CompTIA Network+ Certification Study Guide part 5 pot

When a computer sends data to other computers on the network, it is sent along the cable to a central hub or switch, which can then pass the packets to the other computers or devices tha

on a bus network, it only listens or sends data It doesn’t take data and then resend or regenerate it, so each computer isn’t essential to the network as a whole If one computer fails, it doesn’t crash the entire network

Another benefit of this topology is that it is inexpensive, as less cable is used than other topologies we’ll discuss As we’ll see later, some topologies have redundant connections or require a significant amount of cable In a bus topology, every computer is connected to a single cable

Having a single cable, however, does cause other problems If the cable breaks, then each segment has an end that isn’t terminated, and the entire network goes down If the trunk is long enough, this can make it difficult to isolate where the break is

Another disadvantage of this topology is that it isn’t very scalable The number of computers is limited to the length of the cable, and as your com-pany grows, it can be difficult changing the size and layout of the network Also, if changes or repairs are made to the cable, the network is down because there is no redundancy and termination of the cable is required

STAr (hierarchical)

In a star topology, computers aren’t connected to one another, but are all connected to a central hub or switch When a computer sends data to other computers on the network, it is sent along the cable to a central hub or switch, which can then pass the packets to the other computers or devices that are connected to it As seen in Figure 1.4, when the computers are cabled to the hub, each point in the network can appear similar to points in

a star (hence the name of this topology)

Although this is an older topology that comes from the time when terminals were connected to mainframes as a centralized point, it is still a

popular topology Because cables run

to a central point, if one cable breaks

or fails in some way, only the com-puter that is connected to that cable

is unable to use the network Other computers are unaffected, because they have their own cables running

to the hub This can also make it easier to repair because, unlike the bus topology, it is easy to see where the cable failure has occurred Another benefit of this topol-ogy is that it is scalable As the net-work grows or changes, computers

FIGurE 1.4 A Star Topology.

are simply added or removed from the hub Unfortunately, because there

is so much cabling that is being used to connect individual computers to a

central hub, this also increases the cost of expanding and maintaining the

network

Mesh

A mesh topology has multiple connections, making it the most fault tolerant

topology available Every component of the network is connected directly

to every other component As seen in Figure 1.5, this creates a topology

that provides redundant links across the network If a break occurs in a

segment of cable, traffic can still be rerouted using the other cables In other

words, if one connection fails, a computer can still access another computer

or resource using another connection

Although it is almost impossible for a cable fault to crash a mesh topology,

this topology is rarely used There is significant cost and work involved in

having network components directly connected to every other component

This topology provides redundant cable connections, but exponentially

increases the workload and cost of maintaining them, making them difficult

to manage and creating a cost that’s greater than other topologies

rings

As seen in Figure 1.6, a ring topology consists of computers connected to a cable

that loops around Because the topology is a closed loop, there are no

uncon-nected ends to the ring, so terminators aren’t required Data passes around

FIGurE 1.5 A Mesh Topology.

FIGurE 1.6 A Ring Topology Has All Computers Connected with a Cable That Loops Around.

the loop in one direction As it reaches each computer, the computer examines each packet and checks to see if any of the data packets are meant for it If there aren’t any packets addressed to, the computer it sends the packets on to the next computer in the ring In doing so, each computer acts as a repeater, resending the packet and thereby boosting the signal When the packet reaches the originating computer, it removes the packet from the network

Ring topologies only allow one computer to have access to sending data on the ring, but provides equal access to the network Bus and star topologies also allow only one workstation to communicate on the network

at a time, but in a ring topology each computer is given a turn at having

access A signal called a token is passed from one computer to the next in

the ring When a computer has the token, it has access to the ring, and can send data

In a ring topology, if one computer fails, the entire network goes down Because the topology requires an unbroken ring, if a computer is down or a cable is broken, the ring can’t be completed so the network can’t function properly To avoid this, some rings have features that detect and disconnect failed computers from the ring, or will beacon and notify the network if a break is detected By doing so, the network is able to function until the failed computer can be repaired

Point-to-Point

A point-to-point topology is any network that connects two hosts in a dedi-cated fashion For example, if you were to configure a router in New York to connect and use resources on a network in Atlanta, Georgia you would want

to make sure you had a link between them that can support your needs If you need a permanent connection that is constantly available and depend-able, you may need a T1 circuit Although costly, you will be able to connect your two sites in New York and Georgia together without issue and have a point-to-point connection that is dependable and reliable

Point-to-Multipoint

A point-to-multipoint topology is any network that connects three or more hosts and can grow exponentially based on the hardware and software you choose to manage it For example, if you wanted to create a large network

of many sites (i.e., New York, Georgia, Illinois, and Michigan), you may need to create a point to multipoint network The main connection could be your headquarters location and the other three sites could be smaller sites

accessing resources in the main hub site This type of network is also called

a hub and spoke topology.

