Guide to Networking Essentials, Fifth Edition
Chapter 2
Network Design Essentials
At a Glance
Instructor’s Manual Table of Contents

Overview

Objectives

Teaching Tips

Quick Quizzes

Class Discussion Topics

Additional Projects

Additional Resources

Key Terms

Technical Notes for Hands-On Projects
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Guide to Networking Essentials, Fifth Edition
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Lecture Notes
Overview
Chapter 2 offers an introduction to network design essentials. Students begin by
learning about the basics of a network layout and about the standard networking
topologies, as well as variations on these topologies. Next, they learn about the role of
hubs and switches in a network topology. Finally, at the end of the chapter, students will
be able to construct a basic network layout.
Objectives





Explain the basics of a network layout
Describe the standard networking topologies
Explain the variations on standard networking topologies
Describe the role of hubs and switches in a network topology
Construct a basic network layout
Teaching Tips
Examining the Basics of a Network Layout
1. Explain the basics of a network layout. Introduce the terms topology, physical topology,
and logical topology.
Teaching
Tip
For more information on network topologies, read
http://en.wikipedia.org/wiki/Network_topology.
2. Stress that the topology has a significant effect on the network’s performance and
growth, and equipment decisions.
Understanding Standard Topologies
1. Briefly describe each of the three physical topologies in which networks are based: bus,
star, and ring.
2. Make sure students understand the difference between a physical topology and a logical
topology.
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Physical Bus Topology
1. Use Figure 2-1 to explain how the physical bus topology works. Don’t forget to
introduce the terms bus and backbone.
Teaching
Tip
For more information on the bus network topology, read
http://en.wikipedia.org/wiki/Bus_network.
2. Stress that the main weakness of this topology is that a single cable break can halt the
entire network.
3. Explain why this topology is no longer a practical choice.
4. Signal Propagation. Describe how signals are propagated on a physical bus topology.
5. Signal Bounce. Use Figure 2-2 to describe the signal bounce phenomenon in a physical
bus topology.
6. Cable Termination. Use Figure 2-3 to describe the role of a terminator.
7. Cable Failure. Use Figure 2-4 to explain how a cable break affects the signals
transmitted in a bus.
Logical Bus Topology
1. Explain the role of the logical bus topology.
2. Stress that technology has moved past the physical bus, but a logical bus topology is
still in use on some physical topologies, in particular a star.
3. Sending the signal. Briefly describe the steps required to send data in a logical bus
topology. Explain that all computers on a logical bus receive the signals, but only the
destination accepts the data. Make sure students understand why in this topology,
network performance is reduced as more computers share the bus. Note that a bus
topology is a passive topology. Explain the difference between a passive topology and
an active topology.
Physical Ring Topology
1. Use Figure 2-5 to describe how a physical ring topology works.
Guide to Networking Essentials, Fifth Edition
Teaching
Tip
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Note that although a logical ring topology might be implemented as a physical
ring, it’s much more common for a logical ring to be implemented as a physical
star topology.
2. Explain that although a physical ring topology is sometimes used, as in network
technologies such as FDDI, the most common type of ring is a logical ring topology.
Logical Ring Topology
1. Explain the token passing process of a logical ring topology.
2. Explain that modern logical ring topologies use “smart hubs” that recognize a
computer’s failure and remove the computer from the ring automatically.
3. Note that an advantage of the ring topology lies in its capability to share network
resources fairly.
Physical Star Topology
1. Use Figure 2-6 to describe how a physical star topology works.
Teaching
Tip
For more information on the star network topology, read
http://en.wikipedia.org/wiki/Star_network.
2. Explain that the underlying logical topology in a physical star is likely a bus, a ring, or
switching.
3. Describe the advantages and disadvantages of the physical star topology.
4. Stress that the physical star doesn’t really have a logical counterpart; rather, logical
topologies implemented as a physical star are often referred to as star bus or star ring.
5. A logical bus implemented as a physical star. Use Figure 2-7 to describe how a logical
bus is implemented as a physical star (using a hub).
6. A logical ring implemented as a physical star. Use Figure 2-8 to explain how a logical
ring can be implemented as a physical star (using a concentrator or multistation access
unit (MSAU)).
7. Switching implemented as a physical star. Explain that switching is neither a bus nor a
ring logically, but is always implemented as a physical star. Explain that switching is far
superior to the other logical topologies discussed, because unlike the bus and ring,
multiple computers can communicate simultaneously without affecting each other.
