6. Computer Networks: Questions and Answers

b) an interconnection of two or more computers or computing devices that share data and resources

b) node

A node has a unique network address such as an IP address.

c) Compiler

The five components are sender, receiver, message, medium and protocol.

b) bandwidth

c) latency

a) bits per second (bps)

a) Simplex

For example, keyboard to computer, or TV/radio broadcast.

b) Half duplex

Both directions are possible, but only one at a time.

c) Optical fibre cable

c) Optical fibre

b) Infrared waves

It is short-range and needs a direct line of sight.

c) MAN

d) WAN

a) PAN

b) Modem

Modem stands for Modulator-Demodulator.

c) Switch

a) Gateway

b) attenuation

A repeater amplifies the weak signal and retransmits it.

c) Bus

b) Ring

d) Mesh

c) DNS

b) SMTP

c) HTTPS

Topology.

Bus (backbone cable).

Hub; switch.

One (a single direction; dual-ring networks can use both).

Point-to-point.

Star and bus.

Two.

Cables (wires).

Light.

Buildings.

Point-to-point (for example satellite and cellular communication).

Wired (guided) and wireless (unguided).

Protocol (for example TCP/IP).

Simplex, half duplex and full duplex.

MAC (Media Access Control).

Hub.

IP (destination IP address).

Web server.

World Wide Web.

URL (Uniform Resource Locator).

110 (995 for secure); 143 (993 for secure).

25.

A computer network is an interconnection among two or more computers or computing devices. These interconnections allow the computers to share data and resources with each other. A small network may link a few computers in a room, while a large network can connect thousands of devices across the world.

A node is any device that can send, receive or process data in a network. It is a connection point that allows communication between devices. Examples: computers (desktops, laptops), servers, printers, routers, switches, modems, smartphones and IoT devices. Each node has a unique network address (such as an IP address) to identify it.

Facebook and Instagram (WhatsApp and Telegram are similar networking and chat services).

• Social networks: friends and families connected through relationships.
• Mobile networks: phones connected for calls, messages and internet.
• Computer networks: computers sharing files, videos and information.
• Service networks: airlines, railways, banks and hospitals that connect people, places and services.

Data communication is the process of transmitting digital data between two or more devices through a communication medium such as cables or wireless signals. The main goal is to exchange information efficiently and accurately.

• Sender: the device that sends the data.
• Receiver: the device that receives the data.
• Message: the actual information or data to be transmitted.
• Medium (transmission channel): the path through which data travels, such as cables or airwaves.
• Protocol: a set of rules that governs data transmission, such as TCP/IP.

Bandwidth is the amount of data that can be transmitted over a network in a given time. Think of a water pipe system: the pipe is the communication channel, the water is the data, and the width of the pipe is the bandwidth. A wide pipe lets more water flow at once, like a high-bandwidth network that carries more data per second. A narrow pipe is like a low-bandwidth network where data transfer is slower.

Greater bandwidth allows more data to be transmitted in less time, so transfer is faster. Low bandwidth means slower transfer.

Latency is the time taken for data to travel from source to destination; in simple words, it is the delay in data transmission. Example: when you chat with a friend online, there is a slight delay before your friend receives your message. That delay is latency.

Bit rate is the number of bits transmitted per second, measured in bits per second (bps).

It depends on distance, cost, data rate and environment. For example, twisted pair cable is used in small LANs, optical fibre for high-speed backbone connections, and wireless media for mobile or remote communication.

A PAN connects devices within a very small area, typically around one person, over a range of a few metres. It connects personal devices such as smartphones, tablets, laptops, printers and wireless headsets. It can be wired (USB cables) or wireless (WPAN using Bluetooth, Wi-Fi or infrared). Example: connecting a smartphone to a wireless earphone through Bluetooth.

Devices: smartphone, tablet, laptop, printer, smartwatch and wireless headset. Technologies: Bluetooth, Wi-Fi or infrared for wireless PAN, and USB cables for a wired PAN.

It lets users synchronise data, share files and use devices together without complex network setups. Phones, laptops, printers and headsets work together within a short range, so a person can move around and connect devices quickly. This saves time and makes personal use, home offices and mobile work easier.

A LAN connects the server with computers, mobile phones, tablets, printers and other devices within a small area such as a room, building, school or office. It uses Ethernet cables or Wi-Fi.

