Network Topologies and Standards

Topics: Ethernet, Computer network, Network topology Pages: 31 (7941 words) Published: February 23, 2013
Network Topologies and Standards



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Objective 3.01 Objective 3.02 Objective 3.03 Objective 3.04 Objective 3.05 Objective 3.06

The Bus Topology and Ethernet The Star Bus Topology Ring Topologies Wireless Networking Distributed Star Topology—ARCNet Mesh Topology

4 hours

2 hours

1 hour




A network topology provides a general description of how the devices on the network link to each other, either logically or physically. Topologies do not define specifics about how to implement a network installation. They only provide a very high-level look at how network nodes connect. To move from a theoretical overview to a working solution, you must implement a specific network standard such as Ethernet or Token Ring. Particular network topologies are generally associated with specific networking standards that provide the specifics that define how the network sends data between devices, the type of media used, the maximum network speed (also known as bandwidth), and the number of devices (nodes) that can attach to the network. Questions regarding network topologies and network standards are well represented on the Network+ exam. Pay attention here—there’s a lot to take in, and it’s all important stuff.

Objective 3.01

The Bus Topology and Ethernet


f you can imagine your laundry hanging on a long, straight clothes line, you have a pretty good idea of how a bus topology network is constructed. Everything hangs off one long run of cable, as shown in Figure 3-1. The bus topology has been associated with one network standard in particular—Ethernet.

Ethernet Overview
Ethernet, introduced by Xerox in 1973, remained a largely proprietary technology until 1979, when Xerox looked for partners to help promote Ethernet as an industry standard. Working with Digital Equipment Corporation (DEC) and Intel, the company published what became the Digital-Intel-Xerox (DIX) networking standard. The standard described a bus topology network using coaxial cable that enables multiple computing systems and other devices to communicate with each other at 10 Mbps.


Bus topology, where everything is attached to the one cable

CHAPTER 3 Network Topologies and Standards


Local Lingo
segment A run of cable (media) linking one or more nodes on a network.

How Ethernet Works
Any network design must address a number of key elements: the type of media to use, how to send data across the wire, how to identify the sending and receiving computers, and how to determine which computer should use the shared cable next. In Chapter 2, we discussed the physical cabling used in Ethernet. Ethernet networks can use coaxial cable, UTP, or fiber. Regardless of the physical cabling used, the data moves across the wire in essentially the same way. Any network requires a method for determining which device uses the network media at a given time, and Ethernet uses a technique known as CSMA/CD.

Ethernet networks use Carrier Sense, Multiple Access/Collision Detection (CSMA/ CD) to determine which computer should use the shared media at a given moment. “Carrier Sense” means that each machine on the network, referred to as a node, examines the cable before sending a data packet (see Figure 3-2). If another machine is using the network, the node detects traffic and waits until the cable is free. If the node detects no traffic, the node sends its data packet. Carrier sense is analogous to the process you use to get an outside phone line in a large office building. When you have a call to make, you pick up the phone, press a button, and listen. If you hear a dial tone (that is, if the line is free), you make your call. If you hear a busy signal (that is, if someone else is already using the line), you wait your turn.


A node on an Ethernet network listens for other traffic before sending...
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