ENGINEERING ARTICLES

CSMA/CD: Carrier sense multiple access with collision detection (CSMA/CD) is one of the most popular access methods, with CSMA/CD, every host has equal access to the wire and can place data on the wire when the wire is free from traffic. If a host wishes to place data on the wire, it will “sense” the wire and determine whether there is a signal already on the wire. If there is, the host will wait to transmit the data; if the wire is free, the host will send the data, as shown in Figure 1. Figure 1: A host "sensing" the wire to see if it is free of traffic. The problem with the process just described is that, if there are two systems on the wire that “sense” the wire at the same time to see if the wire is free, they will both send data out at the same time if the wire is free. When the two pieces of data are sent out on the wire at the same time, they will collide with one another, and the data will be destroyed. If the data is destroyed in transit, the data will ne...

Networks are built using a topology of bus, star, or ring, but how the systems will be connected in the topology that you choose. Cabling is the medium for the transmission of data between hosts on the LANs. LANs can be connected together using a variety of cable types, such as unshielded twisted-pair, coax, or fiber. Each cable type has its own advantages and disadvantages. There are three primary types of cable media that can be used to connect systems to a network: Coaxial cable Twisted-pair cable Fiber-optic cable Transmission rates that can be supported on each of these physical media are measured in millions of bits per second, or megabits per second (Mbps). 1. COAXIAL CABLE: Coaxial, or coax, cable looks like the cable used to bring the cable TV signal to your television. One strand (a solid-core copper wire) runs down the middle of the cable. Around that strand is a layer of insulation, and covering that insulation is braided wire and metal foil, which shiel...

Organizations of different sizes, structures, and budgets need different types of networks. A local newspaper company has needs for its network that would be different from the needs of a multinational company. Networks can be divided into one of two categories: peer-to-peer or server-based networks. PEER-TO-PEER NETWORK: A peer-to-peer network has no dedicated servers; instead, a number of workstations are connected together for the purpose of sharing information or devices. When there is no dedicated server, all workstations are considered equal; any one of them can participate as the client or the server. Peer-to-peer networks are designed to satisfy the networking needs of home networks or of small companies that do not want to spend a lot of money on a dedicated server but still want to have the capability to share information or devices. For example, a small accounting firm with three employees that needs to access customer data from any of the three systems or print to ...

There are two different techniques that may be used to transmit the signal along the network wire which are base-band communication and broadband communication. BASEBAND Sends digital signals through the media as a single channel that uses the entire bandwidth of the media. The signal is delivered as a pulse of electricity or light, depending on the type of cabling being used. Baseband communication is also bidirectional, which means that the same channel can be used to send and receive signals. BROADBAND Sends information in the form of an analog signal, which flows as electromagnetic waves or optical waves. Each transmission is assigned to a portion of the bandwidth, so unlike with baseband communication, it is possible to have multiple transmissions at the same time, with each transmission being assigned its own channel or frequency. Broadband communication is unidirectional, so in order to send and receive, two pathways will need to be used. This can be accomplished either ...

It is typical for networks to implement a mixture of topologies to form a hybrid topology. For example, a very popular hybrid topology is a star-bus topology, in which a number of star topologies are connected by a central bus. This is a popular topology because the bus will connect hubs that are spread over distance. Another very popular hybrid topology is the star-ring topology. The star-ring topology is popular because it looks like a star but acts as a ring. For example, there is a network architecture known as Token Ring (more on this later, in the section “Network Architectures”) that uses a central “hub” type device, but the internal wiring makes a ring. Physically it looks like a star, but logically it acts as a ring topology. Figure: Hybrid Topology. Advantages of Hybrid Network Topology 1) Reliable: Unlike other networks, fault detection and troubleshooting is easy in this type of topology. The part in which fault is detected can be isolated from the rest of networ...

Basically, the DSTATCOM system is comprised of three main parts: a Voltage Source Converter (VSC), a set of coupling reactors and a controller. The basic principle of a DSTATCOM installed in a power system is the generation of a controllable ac voltage source by a voltage source inverter (VSI) connected to a dc capacitor (energy storage device). The ac voltage source, in general, appears behind a transformer leakage reactance. The active and reactive power transfer between the power system and the DSTATCOM is caused by the voltage difference across this reactance. The DSTATCOM is connected to the power networks where the voltage-quality problem is a concern. All required voltages and currents are measured and are fed into the controller to be compared with the commands. The controller then performs feedback control and outputs a set of switching signals to drive the main semiconductor switches (IGBT’s, which are used at the distribution level) of the power converter accordingly. Fi...

A network topology is the physical layout of computers, cables, and other components on a network. There are a number of different network topologies, and a network may be built using multiple topologies. The different types of network layouts are Bus topology Star topology Mesh topology Ring topology Hybrid topology Wireless topology 1) BUS TOPOLOGY A bus topology uses one cable as a main trunk to connect all of the systems together. A bus topology is very easy to set up and requires no additional hardware such as a hub. The cable is also called a trunk, a backbone, or a segment. With a bus topology, when a computer sends out a signal, the signal travels the cable length in both directions from the sending computer. When the signal reaches the end of the cable length, it bounces back and returns in the direction it came from. This is known as signal bounce. Signal bounce is a problem, because if another signal is sent on the cable length at the same time, the two...