Computer Networks

Main Idea

Computer networks connect devices so that they can communicate and share data, hardware, software, and services. Effective communication depends on suitable network devices, transmission media, addressing systems, and protocols. The Internet supports services including the World Wide Web, email, file transfer, and online communication, while cyber-safety measures protect networks, information, and users from unauthorized access, malware, fraud, and data loss.

Key Concepts and Definitions

• Computer Network: A group of interconnected computers and devices that communicate and share resources.
• PAN: Personal Area Network covering a very small area, such as devices connected around one person.
• LAN: Local Area Network covering a limited area such as a room, home, school, or office.
• MAN: Metropolitan Area Network covering a city or large campus.
• WAN: Wide Area Network covering large geographical areas; the Internet is the largest example.
• Network Topology: The physical or logical arrangement of devices and communication links in a network.
• Bus Topology: All devices share a single main communication cable.
• Star Topology: Each device is connected to a central device such as a switch or hub.
• Tree Topology: A hierarchical arrangement formed by connecting groups of star networks.
• Mesh Topology: Devices are connected through multiple links, providing high reliability but requiring more wiring.
• Transmission Media: The path through which data travels, including wired media such as cables and wireless media such as radio waves.
• Twisted Pair Cable: A cable made of twisted copper wires, commonly used in telephone and computer networks.
• Coaxial Cable: A shielded copper cable used for carrying signals with reduced interference.
• Optical Fibre: A cable that transmits data as light through glass or plastic fibres; it supports high speed and long-distance communication.
• Modem: A device that converts digital signals to suitable transmission signals and converts received signals back into digital form.
• Repeater: A device that regenerates weak signals to extend the communication distance.
• Hub: A basic connecting device that broadcasts incoming data to all connected devices.
• Switch: A device that forwards data to the intended device within a network using device addresses.
• Router: A device that connects different networks and selects a path for forwarding data packets.
• Gateway: A device or system that connects networks using different communication protocols.
• Wireless Access Point: A device that allows wireless devices to connect to a wired network.
• Network Interface Card: Hardware that enables a computer or device to connect to a network.
• Protocol: A set of rules that controls how devices format, transmit, receive, and interpret data.
• TCP/IP: The main protocol suite used for communication across the Internet; TCP manages reliable delivery and IP handles addressing and routing.
• HTTP: A protocol used to transfer web pages and other web resources.
• HTTPS: The secure version of HTTP that uses encryption to protect web communication.
• FTP: A protocol used to transfer files between computers over a network.
• SMTP: A protocol used for sending email messages.
• POP3: A protocol commonly used to download email messages from a mail server.
• IMAP: A protocol that allows users to access and manage email while messages remain stored on the mail server.
• DNS: The Domain Name System translates human-readable domain names into IP addresses.
• IP Address: A numerical address used to identify a device or network interface on a network.
• IPv4: An IP addressing system using 32-bit addresses, usually written as four decimal numbers separated by dots.
• IPv6: A newer IP addressing system using 128-bit addresses to provide a much larger address space.
• MAC Address: A hardware address assigned to a network interface, generally used for communication within a local network.
• URL: A Uniform Resource Locator that specifies the address of a resource on the Internet.
• Web Browser: Software used to access and display web pages and web applications.
• Web Server: A computer system or software that stores, processes, and delivers web resources to clients.
• World Wide Web: A collection of interlinked web pages and resources accessed through the Internet using web protocols.
• Search Engine: An online service that searches and organizes information available on the web.
• Cloud Computing: The delivery of computing resources such as storage, software, and processing over a network, usually the Internet.
• Bandwidth: The maximum amount of data that can be transmitted through a communication channel per unit time.
• Data Transfer Rate: The amount of data transmitted per second, commonly measured in bits per second.
• Packet: A small unit of data into which a message is divided for transmission across a network.
• Firewall: Hardware or software that monitors and controls network traffic according to security rules.
• Malware: Malicious software such as viruses, worms, Trojan horses, spyware, and ransomware.
• Phishing: A fraudulent attempt to obtain sensitive information by pretending to be a trustworthy person or organization.
• Encryption: The conversion of readable data into an unreadable form so that only authorized users can access it.
• Digital Certificate: An electronic document used to verify the identity of a website or organization and support secure communication.
• Cyber Safety: Safe and responsible practices for protecting devices, accounts, personal data, and online identity.
• Digital Footprint: The record of information and activities a person leaves while using digital services.
• Netiquette: The accepted rules of polite, responsible, and respectful behaviour online.

Supporting Arguments and Evidence

• Networks may be classified by geographical coverage as PAN, LAN, MAN, or WAN. A PAN serves devices around one person, a LAN covers a limited location such as a school or office, a MAN covers a city or large campus, and a WAN covers a large geographical area. The Internet is the largest example of a WAN.

