Business Data Communications 6e Ch01

INTRODUCTION1.1 Information and Communication

1.2 Data Communications and Networking for Todays EnterpriseTrendsBusiness Drivers

1.3 Convergence and Unified CommunicationsConvergenceUnified Communications

1.4 The Nature of Business Information Requirements

1.5 Distributed Data Processing

1.6 The Internet and Distributed ApplicationsThe InternetTCP/IPDistributed ApplicationsClient/Server Architectures and Intranets

1.7 NetworksWide Area NetworksLocal Area NetworksWireless NetworksMetropolitan Area NetworksAn Example Configuration

1.8 The Transmission of InformationTransmission and Transmission MediaCommunication TechniquesTransmission Efficiency

1.9 Managements IssuesNetwork SecurityNetwork Management

1.10 Standards

1.11 Recommended Reading and Web Sites

1.12 Key Terms and Review Questions

APPENDIX 1A Prefixes for Numerical Units

6

CHAPTER

Business Data Communications, Sixth Edition, by William Stallings. Published by Prentice Hall. Copyright 2009 by Pearson Education, Inc.

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1.1 / INFORMATION AND COMMUNICATION 7

Chapter Objectives

After reading this chapter, you should be able to

Understand the basic requirements for data communications and networking tosupport business information needs.

See the big picture of the major topics discussed in the book. Appreciate the importance of the Internet and wireless communications in business

planning.

Understand the central role of standards in data communications and networking.

This introductory chapter begins with an overview of the role of data communicationsand networking in the enterprise.Then a brief discussion introduces each of the parts ofthis book.

1.1 INFORMATION AND COMMUNICATION

A confluence of computers, communication technologies, and demographics istransforming the way any enterprise conducts itself and carries out its organiza-tional mandate. And its happening fast. A business that ignores these changes willfall hopelessly to the rear in the global race for the competitive edge.At the heart ofthe transformation is information. No longer a byproduct and no longer, in manycases, a cost center, the generation, storage, and movement of information havebeen made profitable by companies that have taken up the technological challengeposed by the myriad machines that automate so much of our lives.

We are unquestionably dependent on computers and the communication de-vices and services that connect them. The number of computers and terminals atwork in the world today is in the billions. The overwhelming need of organizationsand their workers now is for connectivity, for integration, for ease of access to infor-mation. So fundamental is information communication technology to business suc-cess that it is emerging as the foundation of a strategy taking shape in Americanbusinesses: using management structures to gain a competitive advantage.

As businesses are challenged by such forces as global competition, mergers,and acquisitions, time-tested management structures are putting a strain on corpo-rate bottom lines. In response, companies are breaking down divisional walls andflattening top-heavy management pyramids to create new corporate structures thathelp them to compete more effectively. The technology that is making much of thispossible is networking.

Communication technology helps companies overcome three kinds of basicorganizational difficulties: Good networks make geographically dispersed companiesmore manageable; they help top-heavy companies trim down middle management;and they help companies break down barriers between divisions. As we examine thetechnology and applications throughout this book, we will see the ways in which infor-mation communication technology solves these and other vital business problems.


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1.2 DATA COMMUNICATIONS AND NETWORKINGFOR TODAYS ENTERPRISE

Effective and efficient data communication and networking facilities are vital to anyenterprise. In this section, we first look at trends that are increasing the challenge forthe business manager in planning and managing such facilities. Next we introducethe concept of business drivers that will guide the enterprise in developing an over-all data communications and networking plan.

Trends

Three different forces have consistently driven the architecture and evolution ofdata communications and networking facilities: traffic growth, development of newservices, and advances in technology.

Communication traffic, both local (within a building or building complex) andlong distance, both voice and data, has been growing at a high and steady rate fordecades. The increasing emphasis on office automation, remote access, online trans-actions, and other productivity measures means that this trend is likely to continue.Thus, managers are constantly struggling to maximize capacity and minimize trans-mission costs.

As businesses rely more and more on information technology, the range ofservices expands.This increases the demand for high-capacity networking and trans-mission facilities. In turn, the continuing growth in high-speed network offeringswith the continuing drop in prices encourages the expansion of services.Thus, growthin services and growth in traffic capacity go hand in hand. Figure 1.1 gives someexamples of information-based services and the data rates needed to support them[ELSA02].

Finally, trends in technology enable the provision of increasing traffic capacityand the support of a wide range of services. Four technology trends are particularlynotable and need to be understood by the manager responsible for informationtechnology:

1. The trend toward faster and cheaper, both in computing and communications,continues. In terms of computing, this means more powerful computers andclusters of computers capable of supporting more demanding applications,such as multimedia applications. In terms of communications, the increasinguse of optical fiber and high-speed wireless has brought transmission pricesdown and greatly increased capacity. For example, for long-distance telecom-munication and data network links, recent offerings of dense wavelength divi-sion multiplexing (DWDM) enable capacities of many terabits per second. Forlocal area networks (LANs), many enterprises now have Gigabit Ethernet or10-Gbps Ethernet backbone networks.1 Further, the need for the next-generation100-Gpbs is pressing, and products at this data rate should appear in the nearfuture. Figure 1.2, based on [MELL07], indicates the Ethernet demand trend.

8 CHAPTER 1 / INTRODUCTION

1See Appendix 1A for an explanation of numerical prefixes, such as tera and giga.


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9.6Speed (kbps)Transaction processing

Messaging/text apps

Voice

Location services

Still image transfers

Internet/VPN access

Database access

Enhanced Web surfing

Low-quality video

High-end audio

Large file transfer

Moderate video

Interactive entertainment

High-quality video

Performance:VPN: virtual private network Poor Adequate Good

14.4 28 64 144 384 2000

Figure 1.1 Services versus Throughput Rates

Figure 1.2 Past and Projected Growth in Ethernet Bandwidth Compared to Existing Ethernet Data Rates

1 Gbps

10 Gbps

100 Gbps

1 Tbps

100 Mbps1995 2000 2005 2010

Ethernet data rate standardService provider/WANEnterprise/server/LAN


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2. Both voice-oriented telecommunications networks, such as the public switchedtelephone network (PSTN), and data networks, including the Internet, are moreintelligent than ever. Two areas of intelligence are noteworthy. First, todaysnetworks can offer differing levels of quality of service (QoS), which includespecifications for maximum delay, minimum throughput, and so on. Second,todays networks provide a variety of customizable services in the areas of net-work management and security.

