k topology
TRANSCRIPT
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k Topology
January 26th, 2008 Related Filed Under
A network topology is how computers, printers, and other devices are connected over a
network. It describes the layout of wires, devices, and routing paths. Essentially there are
six different common topologies you should familiarize yourself with: Bus, Ring, Star,Extended Star, Hierarchical, and Mesh.
network topology
Although it is usually easier to start connecting wires and setting up your network, youll
appreciate the level of organization these models provide- especially when your network
grows in size. And if youre looking to do well on networking exams, consider thesetopologies essential to both learn and memorize.
Bus Topology
bus topology
The bus topology was fairly popular in the early years of networking. Its easy to setup-
not to mention inexpensive. All devices on the Bus Topology are connected using a
single cable. If you need help remembering how the Bus Topology operates, think of it asthe route a bus takes throughout a city.
It is extremely important to note that both ends of the main cable need to be terminated. Ifthere is no terminator, the signal will bounce back when it reaches the end. The result: a
bunch of collisions and noise that will disrupt the entire network.
The Bus Topology is less common these days. In fact, this topology is commonly used to
network computers via coaxial cable- whens the last time you can say youve done that?
Ring Topology
ring topology
The Ring Topology is a very interesting topology indeed. It is a lot more complex that it
may seem- it looks like just a bunch of computers connected in a circle! But behind thescenes, the Ring Topology is providing a collision-free and redundant networking
environment.
Note that since there is no end on a Ring Topology, no terminators are necessary. A
frame travels along the circle, stopping at each node. If that node wants to transmit data,
it adds destination address and data information to the frame. The frame then travels
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around the ring, searching for the destination node. When its found, the data is taken out
of the frame and the cycle continues.
But wait- it gets better! We have two types of Ring Topologies in networking: the one we
just reviewed, and Dual-Ring Topology. In a Dual-Ring Topology, we use two rings
instead of one. This creates a sense of redundancy so that if any point in the networkfails, the second ring will (hopefully) be able to pick up the slack. If both rings were to
fail at separate locations, we can even use the opposite ring at each point to patch the
downed node.
dual ring topology
In the above diagram, you can see that although the outer ring and inner ring failed atseparate parts of the network. Thanks to redundancy, the network is still fully operational.
This is generally more expensive to implement than other topologies- so it isnt as
common as the Star or Extended Star Topology.
Star / Extended Star Topology
star topology
One of the most popular topologies for Ethernet LANs is the star and extended startopology. It is easy to setup, its relatively cheap, and it creates more redundancy than the
Bus Topology.
The Star Topology works by connecting each node to a central device. This central
connection allows us to have a fully functioning network even when other devices fail.
The only real threat to this topology is that if the central device goes down, so does theentire network.
extended star topology
The Extended Star Topology is a bit more advanced. Instead of connecting all devices to
a central unit, we have sub-central devices added to the mix. This allows more
functionality for organization and subnetting- yet also creates more points of failure. Inmany cases it is impractical to use a Star Topology since networks can span an entire
building. In this case, the Extended Star Topology is all but necessary to prevent
degraded signals.
Whereas the Star Topology is better suited for small networks, the Extended Star
Topology is generally better for the larger ones.Hierarchical Topology
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hierarchical tree topology
The Hierarchical Topology is much like the Star Topology, except that it doesnt use acentral node. Although Cisco prefers to call this Hierarchical, you may see it as instead
referred to as the Tree Topology.
This type of topology suffers from the same centralization flaw as the Star Topology. If
the device that is on top of the chain fails, consider the entire network down. Obviously
this is impractical and not used a great deal in real applications.Mesh Topology
mesh topology
If you havent noticed, weve had a little problem with a fully redundant network. The
Dual-Ring Topology helped, but it wasnt perfect. If you are looking for a truly redundantnetwork, look no further than the Mesh Topology. You will see two main types of Mesh
Topology: Full-Mesh and Partial-Mesh.
