Computer Networks and the Internet
What the examiner tests
Network definitions, types and devices, Internet services, IP addressing and protocols, usually as short-answer and “identify the device” questions.
Core rules
- A network is two or more autonomous computers connected to share resources. Each device is a node.
- By size: PAN (personal, ~10 m), LAN (building/campus), MAN (city), WAN (country/global). The Internet is the largest WAN.
- Topologies: bus, star (central switch/hub), ring, mesh (most reliable, most cabling), tree, hybrid.
- Media: guided - twisted pair (Ethernet cable with RJ-45), coaxial, optical fibre (fastest, immune to interference); unguided - radio, microwave, satellite.
- Devices: hub (broadcasts to all ports), switch (forwards to the correct MAC address), router (connects different networks, uses IP), modem (modulates/demodulates for the line), repeater (regenerates a weak signal), gateway (joins dissimilar networks).
- IP address: IPv4 is 32-bit, written as four decimal octets; IPv6 is 128-bit. A MAC address is a fixed hardware address. DNS maps domain names to IP addresses.
- Protocols: TCP/IP (transport/addressing), HTTP/HTTPS (web), FTP (file transfer), SMTP (send mail), POP3/IMAP (receive mail).
Worked example
You type www.wbbse.wb.gov.in in a browser. The PC asks the DNS server for the site’s IP address, then opens a TCP connection to port 80 (or 443 for HTTPS) and sends an HTTP request. The router forwards packets to the ISP and the server returns the page. The modem handles the physical line; the router shares the connection among home devices.
Traps
- Saying the Internet and the World Wide Web are the same; the Web is one service on the Internet.
- Confusing a hub (dumb broadcast) with a switch (address-aware).
- Confusing an IP address with a MAC address.
- Claiming HTTPS encrypts the whole browsing session - it encrypts traffic between browser and server only.