• Share files, printers and internet connections quickly
• Range extends up to about 1 km
• Speed from 10 Mbps (Ethernet) to 1000 Mbps (Gigabit Ethernet)
• Comparatively secure, since only authentic users can access shared resources

Ethernet is a set of rules that decides how computers and other devices connect with each other through cables in a LAN. Speeds range from 10 Mbps (Ethernet) to 1000 Mbps (Gigabit Ethernet).

A MAN covers a larger area than a LAN, about 5 to 50 km, usually a city or a large campus, connecting multiple LANs. It commonly uses high-speed fibre optic cables or wireless connections, with data rates from 10 Mbps to 1 Gbps or higher. Examples: cable TV network, public Wi-Fi hotspots, cable-based broadband internet services.

A MAN covers a city or large campus and connects many separate LANs (for example the LANs of different offices, schools or departments) into one larger network, so it is called a network of LANs.

A WAN connects devices and smaller networks across cities, countries or continents. It is the largest form of network and spans thousands of kilometres. It uses telephone lines, fibre optic cables, satellite links and wireless systems, and is usually owned by ISPs or telecommunication companies. Examples: the Internet, global banking networks, airline reservation systems and multinational corporate networks. WANs are expensive to set up and maintain, more prone to security threats such as hacking, and can be slower than LANs over long distances.

Network devices are the hardware components that connect computers and other electronic devices to form a network. They help in data transmission, communication and network management. Examples: modem, NIC, hub, switch, repeater, router and gateway.

• Modem
• Switch
• Router
• Repeater (others: NIC, hub, gateway)

A modem (Modulator-Demodulator) lets digital computers communicate over analog lines such as telephone lines. Modulation: converts the computer's digital signals into analog signals for transmission. Demodulation: converts incoming analog signals back into digital signals the computer can understand.

Demodulation is the process in which the modem converts analog signals coming from the telephone line back into digital signals that the computer can understand.

An Ethernet card, also called a Network Interface Card (NIC), is a network adaptor that connects a computer to a wired or wireless network. It is a printed circuit board on the motherboard and supports speeds from 10 Mbps to 1 Gbps. Each NIC has a MAC (Media Access Control) address that uniquely identifies the computer on the network.

Attenuation is the gradual weakening of a signal as it travels through cables or wireless channels. A repeater extends the coverage of a network by receiving the weak signal, amplifying or regenerating it and retransmitting it, without changing the original data. It does not filter or manage traffic; it only boosts signals.

A switch connects multiple devices within a LAN and is called an intelligent device because it learns the MAC address of each device on its ports and stores them in a MAC address table.

• It reads the sender's and receiver's MAC addresses from the data packet.
• It forwards data only to the port of the destination device, not to every device.
• It can forward multiple packets at the same time.
• It drops noisy or corrupted signals and asks the sender to resend them.
• This reduces network traffic and prevents data collisions, so networks are faster and more efficient.

A router connects multiple networks together, for example a LAN to the Internet. Its main function is routing: receiving data packets, analysing the destination IP address in the packet header and sending them to the appropriate network. A router can be wired or wireless. Home Wi-Fi routers often act as router, modem and switch together.

A gateway connects two different networks that use different communication protocols. It is an entry and exit point and works like a translator.

1. Protocol conversion: translates data from one network's protocol to another.
2. Data handling: examines the packet and converts it to a format the destination network understands.
3. Routing and forwarding: sends the packet by the correct route.
4. Response transmission: converts the reply back to the source network's format and delivers it.

Gateway.

A firewall is a network security device or software that acts as a barrier between a trusted internal network (like a home or company network) and an untrusted external network (like the Internet). It controls and monitors incoming and outgoing traffic using predefined security rules, deciding what to allow and what to block, to protect against unauthorised access, hackers and malware.

An IP address (Internet Protocol address) is a unique numerical identifier assigned to each device on a network. It identifies and locates devices so that data can be sent and received correctly. IP addresses can be IPv4 (e.g. 192.168.1.1) or IPv6, which has a much larger address space.

A server is a powerful computer that provides services, resources and data to other computers, called clients. Its roles include data storage and sharing, resource management, user authentication, application hosting, network security, and backup and recovery.

Network topology is the arrangement or layout in which devices (nodes) are connected. It can be physical (the actual layout of cables) or logical (the way data moves). Common topologies: bus, star, ring, mesh, tree and hybrid.

All nodes are connected to a single main cable (the bus). Data sent by a computer travels along the cable and reaches all devices, but only the intended receiver accepts it. Terminators at both ends prevent signal reflection.