Stress that switching is the dominant method used in almost every LAN design.
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Wireless Topologies
1. Explain the difference between the ad hoc and the infrastructure mode wireless
topologies. Note that the latter has a star physical topology but a bus logical topology.
Quick Quiz 1
1. In networking, what does the term topology refer to?
Answer: A network’s topology refers not only to the physical layout of its computers,
cables, and other resources, but also to how those components communicate with each
other.
2. All components of the bus topology connect via a(n) ____________________, a single
cable segment that (theoretically) interconnects all the computers in a straight line.
Answer: backbone
3. What does it mean to say that a bus topology is a passive topology?
Answer: This means that computers on the bus only listen for data being sent; they
aren’t responsible for moving data from one computer to the next.
4. Because of the problems in troubleshooting and managing a physical bus or ring
network, and because a single cable failure can bring down the entire network, these
topologies have been largely replaced by the physical ____________________
topology.
Answer: star
Examining Variations of Physical Topologies
1. Note that the major physical topologies have three typical variations or combinations:
extended star, mesh, and combination star and bus.
Extended Star Topology
1. Use Figure 2-9 to describe the extended star topology.
Mesh Topology
1. Use Figure 2-10 to describe the mesh topology. Stress that this type of network is the
most fault tolerant, but also the most expensive.
Teaching
Tip
For more information on the mesh network topology, read
http://en.wikipedia.org/wiki/Mesh_network.
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2. Stress that most often, a mesh topology is used in a WAN to ensure that all sites remain
able to communicate, even with one or more cable failures. Note that one of the best
examples of a mesh topology is the Internet.
Combination Star Bus Topology
1. Use Figure 2-11 to describe how to create a combination star bus topology.
2. Explain that the star configuration minimizes the effect of any single computer’s failure
on the network.
Hubs and Switches
1. Note that both hubs and switches can act as the center of a star topology.
Hubs
1. Explain that in network usage, there are a number of variations on the hub central
theme: active hub, passive hub, repeating hub (just a type of active hub), and switching
hub.
Teaching
Tip
For more information on how Ethernet hubs work, read
http://en.wikipedia.org/wiki/Ethernet_hub.
2. Active hubs. Describe the role of active hubs. Note that this type of hub is the most
common type of hub today. Stress that active hubs are also called multiport repeaters or
repeating hubs. Briefly explain how a hub works (see the steps listed in the book).
Simulation 2-1 shows an animation that depicts the operation of a hub.
Teaching
Tip
Explain that for wireless networks, the hub is referred to as an access point (AP).
Wireless hubs share bandwidth, just as traditional wired hubs do.
3. Passive hubs. Use Figure 2-12 to explain how a passive hub works. Stress that a passive
hub requires no power.
Switches
1. Explain the role of switches and how they work.
Guide to Networking Essentials, Fifth Edition
Teaching
Tip
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For more information on network switches, read
http://en.wikipedia.org/wiki/Network_switch.
2. Stress that a switch can handle several conversations at one time, thereby providing the
full network bandwidth to each device rather than requiring bandwidth sharing.
3. Simulation 2-2 shows the operation of a switch.
Teaching
Tip
You can find useful information on how LAN switches work (including an
animation that depicts the learning process of a LAN switch) at
http://computer.howstuffworks.com/lan-switch.htm.
Constructing a Network Layout
1. Briefly describe the steps involved in constructing a network layout.
Selecting a Topology
1. Explain that most new network designs come down to only one choice: How fast should
the network be?
2. Stress that the physical topology will certainly be a star, and the logical topology is
almost always switching.
3. Note that Ethernet switches are typically used on a LAN. Provide some insight on why
you might consider other logical topologies.
Creating the Layout
1. Explain why it is extremely important to document the network through a network
layout or diagram.
2. Stress that the network diagram must be kept up to date.
3. A diagram similar to the one in Figure 2-13 can be created with a program called
SmartDraw, which you can download as a free trial at www.smartdraw.com.
4. Explain that you should include enough detail in your network diagram so that anyone
can easily understand your network’s construction.
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Quick Quiz 2
1. The ____________________ star topology is the most widely used topology in
networks containing more than just a few computers.
Answer: extended
2. What is a mesh topology?
Answer: A mesh network topology is the most fault tolerant, but also the most
expensive. Connecting each device in a network to every other device in the network
creates a mesh network topology.
