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All networks offer advantages relative to using a standalone computer—that is, a computer that is not connected to other computers and that uses software applications and data stored on

puters connected by a cable in a home office or as large as several thousand computers nected across the world via a combination of cable, phone lines, and satellite links In addition

con-to connecting personal computers, networks may link mainframe computers, printers, plotters,fax machines, and phone systems They may communicate through copper wires, fiber-opticcable, radio waves, infrared, or satellite links This chapter introduces you to the fundamentalcharacteristics of networks

Why Use Networks?

All networks offer advantages relative to using a standalone computer—that is, a computer

that is not connected to other computers and that uses software applications and data stored

on its local disks Most importantly, networks enable multiple users to share devices (for ple, printers) and data (for example, spreadsheet files), which are collectively known as the net-

exam-work’s resources Sharing devices saves money For example, rather than buying 20 printers for

20 staff members, a company can buy one printer and have those 20 staff members share itover a network Sharing devices also saves time For example, it’s faster for coworkers to sharedata over a network than to copy data to a removable storage device and physically transportthe storage device from one computer to another—an outdated file-sharing method com-

monly referred to as sneakernet (presumably because people wore sneakers when walking

from computer to computer) Before networks, transferring data via floppy disks was the onlypossible way to share data

Another advantage to networks is that they allow you to manage, or administer, resources onmultiple computers from a central location Imagine you work in the Information Technology(IT) department of a multinational bank and must verify that each of 5000 employees aroundthe globe uses the same version of a database program Without a network you would have tovisit every employee’s machine to check and install the proper software With a network, how-ever, you could check the software installed on computers around the world from the com-puter on your desk Because they allow you to share devices and administer computers centrally,networks increase productivity It’s not surprising, then, that most businesses depend on theirnetworks to stay competitive

Types of Networks

Computers can be positioned on a network in different ways relative to each other They canhave different levels of control over shared resources They can also be made to communicateand share resources according to different schemes The following sections describe two fun-damental network models: peer-to-peer and client/server

Peer-to-peer Networks

The simplest form of a network is a peer-to-peer network In a peer-to-peer network, every

computer can communicate directly with every other computer By default, no computer on apeer-to-peer network has more authority than another However, each computer can be con-figured to share only some of its resources and keep other resources inaccessible to the net-work Traditional peer-to-peer networks typically consist of two or more general-purposepersonal computers, with modest processing capabilities Every computer is capable of send-ing and receiving information to and from every other computer, as shown in Figure 1-1

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TYPES OF NETWORKS

FIGURE 1-1 Resource sharing on a simple peer-to-peer network

The advantages of using traditional peer-to-peer networks are:

◆ They are simple to configure For this reason, they may be used in environments inwhich time or technical expertise is scarce

◆ They are typically less expensive to set up and maintain than other types of networks.This fact makes them suitable for environments in which saving money is critical

The disadvantages of using traditional peer-to-peer networks are:

◆ They are not very flexible As a peer-to-peer network grows larger, adding or ing significant elements of the network may be difficult

chang-◆ They are also not necessarily secure—meaning that in simple installations, data andother resources shared by network users can be easily discovered and used by unau-thorized people

◆ They are not practical for connecting more than a handful of computers, becausethey do not always centralize resources

For example, if your computer is part of a peer-to-peer network that includes five other puters, and each computer user stores her spreadsheets and word-processing files on her ownhard disk, whenever your colleagues want to edit your files, they must access your machine onthe network If one colleague saves a changed version of one of your spreadsheets on her harddisk, you’ll find it difficult to keep track of which version is the most current As you can imag-ine, the more computers you add to a peer-to-peer network, the more difficult it becomes tofind and manage resources

com-A common way to share resources on a peer-to-peer network is by modifying the file-sharingcontrols via the computer’s operating system For example, you could choose to create a direc-tory on your computer’s hard disk called “SharedDocs” and then configure the directory to allowall networked computers to read its files On a peer-to-peer network each user is responsiblefor configuring her computer to allow access to certain resources and prevent access to others

In other words, resource sharing is not controlled by a central computer or authority Becauseaccess depends on many different users, it typically isn’t uniform and may not be secure.Although traditional peer-to-peer networks are typically small and contained within a home

or office, in the last five years large peer-to-peer networks have connected through the

