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c81e728d9d4c-0 | TABLE OF CONTENTS
COVER
TITLE PAGE
COPYRIGHT
DEDICATION
ABOUT THE AUTHORS
PREFACE
PURPOSE OF THIS BOOK
WHAT’S NEW IN THIS EDITION
LAB EXERCISES
ONLINE SUPPLEMENTS FOR INSTRUCTORS
E-BOOK
ACKNOWLEDGMENTS
PART ONE: INTRODUCTION
CHAPTER 1: INTRODUCTION TO DATA COMMUNICATIONS
1.1 INTRODUCTION
1.2 DATA COMMUNICATIONS NETWORKS
1.3 NETWORK MODELS
1.4 NETWORK STANDARDS
1.5 FUTURE TRENDS
1.6 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 1A
HANDS-ON ACTIVITY 1B
PART TWO: FUNDAMENTAL CONCEPTS
CHAPTER 2: APPLICATION LAYER
2.1 INTRODUCTION
2.2 APPLICATION ARCHITECTURES
2.3 WORLD WIDE WEB
2.4 ELECTRONIC MAIL
2.5 OTHER APPLICATIONS
2.6 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES | Page 2 | Chapter 1 |
37693cfc7480-0 | HANDS-ON ACTIVITY 2A
HANDS-ON ACTIVITY 2B
CHAPTER 3: PHYSICAL LAYER
3.1 INTRODUCTION
3.2 CIRCUITS
3.3 COMMUNICATION MEDIA
3.4 DIGITAL TRANSMISSION OF DIGITAL DATA
3.5 ANALOG TRANSMISSION OF DIGITAL DATA
3.6 DIGITAL TRANSMISSION OF ANALOG DATA
3.7 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 3A
HANDS-ON ACTIVITY 3B
HANDS-ON ACTIVITY 3C
CHAPTER 4: DATA LINK LAYER
4.1 INTRODUCTION
4.2 MEDIA ACCESS CONTROL
4.3 ERROR CONTROL
4.4 DATA LINK PROTOCOLS
4.5 TRANSMISSION EFFICIENCY
4.6 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 4A
CHAPTER 5: NETWORK AND TRANSPORT LAYERS
5.1 INTRODUCTION
5.2 TRANSPORT AND NETWORK LAYER PROTOCOLS
5.3 TRANSPORT LAYER FUNCTIONS
5.4 ADDRESSING
5.5 ROUTING
5.6 TCP/IP EXAMPLE
5.7 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS | Page 3 | Chapter 3 |
289dff07669d-0 | EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 5A
HANDS-ON ACTIVITY 5B
HANDS-ON ACTIVITY 5C
HANDS-ON ACTIVITY 5D
HANDS-ON ACTIVITY 5E
HANDS-ON ACTIVITY 5F
PART THREE: NETWORK TECHNOLOGIES
CHAPTER 6: NETWORK DESIGN
6.1 INTRODUCTION
6.2 NEEDS ANALYSIS
6.3 TECHNOLOGY DESIGN
6.4 COST ASSESSMENT
6.5 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 6A
CHAPTER 7: WIRED AND WIRELESS LOCAL AREA NETWORKS
7.1 INTRODUCTION
7.2 LAN COMPONENTS
7.3 WIRED ETHERNET
7.4 WIRELESS ETHERNET
7.5 THE BEST PRACTICE LAN DESIGN
7.6 IMPROVING LAN PERFORMANCE
7.7 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 7A
HANDS-ON ACTIVITY 7B
HANDS-ON ACTIVITY 7C
CHAPTER 8: BACKBONE NETWORKS
8.1 INTRODUCTION
8.2 SWITCHED BACKBONES
8.3 ROUTED BACKBONES | Page 4 | Chapter 6 |
81b073de9370-0 | 8.4 VIRTUAL LANS
8.5 THE BEST PRACTICE BACKBONE DESIGN
8.6 IMPROVING BACKBONE PERFORMANCE
8.7 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 8A
HANDS-ON ACTIVITY 8B
CHAPTER 9: WIDE AREA NETWORKS
9.1 INTRODUCTION
9.2 DEDICATED-CIRCUIT NETWORKS
