Computer Networks and the Internet
Computer Networks and the Internet tests how devices communicate, from a local LAN to the global Internet. Expect questions on topologies, hardware, protocols, addressing, and the services that make the web and email work.
Core rules and concepts
- A LAN covers a small area and is usually owned by one organisation; a WAN spans larger distances and often uses leased links. The Internet is a worldwide network of networks.
- A client requests services; a server provides them. A router forwards packets between networks, a switch forwards frames within a LAN using MAC addresses, and a hub repeats signals to all ports.
- TCP/IP is the main protocol suite. IP handles addressing and routing; TCP provides reliable, ordered delivery with acknowledgements and retransmission.
- DNS translates domain names into IP addresses. HTTP/HTTPS transfer web pages; HTTPS adds encryption. Email uses SMTP to send and POP3 or IMAP to retrieve.
- Data is split into packets, each carrying source and destination addresses. Bandwidth is capacity; latency is delay.
Worked example
A 24 MB file is downloaded over an 8 Mbps link. Ignoring overheads, time = 24 × 8 megabits ÷ 8 megabits per second = 24 seconds. Reasoning: 1 byte = 8 bits, so convert megabytes to megabits before dividing by the link rate in megabits per second.
Traps
- Mixing bits and bytes: Mbps is megabits per second, MB is megabytes.
- Saying a switch routes between different networks; that is a router’s job.
- Confusing DNS with DHCP: DNS resolves names; DHCP assigns IP addresses.
- Treating HTTPS as a different protocol from HTTP rather than HTTP carried over an encrypted connection.