The Full-Mesh Topology connects every single node together. This will create the most
redundant and reliable network around- especially for large networks. If any link fails, we
(should) always have another link to send data through. So why dont we use it moreoften? Simple: how many wires would it take to link a computer to every device on a
network of over 100 devices? Now multiply that for every device on the network- not a
pleasant number is it? Obviously you should only use this in smaller networks.Alternatively, you could try a Partial-Mesh Topology.
partial mesh topology
The Partial-Mesh Topology is much like the full-mesh, only we dont connect each
device to every other device on the network. Instead we only implement a few alternateroutes. After all- what are the odds a network will fail in multiple times near the same
device?
Youll see the Partial-Mesh Topology in backbone environments, since these are oftenvital networks that depend on redundancy to keep services running (such as an Internet
Service Provider). Full-Mesh Topology is commonly seen in WANs between routers, yet
also on smaller networks that depend on a redundant connection.Closing Comments
Keep in mind that network topology isnt limited to the above examples. There arehybrids and variations of the topologies mentioned above.
Oddly enough, Cisco fails to categorize Point-to-Point Topology in their course material-
but dont worry, its just a simple connection between two endpoints. Perhaps it was
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considered too simple to include in the course material- either way, make sure you
commit the above topologies to memory. Youll be expected to know them when exam
day comes- not to mention it could save you from a disorganized mess of a network!
Network Topology
This lesson describes designs for connecting computers. You will also learn aboutvariations that are often used and what you need to consider when planning your
network.
After this lesson, you will be able to:
Identify the four standard topologies and their variations.
Describe the advantages and disadvantages of each topology.Determine an appropriate topology for a given network plan.
Estimated lesson time: 80 minutes
Designing a Network Topology
The term topology, or more specifically, network topology, refers to the arrangement orphysical layout of computers, cables, and other components on the network. "Topology"
is the standard term that most network professionals use when they refer to the network's
basic design. In addition to the term "topology," you will find several other terms that are
used to define a network's design:
Physical layout
DesignDiagram
Map
A network's topology affects its capabilities. The choice of one topology over another
will have an impact on the:
Type of equipment the network needs.
Capabilities of the equipment.
Growth of the network.
Way the network is managed.
Developing a sense of how to use the different topologies is a key to understanding the
capabilities of the different types of networks.
Before computers can share resources or perform other communication tasks they must
be connected. Most networks use cable to connect one computer to another.
NOTE Wireless networks connect computers without using cable. This technology is
discussed in Chapter 2 in Lesson 3: Wireless Networking.
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However, it is not as simple as just plugging a computer into a cable connecting other
computers. Different types of cablecombined with different network cards, network
operating systems, and other componentsrequire different types of arrangements.
To work well, a network topology takes planning. For example, a particular topology can
determine not only the type of cable used but also how the cabling runs through floors,ceilings, and walls.
Topology can also determine how computers communicate on the network. Differenttopologies require different communication methods, and these methods have a great
influence on the network.
Standard Topologies
All network designs stem from four basic topologies:
Bus
Star
RingMesh
A bus topology consists of devices connected to a common, shared cable. Connecting
computers to cable segments that branch out from a single point, or hub, is referred to as
setting up a star topology. Connecting computers to a cable that forms a loop is referred
to as setting up a ring topology. A mesh topology connects all computers in a network toeach other with separate cables.
These four topologies can be combined in a variety of more complex hybrid topologies.Bus
The bus topology is often referred to as a "linear bus" because the computers are
connected in a straight line. This is the simplest and most common method of networkingcomputers. Figure 1.15 shows a typical bus topology. It consists of a single cable called a
trunk (also called a backbone or segment) that connects all of the computers in the
network in a single line.
Click to view at full size.
Figure 1.15 Bus topology network
Run the c01dem01 video located in the Demos folder on the compact disc accompanying
this book to view a demonstration of a bus-topology connection.
Communication on the Bus
Computers on a bus topology network communicate by addressing data to a particular
computer and sending out that data on the cable as electronic signals. To understand how
computers communicate on a bus, you need to be familiar with three concepts:
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Sending the signal
Signal bounce
Terminator
Sending the Signal Network data in the form of electronic signals is sent to all the
computers on the network. Only the computer whose address matches the addressencoded in the original signal accepts the information. All other computers reject the
data. Figure 1.16 shows a message being sent from 0020af151d8b to 02608c133456.