9.3 PACKET-SWITCHED NETWORKS
9.4 VIRTUAL PRIVATE NETWORKS
9.5 THE BEST PRACTICE WAN DESIGN
9.6 IMPROVING WAN PERFORMANCE
9.7 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 9A
HANDS-ON ACTIVITY 9B
HANDS-ON ACTIVITY 9C
HANDS-ON ACTIVITY 9D
CHAPTER 10: THE INTERNET
10.1 INTRODUCTION
10.2 HOW THE INTERNET WORKS
10.3 INTERNET ACCESS TECHNOLOGIES
10.4 THE FUTURE OF THE INTERNET
10.5 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 10A
HANDS-ON ACTIVITY 10B | Page 5 | Chapter 9 |
adcaec3805aa-0 | HANDS-ON ACTIVITY 10C
PART FOUR: NETWORK MANAGEMENT
CHAPTER 11: NETWORK SECURITY
11.1 INTRODUCTION
11.2 RISK ASSESSMENT
11.3 ENSURING BUSINESS CONTINUITY
11.4 INTRUSION PREVENTION
11.5 BEST PRACTICE RECOMMENDATIONS
11.6 IMPLICATIONS FOR YOUR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 11A
HANDS-ON ACTIVITY 11B
HANDS-ON ACTIVITY 11C
HANDS-ON ACTIVITY 11D
CHAPTER 12: NETWORK MANAGEMENT
12.1 INTRODUCTION
12.2 DESIGNING FOR NETWORK PERFORMANCE
12.3 CONFIGURATION MANAGEMENT
12.4 PERFORMANCE AND FAULT MANAGEMENT
12.5 END USER SUPPORT
12.6 COST MANAGEMENT
12.7 IMPLICATIONS FOR CYBER SECURITY
SUMMARY
KEY TERMS
QUESTIONS
EXERCISES
MINICASES
TECH UPDATES
HANDS-ON ACTIVITY 12A
HANDS-ON ACTIVITY 12B
HANDS-ON ACTIVITY 12C
INDEX
END USER LICENSE AGREEMENT
List of Illustrations
Chapter 1
FIGURE 1-1 What is MIS?
FIGURE 1-2 Example of a local area network (LAN) | Page 6 | Chapter 11 |
508df4cb2f4d-0 | FIGURE 1-3 Network architecture components
FIGURE 1-4 Network models. OSI = Open Systems Interconnection Reference
FIGURE 1-5 Message transmission using layers. IP = Internet Protocol; HTTP =...
FIGURE 1-6 Some common data communications standards. HTML = Hypertext Marku...
FIGURE 1-7 A security robot on the IOT
FIGURE 1-8 One server farm with more than 1,000 servers
FIGURE 1-9 Wireshark capture
Chapter 2
FIGURE 2-1 Host-based architecture
FIGURE 2-2 Client-based architecture
FIGURE 2-3 Two-tier thick client client–server architecture
FIGURE 2-4 Three-tier thin client client–server architecture
FIGURE 2-5 The n-tier thin client client–server architecture
FIGURE 2-6 The typical two-tier thin-client architecture of the Web
FIGURE 2-7 Cloud architecture models compared to thin client–server architec...
FIGURE 2-8 One row of a server farm at Indiana University
FIGURE 2-9 Peer-to-peer architecture
FIGURE 2-10 How the Web works
FIGURE 2-11 An example of a request from a Web browser to a Web server using...
FIGURE 2-12 An example of a response from a Web server to a Web browser usin...
FIGURE 2-13 How SMTP (Simple Mail Transfer Protocol) email works. IMAP = Int...
FIGURE 2-14 Inside the Web. HTTP = Hypertext Transfer Protocol; IMAP = I...