3. The Internet, the Web, and associated applications have emerged as dominantfeatures of both the business and personal world, opening up many opportunitiesand challenges for managers. In addition to exploiting the Internet and the Webto reach customers, suppliers, and partners, enterprises have formed intranets andextranets2 to isolate their proprietary information free from unwanted access.

4. There has been a trend toward ever-increasing mobility for decades, liberatingworkers from the confines of the physical enterprise. Innovations includevoice mail, remote data access, pagers, fax, e-mail, cordless phones, cell phonesand cellular networks, and Internet portals.The result is the ability of employeesto take their business context with them as they move about.We are now seeingthe growth of high-speed wireless access, which further enhances the ability touse enterprise information resources and services anywhere.

Business Drivers

The trends discussed in the preceding subsection are enabling the development ofenterprise network and communications facilities that are increasingly better inte-grated with the information base, which the enterprise itself runs. Network manage-ment and operation depend on some key enterprise-specific information, such asnames, network addresses, security capabilities, end-user groupings, priority desig-nations, mailboxes, and application attributes.With the increasing capacity and func-tionality of enterprise networks, this information can be unified with the enterpriseinformation base so that the information is correct, consistent, and available acrossall business applications.

The nature of the enterprise networking and communications facility dependson the business applications it must support. [MILO00] lists four main applicationareas that will serve as the drivers in determining the design and makeup of theenterprise network. Figure 1.3 lists these areas, along with their business motivatorsand the expected benefits.

1.3 CONVERGENCE AND UNIFIED COMMUNICATIONS

This section introduces two related concepts that are important determinants of re-quirements for business data communications and networking facilities: convergenceand unified communications.

2Briefly, an intranet uses Internet and Web technology in an isolated facility internal to an enterprise; anextranet extends a companys intranet out onto the Internet to allow selected customers, suppliers, andmobile workers to access the companys private data and applications. See Chapter 6 for a discussion.


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Convergence

Convergence refers to the merger of previously distinct telephony and informationtechnologies and markets.We can think of this convergence in terms of a three-layermodel of enterprise communications:

Applications: These are seen by the end users of a business. Convergence inte-grates communications applications, such as voice calling (telephone), voicemail, e-mail, and instant messaging, with business applications, such as work-group collaboration, customer relationship management, and other back-officefunctions. With convergence, applications provide features that incorporatevoice, data, and video in a seamless, organized, and value-added manner. Oneexample is multimedia messaging, which enables a user to employ a singleinterface to access messages from a variety of sources (e.g., office voice mail,office e-mail, beeper, and fax).

Enterprise services: At this level, the manager deals with the informationnetwork in terms of the services it supplies to support applications. The net-work manager needs design, maintenance, and support services related tothe deployment of convergence-based facilities. Also at this level, networkmanagers deal with the enterprise network as a function-providing system.Such management services may include setting up authentication schemes;capacity management for various users, groups, and applications; and QoSprovision.

Infrastructure: The infrastructure consists of the communication links, LANs,WANs, and Internet connections available to the enterprise. The key aspect ofconvergence at this level is the ability to carry voice and video over data net-works, such as the Internet.

Figure 1.3 Applications Driving Enterprise Networks

IP Telephony International and long-distance savings Economics of converged networks Productivity through application integration

e-Business Workflow integration Productivity improvements New applications tied to business needs Better management of suppliers/partners

IP Internet Protocole-Business Enterprise activities based on mobile, global access to enterprise networks

Customer relationship management New customer acquisition Increased satisfaction for existing customers Reduced operating expenses Productivity via workflow management

Multimedia messaging Increased productivity Reduced network expense Integration into business workflow

Benefits Revenue generation Expense reduction Customer acquisition Customer satisfaction and retention Increased productivity


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Figure 1.4, based on [MILL05], illustrates the three layers and their associatedconvergence attributes. In simple terms, convergence involves moving voice into adata infrastructure, integrating all the voice and data networks inside a user organi-zation into a single data network infrastructure, and then extending that into thewireless arena. The foundation of this convergence is packet-based transmissionusing the Internet Protocol (IP). Convergence increases the function and scope ofboth the infrastructure and the application base.

Convergence brings many benefits, including simplified network manage-ment, increased efficiency, and greater flexibility at the application level. For exam-ple, a converged network infrastructure makes it easier to add applications thatcombine video, data, and voice. [POL07] lists the following three key benefits ofconvergence:

Efficiency: Provides a double-digit percent reduction in operating costs throughthe convergence of legacy networks onto a single global IP network, better useof and reduction in existing resources, and implementation of centralizedcapacity planning, asset management, and policy management.

Effectiveness: The converged environment has the potential to provide userswith great flexibility, irrespective of where they are. Such a company-wide en-vironment provides for rapid standardized service deployment and enhancedremote connectivity and mobility.

Transformation: Convergence also enables the enterprise-wide adoption ofglobal standards and associated service levels, thus providing better data, en-hanced real-time global decision-making processes, and improved executionin business planning and operations. This leads to greater agility for the enter-prise in providing new services to its customers and employees.

Figure 1.4 Business-Driven Congergence

Provides common transport for data, voice, image, videoNetwork-based IP VPNs using MPLSIPv6Wired and wireless LANsPublic wireless networksPublic Internet

Driven by business requirementsConvergedDrives underlying layersIntegrated contact centersUnified messagingConverged multimedia services

Provides end-to-end design, integration, support,installation, management, and outsourcing servicesPrivacyAuthenticationLocationStorage

Infrastructure

Applicatoins

Enterprise

Services


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Unified Communications

A concept related to that of convergence is unified communications (UC). Whereasconvergence focuses on the merger of fundamental voice, video, and data communi-cations facilities and the resulting ability to support multimedia applications, UCfocuses on the user perspective to the broad spectrum of business applications. Keyelements of UC include the following include the following:

1. UC is based on an integrated set of user interfaces and backend connectivityfor all communications services.

2. UC merges real-time communications services with non-real-time collabora-tion and business process applications.

Figure 1.5, based on [LAZA07], shows the typical components of a UC archi-tecture and how the relate to one another. The key elements of this architecture areas follows:

Web 2.0: Refers to a second generation of Web capability. Two prominentaspects of Web 2.0 are as follows: (1) Much of the content is user generated,including blogs, wikis, documents, images, and video clips; and (2) the userinterface is rich, easy to use, and provides a desktop-like experience. AlthoughWeb 2.0 services and features are primarily associated with public Web use bythe general population,Web 2.0 has become a significant element of corporatestrategy [MURU07].The term Enterprise 2.0, which is also becoming common,refers to the application of Web 2.0 technologies to workers using networksoftware within an organization or business [MCAF06].