Only one computer at a time can send messages.
Run the c01dem02 video located in the Demos folder on the compact disc accompanying
this book to view a demonstration of how data is transferred in a bus topology.
Click to view at full size.
Figure 1.16 Data is sent to all computers, but only the destination computer accepts it
Because only one computer at a time can send data on a bus network, the number of
computers attached to the bus will affect network performance. The more computersthere are on a bus, the more computers will be waiting to put data on the bus and,
consequently, the slower the network will be.
There is no standard way to measure the impact of a given number of computers on thespeed of any given network. The effect on performance is not related solely to the
number of computers. The following is a list of factors thatin addition to the number of
networked computerswill affect the performance of a network:
Hardware capabilities of computers on the network
Total number of queued commands waiting to be executedTypes of applications (client-server or file system sharing, for example) being run on
the network
Types of cable used on the networkDistances between computers on the network
Computers on a bus either transmit data to other computers on the network or listen for
data from other computers on the network. They are not responsible for moving datafrom one computer to the next. Consequently, if one computer fails, it does not affect the
rest of the network.
Run the c01dem03 video located in the Demos folder on the CD accompanying this book
to view a demonstration that shows how a failed computer does not affect data
transmission in a bus topology.
Signal Bounce Because the data, or electronic signal, is sent to the entire network, it
travels from one end of the cable to the other. If the signal is allowed to continue
uninterrupted, it will keep bouncing back and forth along the cable and prevent other
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computers from sending signals. Therefore, the signal must be stopped after it has had a
chance to reach the proper destination address.
Run the c01dem04 video located in the Demos folder on the CD accompanying this book
to view a demonstration of signal bounce.
Terminator To stop the signal from bouncing, a component called a terminator is placed
at each end of the cable to absorb free signals. Absorbing the signal clears the cable so
that other computers can send data.
Both ends of each cable segment on the network must be plugged into something. For
example, a cable end can be plugged into a computer or a connector to extend the cable
length. Any open cable ends not plugged into something must be terminated to preventsignal bounce. Figure 1.17 shows a properly terminated bus topology network.
Click to view at full size.
Figure 1.17 Terminators absorb free signals
Run the c01dem05 and c01dem06 videos located in the Demos folder on the CD
accompanying this book to view a terminator component and a demonstration of how a
terminator eliminates signal bounce.
Disrupting Network Communication
A break in the cable will occur if the cable is physically separated into two pieces or if atleast one end of the cable becomes disconnected. In either case, one or both ends of the
cable will not have a terminator, the signal will bounce, and all network activity will stop.
This is one of several possible reasons why a network will go "down." Figure 1.18 showsa bus topology with a disconnected cable. This network will not work because it now has
unterminated cables.
The computers on the network will still be able to function as stand-alone computers;
however, as long as the segment is broken, they will not be able to communicate with
each other or otherwise access shared resources. The computers on the down segment
will attempt to establish a connection; while they do so, workstation performance will beslower.
Figure 1.18 An unplugged cable is not terminated and will take down the network
Run the c01dem07 and c01dem08 videos located in the Demos folder on the CD
accompanying this book to view a demonstration of what happens when there is a breakin the cable of a bus-topology network.
Network Expansion
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As the physical size of the site grows, the network will need to grow as well. Cable in the
bus topology can be extended by one of the two following methods:
A component called a barrel connector can connect two pieces of cable together to
make a longer piece of cable (see Figure 1.19). However, connectors weaken the signal
and should be used sparingly. One continuous cable is preferable to connecting severalsmaller ones with connectors. Using too many connectors can prevent the signal from
being correctly received.
Click to view at full size.
Figure 1.19 Barrel connectors can be used to combine cable segments
A device called a repeater can be used to connect two cables. A repeater actuallyboosts the signal before it sends the signal on its way. Figure 1.20 shows a repeater
boosting a weakened signal. A repeater is better than a connector or a longer piece of
cable because it allows a signal to travel farther and still be correctly received.
Click to view at full size.