FIGURE 2-15 An example of an email message using the SMTP (Simple Mail Trans...
FIGURE 2-16 A Cisco telepresence system
FIGURE 2-17 Desktop videoconferencing | Page 7 | Chapter 11 |
95525872e442-1 | FIGURE 2-17 Desktop videoconferencing
FIGURE 2-18 Viewing the SMTP packet header
FIGURE 2-19 Viewing the source of the SMTP packet
FIGURE 2-20 SMTP packets in Wireshark
FIGURE 2-21 POP packets in Wireshark
Chapter 3
FIGURE 3-1 Point-to-point circuit
FIGURE 3-2 Multipoint circuit
FIGURE 3-3 Simplex, half-duplex, and full-duplex transmissions
FIGURE 3-4 Multiplexed circuit
FIGURE 3-5 Category 5e twisted-pair wire
FIGURE 3-6 Coaxial cables. Thinnet and Thicknet Ethernet cables (right)—(1) ...
FIGURE 3-7 Fiber-optic cable
FIGURE 3-8 A microwave tower. The round antennas are microwave antennas and ...
FIGURE 3-9 Satellites in operation | Page 7 | Chapter 11 |
bb0f169a5947-0 | FIGURE 3-10 Binary numbers used to represent different characters using ASCI...
FIGURE 3-11 Parallel transmission of an 8-bit code
FIGURE 3-12 Serial transmission of an 8-bit code
FIGURE 3-13 Unipolar, bipolar, and Manchester signals (digital)
FIGURE 3-14 Sound wave
FIGURE 3-15 Amplitude modulation
FIGURE 3-16 Frequency modulation
FIGURE 3-17 Phase modulation
FIGURE 3-18 Two-bit amplitude modulation
FIGURE 3-19 Pulse amplitude modulation (PAM)
FIGURE 3-20 Pulse amplitude modulation (PAM)
FIGURE 3-21 VoIP phone
FIGURE 3-22 Cat 5 cable
FIGURE 3-23 Inside a Cat 5 cable
FIGURE 3-24 Pin connection for Cat 5 at the computer end
FIGURE 3-25 Tools and materials for making a patch cable
Chapter 4
FIGURE 4-1 Relative response times
FIGURE 4-2 Sources of errors and ways to minimize them
FIGURE 4-3 Using parity for error detection
FIGURE 4-4 Hamming code for forward error correction
FIGURE 4-5 Protocol summary
FIGURE 4-6 Asynchronous transmission. ASCII = United States of America Stand...
FIGURE 4-7 SDLC (synchronous data link control) frame layout
FIGURE 4-8a Ethernet 802.3ac frame layout
FIGURE 4-8b Ethernet II frame layout
FIGURE 4-9 PPP frame layout
FIGURE 4-10 Frame size effects on throughput
FIGURE 4-11 Capturing packets with Wireshark
FIGURE 4-12 Analyzing packets with Wireshark
Chapter 5 | Page 8 | Chapter 11 |
6c4628b734cd-1 | FIGURE 4-12 Analyzing packets with Wireshark
Chapter 5
FIGURE 5-1 Message transmission using layers. SMTP = Simple Mail Transfer Pr...
FIGURE 5-2 Transmission Control Protocol (TCP) segment. ACK = Acknowledgment...
FIGURE 5-3 Internet Protocol (IP) packet (version 4). CRC = Cyclical Redunda...
FIGURE 5-4 Internet Protocol (IP) packet (version 6)
FIGURE 5-5 Linking to application layer services
FIGURE 5-6 Stop-and-wait ARQ (Automatic Repeat reQuest). ACK = Acknowledgmen...
FIGURE 5-7 Continuous ARQ (Automatic Repeat reQuest). ACK = Acknowledgment; ...
FIGURE 5-8 Types of addresses | Page 8 | Chapter 11 |
c68f3a4055bc-0 | FIGURE 5-9 IPv4 public address space
FIGURE 5-10 IPv4 private address space
FIGURE 5-11 Address subnets
FIGURE 5-12 How the DNS system works?