Inter-net These newer types of peer-to-peer networks (commonly abbreviated P2P networks) link

computers from around the world to share files between each others’ hard disks Unlike tional peer-to-peer networks, they require specialized software (besides the computer’s operat-ing system) to allow resource sharing Examples of these networks include Gnutella, Freenet,and the original Napster In 2001, Napster, which allowed users around the globe to share musicfiles, was forced to cease operation due to charges of copyright infringement from musiciansand music producers Later, the service was redesigned to provide legitimate music file-shar-ing services

tradi-Client/Server Networks

Another way of designing a network is to use a central computer, known as a server, to

facil-itate communication and resource sharing between other computers on the network, which are

known as clients Clients usually take the form of personal computers, also known as stations A network that uses a server to enable clients to share data, data storage space, and devices is known as a client/server network (The term client/server architecture is some-

work-times used to refer to the design of a network in which clients rely on servers for resource

shar-ing and processshar-ing.) In terms of resource sharshar-ing and control, you can compare the client/servernetwork to a public library Just as a librarian manages the use of books and other media bypatrons, a server manages the use of shared resources by clients For example, if a patron doesnot have the credentials to check out books, the librarian prevents him from doing so Simi-larly, a server allows only authorized clients to access its resources.

Every computer on a client/server network acts as a client or a server (It’s possible, but mon, for some computers to act as both.) Clients on a network can still run applications fromand save data to their local hard disk But by connecting to a server, they also have the option

uncom-of using shared applications, data, and devices Clients on a client/server network do not sharetheir resources directly with each other, but rather use the server as an intermediary Figure 1-2 illustrates how resources are shared on a client/server network

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FIGURE 1-2 Resource sharing on a client/server network

To function as a server, a computer must be running a network operating system (NOS), a

special type of software designed to:

◆ Manage data and other resources for a number of clients

◆ Ensure that only authorized users access the network

◆ Control which type of files a user can open and read

◆ Restrict when and from where users can access the network

◆ Dictate which rules computers will use to communicate

◆ Supply applications to clients

Examples of popular network operating systems include Microsoft Windows Server 2003,Novell NetWare, UNIX, and Linux (By contrast, a standalone computer, or a client computer,uses a less-powerful operating system, such as Windows XP.)

Usually, servers have more memory, processing, and storage capacity than clients They mayeven be equipped with special hardware designed to provide network management functionsbeyond that provided by the network operating system For example, a server may contain anextra hard disk and specialized software so that if the primary hard disk fails, the secondaryhard disk automatically takes its place

Although client/server networks are typically more complex in their design and maintenancethan peer-to-peer networks, they offer many advantages over peer-to-peer networks, such as:

◆ User logon accounts and passwords for anyone on a server-based network can beassigned in one place

◆ Access to multiple shared resources (such as data files or printers) can be centrallygranted to a single user or groups of users

◆ Problems on the network can be tracked, diagnosed, and often fixed from one location

◆ Servers are optimized to handle heavy processing loads and dedicated to handlingrequests from clients, enabling faster response time

◆ Because of their efficient processing and larger disk storage, servers can connectmore than a handful of computers on a network

Together, these advantages make client/server networks more easily manageable, more secure,

and more powerful than peer-to-peer networks They are also more scalable—that is, they can

be more easily added onto and extended—than peer-to-peer networks

Because client/server networks are the most popular type of network for medium- and scale organizations, most of the concepts covered in this book and on the Network+ exam per-tain to client/server networks Next, you will learn how networks are classified according tosize

large-LANs, MANs, and WANs

As its name suggests, a local area network (LAN) is a network of computers and other devices

that is confined to a relatively small space, such as one building or even one office SmallLANs first became popular in the early 1980s At that time LANs might have consisted of ahandful of computers connected in a peer-to-peer fashion Today’s LANs are typically muchlarger and more complex client/server networks

Often separate LANs are interconnected and rely on several servers running many differentapplications and managing resources other than data For example, imagine an office build-ing in which each of a company’s departments runs its own LAN and all the LANs are con-nected This network may contain many servers, hundreds of workstations, and several sharedCD-ROM devices, printers, plotters, and fax machines Figure 1-3 roughly depicts this type

of network (in reality, the network would probably contain many more clients) As youprogress through this book, you will learn about every part of this diagram In the process,you will learn to integrate these pieces so as to create a variety of networks that are reliable,secure, and manageable