Figure 1.20 Repeaters connect cables and amplify the signal
Star
In the star topology, cable segments from each computer are connected to a centralized
component called a hub. Figure 1.21 shows four computers and a hub connected in a startopology. Signals are transmitted from the sending computer through the hub to all
computers on the network. This topology originated in the early days of computing when
computers were connected to a centralized mainframe computer.
Figure 1.21 Simple star network
Run the c01dem09 and c01dem10 videos located in the Demos folder on the CD
accompanying this book to view demonstrations of a star topology.
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The star network offers the advantage of centralized resources and management.
However, because each computer is connected to a central point, this topology requires a
great deal of cable in a large network installation. Also, if the central point fails, theentire network goes down.
If one computeror the cable that connects it to the hubfails on a star network, onlythe failed computer will not be able to send or receive network data. The rest of the
network continues to function normally.
Run the c01dem11 video located in the Demos folder on the CD accompanying this book
to view a demonstration of what happens when a computer on a star topology network
goes down.
RingThe ring topology connects computers on a single circle of cable. Unlike the bus
topology, there are no terminated ends. The signals travel around the loop in one
direction and pass through each computer, which can act as a repeater to boost the signal
and send it on to the next computer. Figure 1.22 shows a typical ring topology with oneserver and four workstations. The failure of one computer can have an impact on the
entire network.
NOTE A network's physical topology is the wire itself. A network's logical topology is
the way it carries signals on the wire.
Figure 1.22 Simple ring network showing logical ring
Run the c01dem12 and c01dem13 videos located in the Demos folder on the CDaccompanying this book to view demonstrations of logical and actual flows of data on a
ring-topology network.
Token Passing
One method of transmitting data around a ring is called token passing. (A token is aspecial series of bits that travels around a token-ring network. Each network has only one
token.) The token is passed from computer to computer until it gets to a computer that
has data to send. Figure 1.23 shows a token ring topology with the token. The sending
computer modifies the token, puts an electronic address on the data, and sends it aroundthe ring.
Figure 1.23 A computer grabs the token and passes it around the ring
The data passes by each computer until it finds the one with an address that matches the
address on the data.
The receiving computer returns a message to the sending computer indicating that the
data has been received. After verification, the sending computer creates a new token and
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releases it on the network. The token circulates within the ring until a workstation needs
it to send data.
Run the c01dem14 and c01dem15 videos located in the Demos folder on the CD
accompanying this book to view demonstrations of both the logical and actual flows of
token passing on a ring topology network.
It might seem that token passing would take a long time, but the token actually travels at
roughly the speed of light. A token can circle a ring 200 meters (656 feet) in diameterabout 477,376 times per second.
Run the c01dem16 video located in the Demos folder on the CD accompanying this
book to view a demonstration of what happens when a computer on a tokenring_topology network goes down.
Mesh
A mesh topology network offers superior redundancy and reliability. In a mesh topology,
each computer is connected to every other computer by separate cabling. Thisconfiguration provides redundant paths throughout the network so that if one cable fails,
another will take over the traffic. While ease of troubleshooting and increased reliabilityare definite pluses, these networks are expensive to install because they use a lot of
cabling. Often, a mesh topology will be used in conjunction with other topologies to form
a hybrid topology.
Figure 1.24 In a mesh topology, all computers are connected to each other by separate
cables
HubsOne network component that has become standard equipment in networks is the hub.
Figure 1.25 shows a hub as the central component in a star topology.
Figure 1.25 A hub is the central point in a star topology
Active Hubs
Most hubs are active; that is, they regenerate and retransmit signals in the same way as arepeater does. Because hubs usually have eight to twelve ports for network computers to
connect to, they are sometimes called multiport repeaters. Active hubs require electrical
power to run.
Passive HubsSome types of hubs are passive; examples include wiring panels or punch-down blocks.
They act as connection points and do not amplify or regenerate the signal; the signal
passes through the hub. Passive hubs do not require electrical power to run.Hybrid Hubs
Advanced hubs that will accommodate several different types of cables are called hybrid
hubs. Figure 1.26 shows a main hub (the hybrid) with three sub-hubs.
Click to view at full size.
Figure 1.26 Hybrid hub
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Hub Considerations
Hub-based systems are versatile and offer several advantages over systems that do not
use hubs.
