Topology The physical or geographic locations of network nodes and links generally have relatively little effect on a network, but the topology of interconnections of a network can significantly affect its throughput and reliability. With many technologies, such as bus or star networks, a single failure can cause the network to fail entirely. In general, the more interconnections there are, the more robust the network is; but the more expensive it is to install. Therefore, most
network diagrams are arranged by their
network topology which is the map of logical interconnections of network hosts. Common topologies are: •
Bus network: all nodes are connected to a common medium along this medium. This was the layout used in the original
Ethernet, called
10BASE5 and
10BASE2. This is still a common topology on the
data link layer, although modern
physical layer variants use
point-to-point links instead, forming a star or a tree. •
Star network: all nodes are connected to a special central node. This is the typical layout found in a small
switched Ethernet LAN, where each client connects to a central network switch, and logically in a
wireless LAN, where each wireless client associates with the central
wireless access point. •
Ring network: each node is connected to its left and right neighbor node, such that all nodes are connected and that each node can reach each other node by traversing nodes left- or rightwards.
Token Ring networks, and the
Fiber Distributed Data Interface (FDDI), made use of such a topology. •
Mesh network: each node is connected to an arbitrary number of neighbors in such a way that there is at least one traversal from any node to any other. •
Fully connected network: each node is connected to every other node in the network. •
Tree network: nodes are arranged hierarchically. This is the natural topology for a larger Ethernet network with multiple switches and without redundant meshing. The physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, with
FDDI, the network topology is a ring, but the physical topology is often a star, because all neighboring connections can be routed via a central physical location. Physical layout is not completely irrelevant, however, as common ducting and equipment locations can represent single points of failure due to issues like fires, power failures and flooding.
Overlay network An
overlay network is a virtual network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one. For example, many
peer-to-peer networks are overlay networks. They are organized as nodes of a virtual system of links that run on top of the
Internet. Overlay networks have been used since the early days of networking, back when computers were connected via telephone lines using modems, even before data networks were developed. The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the
telephone network. resilient routing and quality of service studies, among others.
Scale Networks may be characterized by many properties or features, such as physical capacity, organizational purpose, user authorization, access rights, and others. Another distinct classification method is that of the physical extent or geographic scale.
Nanoscale network A
nanoscale network has key components implemented at the nanoscale, including message carriers, and leverages physical principles that differ from macroscale communication mechanisms. Nanoscale communication extends communication to very small sensors and actuators such as those found in biological systems and also tends to operate in environments that would be too harsh for other communication techniques.
Personal area network A
personal area network (PAN) is a computer network used for communication among computers and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters. A wired PAN is usually constructed with
USB and
FireWire connections while technologies such as
Bluetooth and
infrared communication typically form a wireless PAN.
Local area network A
local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office building, or closely positioned group of buildings. Wired LANs are most commonly based on Ethernet technology. Other networking technologies such as
ITU-T G.hn also provide a way to create a wired LAN using existing wiring, such as coaxial cables, telephone lines, and power lines. A LAN can be connected to a
wide area network (WAN) using a router. The defining characteristics of a LAN, in contrast to a WAN, include higher
data transfer rates, limited geographic range, and lack of reliance on
leased lines to provide connectivity. Current Ethernet or other IEEE 802.3 LAN technologies operate at data transfer rates up to
800 Gbit/s, standardized by IEEE in 2024. • A
home area network (HAN) is a residential LAN used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a
cable Internet access or
digital subscriber line (DSL) provider. • A
storage area network (SAN) is a dedicated network that provides access to consolidated, block-level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the storage appears as locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium-sized business environments.
Campus area network A
campus area network (CAN) is made up of an interconnection of LANs within a limited geographical area. The networking equipment (switches, routers) and transmission media (optical fiber,
Cat5 cabling, etc.) are almost entirely owned by the campus tenant or owner (an enterprise, university, government, etc.). For example, a university campus network is likely to link a variety of campus buildings to connect academic colleges or departments, the library, and student residence halls.
Backbone network A
backbone network is part of a computer network infrastructure that provides a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks within the same building, across different buildings, or over a wide area. When designing a network backbone,
network performance and
network congestion are critical factors to take into account. Normally, the backbone network's capacity is greater than that of the individual networks connected to it. For example, a large company might implement a backbone network to connect departments that are located around the world. The equipment that ties together the departmental networks constitutes the network backbone. Another example of a backbone network is the
Internet backbone, which is a massive, global system of fiber-optic cable and optical networking that carry the bulk of data between
wide area networks (WANs), metro, regional, national and transoceanic networks. • An
enterprise private network or intranet is a network that a single organization builds to interconnect its office locations (e.g., production sites, head offices, remote offices, shops) so they can share computer resources.
Metropolitan area network A
metropolitan area network (MAN) is a large computer network that interconnects users with computer resources in a geographic region of the size of a
metropolitan area.
Wide area network A
wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances. A WAN uses a communications channel that combines many types of media such as telephone lines, cables, and airwaves. A WAN often makes use of transmission facilities provided by
common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI model: the physical layer, the
data link layer, and the
network layer.
Global area network A
global area network (GAN) is a network used for supporting mobile users across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial
wireless LANs.
Scope An
intranet is a community of interest under private administration usually by an enterprise, and is only accessible by authorized users (e.g. employees). Intranets do not have to be connected to the Internet, but generally have a limited connection. An
extranet is an extension of an intranet that allows secure communications to users outside of the intranet (e.g. business partners, customers). Each line is drawn between two nodes, representing two
IP addresses. The length of the lines indicates the delay between those two nodes. An
internetwork is the connection of multiple different types of computer networks to form a single computer network using higher-layer network protocols and connecting them together using routers. The
Internet is the largest example of internetwork. It is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of the Internet protocol suite. It is the successor of the
Advanced Research Projects Agency Network (ARPANET) developed by
DARPA of the
United States Department of Defense. The Internet utilizes copper communications and an
optical networking backbone to enable the
World Wide Web (WWW), the
Internet of things, video transfer, and a broad range of information services. Participants on the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet protocol suite and the IP addressing system administered by the
Internet Assigned Numbers Authority and
address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the
Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.
Darknet A
darknet is an overlay network, typically running on the Internet, that is only accessible through specialized software. It is an anonymizing network where connections are made only between trusted peers — sometimes called
friends (
F2F) — using non-standard protocols and
ports. Darknets are distinct from other distributed
peer-to-peer networks as
sharing is anonymous (that is, IP addresses are not publicly shared), and therefore users can communicate with little fear of governmental or corporate interference.
Virtual private networks A
virtual private network (VPN) is an
overlay network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features. == Services ==