Real-time communications (RTC) dashboard: May consist of both desktopand mobile software clients, though often with differing levels of functionality.RTC dashboards blend instant messaging, e-mail, audio-and videoconferencing,

Figure 1.5 Elements of Unified Communications Architecture

Web conferencing

Web 2.0/Enterprise 2.0

Real-timecommuni-

cationsdashboard

Audio conferencing

Unified messaging

Instant messaging

Presence

IP enabling contact centers

IP/mobility

Converged IP/wireless infrastructure

Network optimization, management, security

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whiteboarding, and file sharing into a unified view.An RTC dashboard enablesa user to locate other users and invoke collaborative applications with thoseother uses. [GITT06] points out that the RTC dashboard has moved from thenice to have to need to have category for many businesses.

Web conferencing: Refers to live meetings or presentations in which partici-pants access the meeting or presentation via the Web, either over the Internetor a corporate intranet.

Audio conferencing: Also called conference calling, refers to a live meeting inwhich participants are linked together for audio transmission and reception.Aparticipant may be on a landline, mobile phone, or at a computer equippedwith microphone and speaker.

Unified messaging: Allows users to have access to e-mail, voice mail, and faxesvia a common interface either on their computer or on their telephone. Com-puter users can select and play voice-mail recordings that appear in their in-boxes. Telephone users can both retrieve voice mail and hear text-to-voicetranslations of e-mail messages. Messages of any type can be saved, answered,filed, sorted and forwarded.

Instant messaging: Real-time messaging.

Desktop video: Videoconferencing to the desktop.

Presence: The ability to determine, in real time, where someone is, how he orshe prefers to be reached, and even what he or she is doing. Presence was onceconsidered simply an underlying technology to instant messaging. Presencehas been broadened to encompass a users status on phones, wireless devices,video conferencing, and other collaborative tools.

IP enabling contact centers: Refers to the use of IP-based unified communi-cations to enhance customer contact center functionality and performance.The unified communications infrastructure makes use of presence technol-ogy to enable customers and internal enterprise employees to be quicklyconnected to the required expert or support person. Additionally, this tech-nology supports mobility, so that call center personnel need not be locatedat a particular office or remain in a particular place. Finally, the unifiedcommunications infrastructure enables the call center employee to quicklyaccess other employees and information assets, including data, video, image,and audio.

IP/mobility: Refers to the delivery of information to and collection of infor-mation from enterprise personnel who are usually mobile, using an IP networkinfrastructure. In a typical enterprise, upward of 30% of employees use someform of remote access technology in the performance of their jobs. Figure 1.6,from [SENS02], illustrates the typical breakdown of usage profiles for mobileemployees.

Converged IP/wireless infrastructure: A unified networking and communi-cations base that relies on IP packet transfer to support voice, data, and videotransmission and that is extended to include local and wide area wirelesscommunications.


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The importance of unified communications is not only that it integrates com-munication channels, within the enterprise and with key constituents, but also that itoffers a way to integrate communication functions directly into business applica-tions. [ELLI08] notes three functional levels of this integration:

Personal unified communications: Intended to enhance individual productivity.This area includes smart phones, personal digital assistants (PDAs), and otherpersonal devices that provide access to voice, instant messaging (IM), presenceinformation, and business applications.

Workgroup unified communications: Supports collaborative and team effortsto improve performance. Examples include the use of presence to speed iden-tification of an available individual with the right skills to address a problemand automated business rules to route or escalate communications.

Enterprise unified communications: Integrates communications with enterprise-wide and departmental-level applications, business processes, and workflows.

Enterprises are increasingly migrating to some form and level of commitmentto unified communications. The unified communications architecture, together witha converged network approach, will drive requirements for business data communi-cations from the fundamental transmission and networking level up though theapplications and services upon which the enterprise depends.

1.4 THE NATURE OF BUSINESS INFORMATION REQUIREMENTS

A business survives and thrives on information: information within the organizationand information exchanged with suppliers, customers, and regulators. Moreover, theinformation needs to be consistent, accessible, and at the right location. In Part One,Chapters 2 and 3, we consider information in four forms (voice, data, image, andvideo) and the implications of distributed data processing.

In this book, the term voice communications primarily refers to telephone-related communications. By far the most common form of communication in any

Figure 1.6 Three Main Profiles for Mobile Employees

EmployeeProfiles At desk

90%

10% 10% 80%

70%30%

25% 25% 50%

10%

30%70%

100% (Home)

On the moveSomewhereon siteDesk soldierAccountantOn-site roverAssistantHome workerTele-agentRoad warriorSalespersonOff-site roverConsultantGlobal hopperCorporate executivemarketing, pre-sales


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organization and for most personnel is direct telephone conversation.The telephonehas been a basic business tool for decades. Telephone communication has been en-hanced by a variety of computer-based services, including voice mail and computer-ized telephone exchange systems. Voice mail provides the ability to send, forward,and reply to voice messages nonsimultaneously, and it has become a cost-efficienttool even for many small and midsize organizations. It provides savings on answeringmachines and services, as well as a more responsive service to customers and sup-pliers.Advances have also been made in computerized telephone exchange systems,including in-house digital private branch exchanges (PBX) and Centrex systemsprovided by the local telephone company. These new systems provide a host offeatures, including call forwarding, camp-on call waiting, least-cost routing of long-distance calls, and a variety of accounting and auditing features. More recently, themerger of voice and Internet technologies, based on the voice over IP (VoIP) proto-col, has resulted in PBX and IP Centrex offerings that provide full Internet support.

