Network topology

Network topology is the arrangement of the elements 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 fieldbusses and computer networks. Network topology is the topological structure of a network and may be depicted physically or logically, 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. Physical topology is the placement of the various components of a network, while logical topology illustrates how data flows within a network. Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two different networks, yet their topologies may be identical. A network’s physical topology is a particular concern of the physical layer of the OSI model. Examples of network topologies are found in local area networks, a common computer network installation.

Any given node in the LAN has one or more physical links to other devices in the network. A wide variety of physical topologies have been used in LANs, including ring, bus and star. Conversely, mapping the data flow between the components determines the logical topology of the network. In comparison, Controller Area Networks, common in vehicles, are distributed control system networks of one or more controllers interconnected with sensors and actuators over, invariably, a physical bus topology. Two basic categories of network topologies exist, logical topologies; the transmission medium layout used to link devices is the physical topology of the network. For conductive or fiber optical mediums, this refers to the layout of cabling, the locations of nodes, 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, the cost associated with cabling or telecommunication circuits.

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. A network's logical topology is not the same as its physical topology. For example, the original twisted pair Ethernet using repeater hubs was a logical bus topology carried on a physical star topology. Token ring is wired as a physical star from the media access unit. Physically, AFDX can be a cascaded star topology of multiple dual redundant Ethernet switches. Logical topologies are closely associated with media access control methods and protocols; some networks are able to dynamically change their logical topology through configuration changes to their routers and switches. The transmission media used to link devices to form a computer network include electrical cables, optical fiber, radio waves. In the OSI model, these are defined at layers 2 -- the physical layer and the data link layer.

A adopted family of transmission media used in local area network technology is collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3. Ethernet transmits data over both fiber cables. Wireless LAN standards use radio waves. Power line communication uses a building's power cabling to transmit data; the orders of the following wired technologies are from slowest to fastest transmission speed. Coaxial cable is used for cable television systems, office buildings, other work-sites for local area networks; the cables consist of copper or aluminum wire surrounded by an insulating layer, which itself is surrounded by a conductive layer. The insulation helps minimize distortion. Transmission speed ranges from 200 million bits per second to more than 500 million bits per second. ITU-T technology uses existing home wiring to create a high-speed local area network. Signal traces on printed circuit boards are common for board-level serial communication between certain types integrated circuits, a common example being SPI.

Ribbon cable has been a cost-effective media for serial protocols within metallic enclosures or rolled within copper braid or foil, over short distances, or at lower data rates. Several serial network protocols can be deployed without shielded or twisted pair cabling, that is, with "flat" or "ribbon" cable, or a hybrid flat/twisted ribbon cable, should EMC, bandwidth constraints permit: RS-232, RS-422, RS-485, CAN, GPIB, SCSI, etc. Twisted pair wire is the most used medium for all telecommunication. Twisted-pair cabling consist of copper wires. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer network cabling

David M. Diamond

David M. Diamond is a professor at the University of South Florida. Diamond has researched the neurological conditions that lead parents to forget their children in hot cars, he has been quoted as an expert regarding the tendency for travelers to forget their belongings, more for people under stress to become more forgetful. He has explored with Kevin Kip methodology for the selection of therapies for posttraumatic stress disorder in United States Department of Veterans Affairs and United States Department of Defense facilities. Diamond graduated from the University of California, Irvine in 1980 and completed a PhD in biology at UC Irvine in 1985. After postdoctoral research at the UC Irvine Center for the Neurobiology of Learning and Memory, he joined the University of Colorado as an assistant professor in 1986, he moved to the University of South Florida in 1997, has been the director of the university's Center for Preclinical and Clinical Research on PTSD since 2007. Diamond, David M.. "The stressed hippocampus, synaptic plasticity and lost memories", Nature Reviews Neuroscience, 3: 453–462, doi:10.1038/nrn849 Home page


Tyrosine-protein phosphatase non-receptor type 13 is an enzyme that in humans is encoded by the PTPN13 gene. The protein encoded by this gene is a member of the protein tyrosine phosphatase family. PTPs are known to be signaling molecules that regulate a variety of cellular processes including cell growth, mitotic cycle, oncogenic transformation; this PTP is a large protein that possesses a PTP domain at C-terminus, multiple noncatalytic domains, which include a domain with similarity to band 4.1 superfamily of cytoskeletal-associated proteins, a region consisting of five PDZ domains, a leucine zipper motif. This PTP was found to interact with, dephosphorylate Fas receptor, as well as IkappaBalpha through the PDZ domains, which suggested its role in Fas mediated programmed cell death; this PTP was shown to interact with GTPase-activating protein, thus may function as a regulator of Rho signaling pathway. Four alternatively spliced. PTPN13 has been shown to interact with PKN2