Computer networks and their types

Computer Network

A computer network is formed when two (sometimes said to be at least three) or more computers are connected together using a telecommunication system for the purpose of sharing resources. In practice, the most widespread network today is based on ethernet technology and uses the TCP/IP protocol.

Computer networks are classified according to various criteria. For example, by size/scale into PAN (Personal Area Network), LAN (Local Area Network), CAN (Campus Area Network), MAN (Metropolitan Area Network), or WAN (Wide Area Network). By technology used for connecting devices into Ethernet, WLAN, etc. Or by network topology into bus topology, star topology, etc.

Simplified, we can represent a computer network (a large representative of which is the internet) using a tree structure. A nice schematic picture with a description can be found in the article The Internet: How it works. Of course, the actual situation is more complex because many lines are duplicated and connected in multiple places.

Local Area Network - LAN

A local area network is characterized by computers being connected over a smaller geographical area (i.e., within a company, building, room, etc.). Within a LAN, switched ethernet or WiFi (IEEE802.11) is most commonly used. The infrastructure is usually made up of metallic cables and possibly an optical backbone.

A LAN can be a standalone network connecting multiple devices, but nowadays it is mostly connected to the internet, i.e., a WAN network.

Metropolitan Area Network - MAN

A network that connects individual LANs but does not cross the boundaries of a city or metropolitan area is referred to as a metropolitan network - MAN. Within a MAN, wireless connections or optical fibers are often used.

A MAN can be owned by a single organization, but it is usually a connection of several independent entities. For example, we can have several branches of a company in one city connected into a MAN network.

Previously, technologies like ATM and FDDI were used, but today they are mostly replaced by ethernet referred to as metro-ethernet.

Wide Area Network - WAN

A WAN is a communication network that covers a large area, such as connecting countries or continents. Generally, we can say that individual LAN networks are connected through a WAN network to ensure long-distance communication. This is how the internet works as the largest and most well-known WAN.

Today, the most commonly used technologies are Frame relay or ATM.

Virtual Local Area Network - VLAN

A virtual LAN is similar to a traditional local network, except that a LAN depends on physical arrangement and connections, whereas a VLAN is created logically within a physical LAN.

Wireless Local Area Network - WLAN

A wireless local area network is again similar to a regular LAN, but the individual elements are not physically connected by wire (metallic or optical), but are connected wirelessly. Radio waves and certain modulation are used for data transmission.
The advantage of wireless is clear for mobile devices. The disadvantage is, for example, that it is difficult to limit the spread of the signal, and a potential attacker does not need to gain direct physical access to a socket, as in the case of wired networks.