The term data communications is sometimes used to refer to virtually anyform of information transfer other than voice. It is sometimes convenient to limitthis term to information in the form of text (such as reports, memos, and other doc-uments) and numerical data (such as accounting files).The rapid changes in technol-ogy have created fresh challenges for management in making effective use of datacommunications. Later in this chapter we briefly outline the changes in technologyin transmission, networks, and communications software that present the managerwith new and powerful business tools but also the necessity of making choicesamong complex alternatives.

Image communications is now an important component of the office environ-ment. The best-known example of this technology is facsimile (fax). Like the tortoisewho surpasses the hare, facsimile machines have caught up with higher-tech alterna-tives and have achieved status over the past few years as the preferred method ofsending documents over a long distance. With fax, the document can have any con-tent, including text, graphics, signatures, and even photographs. Newer machines cantransmit these documents over telephone networks in seconds, and low-cost hard-ware, including personal computer attachments, is now available. In addition, imagecommunications is starting to play an important role within the office.The arrival of theoptical disc, based on the same technology as that of the familiar compact disc of themusic industry, allows massive amounts of information to be stored inexpensively.Thus, all sorts of images, including engineering and design specifications, mixed docu-ments (text, graphs, signatures, etc.), presentation material, and so on, can be movedquickly around the office and displayed on user workstations.This new technology forstoring and transmitting images creates a demand for high-capacity networks and isone of the driving forces in the development of networking technology.

Video communications is also becoming important in the office environment.Traditionally, this technology has been used as a one-way delivery system of enter-tainment programs. Now, with the availability of high-capacity transmission links andnetworks, it has an increasing business application, most notably videoconferencing.Videoconferencing allows the linkup of two or more remotely located conferencerooms to conduct such meetings as planning sessions, contract negotiations, andproject reviews.The time and money saved on travel, food, and lodging make video-conferencing a powerful tool for increasing efficiency and productivity.


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All these forms of information communications play a key role in todays busi-nesses.The manager responsible for them must understand the technology sufficientlyto deal effectively with vendors of communications products and services and to makecost-effective choices among the growing array of options. Chapter 2 examines thebusiness uses of these four classes of information and the communications require-ments that they generate.

1.5 DISTRIBUTED DATA PROCESSING

The steady drop over many years in the cost of data processing equipment, coupledwith an increase in the capability of such equipment, has led to the introduction ofmany small- and medium-size computers into the business environment. Tradition-ally, the data processing function was centrally organized around a mainframe com-puter.Today, however, it is much more common to find a distributed data processingconfiguration, one that consists of a number of computers and terminals linkedtogether by networks. Chapter 3 examines the motivation for distributed data pro-cessing and discusses the various forms that it takes.

1.6 THE INTERNET AND DISTRIBUTED APPLICATIONS

A business needs to be concerned with two dimensions of computer communica-tions software: the application software that is provided for a community of termi-nals and computers, and the underlying interconnection software that allows theseterminals and computers to work together cooperatively.

The mere existence of a large population of computers and terminals createsthe demand that these devices work together. For example, when most employees inan organization have access to a terminal or a personal computer (PC), one of themost effective means of communication within the organization is electronic mail(e-mail). If one employee needs to communicate with another, a message sent bye-mail can be far more effective than hit-or-miss attempts to reach the person bytelephone.A detailed e-mail message can be left in the recipients electronic mailbox,to be read and answered when the recipient returns to the office. Other applications,such as the exchange of documents, the use of a database that is distributed among anumber of computers, and the ability to access many different computers from a singleterminal, can be provided by applications software that is geared for the networkedenvironment.

The key to the success of these applications is that all the terminals and com-puters in the community speak the same language. This is the role of the under-lying interconnection software. This software must ensure that all the devicestransmit messages in such a way that they can be understood by the other computersand terminals in the community. With the introduction of the Systems NetworkArchitecture (SNA) by IBM in the 1970s, this concept became a reality. However,SNA worked only with IBM equipment. Soon other vendors followed with theirown proprietary communication architectures to tie together their equipment.Such an approach may be good business for the vendor, but it is bad business for


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the customer. Happily, that situation has changed radically with the adoption ofstandards for interconnection software. The manager needs to understand thescope and status of these standards to exploit them in building a multiple-vendor,tailored installation.

Modern data communications and microelectronics are radically changing thearchitecture of modern information systems. Most applications have evolved awayfrom large, general-purpose mainframe computers to distributed computing. Insteadof dumb terminals enslaved to mainframes, high-performance workstations and PCsprovide, local to the user, powerful graphical interfaces and much of the applicationcomputing. The local workstations and PCs are supported by specialized serversspecifically designed for a single function, such as printing, storing files, or support-ing database activities. The workstations and PCs are often connected to the serversby high-speed LANs. This approach, called client/server architecture, requires sophis-ticated, reliable, and secure data communications, but its inherent flexibility andresponsiveness make it an essential tool in the businesspersons information systemsrepertoire.

Part Two looks at a number of topics that deal with the infrastructure for sup-porting distributed applications.

The Internet

Virtually no business, and certainly no medium or large enterprise, can competewithout exploiting the Internet and the Web. The Web provides a way to communi-cate with consumers and to publicize the company and can form the base for anumber of e-commerce applications. Internet technology, in the form of intranetsand extranets, enables secure communication both within an enterprise and withcustomers, suppliers, and partners. Chapter 4 provides important background onthe Internet.

TCP/IP

One of the most difficult problems that has traditionally faced computer users isthat different vendors have used different and incompatible architectures. Chapter 5discusses the use of standardized communications protocols to integrate diverseequipment. The focus is on the TCP/IP (Transmission Control Protocol/InternetProtocol) protocol suite, which is now universally used for the communications soft-ware function across multiple-vendor equipment and is the basis for the operationof the Internet.

Chapter 5 also briefly reviews the Open System Interconnection (OSI) archi-tecture developed by the International Organization for Standardization (ISO).