FIGURE 5-13 A small corporate network
FIGURE 5-14 Sample routing tables
FIGURE 5-15 Routing on the Internet with Border Gateway Protocol (BGP), Open...
FIGURE 5-16 Anatomy of a router
FIGURE 5-17 Example Transmission Control Protocol/Internet Protocol (TCP/IP)...
FIGURE 5-18 TCP/IP configuration information
FIGURE 5-19 Packet nesting. HTTP = Hypertext Transfer Protocol; IP = Interne...
FIGURE 5-20 How messages move through the network layers.
FIGURE 5-25 DNS cache
FIGURE 5-27 DNS capture
Chapter 6
FIGURE 6-1 Network architecture components
FIGURE 6-2 Network design
FIGURE 6-3 The cyclical nature of network design
FIGURE 6-4 Sample needs assessment logical network design for a single build...
FIGURE 6-5 Physical network design for a single building
FIGURE 6-7 SmartDraw software
Chapter 7
FIGURE 7-1 Local area network components
FIGURE 7-2 LAN switches
FIGURE 7-3 Wireless access points
FIGURE 7-4 Ethernet topology using hubs
FIGURE 7-5 Ethernet topology using switches
FIGURE 7-6 Types of Ethernet
FIGURE 7-7 A wireless Ethernet frame
FIGURE 7-8 Design parameters for Wi-Fi access point range
FIGURE 7-9 A Wi-Fi design (the numbers indicate the channel numbers)
FIGURE 7-10 A Wi-Fi design in the three dimensions (the numbers indicate the... | Page 9 | Chapter 11 |
ac3b73049879-1 | FIGURE 7-11 The data center at Indiana University
FIGURE 7-12 Network with load balancer
FIGURE 7-13 The storage area network (SAN) at the Kelley School of Business ...
FIGURE 7-14 SOHO LAN designs
FIGURE 7-15 Powerline adapter
FIGURE 7-17 TracePlus
FIGURE 7-18 WLANs in a neighborhood in Bloomington, Indiana | Page 9 | Chapter 11 |
59c299cb0aee-0 | FIGURE 7-19 WLANs at Indiana University
FIGURE 7-20 Plans for Floors 3–8 of Apollo Residence
FIGURE 7-21 LAN equipment price list
Chapter 8
FIGURE 8-1 Rack-mounted switched backbone network architecture
FIGURE 8-2 An MDF with rack-mounted equipment. A layer 2 chassis switch with...
FIGURE 8-3 MDF network diagram. MDF = main distribution facility
FIGURE 8-4 Switched backbones at Indiana University
FIGURE 8-5 Routed backbone architecture
FIGURE 8-6 VLAN-based backbone network architecture
FIGURE 8-7 Multiswitch VLAN-based backbone network design
FIGURE 8-8 The best practice network design
FIGURE 8-10 Facility map of the Western Trucking headquarters
FIGURE 8-11 Computers and devices at Alan's house
FIGURE 8-12 Network map for Alan's house
FIGURE 8-13 System information for 192.168.1.188
FIGURE 8-14 Apollo Residence first floor
FIGURE 8-15 Apollo Residence second floor
FIGURE 8-16 Equipment price list
Chapter 9
FIGURE 9-1 Dedicated-circuit services. CSU = channel service unit; DSU = dat...
FIGURE 9-2 Ring-based design
FIGURE 9-3 Star-based design
FIGURE 9-4 Mesh design
FIGURE 9-5 T-carrier services
FIGURE 9-6 SONET and SDH services. OC = optical carrier (level); SDH = synch...
FIGURE 9-7 Packet-switched services. PAD = packet assembly/disassembly devic...
