A network is a collection of computers and related devices, connected so that they can communicate with each other and share information, software, peripheral devices, and/or processing power.
- Local Area Network or LAN
- Metropolitan Area Network or MAN
- Wide Area Network or WAN
- personal area network (PAN)
- LAN covers a small region of space, typically a single building. maximum network coverage is about 3 km and is characterized by high speed data transmission
- MAN is a collection of LANs within the same geographical area, for instance a city. It enables network coverage of 10 t0 16 miles.
- WAN is a long distance network: it connects systems together throughout a country or even beyond the border. It is characterized by low data rates and hardware and software components come form a wide variety of vendors.
- A personal area network (PAN) is the interconnection of information technology devices within the range of an individual person, typically within a range of 10 meters. For example, a person traveling with a laptop, a personal digital assistant (PDA), and a portable printer could interconnect them without having to plug anything in, using some form of wireless technology. Typically, this kind of personal area network could also be interconnected without wires to the Internet or other networks.
Topology refers to the layout of connected devices on a network. Network topologies are categorized into the following basic types:
- Bus topology
Bus network use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either “clockwise” or “counterclockwise”). A failure in any cable or device breaks the loop and can take down the entire network.
A star network features a central connection point called a “hub” that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet. Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer’s network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the “root” of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.