Client/Server Architectures and Intranets

A remarkable transformation is taking place in the architecture of todays commer-cial computers. The large mainframe, although still important, has been replaced orsupplemented in many applications by networked PCs and workstations, as is illus-trated by the increased manufacture of computers of different types. The number ofPCs and workstations is growing at a much greater rate than that of mainframes and


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1.7 / NETWORKS 19

midrange computers, with the result that computing is being more widely distributed.Increasingly, computation is provided by the client/server model. Separate computers(servers) support database functions, store files, perform printing services, and pro-vide other specialized functions on a shared basis for many users (clients). Theseservers, which can offer enhanced performance and cost savings through specializa-tion, are accessed over LANs and other communications networks.

Even more recently, a new approach has gained widespread support withinorganizations: the intranet. An intranet provides the same sorts of applications andinterfaces as found on the Internet, especially the World Wide Web.The difference isthat an intranet is confined to use within the organization, with no access to out-siders. The intranet is a flexible, easy-to-use, and easy-to-implement approach tomany business applications.

Chapter 6 looks at client/server computing, intranets, and extranets.

Distributed Applications

Distributed information processing is essential in virtually all businesses. There is agrowing use of applications that are designed to work among a distributed set ofcomputers for both intracompany and intercompany information exchange. Chapter 7examines some of the key applications that are likely to be the most important toa business.

1.7 NETWORKS

The number of computers in use worldwide is in the billions. Moreover, the expand-ing memory and processing power of these computers means that users can put themachines to work on new kinds of applications and functions. Accordingly, thepressure from the users of these systems for ways to communicate among all thesemachines is irresistible. It is changing the way vendors think and the way all automa-tion products and services are sold.This demand for connectivity is manifested in twospecific requirements: the need for communications software, which is previewed inthe next section, and the need for networks.

One type of network that has become increasingly common is the local areanetwork (LAN). Indeed, the LAN is to be found in virtually all medium- and large-sizeoffice buildings. As the number and power of computing devices have grown, so havethe number and capacity of LANs to be found in an office. Although standardshave been developed that reduce somewhat the number of types of LANs, there arestill half a dozen general types of local area networks to choose from. Furthermore,many offices need more than one such network, with the attendant problems of inter-connecting and managing a diverse collection of networks, computers, and terminals.

Beyond the confines of a single office building, networks for voice, data,image, and video are equally important to business. Here, too, there are rapidchanges.Advances in technology have led to greatly increased capacity and the con-cept of integration. Integration means that the customer equipment and networkscan deal simultaneously with voice, data, image, and even video. Thus, a memo orreport can be accompanied by voice commentary, presentation graphics, and perhaps


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even a short video introduction or summary. Image and video services imposelarge demands on wide area network transmission. Moreover, as LANs becomeubiquitous and as their transmission rates increase, the demands on the wide areanetworks to support LAN interconnection have increased the demands on widearea network capacity and switching. On the other hand, fortunately, the enormousand ever-increasing capacity of fiber optic and wireless transmission provides ampleresources to meet these demands. However, developing switching systems with thecapacity and rapid response to support these increased requirements is a chal-lenge not yet conquered.

The opportunities for using networks as an aggressive competitive tool and asa means of enhancing productivity and slashing costs are great. The manager whounderstands the technology and can deal effectively with vendors of service andequipment is able to enhance a companys competitive position.

In the remainder of this section, we provide a brief overview of various net-works. Parts Three and Four cover these topics in depth.

Wide Area Networks

Wide area networks generally cover a large geographical area, require the crossingof public right-of-ways, and rely at least in part on circuits provided by a commoncarrier.Typically, a WAN consists of a number of interconnected switching nodes.Atransmission from any attached device is routed through these internal nodes tothe specified destination device. These nodes (including the boundary nodes) arenot concerned with the content of the data; rather, their purpose is to provide aswitching facility that will move the data from node to node until they reach theirdestination.

Traditionally, WANs have been implemented using one of two technologies:circuit switching and packet switching. More recently, frame relay and ATM net-works have assumed major roles. Chapter 13 looks at frame relay and ATM.

CIRCUIT SWITCHING In a circuit-switching network, a dedicated communicationpath is established between two stations through the nodes of the network. Thatpath is a connected sequence of physical links between nodes. On each link, a logi-cal channel is dedicated to the connection. Data generated by the source station aretransmitted along the dedicated path as rapidly as possible. At each node, incomingdata are routed or switched to the appropriate outgoing channel without delay. Themost common example of circuit switching is the telephone network.

PACKET SWITCHING A different approach is used in a packet-switching network. Inthis case, it is not necessary to dedicate transmission capacity along a path throughthe network. Rather, data are sent out in a sequence of small chunks, called packets.Each packet is passed through the network from node to node along some path lead-ing from source to destination. At each node, the entire packet is received, storedbriefly, and then transmitted to the next node. Packet-switching networks are com-monly used for terminal-to-computer and computer-to-computer communications.

FRAME RELAY Packet switching was developed at a time when digital long-distancetransmission facilities exhibited a relatively high error rate compared to todays


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facilities. As a result, there is a considerable amount of overhead built into packet-switching schemes to compensate for errors. The overhead includes additional bitsadded to each packet to introduce redundancy and additional processing at the endstations and the intermediate switching nodes to detect and recover from errors.

With modern high-speed telecommunications systems, this overhead is unnec-essary and counterproductive. It is unnecessary because the rate of errors has beendramatically lowered and any remaining errors can easily be caught in the end sys-tems by logic that operates above the level of the packet-switching logic. It is coun-terproductive because the overhead involved soaks up a significant fraction of thehigh capacity provided by the network.

Frame relay was developed to take advantage of these high data rates and lowerror rates. Whereas the original packet-switching networks were designed with adata rate to the end user of about 64 kbps, frame relay networks are designed tooperate efficiently at user data rates of up to 2 Mbps. The key to achieving thesehigh data rates is to strip out most of the overhead involved with error control.

ATM Asynchronous transfer mode (ATM), sometimes referred to as cell relay, isa culmination of developments in circuit switching and packet switching. ATM canbe viewed as an evolution from frame relay. The most obvious difference betweenframe relay and ATM is that frame relay uses variable-length packets, called frames,and ATM uses fixed-length packets, called cells. As with frame relay, ATM provideslittle overhead for error control, depending on the inherent reliability of the trans-mission system and on higher layers of logic in the end systems to catch and correcterrors. By using a fixed packet length, the processing overhead is reduced even fur-ther for ATM compared to frame relay. The result is that ATM is designed to workin the range of 10s and 100s of Mbps, and in the Gbps range.

