Computer Network and Communication

ISP (Internet Service Provider)

Data backup

The process of making an extra copy of data so that it can be restored if the original is lost or damaged is called data backup.

Internet

Server

A server is a powerful computer in a network that provides services and shares resources such as files, printers or Internet access with the client computers.

Peer-to-peer (P2P) network

In this network every computer can act both as a client and as a server, so no dedicated server is needed.

Network topology is the physical or logical arrangement of computers, cables and other devices in a computer network. It shows how the nodes of a network are connected to each other.

Star topology: All computers (nodes) are connected to a central device such as a hub or switch, and data passes through this central device.

        PC1        PC2
          \         /
           \       /
   PC6 ----- HUB ----- PC3
           /       \
          /         \
        PC5        PC4

Here the central circle/box is the hub or switch, and each PC is joined to it by its own separate cable.

A network protocol is a set of rules and conventions that governs how data is formatted, sent and received between devices on a network. Examples are TCP/IP, HTTP and FTP.

POP (Post Office Protocol), usually POP3

It is the protocol an e-mail client uses to retrieve (receive) e-mail messages from the mail server.

Shielded Twisted Pair

STP is a guided transmission medium in which each pair of insulated copper wires is wrapped in a metallic foil or braid (the shield) to reduce electromagnetic interference and crosstalk.

Gateway

A gateway is a network device that connects two networks that use different protocols or architectures and translates data between them.

The two common LAN topologies are the star topology and the bus topology.

A LAN topology is the physical or logical arrangement of computers and other devices in a local area network. In a star topology all nodes connect to a central hub or switch; in a bus topology all nodes share a single common backbone cable.

A computer network is a collection of two or more computers and other devices connected together by wired or wireless media so that they can share data, resources and services with each other.

Two advantages of a computer network:

1. Resource sharing — hardware such as printers, scanners and storage devices, as well as software and files, can be used by all computers on the network, which reduces cost.
2. Fast and easy communication — data and messages can be sent and received quickly between users through email, chat or file transfer, even over long distances.

Search engine

A search engine (such as Google or Bing) is a website that searches documents on the World Wide Web for specified keywords and returns a list of matching pages.

Unshielded Twisted Pair

UTP is a network cable made of pairs of insulated copper wires twisted together without any metallic shield, commonly used in LANs.

Full duplex mode

In this mode both sender and receiver can send and receive data at the same time, as in a telephone conversation.

Modem

A modem (modulator-demodulator) converts digital signals of a computer into analog signals for the telephone line and converts incoming analog signals back to digital.

Bandwidth

Bandwidth is the maximum amount of data that can be transferred per second through a communication channel, measured in bits per second (bps).

Uploading

Uploading is the process of sending or copying a file from a user's computer to a web server or remote computer; the reverse process is downloading.

Web browser

A web browser is software used to access, view and navigate web pages on the World Wide Web. Examples: Google Chrome, Mozilla Firefox, Microsoft Edge.

LAN (Local Area Network) vs WAN (Wide Area Network)

Examples: LAN — a computer network inside a school computer lab or an office. WAN — the Internet, or a bank's network connecting its branches across Nepal.

Power protection device: A power protection device is a hardware device that supplies regulated, uninterrupted electric power to a computer and protects it from power problems such as voltage fluctuation, spikes, surges, brownouts and sudden power failure. Examples: UPS (Uninterruptible Power Supply), spike guard/surge protector, voltage stabilizer and inverter.

Role in computer security:

1. Prevents data loss — during a sudden power cut, a UPS provides backup power for a few minutes so that the user can save open files and shut down the computer properly. This prevents loss of unsaved data.
2. Prevents data corruption — an abrupt shutdown can corrupt files, the operating system and the file system on the hard disk. A UPS allows a safe, orderly shutdown, keeping stored data intact.
3. Protects hardware — a spike guard or stabilizer absorbs sudden high-voltage surges and keeps the voltage within the safe range, so that the motherboard, SMPS, RAM and hard disk are not burnt or damaged.
4. Ensures availability — by keeping the system running during short power failures, it maintains the continuous availability of the system and its data, which is an important part of computer security.