In the standard linear-bus topology, a break in the cable will take the network down. With
hubs, however, a break in any of the cables attached to the hub affects only a limitedsegment of the network. Figure 1.27 shows that a break or disconnected cable affects
only one workstation while the rest of the network keeps functioning.
Figure 1.27 A break or unplugged cable takes down only the unplugged computer
Hub-based topologies include the following benefits:
Wiring systems can be changed or expanded as needed.
Different ports can be used to accommodate a variety of cabling types.
Monitoring of network activity and traffic can be centralized.
NOTE Many active hubs have diagnostic capabilities that can indicate whether or not a
connection is working.
Run the c01dem017 video located in the Demos folder on the CD accompanying this
book to view a discussion and demonstration of the role of hubs in network topologies.
Variations on the Standard TopologiesMany working topologies are hybrid combinations of the bus, star, ring, and mesh
topologies.
Star BusThe star bus is a combination of the bus and star topologies. In a star-bus topology,
several star topology networks are linked together with linear bus trunks. Figure 1.28
shows a typical star-bus topology.
If one computer goes down, it will not affect the rest of the network. The other computers
can continue to communicate. If a hub goes down, all computers on that hub are unable tocommunicate. If a hub is linked to other hubs, those connections will be broken as well.
Click to view at full size.
Figure 1.28 Star-bus network
Run the c01dem018, c01dem19, and c01dem20 videos located in the Demos folder onthe CD accompanying this book to view demonstrations of what happens when
computers and hubs in a star-bus topology go down.
Star RingThe star ring (sometimes called a star-wired ring) appears similar to the star bus. Both the
star ring and the star bus are centered in a hub that contains the actual ring or bus. Figure
1.29 shows a star-ring network. Linear-bus trunks connect the hubs in a star bus, while
the hubs in a star ring are connected in a star pattern by the main hub.
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Click to view at full size.
Figure 1.29 Star-ring network
Peer-to-Peer
Many small offices use a peer-to-peer network as described earlier in this chapter inLesson 2: Network Configuration. Such a network can be configured as either a physical
star or a bus topology. However, because all computers on the network are equal (each
can be both client and server), the logical topology looks somewhat different. Figure 1.30shows the logical topology of a peer-to-peer network.
Click to view at full size.
Figure 1.30 Logical peer-to-peer topology
Selecting a Topology
There are many factors to consider when deciding which topology best suits the needs of
an organization. Table 1.2 provides some guidelines for selecting a topology.
Table 1.2 Topology Advantages and DisadvantagesTopology Advantages Disadvantages
Bus Use of cable is economical.
Media is inexpensive and easy to work with.
System is simple and reliable.
Bus is easy to extend.
Network can slow down in heavy traffic.
Problems are difficult to isolate.
Cable break can affect many users.
Ring System provides equal access for all computers.
Performance is even despite many users.
Failure of one computer can impact the rest of the network.
Problems are hard to isolate.
Network reconfiguration disrupts operation.Star Modifying system and adding new computers is easy.
Centralized monitoring and management are possible.
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Failure of one computer does not affect the rest of the network.
If the centralized point fails, the network fails.
Mesh System provides increased redundancy and reliability as well as ease oftroubleshooting. System is expensive to install because it uses a lot of cabling.
Exercise 1.1: Case Study Problem
A small, independent, business/home/life insurance company consisting of an owner, a
business manager, an administrator, and four agents decides to implement a network. Thecompany occupies half of a small building in an office park. Their volume of business
had been stable for the past three years, but recently it has been increasing. To handle the
increased business volume, two new agents will be hired.
Figure 1.31 illustrates the current arrangement.
Click to view at full size.
Figure 1.31 Case study model
Everyone in the company has a computer, but the business manager has the only printer.
These computers are not connected by any form of networking. When agents need to
print a document, they must first copy the file to a floppy disk, then carry it to the
business manager's computer, where they are finally able to print it. Similarly, when staffmembers want to share data, the only means available is to copy the data on one
computer to a floppy disk and insert the disk in another computer.
