those defined by IEEE 802.11 ) use radio waves, or others use infrared signals as a transmission medium. Power line communication uses a building's power cabling to transmit data. Ethernet transmits data over both copper and fiber cables. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3. In the OSI model, these are defined at layers 1 and 2 - the physical layer and the data link layer.Ī widely adopted family of transmission media used in local area network (LAN ) technology is collectively known as Ethernet.
The transmission media (often referred to in the literature as the physical media) used to link devices to form a computer network include electrical cables (Ethernet, HomePNA , power line communication, G.hn ), optical fiber (fiber-optic communication ), and radio waves (wireless networking). Some networks are able to dynamically change their logical topology through configuration changes to their routers and switches. Logical topologies are often closely associated with media access control methods and protocols. Physically, AFDX can be a cascaded star topology of multiple dual redundant Ethernet switches however, the AFDX Virtual links are modeled as time-switched single-transmitter bus connections, thus following the safety model of a single-transmitter bus topology previously used in aircraft. For example, the original twisted pair Ethernet using repeater hubs was a logical bus topology carried on a physical star topology. Token ring is a logical ring topology, but is wired as a physical star from the media access unit. A network's logical topology is not necessarily the same as its physical topology. In contrast, logical topology is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. For conductive or fiber optical mediums, this refers to the layout of cabling, the locations of nodes, and the links between the nodes and the cabling. The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunication circuits. The transmission medium layout used to link devices is the physical topology of the network. Two basic categories of network topologies exist, physical topologies and logical topologies. In comparison, Controller Area Networks, common in vehicles, are primarily distributed control system networks of one or more controllers interconnected with sensors and actuators over, invariably, a physical bus topology. Conversely, mapping the data flow between the components determines the logical topology of the network. A wide variety of physical topologies have been used in LANs, including ring, bus, mesh, and star.
Any given node in the LAN has one or more physical links to other devices in the network graphically mapping these links results in a geometric shape that can be used to describe the physical topology of the network. A network’s physical topology is a particular concern of the physical layer of the OSI model.Įxamples of network topologies are found in local area networks (LAN), a common computer network installation. Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two different networks, yet their logical topologies may be identical. Physical topology is the placement of the various components of a network (e.g., device location and cable installation), while logical topology illustrates how data flows within a network. It is an application of graph theory wherein communicating devices are modeled as nodes and the connections between the devices are modeled as links or lines between the nodes. Network topology is the topological structure of a network and may be depicted physically or logically. Network topology is the arrangement of the elements (links, nodes, etc.) of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and control radio networks, industrial field busses, and computer networks.