in ensuring efficient and reliable communication.

These three devices operate differently and at different layers:

Hub:

• Operates at the Physical layer (Layer 1).
• Broadcasts data to all connected ports regardless of destination.
• Causes collisions and wastes bandwidth.
• Least intelligent and cheapest.

Switch:

• Operates at the Data Link layer (Layer 2).
• Uses MAC addresses to forward data only to the intended device.
• Reduces collisions and improves performance.
• Used within a single LAN.

Router:

• Operates at the Network layer (Layer 3).
• Uses IP addresses to route packets between different networks.
• Connects a LAN to the Internet or other networks.
• Most intelligent of the three.

Wireless networks transmit data through the air using radio waves, while wired networks use physical cables.

Advantages of Wireless:

• Mobility: Users can move freely while staying connected.
• Easy installation: No cabling required, faster to set up.
• Scalability: Easy to add new devices.
• Convenience: Ideal for laptops, phones, and IoT devices.

Disadvantages of Wireless:

• Security risks: Signals can be intercepted; requires strong encryption.
• Interference: Affected by walls, distance, and other signals.
• Slower/variable speed: Generally lower and less stable than wired.
• Reliability: More prone to signal loss.

Wired advantages: Higher speed, stable, and more secure.
Wired disadvantages: Limited mobility, costly cabling, harder installation.

The choice depends on the need for mobility versus speed and security.

A topology defines how devices are arranged and connected. The major topologies are:

1. Bus Topology:

• All devices share one backbone cable.
• Advantages: Cheap, easy to install.
• Disadvantages: Single cable failure stops the network; poor performance with heavy traffic.

2. Star Topology:

• All devices connect to a central hub/switch.
• Advantages: Easy to manage; single device failure does not affect others.
• Disadvantages: Central device failure stops the whole network; more cabling.

3. Ring Topology:

• Devices form a closed loop; data passes node to node.
• Advantages: Orderly data flow, no collisions.
• Disadvantages: One break can disrupt the entire network.

4. Mesh Topology:

• Every device connects to every other, requiring links.
• Advantages: Highly reliable, multiple paths.
• Disadvantages: Very expensive, complex cabling.

5. Tree/Hierarchical Topology:

• Combines star networks connected in a hierarchy.
• Advantages: Scalable, easy to expand.
• Disadvantages: Depends on the root node.

Suitability: Star and tree for offices/LANs; mesh for critical/backbone networks; bus and ring for small or legacy setups.

Modern networks enable seamless data access regardless of location and time through several technologies:

How data is shared:

• Data is broken into packets, transmitted over media, routed via protocols (TCP/IP), and reassembled at the destination.
• Shared resources reside on servers or the cloud, accessible to authorized clients.

Enabling technologies:

• Internet: Global WAN connecting billions of devices.
• Cloud computing: Data stored on remote servers accessible from any device (e.g., Google Drive, OneDrive).
• Wireless networks (Wi-Fi, 4G/5G): Provide mobility and connectivity without cables.
• VPN (Virtual Private Network): Secure remote access to organizational networks.
• Mobile devices: Smartphones and tablets allow access on the move.
• Synchronization: Keeps data consistent across multiple devices.

Benefits: Remote work, global collaboration, real-time updates, and improved productivity.

Concerns: Security, privacy, and dependence on connectivity must be managed with encryption and authentication.

Both addresses identify devices on a network but serve different purposes.

MAC Address (Media Access Control):

• A physical hardware address permanently assigned to a NIC by the manufacturer.
• 48-bit address, usually written in hexadecimal (e.g., 00:1A:2B:3C:4D:5E).
• Operates at the Data Link layer and is used for local delivery within a network.
• Does not change.

IP Address (Internet Protocol):

• A logical address assigned to a device on a network, either manually or via DHCP.
• IPv4 uses 32 bits (e.g., 192.168.1.1); IPv6 uses 128 bits.
• Operates at the Network layer and is used for routing across networks.
• Can change depending on the network.