FIGURE 9-8 Virtual private network (VPN) services
FIGURE 9-9 A virtual private network (VPN) | Page 10 | Chapter 11 |
729c70f33509-1 | FIGURE 9-9 A virtual private network (VPN)
FIGURE 9-10 Using VPN software. Shaded area depicts encrypted packets
FIGURE 9-11 WAN services
FIGURE 9-14 100 Gbps network for a U.S. Internet service provider
FIGURE 9-15 Starting Wireshark
FIGURE 9-16 Viewing encrypted packets
FIGURE 9-17 Packets that enter the VPN tunnel
FIGURE 9-18 Tracert without a VPN
FIGURE 9-19 Tracert with a VPN
Chapter 10
FIGURE 10-1 The Internet is a lot like the universe—many independent systems... | Page 10 | Chapter 11 |
c8c7bdfbbab7-0 | FIGURE 10-2 Basic Internet architecture. ISP = Internet service provider; IX...
FIGURE 10-3 A typical Internet backbone of a major ISP
FIGURE 10-4 DSL architecture. DSL = digital subscriber line; ISP = Internet ...
FIGURE 10-5 Some typical digital subscriber line data rates
FIGURE 10-6 Cable modem architecture. ISP = Internet service provider; POP =...
FIGURE 10-7 Internet2 network map
FIGURE 10-9 Visual trace route
FIGURE 10-10 Internet traffic reports
FIGURE 10-11 A speed test on my computer in Indiana
Chapter 11
FIGURE 11-4 Likelihood of a threat
FIGURE 11-5 Threat scenario for theft of customer information
FIGURE 11-6 Threat scenario for destruction of customer information by a tor...
FIGURE 11-7 A distributed denial-of-service attack
FIGURE 11-8 Traffic analysis reduces the impact of denial-of-service attacks...
FIGURE 11-9 Security cables protecting computers
FIGURE 11-12 Using a firewall to protect networks
FIGURE 11-13 How packet-level firewalls work
FIGURE 11-14 A typical network design using firewalls
FIGURE 11-15 One menu on the control console for the Optix Pro Trojan
FIGURE 11-16 Secure transmission with public key encryption
FIGURE 11-17 Authenticated and secure transmission with public key encryptio...
FIGURE 11-18 Two-factor authentication with the Duo app for mobile phones
FIGURE 11-19 Intrusion prevention system (IPS). DMZ = demilitarized zone; DN...
FIGURE 11-20 Commonly used security controls
FIGURE 11-21 BitLocker
FIGURE 11-22 Selecting the encryption mode
FIGURE 11-23 Starting the encryption | Page 11 | Chapter 11 |
26d79f8d1b5b-1 | FIGURE 11-23 Starting the encryption
FIGURE 11-24 System Preferences for a Mac
FIGURE 11-25 Searching system preferences
FIGURE 11-26 Security & Privacy: FileVault
FIGURE 11-27 PGP key generator
FIGURE 11-28 PGP encryption
FIGURE 11-29 PGP decryption
FIGURE 11-30 Selecting a recipient of an encrypted message
FIGURE 11-31 Security hardware, software, and services
Chapter 12
FIGURE 12-1 Device management software used on Indiana University’s core bac...
FIGURE 12-2 Network management with Simple Network Management Protocol (SNMP... | Page 11 | Chapter 11 |
617332afd17b-0 | FIGURE 12-3 Network with load balancer
FIGURE 12-4 Capacity management software
FIGURE 12-5 Network with content engine
FIGURE 12-6 Network with content delivery
FIGURE 12-7 Network configuration diagram
FIGURE 12-8 Part of the Network Operations Center at Indiana University
FIGURE 12-9 Network traffic versus network management budgets
FIGURE 12-11 Network management personnel costs
FIGURE 12-13 Total cost of ownership (per client computer per year) for a Mi...
