Unit 5 in 30 seconds
- A network connects computers so they can share data, files, hardware (printers) and internet.
- LAN (a building), MAN (a city), WAN (a country or the world) — they differ in size, speed and ownership.
- Topology = the physical layout of nodes: star, bus, ring, mesh, tree and hybrid.
- Devices: hub (broadcasts to all), switch (intelligent hub), router (connects different networks), bridge (joins LAN segments), gateway (translates protocols), repeater (boosts weak signals).
- A modem converts digital ↔ analog signals for telephone lines; TCP/IP is the protocol suite of the Internet.
- ISDN = digital voice + data over phone lines; a leased line = a private, always-on dedicated connection.
- Teleconferencing = audio-only meeting; videoconferencing = audio + video meeting.
1. What is a Computer Network?
A computer network is a collection of two or more computers and devices connected through a communication channel so that they can share data, files, hardware resources (printers, scanners) and software. Each connected machine is called a node, and every node needs a NIC (Network Interface Card) to attach to the network.
2. Advantages of a Network
- Resource sharing — one printer or software licence serves many users.
- Data sharing — files are available to all users from a central server.
- Communication — email, messaging and video calls between users.
- Cost saving — expensive hardware and software need not be bought per computer.
- Reliability and backup — data can be backed up centrally on a server.
- Centralised management — updates and security policies apply from one place.
3. Types of Networks
| Network | Full form | Area covered | Speed | Ownership | Example |
|---|---|---|---|---|---|
| LAN | Local Area Network | One building or campus (up to a few km) | High (10 Mbps – 10 Gbps) | Single organisation | Office or college computer lab |
| MAN | Metropolitan Area Network | A city (10 – 50 km) | Moderate to high | One organisation or a consortium/ISP | Cable TV network, bank branches in a city |
| WAN | Wide Area Network | Country, continent or the whole world | Lower than LAN | Multiple organisations (leased lines) | The Internet, railway reservation system |
| PAN | Personal Area Network | About 10 metres around a person | Moderate | Individual | Bluetooth, phone-to-laptop USB connection |
Exam-favourite full forms: LAN = Local Area Network · MAN = Metropolitan Area Network · WAN = Wide Area Network · PAN = Personal Area Network · NIC = Network Interface Card.
Key differences to remember: LAN is the fastest and fully owned by one organisation; WAN is the largest and slowest because data travels long distances over lines owned by others. MAN sits between the two. The Internet is the largest example of a WAN.
4. Network Topology
Topology means the physical arrangement (shape) in which computers are connected — the pattern of cables and nodes.
| Topology | Layout | Advantages | Disadvantages |
|---|---|---|---|
| Star | All nodes connect to a central hub/switch | Easy to add nodes; fault in one cable affects only one node | If the central device fails, the whole network fails; uses more cable |
| Bus | All nodes share one backbone cable with terminators | Cheapest; simple to set up | One cable break kills the whole network; hard to find faults |
| Ring | Each node connects to two neighbours, forming a loop | Equal access for all; no data collisions (token passing) | One break disturbs the loop; adding/removing nodes is difficult |
| Mesh | Every node connects directly to every other node | Most reliable — many backup paths; no single failure point | Very expensive and complex cabling |
| Tree | Hierarchy of star networks connected to a backbone | Scalable; easy to extend branch by branch | Backbone failure affects whole branches; complex wiring |
| Hybrid | Combination of two or more topologies | Flexible; strengths of each topology combined | Complex design; costly to build and maintain |
PYQ Alert: "Star topology me central device kharab ho jaye to kya hota hai?" is a classic question — the entire network stops working, while in bus topology a cable break stops the whole network. Examiners love testing the single point of failure in each topology.