ATM can also be viewed as an evolution from circuit switching. With circuitswitching, only fixed-data-rate circuits are available to the end system. ATM allowsthe definition of multiple virtual channels with data rates that are dynamicallydefined at the time the virtual channel is created. By using small, fixed-size cells,ATM is so efficient that it can offer a constant-data-rate channel even though it isusing a packet-switching technique. Thus, ATM extends circuit switching to allowmultiple channels with the data rate on each channel dynamically set on demand.

Local Area Networks

As with WANs, a LAN is a communications network that interconnects a variety ofdevices and provides a means for information exchange among those devices. Thereare several key distinctions between LANs and WANs:

1. The scope of the LAN is small, typically a single building or a cluster of build-ings. This difference in geographic scope leads to different technical solutions,as we shall see.

2. It is usually the case that the LAN is owned by the same organization that ownsthe attached devices. For WANs, this is less often the case, or at least a significantfraction of the network assets are not owned.This has two implications. First, caremust be taken in the choice of LAN, because there may be a substantial capitalinvestment (compared to dial-up or leased charges for WANs) for both purchase


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and maintenance. Second, the network management responsibility for a LANfalls solely on the owner.

3. The internal data rates of LANs are typically much greater than those ofWANs.

LANs come in a number of different configurations. The most common areswitched LANs and wireless LANs. The most common switched LAN is a switchedEthernet LAN, which consists of a single switch with a number of attached devices,or a number of interconnected switches. Two other prominent examples are ATMLANs, which simply use an ATM network in a local area, and Fibre Channel. Wire-less LANs use a variety of wireless transmission technologies and organizations.

Part Three covers LANs.

Wireless Networks

As was just mentioned, wireless LANs are common and are being widely used inbusiness environments. Wireless technology is also common for both wide areavoice and data networks. Wireless networks provide advantages in the areas ofmobility and ease of installation and configuration. Chapter 14 covers wirelessWANs.

Metropolitan Area Networks

As the name suggests, a metropolitan area network (MAN) occupies a middleground between LANs and WANs. Interest in MANs has come about as a result ofa recognition that the traditional point-to-point and switched network techniquesused in WANs may be inadequate for the growing needs of organizations. Whileframe relay and ATM promise to meet a wide range of high-speed needs, there is arequirement now for both private and public networks that provide high capacityat low costs over a large area. A number of approaches have been implemented,including wireless networks and metropolitan extensions to Ethernet.

The primary market for MANs is the customer that has high capacity needs ina metropolitan area. A MAN is intended to provide the required capacity at lowercost and greater efficiency than obtaining an equivalent service from the local tele-phone company.

An Example Configuration

To give some feel for the scope of concerns of Parts Two through Four, Figure 1.7illustrates some of the typical communications and network elements in usetoday. In the upper left-hand portion of the Figure 1.7, we see an individual resi-dential user connected to an Internet service provider (ISP) through some sort ofsubscriber connection. Common examples of such a connection are the publicswitched telephone network, for which the user requires a dial-up modem (e.g., a56-kbps modem); a digital subscriber line (DSL), which provides a high-speedlink over telephone lines and requires a special DSL modem; and a cable TV fa-cility, which requires a cable modem. In each case, there are separate issues con-cerning signal encoding, error control, and the internal structure of the subscribernetwork.


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Typically, an ISP will consist of a number of interconnected servers (only asingle server is shown) connected to the Internet through a high-speed link. Oneexample of such a link is a SONET (synchronous optical network) line, describedin Chapter 17. The Internet consists of a number of interconnected routers thatspan the globe. These routers forward packets of data from source to destinationthrough the Internet.

Internet

Router

RouterEthernetswitch

Informationserver

Firewallhost

High-speed link(e.g., SONET)

LAN PCsand workstations

PrivateWAN

ATMNetwork

ATMswitch

High-speedlink

Subscriberconnection

Residentialuser

Internet serviceprovider (ISP)

Figure 1.7 Networking Configuration


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The lower portion of Figure 1.7 shows a LAN implemented using a singleEthernet switch.This is a common configuration at small businesses and other smallorganizations. The LAN is connected to the Internet through a firewall host thatprovides security services. In this example the firewall connects to the Internetthrough an ATM network. There is also a router off of the LAN hooked into a pri-vate WAN, which might be a private ATM or frame relay network.

A variety of design issues, such as signal encoding and error control, relate tothe links between adjacent elements. Examples are links between routers on theInternet, between switches in the ATM network, and between a subscriber and an ISP.The internal structure of the various networks (telephone, ATM, Ethernet) raisesadditional issues.We will be occupied in Parts Two through Four with the design fea-tures suggested by Figure 1.7.

1.8 THE TRANSMISSION OF INFORMATION

The basic building block of any communications facility is the transmission line.Much of the technical detail of how information is encoded and transmitted acrossa line is of no real interest to the business manager. The manager is concernedwith whether the particular facility provides the required capacity, with acceptablereliability, at minimum cost. However, there are certain aspects of transmissiontechnology that a manager must understand to ask the right questions and makeinformed decisions.

One of the basic choices facing a business user is the transmission medium. Foruse within the business premises, this choice is generally completely up to the busi-ness. For long-distance communications, the choice is generally but not always madeby the long-distance carrier. In either case, changes in technology are rapidly changingthe mix of media used. Of particular note are fiber optic transmission and wirelesstransmission (e.g., satellite and radio).These two media are now driving the evolutionof data communications transmission.

The ever-increasing capacity of fiber optic channels is making channel capac-ity a virtually free resource. The growth of the market for optical fiber transmissionsystems since the beginning of the 1980s is without precedent. During the past10 years, the cost of fiber optic transmission has dropped by more than an order ofmagnitude, and the capacity of such systems has grown at almost as rapid a rate.Long-distance telephone communications trunks within the United States willsoon consist almost completely of fiber optic cable. Because of its high capacity andits security characteristics (fiber is difficult to tap), it is becoming increasingly usedwithin office buildings to carry the growing load of business information. However,switching is now becoming the bottleneck. This problem is causing radical changesin communication architecture, including asynchronous transfer mode (ATM)switching, highly parallel processing in switches, and integrated network manage-ment schemes.

