How networks connect computers
A network lets computers share data. From two laptops on a home Wi-Fi to the global internet, the same core ideas apply: addresses, links, and agreed rules called protocols.
What a network is
A computer network is a set of devices, called nodes or hosts, joined by links so they can exchange data. Links can be wired, such as copper Ethernet cable or fibre-optic glass, or wireless, such as Wi-Fi radio or cellular signals. A local area network (LAN) covers a home, school, or office; a wide area network (WAN) spans cities or countries.
Protocols
A protocol is an agreed set of rules for communication: how messages are formatted, in what order they are sent, and what to do when something goes wrong. Without shared protocols, devices from different makers could not understand each other. Internet standards are developed openly, largely through the Internet Engineering Task Force (IETF).
Packet switching
The internet breaks data into small chunks called packets. Each packet carries a header with source and destination addresses and travels independently, possibly by different routes, before being reassembled. This is packet switching. It differs from the old telephone system's circuit switching, which reserved a dedicated path for each call, and it shares links efficiently among many users.
Network hardware
A network interface card connects a device to a network. A switch connects devices within a LAN and forwards data to the right one using hardware (MAC) addresses. A router connects different networks and chooses paths for packets between them. A home 'router' usually combines a router, switch, Wi-Fi access point, and modem in one box.
Bandwidth and latency
Bandwidth is how much data a link can carry per second, measured in bits per second, such as 100 megabits per second. Latency is the delay for data to travel from one point to another, measured in milliseconds. A link can have high bandwidth but high latency, like a satellite connection; games and video calls are especially sensitive to latency.
Topologies
Topology describes how nodes are arranged. In a star topology, every device connects to a central switch or access point, which is common in homes and offices. A mesh topology has many interconnections, so data can take alternative paths if a link fails; the internet's core behaves like a large mesh. Bus and ring topologies appear in older or specialised networks.
The internet as a network of networks
The internet is not one network but tens of thousands of independently run networks, such as internet service providers, universities, companies, and cloud providers, that agree to exchange traffic. They connect at internet exchange points and through private agreements. No single organisation owns the whole internet.
Worked example
Downloading a 500-megabyte game over a 100-megabit-per-second connection: 500 megabytes is 4,000 megabits, so the transfer needs at least 4,000 / 100 = 40 seconds. Real downloads take longer because of protocol overhead, congestion, and the speed of the server. Latency hardly matters for one big file, but it matters a lot for many small requests.
Key takeaways
Networks link nodes by wired or wireless links; LANs are local, WANs wide. Protocols are shared rules, many standardised by the IETF. The internet uses packet switching, not circuit switching. Switches connect devices within a LAN; routers connect networks. Bandwidth measures capacity; latency measures delay. Star and mesh are common topologies. The internet is a network of independently run networks.
Flashcard
Nodes joined by links to exchange data
Check your understanding
What is the main job of a router?