5. Network Devices
| Device | Works at (OSI layer) | Main function | Exam point |
|---|---|---|---|
| Repeater | Physical layer | Regenerates/amplifies weak signals to extend distance | Does NOT filter traffic; just boosts the signal |
| Hub | Physical layer | Broadcasts incoming data to all connected ports | "Dumb" device; creates collisions; slowest |
| Bridge | Data Link layer | Connects two LAN segments; filters traffic by MAC address | Has only 2 ports; reduces traffic on each segment |
| Switch | Data Link layer | Sends data only to the destination port using MAC addresses | "Intelligent hub"; multi-port bridge |
| Router | Network layer | Connects different networks (e.g. LAN to WAN); forwards by IP address | Most intelligent; decides the best path |
| Gateway | All layers | Connects networks using different protocols (protocol conversion) | Acts as a translator between different network types |
One-line memory map: Repeater boosts · Hub broadcasts · Bridge joins two LANs · Switch selects the port · Router connects networks · Gateway translates protocols.
PYQ Alert: The hub vs switch vs router difference is the most repeated device question. Remember: hub sends to everyone, switch sends only to the destination computer, and router connects one network to another (e.g. your home network to the Internet).
6. Modem
MODEM = MOdulator + DEModulator. Computer data is digital, but telephone lines carry analog signals, so a modem converts between them:
- Modulation — digital → analog (while sending data over the phone line).
- Demodulation — analog → digital (while receiving data from the phone line).
Internal modem sits inside the computer (a card); external modem is a separate box connected outside. DSL and cable modems give faster, always-on internet over the same idea.
7. Transmission Media
Media are of two types — guided (signals travel inside a cable) and unguided (signals travel through air/space).
| Medium | Type | Key facts |
|---|---|---|
| Twisted pair cable | Guided | Ordinary telephone wire; cheapest; used for short distances (LAN, telephone) |
| Coaxial cable | Guided | Copper core with shielding; higher bandwidth than twisted pair; used for cable TV |
| Fibre optic cable | Guided | Carries data as light; fastest, immune to interference; most expensive |
| Radio waves | Unguided | Travel in all directions; used for AM/FM radio and Wi-Fi/Bluetooth |
| Microwaves | Unguided | Need line-of-sight between towers/dishes; used for long-distance links |
| Satellite | Unguided | Geostationary satellites relay signals; cover the whole globe; slight delay |
8. ISDN
ISDN = Integrated Services Digital Network. It is a digital telephone service that carries voice, data and video together over the existing telephone lines — much faster and cleaner than old dial-up modems. Basic types: BRI (2 data channels + 1 control channel, for homes/small offices) and PRI (30 channels, for large organisations).
9. Leased Lines
A leased line is a dedicated, permanent connection between two fixed points, rented from a telecom company. It offers fixed bandwidth, 24-hour availability, high security and reliability — banks and companies use it to link branch offices. It is more expensive than ordinary dial-up or broadband because the line is reserved only for you.
10. Protocols — TCP/IP
A protocol is a set of rules that computers must follow to communicate. The Internet runs on TCP/IP:
- TCP (Transmission Control Protocol) — breaks data into small packets, checks they arrive correctly and reassembles them.
- IP (Internet Protocol) — gives every device an IP address and routes packets to the right destination.
TCP/IP full forms (MCQ favourite): TCP = Transmission Control Protocol · IP = Internet Protocol · ISDN = Integrated Services Digital Network · OSI = Open Systems Interconnection.
11. Teleconferencing vs Videoconferencing
| Feature | Teleconferencing | Videoconferencing |
|---|---|---|
| Meaning | A meeting conducted over telephone/audio lines | A meeting with live audio and video |
| Equipment | Telephone, speakerphone | Camera, microphone, screen, internet (e.g. Zoom, Meet) |
| Bandwidth needed | Low | High |
| Feel | Only voices — no visual contact | Face-to-face like, with screen sharing and presentations |
| Cost | Cheaper | Costlier (equipment + internet) |
Both save travel time and money, and both let people in different places meet in real time — videoconferencing simply adds the visual element.
PYQ Alert: Full forms are the highest-yield MCQs of this unit — drill LAN, MAN, WAN, NIC, TCP, IP, ISDN, MODEM until you can write them without thinking. Second favourite: one-line device jobs (hub = broadcast, switch = selected port, router = connects networks, gateway = protocol translator).