A hybrid topology is any mixture of at least two or more of any network

topologies So, it’s easy to say that any network that isn’t purely configured

as one type of topology is configured as some form of hybrid network

wireless

A wireless topology broadcasts data over the air, so very few cables are used

to connect systems together As seen in Figure 1.7, this topology uses

trans-mitters called cells, which broadcast the packets using radio frequencies

The cells extend a radio sphere around the transmitter in the shape of a

bubble that can extend to multiple rooms and possibly different floors in

a building Each cell is connected to the network using cabling, so that it

can receive and send data to servers, other cells, and networked peripherals

Computers and other devices have a device installed in them that transmits

and receives data to and from the cell, allowing them to communicate with

the network

Wireless networks can also extend their transmission to wireless devices

by implementing radio antennas that are situated on buildings or towers

The antenna serves as a cell that will cover a wider area, such as a building

or campus This type of wireless network is particularly beneficial for pools

of buildings that are close together and have some difficulty in connecting

LANs in the buildings together using cables

Another method of wireless networking uses infrared communications,

which requires a direct line of site and close proximity for the

communica-tion to work This type of wireless networking is similar to using a remote

control for a TV, where each device needs to be lined up and within range of

one another Because of these limitations, it isn’t generally used for

network-ing, but may be seen in a networked

environment for connecting laptops

and other computers to devices like

printers

Because very little may be directly

cabled together on a wireless network,

there is a greater chance of

transmis-sions being blocked or experiencing

interference Machinery and other

devices can emit radio frequencies or

electrical interference that disrupts

signals being exchanged between FIGurE 1.7 A Wireless Network.

the cell and wireless devices Also, some buildings using cinderblocks, large amounts of metal or insulation to prevent transmissions from interfering with equipment can keep a wireless network from working between rooms You may have experienced a blockage like this when you tried using a cell phone in certain buildings, and found it didn’t work Signals are prevented from passing through these materials, and may require different frequencies

to be used

ExErcisE 1.1 Understanding Types and Topologies

The Freedom Fry Corporation has a network that’s contained within a single building A foreign company that is located in Paris has bought them and would like to share data with them The Paris firm has a similar network and

it consists of several servers and computers networked together in a single building However, each of the computers in the Paris firm is connected to a single hub, while the Freedom Fry Corporation’s client computers don’t use cables Servers are connected to cables, which then branch off to hubs that connect to cells On the basis of the information provided, answer the fol-lowing questions:

What is the purpose of a WAN, and how could it be applied to this

1

network?

What topology does the Paris firm use?

2

What topology does the Freedom Fry Corporation use?

3

On both networks, which networking component will be most

4

likely to fail?

Exercise Answers

A WAN allows an organization in diverse geographical locations to

1

be connected, and function as if they were part of the same LAN It can be applied to this network by implementing a high-speed con-nection between the two offices

The Paris firm uses a star topology, which has computers of the

2

network all connected to a single hub

The Freedom Fry Corporation uses a wireless topology in which

3

the servers, hubs, and cells are all connected with cables, but computers use wireless adapters to connect to the cells

Cables Both networks use cables, which are a common point of

4

failure Each of the other network components has less chance of

failing than a damaged or faulty cable

NETworK TypES

Just as we saw the Internet evolve from a relatively small network named

ARPANet, networks can extend beyond their initial creation of a few

comput-ers connected together A network can be in a single building, or comprised of

computers connected together over a broader geographical area To categorize

the scope of a network, different terms have been created to classify these

dif-ferent network types The types of networks that could be created include:

