Computer Networks and the Internet: Topologies, Protocols, Services and Security
Computer networks and the internet covers how computers share data: topologies, transmission media, hardware, addressing, protocols and the security measures that protect traffic. Questions ask you to choose a topology or device for a scenario and justify it, and to explain how a request reaches a web server.
Types, topologies and media
A LAN covers one site and is usually owned by the organisation; a WAN spans sites and often uses a telecommunications provider. Client–server puts shared resources and security on a central server; peer-to-peer shares directly between equals, cheap but hard to secure. Star: every device connects to a central switch - easy to extend, one fault affects one device, but the switch is a single point of failure and cabling costs more. Bus: one backbone, cheap, but a break stops the network and collisions rise. Ring: data passes node to node, predictable, but a failure can disrupt the loop. Mesh: multiple paths, highly reliable, expensive to cable. Media: twisted-pair copper (cheap, short range), fibre optic (high bandwidth, immune to electrical interference, long distance), wireless (mobile, but interference and security risks).
Devices and addressing
A hub broadcasts to all ports; a switch forwards frames using MAC addresses; a router forwards packets between networks using IP addresses; a NIC joins a device to the network; a modem converts between digital data and the ISP's signal; an access point links wireless devices. A MAC address is fixed in the NIC; an IP address is logical, can change, and is assigned automatically by DHCP.
Protocols and services
TCP/IP is the core suite: TCP splits data into numbered packets and requests retransmission of lost ones; IP addresses and routes packets. HTTP/HTTPS retrieve web pages (HTTPS encrypts with TLS), FTP transfers files, SMTP sends mail while POP3/IMAP retrieve it, and DNS resolves domain names into IP addresses.
Worked example
A school wants to network 30 computers in one laboratory. A star topology with a switch is recommended. Reasoning: faults are isolated, so one broken cable affects one machine only; adding a computer means one new cable; a switch cuts collisions compared with a hub; the extra cabling cost is acceptable indoors; and the switch can be replaced cheaply to reduce the single-point-of-failure risk.
Traps
Do not say a hub sends only to the destination, or that a switch uses IP addresses. HTTP is not secure; a firewall filters traffic but does not remove malware already installed; encryption protects confidentiality, not availability.