A computer network is a system that connects multiple computers and devices to share information and resources. It allows for communication and data exchange between connected devices, much like a group of friends communicating via phones.
Basic Structure
A group of interconnected entities is called a network. The entities are called the nodes of the network. For instance, all the one billion WeChat users form a network with one billion nodes. As another example, all articles of computing form a network of computer science literature. The nodes (articles) are interconnected by citations. The nodes may refer to one another, but do not necessarily communicate with one another by sending or receiving messages.
A computational process may treat a network as an object. For instance, we may design a computational process to compute the topology of the network of WeChat users. Then, the network is an input object, and the topology of the network is an output object. A network may also be the subject of a computational process. For example, a network of computers may be used to execute the above task of topology computation: the network computes the topology.
Terms
A local area network (LAN) connects devices in the same building or even on the same campus. A metropolitan area network (MAN) connects LANs in the same city. A wide area network (WAN) spans multiple cities or even multiple countries.
An institution providing Internet connection services is called an Internet service provider (ISP).
Any device connected to a network is called a host. It could be a laptop computer, a printer, a server, or an environment sensor. A host directly used by the user is called a client, which makes requests to be served by another host called server.
If someone uses a wireless protocol called Wi-Fi to access the Internet, his laptop computer first needs to connect to an access point (AP). The AP device converts wireless signals to wired signals and vice versa.
A small LAN is often a bus structure realized by connecting a few hosts to a central device called a network hub. Multiple small LANs can be connected to form a bigger LAN to accommodate more hosts or to extend the distance covered. A network switch connects multiple hosts or LANs. The same protocol, e.g., Ethernet, must be used within a LAN, small or big. In such a homogeneous network, hosts are said to be homogeneously connected.
Networking devices called routers are used to connect multiple member networks into a bigger heterogeneous network, e.g., the Internet. Each member network of the Internet may internally use a different networking technology of its own choice, such as Wi-Fi, Ethernet, or InfiniBand. A gateway of a member network is the router connecting the member network to a bigger network
See Also
Network Thinking (Perspective from the course Introduction to Computer Science)