Topics: Network topology, Star network, Bus network Pages: 11 (4499 words) Published: July 6, 2014
﻿Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network.[1][2] Essentially, it is the topological[3] structure of a network, and may be depicted physically or logically. Physical topology refers to the placement of the network's various components, including device location and cable installation, while logical topology shows how data flows within a network, regardless of its physical design. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ between two networks, yet their topologies may be identical. A good example is a local area network (LAN): 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. Conversely, mapping the data flow between the components determines the logical topology of the network. The way in which the connections are made is called the topology of thecomputer network. Now I am discussing about network topology, Network topology specifically refers to the physical layout of the network, especially the locations of the computers and how the cable is run between them. Four most common topologies are:

Bus
Star
Ring
Mesh
Bus Topology:

Bus topologies
All the devices on a bus topology are connected by one single cable. When one computer sends a signal up the wire, all the computers on the network receive the information, but only one accepts the information. The rest regrets the message. One computer can send a message at a time. A computer must wait until the bus is free before it can transmit. When the signal reaches the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an unterminated bus, it is called ringing. To stop the signals from ringing, attach terminators at either end of the segment. The terminators absorb the electrical energy and stop the reflection. Advantages and disadvantages of network topology:

1. The bus is simple, reliable in small network, easy to use and understand 2. Requires the least amount of cable to connect the computers and less expensive 3.  Easy to extend the bus
1. Heavy network traffic can slow a bus considerably
2. Each barrel connector weakens the electrical signal
3.  Difficult to troubleshoot a bus
Star Topology:

Star Topology
All the cables run from the computers to a central location, where they are all connected by a device called a hub. Each computer on a star network communicates with a central hub that resends the message either to all the computers or only to the destination computers. Hub can be active or passive in the star network Active hub regenerates the electrical signal and sends it to all the computers connected to it. Passive hub does not amplify or regenerate signal and does not require electrical power to run. We can expand a star network by placing another star hub. Advantages:

Easy to modify and add new computers to a star net
Center of a star net is a good place to diagnose network faults Single computer failure do not necessarily bring down the whole net Several cable types can be used with the hub
Central hub fails, the whole network fails to operate
Many star networks require a device at the central point to rebroadcast or switch network traffic. Costs more for cabling in star net than bus.
Ring Topology:

Ring Topology
Each computer is connected to the next computer ,with the last one connected to the first. Every computer is connected to the next computer in the ring, and each retransmits what it receives from the previous computer. The message flow around the ring in one direction. Some ring networks do token passing. It passes around the ring until a computer wishes to send information to...