FIGURE 12-14 SolarWinds network management software, used with permission
FIGURE 12-15 SolarWinds network management software, used with permission
FIGURE 12-16 SolarWinds network management software, used with permission
FIGURE 12-17 Equipment list | Page 12 | Chapter 11 |
d7c4e61be700-0 | Business Data Communications and Networking
Fourteenth Edition
Jerry FitzGerald
Jerry FitzGerald & Associates
Alan Dennis
Indiana University
Alexandra Durcikova
University of Oklahoma | Page 13 | Chapter 11 |
5ea438bb2205-0 | VP AND EDITORIAL DIRECTOR
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COVER PHOTO CREDIT
© Photographer is my life./Getty Images
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ISBN: 978-1-119-70284-9 (PBK)
ISBN: 978-1-119-71365-4 (EVALC)
Library of Congress Cataloging-in-Publication Data:
Names: FitzGerald, Jerry, 1936- author. | Dennis, Alan, author. | Durcikova, Alexandra, author.
Title: Business data communications and networking / Jerry FitzGerald, Alan Dennis, Alexandra Durcikova.
Description: Fourteenth edition. | Hoboken, NJ : Wiley, [2021] | Includes index.
Identifiers: LCCN 2020028461 (print) | LCCN 2020028462 (ebook) | ISBN 9781119702849 (paperback) | ISBN 9781119713661 (adobe pdf) | | Page 14 | Chapter 11 |
ea28d914bcc6-2 | ISBN 9781119702665 (epub)
Subjects: LCSH: Data transmission systems. | Computer networks. | Office practice–Automation.
Classification: LCC TK5105 .F577 2021 (print) | LCC TK5105 (ebook) | DDC 004.6–dc23
LC record available at https://lccn.loc.gov/2020028461
LC ebook record available at https://lccn.loc.gov/2020028462
The inside back cover will contain printing identification and country of origin if omitted from this page. In addition, if the ISBN on the back
cover differs from the ISBN on this page, the one on the back cover is correct. | Page 14 | Chapter 11 |
2ede479f4a85-0 | To my son Alec,
Alan
To all curious minds who want to know how today’s modern world works.
Alexandra | Page 15 | Chapter 11 |
4bbed9fe1c0c-0 | ABOUT THE AUTHORS
Alan Dennis is a Fellow of the Association for Information Systems and a professor of information
systems in the Kelley School of Business at Indiana University. He holds the John T. Chambers Chair in
Internet Systems, which was established to honor John Chambers, president and chief executive officer of
Cisco Systems, the worldwide leader of networking technologies for the Internet.
Prior to joining Indiana University, Alan spent nine years as a professor at the University of Georgia,
where he won the Richard B. Russell Award for Excellence in Undergraduate Teaching. He has a
bachelor’s degree in Computer Science from Acadia University in Nova Scotia, Canada, and an MBA from
Queen’s University in Ontario, Canada. His PhD in management of information systems is from the
University of Arizona. Prior to entering the Arizona doctoral program, he spent three years on the faculty
of the Queen’s School of Business.
Alan has extensive experience in the development and application of groupware and Internet technologies
and co-founded Courseload, an electronic textbook company whose goal is to improve learning and
reduce the cost of textbooks. He has won many awards for theoretical and applied research and has
published more than 150 business and research articles, including those in Management Science, MIS
Quarterly, Information Systems Research, Academy of Management Journal, Organization Behavior
and Human Decision Making, Journal of Applied Psychology, Communications of the ACM, and IEEE
Transactions of Systems, Man, and Cybernetics. His first book was Getting Started with
Microcomputers, published in 1986. Alan is also an author of two systems analysis and design books
published by Wiley. He is the cochair of the Internet Technologies Track of the Hawaii International
Conference on System Sciences. He has served as a consultant to BellSouth, Boeing, IBM, Hughes Missile
Systems, the U.S. Department of Defense, and the Australian Army. | Page 16 | Chapter 11 |
d3c2826a5fd3-1 | Systems, the U.S. Department of Defense, and the Australian Army.
Alexandra Durcikova is an Associate Professor at the Price College of Business, University of Oklahoma.