Recently, problems have arisen. The business manager is spending too much time
printing other people's documents; and it is frequently unclear which copy of a given
document is the current and authoritative version.
Your task is to design a network for this company.
To clarify the task of choosing a solution, you ask some questions.
Circle the most appropriate answers to the following questions:
Which type of network would you suggest for this company?
Peer-to-peer
Server-basedWhich network topology would be most appropriate in this situation?
Bus
RingStar
Mesh
Star bus
Star ring
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Answers
Exercise 1.2: Troubleshooting Problem
Use the information in the next section to help you solve the troubleshooting problem thatfollows.
Background Information
Choosing a network that does not meet an organization's needs leads directly to trouble.A common problem arises from choosing a peer-to-peer network when the situation calls
for a server-based network.
A peer-to-peer, or workgroup, network might begin to exhibit problems with changes inthe network site. These are more likely to be logistical or operational problems than
hardware or software problems. The presence of several indicators is a sign that a peer-
to-peer network is inadequate. Possible scenarios include the following:
Lack of centralized security is causing difficulty.
Users are turning off computers that are providing resources to others on the network.
When a network's design is too limited, it cannot perform satisfactorily in some
environments. Problems can vary depending on the type of network topology in effect.
Bus Topology
A few situations will cause a bus network's termination to fail and thereby take thenetwork down. Possible scenarios include the following:
A cable on the network breaks, causing each end of the cable on either side of thebreak to lose its termination. Signals will bounce, and this will take the network down.
A cable becomes loose or is disconnected, thereby separating the computer from the
network. It will also create an end that is not terminated, which in turn will cause signalsto bounce and the network to go down.
A terminator becomes loose; thereby creating an end that is not terminated. Signals
will start to bounce and the network will go down.
Hub-Based Topology
While problems with hubs are infrequent, they do occur. Possible scenarios include thefollowing:
A hub drops a connection. When a computer becomes disconnected from the hub, thatcomputer will be off the network, but the rest of the network will continue to function
normally.
An active hub loses power, causing the network to stop functioning.
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Ring Topology
A ring network is usually very reliable, but problems can occur. Possible scenariosinclude the following:
One of the cables in the ring breaks, causing the network to stop functioningtemporarily. In token-ring networks, restoring the cable will immediately restore the
network.
One of the cables in the ring becomes disconnected, causing the network totemporarily stop functioning. In token-ring networks, restoring the cable will
immediately restore the network.
The ProblemUse what you have just read to troubleshoot the scenario that follows.
A small company with three departments recently began networking and has installed
peer-to-peer networks in each department. The peer-to-peer networks are not connectedto each other. A user in one department must make a diskette of the information to be
loaded on the next network. Four employees in one department are working on a project.Each person has a different set of responsibilities, and each produces documentation for a
different part of the project. Employees have each made the hard drive on their own
computers available to everyone else on the project.
As the project grows, each user produces more documents, and questions arise about who
has which document and which employee last revised a given document. Also,
employees outside the department who have an interest in the project are asking to seesome of the completed material.
Why are problems arising concerning who has which document? Suggest at least onereason.
What one change could you make that would give you centralized control of the access
to these documents?Describe one change that your solution will bring to the users' operating environment.
Answers
Exercise 1.3: Network Planning Problem
The following exercise will not only help you determine whether a peer-to-peerenvironment or a centralized, server-based environment is most appropriate for your site,
but it will also help you form a general picture of the role that servers should play in your
network and help you choose an appropriate topology.
IMPORTANT This network planning problem assumes there is no network on your
site. If your site has an existing network, use these questions as a guide, and apply the
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information in the text to the network on your site to help familiarize yourself with an
actual network environment.
Part 1
Put a check mark on the line next to the choice that applies to your site. To determine
which type of network would be most appropriate for your site, add up the number ofpeer-to-peer selections with check marks next to them, and compare the total with the
number of server-based selections that have check marks next to them. The network with
the most check marks should be the first option you consider.
Approximately how many users will the network at your site serve?
0-10 ____ Peer-to-peer
11 + ____ Server-based
Will data and resources on your network need to be restricted or regulated?