In short, a power protection device safeguards both the hardware and the data of a computer from damage and loss caused by electrical power problems.

Radio and television are two simplex transmission modes.

In simplex mode data travels in only one direction: the sender can only send and the receiver can only receive. A radio or TV station transmits, and listeners or viewers only receive.

Transmission Control Protocol / Internet Protocol

TCP/IP is the suite of protocols used to connect devices on the internet. TCP ensures reliable delivery of data packets, while IP handles their addressing and routing.

Internet is called the network of networks because it is not a single network but a huge collection of many separate networks — LANs, MANs and WANs — that are joined together.

Each of these networks is independent and may be owned by different organisations, yet they all connect through common protocols (TCP/IP) and share data with one another. For example, your school LAN connects to an ISP's network, which connects to other ISPs worldwide, and all of them together form the Internet. Since the Internet is formed by interconnecting millions of such networks, it is rightly called the network of networks.

Telecommunication is the transmission of information such as voice, data, text or images over a distance using electronic or electromagnetic means.

Two examples of simplex mode are radio broadcasting and television broadcasting.

In simplex mode data flows in one direction only, from the station (sender) to the listeners or viewers (receivers).

Guided media and unguided media differ as follows:

In short, guided media carry data through a bounded cable, while unguided media carry data wirelessly through open space.

Unguided media is a transmission medium that carries data signals through the air, vacuum or water in the form of electromagnetic waves without using any physical cable or wire.

Uniform Resource Locator

A URL is the address used to locate and access a resource, such as a web page, on the internet.

Guided transmission media is a wired medium, such as twisted pair cable, coaxial cable or optical fibre, in which data signals travel along a physical cable from the sender to the receiver.

Computer network: A computer network is a group of two or more computers and other devices connected to each other by cables or wireless media so that they can share data, hardware and software resources.

Two disadvantages:

1. Security risk – Unauthorized users, hackers and viruses can spread easily through the network and steal or damage data.
2. High cost of setup and maintenance – Network devices, cabling and a skilled network administrator are expensive, and if the main server fails the whole network may stop working.

Simplex mode is a mode of communication in which data flows in only one direction, from sender to receiver, and the receiver cannot reply (for example, a keyboard to a computer or radio broadcasting).

Hypertext Transfer Protocol

HTTP is the protocol used to transfer web pages between a web server and a web browser on the World Wide Web.

Guided media are the wired transmission media in which data signals travel through a physical cable that guides them from one device to another.

Two examples:

1. Twisted pair cable
2. Optical fibre cable (coaxial cable is another example)

Power backup system: A power backup system is a device or arrangement, such as a UPS (Uninterruptible Power Supply), inverter or generator, that supplies electricity to computers when the main power supply fails.

Importance in a computer system:

1. It prevents loss of unsaved data and file damage caused by sudden power cut-off.
2. It protects the hardware from damage due to power fluctuations, and keeps the system running so that work can be saved and shut down safely.

Two services provided by the Internet are:

• E-mail (electronic mail)
• World Wide Web (WWW)

FTP: File Transfer Protocol

MAN: Metropolitan Area Network

Network topology is the geometrical arrangement or layout of the computers, cables and other devices in a network, showing how they are connected.

Two types of network topology:

• Bus topology
• Star topology (ring, mesh and tree are also types)

POP: Post Office Protocol

Two advantages of a computer network:

• Resources such as printers, scanners and files can be shared, which saves cost.
• Fast communication and data sharing among users, for example by e-mail and messaging.

Two disadvantages of a computer network:

• Setup and maintenance are expensive, and a skilled network administrator is needed.
• Security risks: hackers and viruses can spread easily to all connected computers.

