🌐 Networks & Protocols

LANs, WANs & topologies

A LAN covers one site using your own equipment, while a WAN joins LANs together across distances using third-party links. The internet is the largest WAN of all, and the web is just one service that runs on it, made up of HTTP pages. Networking brings a trade-off: it lets you share files, printers, connections and backups, but it also means sharing the costs, the malware risk and any downtime.

Performance on a network depends on the bandwidth available, which is the maximum number of bits per second the link can carry and which is shared between every device using it, along with how many users there are and whether the connection is wired or wireless. A client-server network keeps files and accounts centrally, which is convenient but creates a single point of failure, whereas a peer-to-peer network treats every device as an equal, which is cheaper but harder to manage.

Every device needs a NIC to connect to a network, a switch connects devices within a LAN, and a router connects different networks together by reading each packet's destination IP address and forwarding it along the best route. A WAP provides a wireless connection point. DNS translates domain names into IP addresses, hosting means renting space on someone else's server, and the cloud means your files can be reached from anywhere, provided you trust the provider and have an internet connection.

Wired, wireless & protocols

Ethernet is a wired connection and is the fastest and most secure option. Wi-Fi uses radio waves: the 2.4 GHz band has better range through walls but is more crowded, while the 5 GHz band is faster but has shorter reach, and channels are used to stop neighbouring networks interfering with each other. Bluetooth is used for short-range pairing between devices. Because wireless signals broadcast to everyone in range, encryption such as WPA2 or WPA3 is used to turn any intercepted traffic into useless ciphertext.

Each packet carries a header, containing the sender's IP address, the receiver's IP address, a packet number and a checksum, plus the payload, which is the actual data. Packet switching splits a message into packets, sends them along whatever routes are best at the time, and lets the receiver reassemble them in order using their packet numbers, requesting a re-send of any that go missing. An IP address is a logical address that changes depending on which network you join, whereas a MAC address is the NIC's fixed hardware fingerprint, which never changes.