3. The majority of hubs installed in networks today are ____________________ hubs.
Answer: active
4. Instead of simply regenerating an incoming signal and repeating that signal to all other
ports, a(n) ____________________ actually determines to which port the destination
device is connected and forwards the message to only that port.
Answer: switch
Class Discussion Topics
1. Have students used/configured hubs or switches? If so, ask them to discuss their
experiences.
2. Have students implemented a LAN before? If so, ask them to describe the topology they
used.
Additional Projects
1. Ethereal (www.ethereal.com) is a free network protocol analyzer program. It can be
used to see the data received in a NIC. Ask students to use the program to capture the
packets being received on the network interface card (use promiscuous mode). Can they
see packets being sent by other computers? In either case, ask them to infer which type
of topology is being used (logical bus or switching) in the network.
2. Ask students to create a table with the advantages and disadvantages of each of the
topologies studied in this chapter.
Additional Resources
1. Network Topology:
http://en.wikipedia.org/wiki/Network_topology
2. Bus Network:
Guide to Networking Essentials, Fifth Edition
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http://en.wikipedia.org/wiki/Bus_network
3. Ring Network:
http://en.wikipedia.org/wiki/Ring_network
4. Star Network:
http://en.wikipedia.org/wiki/Star_network
5. Mesh Networking:
http://en.wikipedia.org/wiki/Mesh_network
6. Ethernet Hub:
http://en.wikipedia.org/wiki/Ethernet_hub
7. Network Switch:
http://en.wikipedia.org/wiki/Network_switch
8. How LAN Switches Work:
http://computer.howstuffworks.com/lan-switch.htm
Key Terms
 access point (AP) — The central device, or hub, through which signals pass in a
wireless network.
 active hubs — Network devices that regenerate received signals and send them along
the network.
 active topology — A network topology in which computers are responsible for sending
data along the network.
 ad hoc topology — A wireless communication scheme by which devices communicate
directly with one another without using a central hub.
 backbone — A single cable segment used in a bus topology to connect computers in a
straight line.
 bus — A network topology in which the computers connect to a backbone cable
segment to form a straight line.
 extended star — Sometimes referred to as a hierarchical star topology, in which
devices are connected in a star of stars. A central device, usually a switch, sits in the
middle of the topology. Instead of attached computers forming the arms of the star,
other switches (or hubs) are connected to the central switch’s ports. Computers and
peripherals are then attached to these switches or hubs, forming additional stars.
 hub — The central point of connection of a star network.
 infrastructure mode — The mode of wireless communication in which wireless
devices are configured to use an access point.
 logical topology — The path that data travels between computers on a network.
 mesh — A hybrid network topology in which all computers connect to each other; this
topology is used for fault tolerance.
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 multiport repeater — A device used in a star topology that takes a signal coming in on
one port, cleans it up, strengthens it, and then sends the regenerated signal out all other
ports. Also see active hubs.
 passive hub — A central connection point through which signals pass without
regeneration.
 passive topology — A network topology in which computers listen to the data signals
being sent but do not participate in network communications.
 physical topology — The arrangement of the cabling that interconnects network
devices.
 ring — A network topology consisting of computers connected in a circle, forming a
closed ring.
 signal bounce — A phenomenon that occurs when a bus is not terminated and signals
continue to traverse the network.
 signal propagation — Signals traveling across a medium until they weaken or are
absorbed.
 star — A network topology in which computers connect through a central connecting
point, usually a hub.
 switch — A special device that manages connections between any pair of star-wired
devices on a network.
 terminator — A hardware device used to absorb signals as they reach the end of a bus,
thus freeing the network for new communications.
 token — A small data packet used in some ring topology networks to ensure fair
communications between all computers.
 token passing — A method of passing data around a ring network.
 topology — The basic physical layout of a network and the way in which network
components communicate with each other. Also see logical topology and physical
topology.
Technical Notes for Hands-On Projects
Hands-On Project 2-1: This project requires no special software, although it is recommended
that students use a network drawing program.
Hands-On Project 2-2: This project requires no special software.
Hands-On Project 2-3: This project requires no special software, although it is recommended
that students use a network drawing program.
Hands-On Project 2-4: This project requires no special software, although it is recommended
that students use a network drawing program.
Hands-On Project 2-5: This project requires no special software.