All computers are connected to a central device (hub or switch), each with a dedicated connection. A hub broadcasts data to all nodes, while a switch forwards data only to the intended node using MAC addresses.

Computers are connected in a closed loop; each device is connected to exactly two neighbours and data travels in one direction (or both in dual-ring networks). A token circulates around the ring, and a device can send data only when it has the token, which reduces collisions.

Each node is connected to every other node through dedicated point-to-point links. This gives multiple paths for data, so if one link fails the data is automatically routed through an alternate path.

A hierarchical structure combining star and bus topologies. Groups of computers are connected to hubs or switches (forming stars), and these are connected to a main backbone cable.

A hybrid topology combines two or more different topologies (star, bus, ring, mesh) to take advantage of the strengths of each. For example, one department may use star and another bus, interconnected by routers, switches or main cable links.

The Internet is a global network connecting millions of computers and devices worldwide using standard protocols such as TCP/IP. When a user opens a website, the client device sends a request through an ISP to the web server hosting the site. The request passes through routers, switches and gateways. The server sends back the data (pages, images, videos) as packets that travel over multiple paths and are reassembled at the destination. TCP ensures that all packets arrive correctly, and IP manages addressing and routing.

Protocols are sets of rules that define how data is formatted, transmitted and received over a network. They ensure accurate, reliable and efficient data transfer so that computers around the world can understand each other, just as people use a common language to talk.

File Transfer Protocol (FTP) is a standard protocol for transferring files between a client and a server over the Internet or a local network. Users can upload, download, rename or delete files on a remote computer. Standard FTP is not encrypted; secure versions are FTPS and SFTP.

TCP/IP (Transmission Control Protocol / Internet Protocol) is the set of communication rules used to connect computers on the Internet and other networks. It defines how data is divided into packets, transmitted and reassembled. TCP ensures reliable transfer (checks errors, maintains sequence, retransmits lost packets, confirms delivery), while IP handles addressing and routing. It supports HTTP, FTP, SMTP and DNS.

Simple Mail Transfer Protocol (SMTP) is used to send and route emails over the Internet between email clients and mail servers. It uses port 25 by default and relies on TCP. The sender's device passes the email to the outgoing mail server, which forwards it to the recipient's mail server. The recipient retrieves it using POP3 or IMAP.

MIME (Multipurpose Internet Mail Extensions) extends the email format to support images, audio, video and application files. Early email supported only plain ASCII text. With MIME, an email can contain several parts (text, images, attachments) in one message, separated by boundaries.

The Domain Name System (DNS) is a hierarchical, distributed naming system that translates human-readable domain names (like www.google.com) into IP addresses (like 142.250.190.68). It works like a telephone directory of the Internet.

1. The user types a website address in the browser.
2. The local DNS cache is checked for the IP address.
3. If not found, the request goes to a DNS resolver.
4. The resolver contacts the root DNS server, then the Top-Level Domain (TLD) server, then the authoritative DNS server that holds the actual IP address.
5. The IP address is sent back to the user's device.
6. The browser connects to the web server and displays the website (this takes milliseconds).

Network-based services are the functions and resources provided over a computer network, especially the Internet, that let users and devices communicate, share data, access resources and perform online activities. Examples: e-mail, file transfer, web, chat, video conferencing, remote login, cloud storage, streaming, online transactions and social networking services.

In a computer lab, all computers can be connected to one printer through a network. To print an assignment, a student gives the print command and the printer receives it through the network. This saves time, avoids extra work and avoids buying a printer for every computer. Files, storage, software and internet connections can be shared in the same way.

Networks let people communicate within seconds across cities and countries. When we use the Internet, send email, attend online classes, watch videos or play online games, we are using computer networks. Mobile phones, printers and smart TVs also connect through networks, so a network acts like a digital bridge between people and devices, making communication fast, easy and efficient.

A LAN lets staff and students share files, printers, software and the internet connection, and communicate by email and messaging. A central server stores data and manages users, so work is easier to back up and secure. This reduces cost and duplication and speeds up work.

A keyboard sending keystrokes to a computer (simplex), two guards talking on walkie-talkies (half duplex) and two people talking on a mobile phone call (full duplex).

Electromagnetic signals (radio waves, microwaves, infrared) are used to carry data through free space.

Twisted pair cable and optical fibre cable (coaxial cable is another).