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FIGURE 1-3 A more complex client/server network

Networks may extend beyond the boundaries of a building A network that is larger than aLAN and connects clients and servers from multiple buildings—for example, a handful of

government offices surrounding a state capitol—is known as a metropolitan area network (MAN) Because of the distance it covers, a MAN may use different transmission technology

and media than a LAN

A network that connects two or more geographically distinct LANs or MANs is called a wide area network (WAN) Because they carry data over longer distances than LANs, WANs

require slightly different transmission methods and media and often use a greater variety oftechnologies than LANs Most MANs can also be described as WANs; in fact, network engi-neers are more likely to refer to all networks that cover a broad geographical range as WANs.WANs commonly connect separate offices in the same organization, whether they are acrosstown or across the world from each other For example, imagine you work for a nationwidesoftware reseller that keeps its software inventory in warehouses in Topeka, Kansas, and PanamaCity, Florida Suppose also that your office is located in New York When a customer calls andasks whether you have 70 copies of Lotus Notes—an e-mail client/server application—avail-able to ship overnight, you need to check the inventory database located on servers at both theTopeka and Panama City warehouses To access these servers, you could connect to the ware-houses’ LANs through a WAN link, then log on to their servers

WANs are also used to connect LANs that belong to different organizations For example, all thepublic universities within a state might combine and share their resources via a WAN The

largest and most varied WAN in the world is the Internet Figure 1-4 depicts a simple WAN.

FIGURE 1-4 A simple WAN

Elements Common to Client/Server

Networks

You have learned that networks—no matter how simple or how complex—provide some efits over standalone computers They also share terminology and common building blocks,some of which you’ve already encountered The following list provides a more complete run-down of basic elements common to all client/server networks You will learn more about thesetopics throughout this book

ben-◆ Client A computer on the network that requests resources or services from another

computer on a network In some cases, a client could also act as a server The term

“client” may also refer to the human user of a client workstation or to client software

installed on the workstation

◆ Server A computer on the network that manages shared resources Servers usually

have more processing power, memory, and hard disk space than clients They runnetwork operating software that can manage not only data, but also users, groups,security, and applications on the network

◆ Workstation A personal computer (such as a desktop or laptop), which may or may

not be connected to a network Most clients are workstation computers

◆ Network interface card (NIC) The device inside a computer that connects a computer

to the network media, thus allowing it to communicate with other computers Manycompanies (such as 3Com, IBM, Intel, SMC, and Xircom) manufacture NICs,which come with a variety of specifications that are tailored to the requirements of

the workstation and the network Some connect to the motherboard, which is the

main circuit that controls the computer, some are integrated as part of the

mother-board, and others connect via an external port NICs are also known as network adapters Figure 1-5 depicts a NIC connected to a computer’s motherboard.

◆ Network operating system (NOS) The software that runs on a server and enables the

server to manage data, users, groups, security, applications, and other networkingfunctions The most popular network operating systems are Microsoft WindowsServer 2003, Novell NetWare, UNIX, and Linux

◆ Host A computer that enables resource sharing by other computers on the same

net-work

◆ Node A client, server, or other device that can communicate over a network and that

is identified by a unique number, known as its network address

◆ Connectivity device A specialized device that allows multiple networks or multiple

parts of one network to connect and exchange data A client/server network canoperate without connectivity devices However, medium- and large-sized LANs usethem to extend the network and to connect with WANs

◆ Segment A part of a network Usually, a segment is composed of a group of nodes

that use the same communications channel for all their traffic

◆ Backbone The part of a network to which segments and significant shared devices

(such as routers, switches, and servers) connect A backbone is sometimes referred to

as “a network of networks,” because of its role in interconnecting smaller parts of aLAN or WAN Figure 1-6 shows a LAN with its backbone highlighted

◆ Topology The physical layout of a computer network Topologies vary according to

the needs of the organization and available hardware and expertise Networks areusually arranged in a ring, bus, or star formation; hybrid combinations of these pat-terns are also possible Figure 1-7 illustrates the most common network topologies,which you must understand to design and troubleshoot networks

◆ Protocol A standard method or format for communication between networked

devices Protocols ensure that data are transferred whole, in sequence, and withouterror from one node on the network to another

◆ Data packets The distinct units of data that are transmitted from one node on a

net-work to another Breaking a large stream of data into many packets allows a netnet-work

to deliver that data more efficiently and reliably

FIGURE 1-7 Common network topologies

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3.2

◆ Addressing The scheme for assigning a unique identifying number to every node on

the network The type of addressing used depends on the network’s protocols and

network operating system Each network device must have a unique address so that

data can be transmitted reliably to and from that device

◆ Transmission media The means through which data is transmitted and received.