Local area network

■

■

Wide area network

■

■

Metropolitan area network

■

■

Storage area network

■

■

Personal area network

■

■

Campus area network

■

■

lAN and wAN

LANs and WANs were the first types of networks to be classified by the area

they covered and are still the ones most commonly referred to Although

each of the names refer to an area, an exact range has never been firmly

established and is left vague Although IEEE (which we’ll discuss later in

this chapter) defines a local area as being up to 4 km, no one will accuse it

of not being a LAN if it is slightly over that LANs are networks spanning

a limited distance, while a WAN is a network that is larger than a LAN

What distinguishes a LAN from a WAN in terms of area is ambiguous and

speculative at best

LANs are small- to medium-size networks, and generally connect

net-work devices that are no more than a few miles of one another They include

networks that have been set up in homes, offices, the floor of a building, an

entire building, a campus or group of nearby buildings, or facilities that are

relatively close to one another Basically, if you can walk or drive the distance

of the network in a short time, you’re dealing with a LAN

Another way to characterize a LAN is through ownership Typically, the network is owned by a single person or organization and is managed by a single person or group of people For example, your home network would be

a LAN that’s owned and managed by you In the same way, a large company with several buildings in a region that’s run by a network administrator or IT department would also be a LAN When you look at LANs in this way, you can see that most networks are actually LANs

WANs can span great geographical distances, and connect different LANs together using high-speed solutions or telephone lines A WAN may connect LANs in different cities, regions, states/provinces, or even countries This

is something we saw when we discussed the first WAN, ARPANet, which connected the LANs of several institutions in different cities together Over time, the number of computers and networks connecting to it grew until it spanned the world and became the Internet By internetworking individual LANs together, the LANs become parts of a WAN

When looking at WANs, ownership isn’t a defining factor WANs are often owned and managed by more than one organization Each LAN that

is part of the WAN may be managed by individuals or IT departments, and either maintains their connection to the rest of the LAN or hires outside parties to perform that function For example, in the case of the Internet, you may maintain your home network, but you hire an ISP to maintain the connection to the World Wide Web In the same way, a company with offices

in different cities may hire the phone company to maintain a T1 line that connects the network together

An effective way of understanding how a LAN is related to a WAN is to look at how they are connected and how data is sent This may differ from organization to organization, as there are several different ways of getting data from a LAN to a WAN, including:

Modem, which is a device that allows you to connect to other

com-■

■

puters and devices using telephone lines Generally, when a modem

is mentioned, it refers to a dial-up modem (as opposed to the digital modems for other methods mentioned later) This type of connection

is slow, and allows connections at a maximum of 56 Kbps (meaning that 56,000 bits of data can be sent or received per second)

Integrated Services Digital Network (ISDN), which also sends data

■

■

over the telephone lines but at higher speeds, up to 128 kbps but averaging at 64 kbps using an ISDN modem or router

Digital Subscriber Line (DSL), which sends data across telephone

■

■

lines at speeds ranging from 1.5 Mbps (1.5 million bits per second) using a router or digital modem and configured phone lines

