Summary

Chapter 8: Fundamental Networks 31Physical TopologiesThe common LAN physical topologies are as follows:■■■■■Bus topology: In the bus topology, each computer connects to a common cable. Thecable connects one computer to the next, like a bus line going through a city. The cablehas a small cap installed at the end, called a terminator. The terminator prevents signalsfrom bouncing back and causing network errors.Ring topology: In a ring topology, hosts are connected in a physical ring or circle.Because the ring topology has no beginning or end, the cable does not need to be terminated.A specially formatted frame, called a token, travels around the ring, stoppingat each host. If a host wants to transmit data, it adds the data and the destinationaddress to the frame. The frame then continues around the ring until it stops at the hostwith the destination address. The destination host takes the data out of the frame.Star topology: The star topology has a central connection point, which normally is adevice such as a hub, switch, or router. Each host on a network has a cable segmentthat attaches the host directly to the central connection point. The advantage of a startopology is that it is easy to troubleshoot. Each host is connected to the central devicewith its own wire. If there is a problem with that cable, only that host is affected. Therest of the network remains operational.Hierarchical or extended star topology: A hierarchical or extended star topology is astar network with an additional networking device connected to the main networkingdevice. Typically, a network cable connects to one hub, and then several other hubsconnect to the first hub. Larger networks, such as those of corporations or universities,use the hierarchical star topology.Mesh topology: The mesh topology connects all devices to each other. When everydevice is connected to every other device, a failure of any cable does not affect the network.The mesh topology is used in WANs that interconnect LANs.Logical TopologiesThe two most common types of logical topologies are broadcast and token passing.In a broadcast topology, each host addresses data to either a particular host or to all hostsconnected on a network. There is no order that the hosts must follow to use the network. Itis first come, first served for transmitting data on the network.Token passing controls network access by passing an electronic token sequentially to eachhost. When a host receives the token, it can send data on the network. If the host has nodata to send, it passes the token to the next host, and the process repeats.