Yes ____ Server-based
No ____ Peer-to-peerWill your computer be used primarily as a:
Client computer ____ Server-based
Server ____ Server-based
Both ____ Peer-to-peer
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NOTE If you want your computer to be used as both a client and a server, you might
think you need to choose a peer-to-peer environment; however, in many server-based
networks today, client computers share in a peer-to-peer fashion. This type of combinednetwork has become the most common kind of network used for new installations,
primarily because networking capabilities are now an integral part of most client-
computer operating systems.
Will the users on your network be able to meet their own network administration and
management needs?
Yes ____ Peer-to-peer
No ____ Server-basedWill users be allowed to share their own resources and set other network policies for
their own computer?
Yes ____ Peer-to-peer
No ____ Server-based
Will your network use centralized servers?
Yes ____ Server-based
No ____ Peer-to-peerWill your network have one central administrator who sets network policies?
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Yes ____ Server-based
No ____ Peer-to-peer
Will your network have more than one server?
Yes ____ Peer-to-peer or server-based, depending on other issues
No ____ Server-based
Answers
Part 2
The following questions help you identify and resolve issues that arise in a server-based
environment.
Check the tasks below that will apply to your servers:
Communication ____
Backup/redundancy ____
Application ____
Database ____
E-mail ____
Fax ____
Print ____
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User directories ____
General data storage ____Are some of the servers designated for special tasks?
Yes ____
No ____
Approximately how many servers does your network have?
0-5 ____
6-10 ____
11-50 ____
51-100 ____Will your network's servers be centrally located or spread out in different locations?
Centrally located ____
Spread out ____
Will some of your network's servers be in a secure location?
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Yes ____
No ____
If not, why not? _______________________________________________
AnswersPart 3
The following section helps you to choose an appropriate topology for your network.
(The answers to these questions can be used in conjunction with Table 1.2 in Lesson 3:
Network Topology earlier in this chapter.)
Put a check mark on the line next to the choice that applies to your site. To determine
which type of topology would be most appropriate for your site, add up the number of
bus selections with check marks next to them, the number of star-bus selections withcheck marks next to them, and the number of star-ring selections with check marks next
to them. The topology with the most check marks should be the option you consider first.
NOTE Because the ring is more expensive than the bus, a star bus would be more
economical than a star ring. In a case where both star bus and star ring would work, star
bus would usually be the preferred choice.
Approximately how many users will the network at your site serve?
0-10 ____ All
11 + ____ Star bus, star ring
Is cost a consideration in choosing your network topology?
Yes ____ Star bus
No ____ All
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Does your building have drop ceilings?
Yes ____ All
No ____ Star bus, star ring
Does your building afford easy access to crawl spaces or wiring conduits?
Yes ____ All
No ____ Star bus, star ring
Is ease of troubleshooting important?
Yes ____ Star bus, star ring
No ____ All
Does the physical layout of the computers and office spaces naturally lend itself to a
particular topology?
Yes ____
No ____
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If the answer to Question 6 is No, go on to Question 8. If the answer to Question 6 is
Yes, which topology does the layout lend itself to using?
Circle one: bus star bus
Is ease of reconfiguration important?
Yes ____ Star bus, star ring
No ____ All
Can the existing wiring in the building be used for your new network?
Yes ____
No ____If the answer to question 9 is yes, which kind of topology could it be part of?
Circle one: bus star bus
Answers
Exercise Summary
Based on the information generated in the three parts of this Network Planning Problem,
your network components should be:
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Type of network:
Type of topology:
AnswersLesson Summary
The following points summarize the main elements of this lesson:
The physical layout of computers on a network is called a topology.
There are four primary topologies: star, bus, ring, and mesh.
Topologies can be physical (actual wiring) or logical (the way they work).
In a bus topology, the computers are connected in a linear fashion on a single cable.Bus topologies require a terminator on each end of the cable.
In a star topology, the computers are connected to a centralized hub.
Mesh topologies connect all computers in a network to one another with separate
cables.In a token-ring topology, the computers are connected physically in a star shape, but
logically in a ring or circle. The data is passed from one computer to another around thecircle.
Hubs are used to centralize the data traffic and localize failures. If one cable breaks, it
will not shut down the entire network.