The second medium, wireless transmission, is a result of the trend toward uni-versal personal telecommunications and universal access to communications. Thefirst concept refers to the ability of a person to identify himself or herself easily andto use conveniently any communication system in a large area (e.g., globally, over a


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continent, or in an entire country) in terms of a single account. The second refers tothe capability of using ones terminal in a wide variety of environments to connectto information services (e.g., to have a portable terminal that will work in the office,on the street, and on airplanes equally well). This revolution in personal computingobviously involves wireless communication in a fundamental way.

Despite the growth in the capacity and the drop in the cost of transmissionfacilities, transmission services remain the most costly component of a communi-cations budget for most businesses.Thus, the manager needs to be aware of techniquesthat increase the efficiency of the use of these facilities. The two major approachesto greater efficiency are multiplexing and compression. Multiplexing refers to theability of a number of devices to share a transmission facility. If each device needsthe facility only a fraction of the time, then a sharing arrangement allows the cost ofthe facility to be spread over many users. Compression, as the name indicates, involvessqueezing the data down so that a lower-capacity, cheaper transmission facility canbe used to meet a given demand. These two techniques show up separately and incombination in a number of types of communications equipment.The manager needsto understand these technologies to assess the appropriateness and cost-effectivenessof the various products on the market.

Chapters 15 and 16, in Part Five, examine the key issues and technologies inthe area of information transmission.

Transmission and Transmission Media

Information can be communicated by converting it into an electromagnetic signaland transmitting that signal over some medium, such as a twisted-pair telephone line.The most commonly used transmission media are twisted-pair lines, coaxial cable,optical fiber cable, and terrestrial and satellite microwave. The data rates that can beachieved and the rate at which errors can occur depend on the nature of the signaland the type of medium. Chapter 15 examines the significant properties of electro-magnetic signals. Chapters 9, 11, and 14 discuss the various transmission media.

Communication Techniques

The transmission of information across a transmission medium involves more thansimply inserting a signal on the medium. The technique used to encode the informa-tion into an electromagnetic signal must be determined. There are various ways inwhich the encoding can be done, and the choice affects performance and reliability.Furthermore, the successful transmission of information involves a high degree ofcooperation. The interface between a device and the transmission medium must beagreed on. Some means of controlling the flow of information and recovering fromits loss or corruption must be used. These latter functions may be performed by adata link control protocol. All these issues are examined in Chapters 16 and 17.

Transmission Efficiency

A major cost in any computer/communications facility is transmission cost. Becauseof this, it is important to maximize the amount of information that can be carriedover a given resource or, alternatively, to minimize the transmission capacity needed


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to satisfy a given information communications requirement.The standard techniquefor achieving this objective is multiplexing. Chapter 17 examines both multiplexingfrequency division, and synchronous time division.

1.9 MANAGEMENT ISSUES

Part Six concludes the book by examining key management issues related to busi-ness data communications.

Network Security

As companies rely increasingly on networks and as access by outsiders via the Internetand other links grows, the vexing question of security becomes ever more important.Companies are at risk for the disclosure of confidential information and for the un-authorized altering of corporate data. Chapters 18 and 19 look at the basic tools forachieving network security and discusses how they can be adapted to meet a com-panys needs.

Network Management

In the early years of data communications, in the 1970s, the key focus was the func-tionality and performance of the technology. The key questions were, What couldthe technology do? How fast? For how many transactions? As electronic informationsystems became part of the basic fabric of many businesses, managers discoveredthat the operation of their businesses had become dependent on their informationsystems and that the economic performance of their firms depended on the cost-effective use of the technology. That is, like any resource, information technologyhad to be managed. For example, managers of data communications are often mostconcerned today about network reliability. Many of the management functionsrequired are common to other aspects of business management, but the followingrequirements are special to information technology:

Networks have evolved from an easily controlled client/server (i.e., main-frame/dumb terminal) approach into peer-to-peer interconnections amonghighly distributed systems.

Peer-to-peer networks have grown larger and largersome have tens or hun-dreds of thousands of attached devicesso that managing, monitoring, andmaintaining them has become very complex.

In many business sectors, such as banking, retailing, and other service indus-tries, networks of computing devices constitute a critical strategic resourcethat cannot be allowed to fail.

Communications costs, meanwhile, are climbing, and there is a shortage ofskilled personnel to staff network command centers and to handle networkmanagement.

Network management must provide global visibility on corporate informa-tion flow. Techniques of centralized, remote monitoring and control provide rapid


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notification of failures and automatic invocation of recovery measures. On-the-flyanalysis of network performance and dynamic adjustment of network parametersprovide adaptation to varying cycles of business activity. Network management is acomplex discipline, particularly in a multivendor environment. The manager mustunderstand the requirements for network management and the tools and technolo-gies available to plan effectively for an automated network management strategy.

Chapters 20 and 21 focus on network management.

1.10 STANDARDS

Standards have come to play a dominant role in the information communicationsmarketplace. Virtually all vendors of products and services are committed to sup-porting international standards. Throughout this book, we describe the most impor-tant standards in use or being developed for various aspects of data communicationsand networking. Various organizations have been involved in the development orpromotion of these standards. The most important (in the current context) of theseorganizations are as follows:

Internet Society: ISOC is a professional membership society with worldwideorganizational and individual membership. It provides leadership in address-ing issues that confront the future of the Internet and is the organization homefor the groups responsible for Internet infrastructure standards, including theInternet Engineering Task Force (IETF) and the Internet Architecture Board(IAB). These organizations develop Internet standards and related specifica-tions, all of which are published as Requests for Comments (RFCs).

ITU-T: The International Telecommunication Union (ITU) is an internationalorganization within the United Nations System in which governments and theprivate sector coordinate global telecom networks and services The ITUTelecommunication Standardization Sector (ITU-T) is one of the three sectorsof the ITU. ITU-Ts mission is the production of standards covering all fields oftelecommunications. ITU-T standards are referred to as Recommendations.

ISO: The International Organization for Standardization (ISO)3 is a world-wide federation of national standards bodies from more than 140 countries,one from each country. ISO is a nongovernmental organization that promotesthe development of standardization and related activities with a view to facili-tating the international exchange of goods and services, and to developing co-operation in the spheres of intellectual, scientific, technological, and economicactivity. ISOs work results in international agreements that are published asInternational Standards.