The customer's phone (sender) sends a message containing the transfer request through the mobile network or Wi-Fi (medium) via an ISP to the bank's server (receiver). The data is split into packets, routed across the Internet through routers and gateways, and reassembled at the server, which sends back a confirmation. Protocols are important because they set the rules for formatting, addressing, sending and receiving data: TCP/IP delivers the packets correctly and in order, and HTTPS (SSL/TLS) encrypts the data so that passwords and account details are secure and accurate.

Simplex mode. Data flows in only one direction, from the keyboard (sender) to the computer (receiver), and never the other way.

Optical fibre cable. It uses light signals, gives extremely high speed, is immune to electromagnetic interference and is secure, so it suits a high-speed link between buildings.

Radio waves (the cellular network, which also uses microwaves between towers). They support mobility, can penetrate buildings and cover wide areas, so the call continues while the user moves.

A router. It connects the two networks, reads the destination IP address of each packet and forwards it to the correct network. For a secure private link over the Internet, the routers use a Virtual Private Network (VPN) connection.

Star topology. Every computer has a dedicated connection to the central hub or switch, so failure of one node does not affect the others. It is also easy to install, manage and troubleshoot. (The central device is a single point of failure.)

Mesh topology. Every node is connected to every other node by dedicated point-to-point links, so there are multiple paths. If one link fails, data is automatically routed through an alternate path and communication is uninterrupted. It also gives high security and fault tolerance.

HTTPS (HyperText Transfer Protocol Secure). It uses SSL/TLS to encrypt data between the browser and the web server, so passwords, banking details and personal data cannot be read or stolen. The address begins with https:// and a lock icon appears.

Video conferencing service. It supports live audio and video communication over a network. Example: Zoom or Google Meet.

The online transaction service. It enables financial transactions through networks, for banking and shopping. Examples: online banking, Amazon.

Data communication is the transmission of digital data between two or more devices through a medium such as cables or wireless signals. Its goal is to exchange information efficiently and accurately.

• Sender, receiver, message, medium and protocol are the five basic components.
• Node: any device that can send, receive or process data.
• Bandwidth: the amount of data that can be sent in a given time.
• Latency: the delay in transmission.
• Bit rate: bits transmitted per second (bps).
• Transmission modes: simplex, half duplex and full duplex.

Data is divided into smaller packets, which are carried through guided media (cables, fibre) or unguided media (free space).

By transmission media: guided (wired) networks use twisted pair, coaxial or optical fibre cables; unguided (wireless) networks use radio waves, microwaves, infrared or satellite.

Guided media are reliable, secure and suit high-quality transmission. Unguided media give flexibility and mobility.

• Modem: converts digital signals to analog (modulation) and back (demodulation) so computers can use telephone and other analog lines; types include dial-up, DSL, cable, wireless, fibre (ONT) and satellite.
• NIC (Ethernet card): connects a computer to a network; has a unique MAC address; speeds from 10 Mbps to 1 Gbps.
• Repeater: amplifies and retransmits weak signals to extend the network over longer distances.
• Switch: intelligent LAN device using a MAC address table to forward data only to the destination port.
• Router: connects different networks and forwards packets using destination IP addresses.
• Gateway: connects networks with different protocols and converts data between them.

A hub simply broadcasts data to all ports, and a firewall controls traffic between trusted and untrusted networks.

The Internet is a global network of networks that uses TCP/IP. A client sends a request via an ISP to a web server; routers, switches and gateways direct it; the server returns the web page as packets that travel over different paths and are reassembled at the destination. TCP makes sure all packets arrive correctly, and IP handles addressing and routing.

DNS works like the Internet's telephone directory. When a user types a domain name, the local DNS cache is checked; if the address is not found, a resolver asks the root server, then the TLD server and finally the authoritative server, which gives the IP address. The browser then connects to the web server. This takes milliseconds and lets users use names instead of numbers.

Network-based services are the functions and resources provided over a network, especially the Internet. They are the foundation of modern digital communication and play a vital role in education, business, entertainment and government operations.

Sender -> (message, sent through a medium following a protocol) -> Receiver.

+--------+     message      +-----------+     message      +----------+
| SENDER | ---------------> |  MEDIUM   | ---------------> | RECEIVER |
+--------+                  | (cable or |                  +----------+
     ^                      |  airwaves)|                        ^
     |                      +-----------+                        |
     +------------ PROTOCOL (rules, e.g. TCP/IP) ----------------+

• Sender: the device that sends the data.
• Receiver: the device that receives it.
• Message: the information to be transmitted.
• Medium: the path the data travels (cables or airwaves).
• Protocol: the rules both sides follow for correct transmission.