• Network topology determines how devices and communication links are arranged. In a bus topology, all devices share one main cable. In a star topology, each device connects to a central switch or hub. A tree topology connects groups of star networks hierarchically, while a mesh topology uses multiple links to provide high reliability at the cost of additional wiring.

• Transmission media provide the path for data. Twisted pair cable uses twisted copper wires and is common in telephone and computer networks. Coaxial cable is shielded to reduce interference. Optical fibre transmits data as light through glass or plastic fibres and supports high-speed, long-distance communication. Wireless media transmit data using radio waves.

• Network devices perform different functions. A modem performs modulation and demodulation, converting digital signals into suitable transmission signals and converting received signals back into digital form. A repeater regenerates weak signals. A hub broadcasts incoming data to every connected device, whereas a switch forwards data mainly to the intended device using device addresses. A router connects different networks and selects paths for packets, while a gateway connects networks using different protocols. A wireless access point connects wireless devices to a wired network, and a network interface card enables a device to connect to a network.

• Communication requires compatible protocols. TCP/IP is the principal Internet protocol suite: TCP provides reliable, ordered, and error-checked delivery, while IP is mainly responsible for addressing and routing packets. HTTP commonly transfers web pages, whereas HTTPS provides encryption and authentication for safer web communication. FTP transfers files. SMTP sends email, while POP3 and IMAP support receiving or managing email.

• Common protocol ports include HTTP on port 80, HTTPS on port 443, FTP on ports 20 and 21, SMTP on port 25, and DNS on port 53. DNS converts human-readable domain names such as example.com into IP addresses used by network devices.

• Addressing systems identify devices and network resources. IPv4 uses 32-bit addresses and can provide approximately $2^{32}$ possible addresses; an IPv4 address is commonly written in dotted-decimal form, such as 192.168.1.10. IPv6 uses 128-bit addresses and therefore provides a much larger address space. A MAC address is a hardware address assigned to a network interface and is generally used within a local network.

• Data is divided into packets for transmission. Bandwidth refers to the maximum amount of data that a channel can carry per unit time, while data transfer rate refers to the amount transmitted per second. Rates are commonly measured as follows: $1\text{Kbps}=10^3\text{bps}$, $1\text{Mbps}=10^6\text{bps}$, and $1\text{Gbps}=10^9\text{bps}$. Data transfer time is calculated using:

$$\text{time}=\frac{\text{amount of data in bits}}{\text{data transfer rate in bits per second}}$$

• The Internet is the global network of networks, whereas the World Wide Web is a service operating on the Internet. A URL may contain a protocol, domain name, path, and optional query information. Web browsers access and display web pages and applications, web servers store and deliver web resources, and search engines organize information available on the Web. Cloud computing delivers storage, software, and processing over a network, usually the Internet.

• Networked systems improve resource sharing and communication but create risks involving privacy, security, reliability, and misuse. A firewall monitors and controls traffic according to security rules. Malware includes viruses, worms, Trojan horses, spyware, and ransomware. Phishing attempts to obtain sensitive information by pretending to be a trustworthy person or organization. Encryption converts readable data into unreadable form, while a digital certificate verifies the identity of a website or organization and supports secure communication.

• Effective cyber-safety requires layered protection. Strong passwords should be long, unique, difficult to guess, and different for different accounts. Two-factor authentication provides an additional security layer. Users should avoid suspicious links and attachments, verify senders, update software, operating systems, browsers, and antivirus tools regularly, and back up important data using secure local or cloud-based storage.

• Personal information, passwords, one-time passwords, and financial details should not be shared through unverified messages. Public Wi-Fi may be unsafe, so sensitive transactions should preferably use trusted networks and secure websites. Cyberbullying, identity theft, unauthorized access, copyright violation, and online fraud are harmful or unethical digital activities. Digital communication should respect privacy, consent, intellectual property, and applicable cyber laws.

• Choosing a network design or device requires consideration of cost, speed, coverage, scalability, reliability, and security. Effective network communication therefore depends on the combined use of suitable devices, reliable transmission media, correct addressing, compatible protocols, and responsible user behaviour.

What to Remember

Computer networks enable communication and resource sharing, but successful communication depends on devices, transmission media, addressing systems, and protocols. Distinguish carefully between the Internet and the World Wide Web, between hubs, switches, and routers, and between TCP’s reliable delivery and IP’s addressing and routing functions. For cyber-safety, retain the importance of strong authentication, encryption, firewalls, updates, backups, cautious online behaviour, and respect for privacy and cyber law.