Computer Science · Ch 10 — Computer Networks
Summary
Summary
- Networks and nodes: A computer network is an interconnection among two or more computers or computing devices that lets them share data and resources. Any device in the network that can receive, create, store, or send data is called a node.
- Network types (by geographical area and data-transfer rate): PAN (Personal Area Network — a few personal devices within ~10 m, e.g. a phone tethered to a laptop, or two phones paired over Bluetooth). LAN (Local Area Network — a room, floor, office, or campus, extendable up to ~1 km, 10 Mbps to 1000 Mbps Ethernet). MAN (Metropolitan Area Network — an extended LAN covering a city/town, up to ~30-40 km, e.g. cable-TV/broadband networks). WAN (Wide Area Network — connects LANs and MANs across a country, countries, or continents; the Internet is the largest WAN).
- Network devices: Modem (Modulator-DEModulator — converts digital data to analog signals for transmission and back). Hub (broadcasts incoming data to every connected port; collisions occur if two devices send at once). Switch (reads the destination address and forwards data only to the intended port; can carry multiple transmissions at once and drops corrupted signals). Repeater (an analog device that regenerates a signal that has weakened after travelling its cable's distance limit). Router (analyses data, can repackage it, and forwards it to another, possibly different, type of network; connects a LAN to the Internet). Gateway (the entry/exit point between a network and the outside world; can be software, hardware, or both, and often has a firewall integrated with it).
- Ethernet and connectors: Ethernet is the set of rules for how devices connect via cables in a LAN. An Ethernet/Network Interface Card (NIC) is the circuit board that lets a computer join a wired network, and an RJ45 connector is the eight-pin plug used with Ethernet cables.
- Network topologies: The arrangement of devices in a network is its topology. The five common ones are Mesh (every device connected to every other — n(n-1)/2 links, reliable and secure but expensive), Ring (each node linked to two neighbours in a closed loop, data flows one way), Bus (all devices share one backbone cable), Star (every device links to one central hub/switch), and Tree/Hybrid (multiple star/ring/bus segments joined by a common bus).
- Addressing: A MAC address (Media Access Control, also called the physical/hardware address) is a permanent 12-digit hexadecimal (48-bit) number burned into a NIC at manufacture — the first six digits are the manufacturer's OUI and the last six are the card's serial number. An IP address also uniquely identifies a node, but unlike a MAC address it can change when a device moves to a different network. IPv4 is a 32-bit address written as four dot-separated decimal numbers (0-255); IPv6 is a 128-bit address written as eight colon-separated hexadecimal groups. …