Computer Networks and the Internet
A network links devices so they can share data and resources. The exam tests network types and topologies, hardware, protocols, addressing, and how data travels across the internet.
Categories and topologies
PAN (personal), LAN (one site), MAN (a city), WAN (countries, e.g. the internet). Star topology: all nodes connect to a central switch - easy to fault-find, but the switch is a single point of failure. Bus: one backbone cable, cheap, prone to collisions. Ring: data passes node to node. Mesh: many redundant links, expensive but resilient.
Hardware
A hub repeats a signal to every port (one collision domain); a switch forwards frames using MAC addresses; a router joins different networks and forwards packets using IP addresses; a repeater/access point extends a signal; a NIC connects a device to the medium; a gateway translates between different protocols.
Protocols and services
HTTP/HTTPS for web pages, SMTP to send mail, POP3/IMAP to collect mail, FTP for file transfer, DNS to resolve domain names into IP addresses, DHCP to lease IP configuration automatically, TCP for reliable delivery and IP for addressing and routing. A MAC address identifies hardware on the local link; an IP address identifies a host across networks.
Packets and the internet
The internet is the global network of networks; the World Wide Web is one service running on it. Packet switching splits data into packets carrying source and destination addresses; packets may take different routes and are reassembled at the destination.
Worked example
A 6 MB file is sent over an 8 Mbps link. Convert first: 6 MB = 6 × 8 = 48 Mbit. Time = 48 ÷ 8 = 6 seconds, ignoring overhead. The trap is mixing bits and bytes before dividing.
Traps that cost marks
- Treating Mb and MB as the same unit.
- Saying DNS assigns IP addresses - that is DHCP.
- Calling a hub a switch, or a switch a router.