Transmission media may be physical, such as wire or cable, or atmospheric less), such as radio waves Figure 1-8 shows several examples of transmission media

(wire-FIGURE 1-8 Examples of network transmission media

Now that you are familiar with basic network terminology, you are ready to appreciate the manyuses of computer networks.

How Networks Are Used

The functions provided by a network are usually referred to as network services Any networkmanager will tell you that the network service with the highest visibility is e-mail If your com-pany’s e-mail system fails, users will notice within minutes—and they will not be shy aboutinforming you of the failure Although e-mail may be the most visible network service, otherservices are just as vital Printer sharing, file sharing, Internet access, remote access capabilities,and management services are all critical business functions provided through networks In largeorganizations, separate servers may be dedicated to performing each of these functions Inoffices with only a few users and little network traffic, one server may perform all functions

File and Print Services

File services refer to the capability of a server to share data files, applications (such as

word-processing or spreadsheet programs), and disk storage space A server that provides file

ser-vices is called a file server File serser-vices accounted for the first use of networks and remain the

foundation of networking today, for a number of reasons As mentioned earlier, it’s easier andfaster to store shared data at a central location than to copy files to disks and then pass thedisks around Data stored at a central location is typically more secure because a networkadministrator can take charge of backing up this data, rather than relying on individual users

to make their own copies In addition, using a file server to run applications for multiple usersrequires the purchase of fewer copies of the application and less maintenance work for the net-work administrator

Using print services to share printers across a network also saves time and money A

high-capacity printer can cost thousands of dollars, but can handle the printing tasks of an entiredepartment, thereby eliminating the need to buy a desktop printer for each worker With oneprinter, less time is spent on maintenance and management If a shared printer fails, the net-work administrator can diagnose the problem from a workstation anywhere on the networkusing the network operating system’s printer control functions Often, the administrator cansolve the problem without even visiting the printer

Communications Services

A network’s communications services allow remote users to connect to the network (The term

remote user refers to a person working on a computer on a different network or in a different

geographical location from the LAN’s server.) Less frequently, communications services allownetwork users to connect to machines outside the network Most network operating systems

include built-in communications services that enable users to dial into an access server, log on

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HOW NETWORKS ARE USED

to the network, and take advantage of the network just as if they were logged on to a

work-station on the office LAN A remote access server may also be known as a communications server or an access server.

Organizations commonly use communications services to provide LAN access for workers athome, workers on the road, and workers at small satellite offices where dedicated WAN con-nections are not cost-effective In addition, they may use communications services to allow stafffrom other organizations (such as a software or hardware vendor) to help diagnose a networkproblem For example, suppose you work for a clothing manufacturer that uses embroidery soft-ware to control the machines that sew insignias on shirts and hats You are an expert on net-working, but less adept with the automated embroidery software When the software causesproblems, you turn to the software vendor for help But suppose the vendor’s technician can’tsolve the problem except by logging on to your network In that case, it’s much more efficientand less expensive to allow the technician to dial in to your network through a communica-tions server than to fly the technician to your office

It’s important to remember that remote access servers—no matter which platform (hardware

or operating system software) they run on—allow external users to use network resources anddevices just as if they were logged on to a workstation in the office From a remote location,users can print files to shared printers, log on to hosts, retrieve mail from an internal messag-ing system, or run queries on internal databases Because they can be accessed by the world out-side the local network, remote access servers necessitate strict security measures

In addition to simply sending, receiving, and storing mail, mail servers can:

◆ Intercept or filter unsolicited e-mail, known as spam

◆ Find objectionable content in e-mails and perform functions (such as user tion) on that content

notifica-◆ Route messages according to particular rules—for example, if a technical support sentative has not opened a customer’s message within 15 minutes of delivery, a mail servercould automatically forward the message to a supervisor

repre-◆ Provide a Web-based client for checking e-mail

◆ Notify administrators or users if certain events occur (for example, if a user’s mailbox

is close to exceeding its maximum amount of space on a server)

◆ Schedule e-mail transmission, retrieval, storage, and maintenance functions

◆ Communicate with mail servers on other networks so that mail can be exchangedbetween users who do not connect to the same LAN

To supply these services, a mail server runs specialized mail server software, examples of whichinclude Sendmail, Microsoft Exchange Server, and Novell GroupWise Because of their crit-ical nature and heavy use, maintaining a mail server in any sizable organization requires a sig-nificant commitment of technical support and administration resources.

