k Topology

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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.


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.


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.


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


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.


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.


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


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.


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.


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.


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.


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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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.


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.


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?


No ____ Peer-to-peerWill your network have one central administrator who sets network policies?

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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.

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