Cable, which transmits the data across cable lines using the same

■

■

lines used for cable television at speeds of up to 1.5 Mbps

Satellite, which transmits data to a satellite at speeds of up to

■

■

400 Kbps

T1 and T3, which are dedicated connections that provide extremely

■

■

high speeds A T1 line provides speeds of 1.544 Mbps, while a T3

line provides speeds ranging from 3 Mbps to 44.736 Mbps

To illustrate the relationships between LANs and WANs, let’s look at

a situation that may be familiar to you: sending e-mail to another person

Using the e-mail program on your computer, you would click the send

but-ton, and the data (i.e your e-mail) would be sent to the device responsible

for sending it to the Internet If you had a dial-up account to the Internet,

it might be a standard modem If you had a LAN in your home and sent

e-mail, it might be sent to a network adapter and sent over a network

As we mentioned earlier, when a network is created, two or more

com-puters are connected together In a LAN, these comcom-puters are in the same

locale, such as being in the same room Although wireless networking will

be introduced in the next section, it’s important to know that wireless

can operate globally via satellite, or on your local LAN This differentiates

between a Wireless LAN (WLAN) and satellite communications Regardless,

each computer has a network adapter installed in it, which transmits and

receives data through a network cable or using wireless technology When

your data is sent to the network adapter, it is broken up into smaller chunks

called packets that can be sent more efficiently over the network As such,

your e-mail would be broken into smaller packets, which would then be put

together by the computer receiving it

If you used DSL, these packets would be transmitted over your home

LAN to a router that is used to connect to the Internet, and also used to

connect different computers on your LAN together In cases where network

cable is used, one end of a cable would be plugged into a network adapter,

and the other would plug into the router Data is sent over the cable with

information on its destination, and the router determines if it’s for a

com-puter on the LAN or needs to be sent to the ISP who provides DSL to you

As you’re sending e-mail to someone who isn’t on your home network, the

router would use the DSL connection to send it from your LAN to the ISP’s

LAN In doing so, it has gone beyond the boundaries of your local network,

and has been transmitted over a WAN

When the ISP receives your e-mail, it also looks at where the data is

tined Because the ISP also has a LAN, it looks at whether the e-mail is

des-tined for someone else who uses their service, a computer on their network,

or another network connected to the Internet Because you’re sending the e-mail to someone who uses a different ISP, it sends the e-mail over the Internet, which is a giant WAN, to be received by the other ISP’s e-mail server

When the other ISP receives the data, it will store the e-mail you sent

on its e-mail server, until your friend dials into the Internet using a modem Your friend’s computer connects to the ISP’s server, and then requests any e-mail that the server might have This data is again broken into packets, and sent over the telephone line so that your friend’s modem can receive the data, and the computer can reassemble these packets and display them in your friend’s e-mail program

As you can see by this example, there are many different kinds of LANs and WANs that data may pass through LANs may be as small as a couple of computers networked together, and a WAN may be as large as the Internet or

as small as two LANs (yours and your ISP’s) interconnected together using routers In each case though, the LAN consists of computers that are part of the same network, and the WAN consists of geographically dispersed LANs that are internetworked

MAN

Although most people refer to a network in terms of being either a LAN or

a WAN, there are other terms to further categorize a network One such category is a MAN, which is an acronym for metropolitan area network (MAN) A MAN will generally cover a metropolitan area like a city, but this isn’t always the case For example, if you lived in a small town, and had your LAN connecting to another LAN in a neighboring town, you could also refer

to this as a MAN When LANs are connected together with high-speed solu-tions over a territory that is relatively close together (such as several build-ings in a city, region or county), it can be considered a MAN A MAN is a group of LANs that are internetworked within a local geographic area, which IEEE (an organization we’ll discuss later in this chapter) defines as being

50 km or less in diameter

Exam warning

Being that the Network+ exam is an exam on networks, it should come as no surprise that questions dealing with LANs and WANs will appear Make sure that you know the difference between a LAN and a WAN, and that a WAN is a group of internetworked LANs Other types of networks discussed below (MAN, SAN, CAN, and PAN) aren’t covered extensively on the exam Specific elements of LANs and WANs are discussed throughout this book, and you will need to know them to pass the exam.

A SAN is a storage area network, and it is used to connect storage devices

together using high-speed connections It is a segment of a network, and

allows storage devices to be accessed by computers within the larger LAN

or WAN These storage devices consist of hard disks or other methods of

storing data, and allow users of the network to view and/or save data to a

centralized location

PAN

A PAN is a personal area network, which is a wireless network that allows

devices to exchange data with computers Personal digital assistants

(PDAs), cell phones, and other devices that someone can carry on their

person and support this technology have a wireless transmitter in them

When they are within a certain distance of a receiver that’s installed on

a computer, data can be exchanged between the computer and the device

Using a PAN allows you to do such things as update a calendar in a PDA,

address book in a cell phone, and other tasks that are supported by the

device

CAN

A CAN is a campus area network, and refers to a series of LANs that are

internetworked between several nearby buildings This is a common type

of network that’s used in organizations with facilities that are close to one

another, such as when there is a pool of office buildings or a campus It is

larger than a LAN but smaller than a MAN

Note

With virtualization technologies becoming increasingly popular the need for centrally

accessible storage arrays has become increasing important.

Test day Tip

It is wise to quickly review information dealing with the Network+ exam shortly before

taking the exam itself A fast approach to reviewing is to look over the Exam Watch

information, Summary of Exam Objectives, and Exam Objectives Fast Track sections

of this book To make it easy reviewing items you have a problem remembering and

that may appear on the exam, highlight or bookmark these items in the book, so you

can review them at crunch time They will provide a quick approach to re-examining

important information.