Internet Services

You have probably connected to the Internet without knowing or caring about all of the vices running behind the scenes But in fact, many servers are working together to bring Web

ser-pages to your desktop For example, a Web server is a computer installed with the

appropri-ate software to supply Web pages to many different clients upon demand Supplying Web pages

is only one type of Internet service Other Internet services include file transfer capabilities,

Internet addressing schemes, security filters, and a means for directly logging on to other puters on the Internet Internet services are a broad category of network functions; reflectingtheir growing importance, entire books have been devoted to them

com-Management Services

When networks were small, they could be managed easily by a single network administratorand the network operating system’s internal functions For instance, suppose a user called toreport a problem logging on to the network The administrator diagnosed the problem as anaddressing conflict (that is, two workstations having the same network address) In a verysmall network, the conflicting workstations might be located right around the corner from eachother, and one address could be changed quickly In another example, if a manager needed toreport the number of copies of Adobe Photoshop in use in a certain department, the networkadministrator could probably get the desired information by just walking through the depart-ment and checking the various workstations

As networks grow larger and more complex, however, they become more difficult to manage

Using network management services can help you keep track of a large network Network agement services centrally administer management tasks on the network, such as ensuring that

man-no more than 20 workstations are using Adobe Photoshop at one time in an organization thatpurchased a 20-user license for the software Some organizations dedicate a number of servers

to network management functions, with each server performing only one or two unique vices

ser-Numerous services fall under the category of network management Some of the most tant ones include the following:

impor-◆ Traffic monitoring and control Determining how much traffic (that is, data

transmis-sion activity) is taking place on a network and notifying administrators when the

network becomes overloaded In general, the larger the network, the more critical it

is to monitor traffic

◆ Load balancing Distributing data transfer activity evenly across a network so that no

single device becomes overwhelmed Load balancing is especially important for

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HOW NETWORKS ARE USED

works in which it’s difficult to predict the number of requests that will be issued to aserver, as is the case with Web servers.

◆ Hardware diagnosis and failure alert Determining when a network component fails

and automatically notifying the network administrator through e-mail or paging

◆ Asset management Collecting and storing data on the number and types of software

and hardware assets in an organization’s network With asset management software,

a server can electronically examine each client’s software and hardware and ically save the data in a database Before asset management services, this data had to

automat-be gathered manually and typed into spreadsheets

◆ License tracking Determining how many copies of a single application are currently

in use on the network and ensuring that number does not exceed the number oflicenses purchased This information is important for legal reasons, as software com-panies are vigilant about illegally copying software or using more than the autho-rized number of copies

◆ Security auditing Evaluating what security measures are currently in force and

noti-fying the network administrator if a security breach occurs

◆ Software distribution Automatically transferring a file or installing an application

from the server to a client on the network The installation process can be startedfrom either the server or the client Several options are available when distributingsoftware, such as warning users about updates, writing changes to a workstation’ssystem files, and restarting the workstation after the update

◆ Address management Centrally managing a finite number of network addresses for an

entire network Usually this task can be accomplished without manually modifyingthe client workstation configurations

◆ Backup and restoration of data Copying (or backing up) critical data files to a secure

storage area and then restoring (or retrieving) data if the original files are lost or

deleted Often backups are performed according to a formulaic schedule Backupand data restoration services provide centralized management of data backup onmultiple servers and on-demand restoration of files and directories

Network management services will be covered in depth later in the book For now, it is enough

to be aware of the variety of services and the importance of this growing area of networking

Becoming a Networking Professional

Examine the classified ad section of any city newspaper, and you will probably find dozens ofads for computer professionals Of course, the level of expertise required for each of these jobsdiffers Some companies simply need “warm bodies” to ensure that a backup process doesn’tfail during the night; other companies are looking for people to plan their information tech-nology strategies Needless to say, the more extensive your skills, the better your chances forlanding a lucrative and interesting job in networking To prepare yourself to enter this job mar-