IEEE 802: The IEEE (Institute of Electrical and Electronics Engineers) 802LAN/MAN Standards Committee develops local area network standards andmetropolitan area network standards. The most widely used standards are for

3ISO is not an acronym (in which case it would be IOS), but a word, derived from the Greek, meaningequal.


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the Ethernet family, wireless LAN, bridging, and virtual bridged LANs. Anindividual working group provides the focus for each area.

National Institute of Standards and Technology: NIST is a U.S. federal agencythat deals with measurement science, standards, and technology related to U.S.government use and to the promotion of U.S. private-sector innovation.Despite its national scope, NIST Federal Information Processing Standards(FIPS) and Special Publications (SP) have a worldwide impact.

A more detailed discussion of these organizations is contained in Appendix B.

1.11 RECOMMENDED READING AND WEB SITES

Good overview articles on convergence include [AUDI04a], [HETT03], and[MILO00]. [MILL05] and [AUDI04b] look at the business implications of evolvingtoward a convergence architecture.

[LAZA07] is a good overview of unified communications. [TARL07] makes thebusiness case for unified communications. [KERR06] compares the Microsoft andCisco approaches to unified communications, from a Cisco perspective. [TURE04]provides a detailed discussion of presence.

AUDI04a Audin, G. Architectures for Convergence. Business Communications Review,October 2004.

AUDI04b Audin, G. A Roadmap to Convergence. Business Communications Review,October 2004.

HETT03 Hettick, L. Building Blocks for Converged Applications. Business Communi-cations Review, June 2003.

KERR06 Kerravala, Z. The Impact of Microsofts Unified Communications Launch. WhitePaper, Yankee Group, August 2006.

LAZA07 Laxar, I.Unified Communications:What,Why, and How? Issue Paper, NemertesResearch, 2007.

MILL05 Miller, H.; Levine, H.; and Bates, S. Welcome to Convergence. IT Pro, May/June 2005.

MILO00 Milonas,A.Enterprise Networking for the New Millennium. Bell Labs TechnicalJournal, JanuaryMarch 2000.

TARL07 Tarleja, M.; Chandra, S.; and Tantzen, B. UC: Adding to the Bottom and TopLines Today. Business Communications Review, November 2007.

TURE04 Turek, M.The Future of Presence. Business Communications Review, May 2004.

Recommended Web sites:

IEEE Standards in Education: A wealth of information on standards, including casestudies, tutorials, news, and links to standards organizations.


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No Jitter: Oriented toward the business user, this site integrates data and voice communicationstopics well. The site focuses on unified communications, convergence, and IP communications.

ZDNet: A rich collection of material on business and information technology, including whitepapers, computer magazine articles, news, blogs, and cases studies.

asynchronous transfer mode(ATM)

circuit switchingclient/serverconvergencedata communicationsdistributed applications

frame relayimage communicationsInternetlocal area network (LAN)metropolitan area network

(MAN)packet switching

TCP/IPunified communicationsvideo communicationsvoice communicationswide area network (WAN)wireless network

1.12 KEY TERMS AND REVIEW QUESTIONS

Key Terms

Review Questions

1.1 What three kinds of basic organizational difficulties can communications technologyhelp companies overcome?

1.2 Name four types of information that are found on networks.1.3 Briefly define convergence and unified communications.1.4 How has the technology of the compact disc used in the music industry been used in

image communications?1.5 Why are the burdens on the manager greater today than in previous years when it

comes to using new technology efficiently?1.6 Why has optical fiber transmission become popular in the past few years?1.7 What types of communications can be carried by satellite transmission?1.8 Name two approaches that can be used for increasing the efficiency of transmission

services.1.9 Contrast the function of application software with that of interconnection software.

APPENDIX 1A PREFIXES FOR NUMERICAL UNITS

The bit (b) is the fundamental unit of discrete information. It represents the outcomeof one choice: 1 or 0, yes or no, on or off. One bit represents two potential outcomes.So, for example, one bit can represent the on/off state of a switch.Two bits can repre-sent four outcomes: 00, 01, 10, 11. Three bits represent eight outcomes: 000, 001, 010,011, 100, 101, 110, 111. Each time another bit is added, the numbers of outcomes double(Table 1.1). A byte (or octet, usually abbreviated as B) is the name given to 8 bits(e.g., 8 b = 1 B).The number of potential outcomes a byte represents is 2 2 2 2 2 2 2 2 28 256. Bytes are usually used in representing quantities of storagein computers. Bits are traditionally used in describing communications rates.


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In the computer science literature, the prefixes kilo, mega, and so forth areoften used on numerical units. These have two different interpretations (Table 1.2):

Data transmission: For data transmission, the prefixes used are those definedfor the International System of Units (SI), the international standard. In thisscheme, prefixes are used as a shorthand method of expressing powers of 10.For example, one kilobit per second (1 kbps) 103 bps 1000 bps.

Computer storage: The amount of data in computer memory, in a file, or amessage that is transmitted is typically measured in bytes. Because memory isindicated by binary addresses, the size of memory is expressed as powers of 2.The same prefixes are used in a way that approximates their use in the SI scheme.For example, one kilobyte (1 kB) 210 bytes 1024 bytes.

Table 1.1 Bits and Outcomes

Number of Bits (x)

Number of Outcomes (2x) Typical Use

1 2 Basic unit of information

4 16 Hexadecimal digit

7 128 IRA (International Reference Alphabet) characterwithout parity bit

8 256 Byte; character with parity bit

10 1,024 Number of bytes in a kilobyte of storage

13 8,192 Number of bits in a kilobyte of storage

16 65,536 Address size in older computers

20 1,048,576 Number of bytes in a megabyte of storage

23 8,388,608 Number of bits in a megabyte of storage

32 4.3 + 109 Common memory address size

64 1.84 + 1019 Memory address size on newer computers

Table 1.2 Numerical Prefixes

Factor

Prefix Name Prefix Symbol SI Computer Storage

tera T 1012 240

giga G 109 230 1,073,741,824mega M 106 220 1,048,576kilo k 103 210 1024milli m 103

micro 106

nano n 109


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