ISP: Internet Service Provider

TCP/IP (Transmission Control Protocol / Internet Protocol)

It is the set of rules that allows different computers and networks to communicate; TCP ensures reliable delivery of data packets and IP addresses and routes them.

FTP (File Transfer Protocol)

FTP is an Internet service used to upload files to, and download files from, a server over a network.

IP address (Internet Protocol address)

It is a unique numerical address assigned to each device on a network or the Internet so that it can be identified and located, for example 192.168.1.1.

UPS (Uninterruptible Power Supply)

A UPS is an electronic device with a battery that supplies power to a computer for a short time when the main electricity fails, so work can be saved and the system shut down safely.

(a) Bandwidth

Bandwidth is the maximum amount of data a communication channel can carry per unit time (measured in bps, kbps, Mbps). Throughput is the actual rate achieved, frequency is the number of cycles per second, and broadband is a high-capacity transmission type.

(b) It allows wireless communication between nearby devices.

Bluetooth is a short-range wireless technology (about 10 m), so nearby devices such as mobiles, earphones and speakers can be connected without any cable — whereas CAT6, coaxial cable and optical fiber are all guided (wired) media that need physical cabling.

(a) ping

The ping command sends a small test packet to another computer's IP address and waits for a reply; if the reply comes back, the two computers are communicating successfully. The other options are unrelated — format prepares a disk, compile converts source code, and merge combines files.

Internet vs Intranet

(Any two valid points earn full marks.)

The technology being used is Wi-Fi (Wireless Fidelity).

How it works:

1. A wireless router (access point) is connected to the internet through a modem or cable.
2. The router converts the data into radio waves and transmits them through the air using built-in antennas.
3. The laptop has a wireless network adapter (Wi-Fi card) with an antenna that receives these radio waves.
4. The adapter converts the radio waves back into digital data that the laptop can understand.
5. When the laptop sends data, the same process happens in reverse — the laptop's adapter converts data into radio waves and sends them to the router, which forwards them to the internet.

Wi-Fi works within a limited range (about 30–100 metres indoors), so the laptop must stay within the range of the router to remain connected.

Broadband connections are high-speed, always-on internet connections that transmit data over a wide frequency band, allowing voice, data and video to travel at the same time. The main types are:

1. DSL (Digital Subscriber Line)

• Main features: Runs over ordinary copper telephone lines; always-on; speed typically 1–100 Mbps; download speed is faster than upload speed (ADSL).
• Uses: Home and small-office internet where cable or fibre is not available; web browsing, email, video streaming.

2. Cable Internet

• Main features: Uses the same coaxial cable as cable TV; always-on; speed usually higher than DSL (up to a few hundred Mbps); bandwidth is shared among users in the same area.
• Uses: Homes in cable-TV covered areas; streaming HD video, online gaming, large downloads.

3. Fibre (FTTH – Fibre to the Home)

• Main features: Uses light signals through optical fibre; highest speed (100 Mbps to 1 Gbps and above); equal upload and download speed; very low latency; not affected by electromagnetic interference.
• Uses: Heavy internet users, offices, cloud services, video conferencing and IPTV.

4. Wireless / Mobile Broadband (3G, 4G, 5G)

• Main features: Uses radio signals through mobile networks or Wi-Fi hotspots; no cable needed; mobility — internet access while travelling; speed depends on signal strength and network generation.
• Uses: Smartphones, laptops and tablets on the move; rural or remote areas where cables cannot reach.

5. Satellite Broadband

• Main features: Uses a satellite dish to send and receive signals from a satellite in space; available almost everywhere; higher latency and cost; speed moderate.
• Uses: Very remote areas, ships, aircraft and places where no other connection is possible.

6. Broadband over Power Lines (BPL)

• Main features: Sends data over existing electric power lines; uses the same wiring that supplies electricity.
• Uses: Areas with electricity supply but no telephone or cable network.

In short: DSL and cable are common in cities, fibre gives the fastest and most reliable service, wireless/mobile broadband provides mobility, and satellite serves the most remote locations.