📑 Topics on this page (Jump to Topic):
📌 1. Network Types & Topologies
| Type | Area | Example |
|---|---|---|
| PAN (Personal Area Network) | About 10 metres | Bluetooth, USB tethering |
| LAN (Local Area Network) | Room/building/campus | Office, school lab |
| MAN (Metropolitan Area Network) | City | Cable TV network |
| WAN (Wide Area Network) | Country/world | Internet (largest WAN) |
| Topology | Feature |
|---|---|
| Bus | One main cable (backbone); if it breaks the whole network fails |
| Star | All connect to a central hub/switch; one failed computer does not stop others |
| Ring | Closed loop; data in one direction (token) |
| Mesh | Every device connected to every other; most reliable, most costly |
| Tree | Hierarchy of star + bus |
| Hybrid | Mix of two or more |
- In a full mesh with n devices, links = n(n−1)/2.
⚠️ Exam Traps:
- Topology with a central hub = star; most reliable = mesh.
- Bluetooth = PAN, not LAN.
📌 2. Network Devices & Transmission Media
| Device | Function |
|---|---|
| Hub | Sends data to all ports (broadcast) — "dumb" |
| Switch | Uses MAC addresses to send only to the right port — "smart" |
| Router | Joins different networks using IP addresses; chooses the best route |
| Bridge | Joins two LAN segments |
| Repeater | Regenerates weak signals |
| Gateway | Joins networks with different protocols |
| Modem | Modulator-demodulator: digital ↔ analog |
| NIC | Network Interface Card — in every computer; carries the MAC address |
| Medium | Fact |
|---|---|
| Twisted pair | Cheapest; telephone and LAN (UTP/STP) |
| Coaxial | Cable TV |
| Optical fibre | Data as light; total internal reflection; fastest, immune to electromagnetic interference |
| Wireless | Radio, microwave, infrared (TV remote), satellite, Wi-Fi, Bluetooth |
- Simplex = one direction (radio, keyboard); half-duplex = both directions, one at a time (walkie-talkie); full-duplex = both at once (telephone).
- Data rate is in bps (bits per second); bandwidth = maximum data capacity.
⚠️ Exam Traps:
- A router works on IP addresses; a switch on MAC addresses.
- Walkie-talkie = half-duplex; telephone = full-duplex.
📌 3. OSI & TCP/IP Models, Protocols
| Layer | Name | Example/device |
|---|---|---|
| 7 | Application | HTTP, FTP, SMTP, DNS |
| 6 | Presentation | Encryption, compression, translation |
| 5 | Session | Opens/closes sessions |
| 4 | Transport | TCP, UDP |
| 3 | Network | IP, Router |
| 2 | Data Link | Switch, Bridge, MAC |
| 1 | Physical | Hub, repeater, cable |
💡 Memory Tip: Bottom to top: "Please Do Not Throw Sausage Pizza Away" = Physical, Data link, Network, Transport, Session, Presentation, Application.
- The OSI model was made by ISO — 7 layers. The TCP/IP model — 4 layers (Application, Transport, Internet, Network Access).
- TCP = connection-oriented, reliable; UDP = connectionless, fast (video calls, games).
| Protocol | Use | Port |
|---|---|---|
| HTTP | Web pages | 80 |
| HTTPS | Secure web | 443 |
| FTP | File transfer | 20/21 |
| SMTP | Send mail | 25 |
| POP3 | Receive mail | 110 |
| IMAP | Receive mail (stays on server) | 143 |
| DNS | Name → IP | 53 |
| Telnet / SSH | Remote login (SSH secure) | 23 / 22 |
| DHCP | Assigns IP automatically | 67/68 |
⚠️ Exam Traps:
- Router = network layer (3); switch = data link (2); hub = physical (1).
- HTTP port 80, HTTPS 443 — do not swap them.
📌 4. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. A network limited to a building or campus is called: Practice
Correct answer: (B)
LAN = Local Area Network.
LAN = Local Area Network.
Q2. Bluetooth is an example of which type of network? Practice
Correct answer: (C)
A PAN connects personal devices within about 10 metres.
A PAN connects personal devices within about 10 metres.
Q3. Which is the largest WAN in the world? Practice
Correct answer: (D)
The internet is a WAN spread across the whole world.
The internet is a WAN spread across the whole world.
Q4. In which topology are all computers connected to a central hub/switch? Practice
Correct answer: (A)
In a star topology, failure of the centre stops the network, but one failed computer does not.
In a star topology, failure of the centre stops the network, but one failed computer does not.
Q5. In which topology is every device directly connected to every other device? Practice
Correct answer: (B)
Mesh is the most reliable but most expensive.
Mesh is the most reliable but most expensive.
Q6. How many links are needed in a full mesh of 6 computers? Practice
Correct answer: (C)
n(n−1)/2 = 6×5/2 = 15.
n(n−1)/2 = 6×5/2 = 15.
Q7. The device that joins different networks and chooses the best path for data is a: Practice
Correct answer: (D)
A router forwards packets based on IP addresses.
A router forwards packets based on IP addresses.
Q8. Which device sends data to all its ports? Practice
Correct answer: (A)
A hub broadcasts; a switch sends only to the right port.
A hub broadcasts; a switch sends only to the right port.
Q9. The function of a modem is to: Practice
Correct answer: (B)
Modem = modulator + demodulator.
Modem = modulator + demodulator.
Q10. The device that regenerates a weak signal and passes it on is a: Practice
Correct answer: (C)
A repeater works at the physical layer of OSI.
A repeater works at the physical layer of OSI.
Q11. The fastest transmission medium that is immune to electromagnetic interference is: Practice
Correct answer: (D)
Optical fibre carries data as light using total internal reflection.
Optical fibre carries data as light using total internal reflection.
Q12. A walkie-talkie is an example of which communication mode? Practice
Correct answer: (A)
Both can talk, but only one at a time.
Both can talk, but only one at a time.
Q13. How many layers are there in the OSI model? Practice
Correct answer: (B)
OSI = 7 layers; TCP/IP = 4 layers.
OSI = 7 layers; TCP/IP = 4 layers.
Q14. At which OSI layer does a router work? Practice
Correct answer: (C)
The network layer (layer 3) handles IP addresses and routing.
The network layer (layer 3) handles IP addresses and routing.
Q15. Encryption and data compression are functions of which OSI layer? Practice
Correct answer: (D)
The presentation layer (layer 6) changes the form of data.
The presentation layer (layer 6) changes the form of data.
Q16. A connectionless, fast but less reliable protocol is: Practice
Correct answer: (A)
UDP is used in video streaming, games and DNS.
UDP is used in video streaming, games and DNS.
Q17. The default port number of HTTPS is: Practice
Correct answer: (B)
HTTP = 80, HTTPS = 443, FTP = 21, SMTP = 25.
HTTP = 80, HTTPS = 443, FTP = 21, SMTP = 25.
Q18. The protocol that automatically assigns IP addresses on a network is: Practice
Correct answer: (C)
DHCP = Dynamic Host Configuration Protocol.
DHCP = Dynamic Host Configuration Protocol.
Q19. The protocol for transferring files between computers over the internet is: Practice
Correct answer: (D)
FTP = File Transfer Protocol (ports 20/21).
FTP = File Transfer Protocol (ports 20/21).
Q20. A MAC address is stored on the: Practice
Correct answer: (A)
MAC = 48-bit hardware address on the network card.
MAC = 48-bit hardware address on the network card.