Computer Network

A computer network is a set of computers and other devices, called nodes, connected by wired or wireless links so that they can exchange data and share resources such as files, printers, services and internet access. What makes a collection of connected machines a network is not the cabling but the agreement on how to send data: a set of rules, called protocols, that define addressing, formatting, error handling and the order of messages.

Modern networks are built on packet switching, in which data is cut into small, individually addressed packets that share links instead of reserving a dedicated circuit for the duration of a conversation. The idea was developed independently in the 1960s by Paul Baran at the RAND Corporation, who studied communications that could survive damage, and by Donald Davies at the UK National Physical Laboratory, who coined the word packet. Each packet carries source and destination addresses, may take a different path, and is reassembled by the receiver, so a busy link can interleave traffic from many users and a failed link can be bypassed. This contrasts with the circuit switching of traditional telephone systems, and it is the foundation of ARPANET and everything descended from it.

Networks are organized in layers, each solving one problem and relying on the layer below, which is what lets very different technologies interoperate. In the simplified TCP/IP model, a link layer moves frames across one physical connection (Ethernet, invented by Robert Metcalfe and colleagues at Xerox PARC in 1973, or Wi-Fi), an internet layer (IP) addresses packets across many networks, a transport layer (TCP or UDP) provides reliable streams or fast datagrams between programs, and an application layer holds protocols such as HTTP, DNS and SMTP. The seven-layer OSI reference model, published in 1984, offers a more detailed vocabulary that engineers still use when they refer to layer 2 or layer 3 devices. Because of the layering, a web browser neither knows nor cares whether its packets travel over fiber, cable or radio.

Networks are classified by scale, topology and role, and each choice trades cost, speed and resilience. By scale, a personal-area network spans a desk, a local area network a building, and a wide area network cities or continents, each treated in its own entry, while the internet is the global interconnection of many such networks. Topology describes the pattern of links: a star around a central switch is typical of offices, a mesh gives redundant paths, and the older shared bus of early Ethernet is largely gone. By role, client-server networks centralize services on dedicated machines, whereas peer-to-peer networks let participants exchange data with one another directly, as in file-sharing and some blockchain systems. Devices such as hubs, switches, routers, modems and access points each perform a different job inside a network and should not be treated as interchangeable.

A frequent misconception is that a network and the internet, or a network and Wi-Fi, are the same thing, and a related one is that more bandwidth always means a faster experience. A network can exist with no internet connection at all, such as a factory floor or a home that shares a printer, and Wi-Fi is merely one way of attaching a device to a network. Bandwidth, the amount of data per second a link can carry, is distinct from latency, the delay for one packet to arrive, and a high-bandwidth satellite link can still feel sluggish for interactive work. Networks are central to current computing: cloud services are networks of data centers, distributed databases depend on them, and large AI models are trained on clusters of accelerators tied together by specialized high-speed Ethernet or InfiniBand fabrics where network performance directly limits training speed.

Read a computer network as an agreement as much as a wire: nodes, links and protocols layered so that any device can send addressed packets to any other, with each layer hiding the details of the one beneath it so that the same web page can cross fiber, copper and radio unchanged.