Alexandra has a PhD in management information systems from the University of Pittsburgh. She has
earned an MSc degree in solid state physics from Comenius University, Bratislava, worked as an
experimental physics researcher in the area of superconductivity and as an instructor of executive MBA
students prior to pursuing her PhD. Alexandra’s research interests include knowledge management and
knowledge management systems, the role of organizational climate in the use of knowledge management
systems, knowledge management system characteristics, governance mechanisms in the use of knowledge
management systems, and human compliance with security policy and characteristics of successful
phishing attempts within the area of network security. Her research appears in Information Systems
Research, MIS Quarterly, Journal of Management Information Systems, Information Systems Journal,
Journal of Organizational and End User Computing, International Journal of Human–Computer
Studies, International Journal of Human–Computer Studies, and Communications of the ACM.
Alexandra has been teaching business data communications to both undergraduate and graduate students
for several years. In addition, she has been teaching classes on information technology strategy and most
recently won the Dean’s Award for Undergraduate Teaching Excellence while teaching at the University of
Arizona.
Dr. Jerry FitzGerald wrote the early editions of this book in the 1980s. At the time, he was the principal in
Jerry FitzGerald & Associates, a firm he started in 1977. | Page 16 | Chapter 11 |
75ca7225c221-0 | PREFACE
The field of data communications has grown faster and become more important than computer
processing itself. Though they go hand in hand, the ability to communicate and connect with other
computers and mobile devices is what makes or breaks a business today. There are three trends that
support this notion. First, the wireless LAN and Bring-Your-Own-Device (BYOD) allow us to stay
connected not only with the workplace but also with family and friends. Second, computers and networks
are becoming an essential part of not only computers but also devices we use for other purpose, such as
home appliances. This Internet of Things allows you to set the thermostat in your home from your mobile
phone, can help you cook a dinner, or eventually can allow you to drive to work without ever touching the
steering wheel. Lastly, we see that a lot of life is moving online. At first this started with games, but
education, politics, and activism followed swiftly. Therefore, understanding how networks work; how they
should be set up to support scalability, mobility, and security; and how to manage them is of utmost
importance to any business. This need will call not only for engineers who deeply understand the technical
aspects of networks but also for highly social individuals who embrace technology in creative ways to
allow business to achieve a competitive edge through utilizing this technology. So the call is for you who
are reading this book—you are at the right place at the right time!
PURPOSE OF THIS BOOK
Our goal is to combine the fundamental concepts of data communications and networking with practical
applications. Although technologies and applications change rapidly, the fundamental concepts evolve
much more slowly; they provide the foundation from which new technologies and applications can be
understood, evaluated, and compared.
This book has two intended audiences. First and foremost, it is a university textbook. Each chapter | Page 17 | Chapter 11 |
1a77dd76cf0c-1 | This book has two intended audiences. First and foremost, it is a university textbook. Each chapter
introduces, describes, and then summarizes fundamental concepts and applications. Management Focus
boxes highlight key issues and describe how networks are actually being used today. Technical Focus
boxes highlight key technical issues and provide additional detail. Mini case studies at the end of each
chapter provide the opportunity to apply these technical and management concepts. Hands-on exercises
help to reinforce the concepts introduced in the chapter. Moreover, the text is accompanied by a detailed
Instructor’s Manual that provides additional background information, teaching tips, and sources of
material for student exercises, assignments, and exams. Finally, our Web page contains supplements to
our book.
Second, this book is intended for the professional who works in data communications and networking.
The book has many detailed descriptions of the technical aspects of communications from a business
perspective. Moreover, managerial, technical, and sales personnel can use this book to gain a better
understanding of fundamental concepts and trade-offs not presented in technical books or product
summaries.
WHAT’S NEW IN THIS EDITION
This edition maintains the three main themes of the prior edition, namely, (1) how networks work
(Chapters 1–5); (2) network technologies (Chapters 6–10); and (3) network security and management
(Chapters 11 and 12). In the new edition, we removed older technologies and replaced them with new
ones. Accordingly, new hands-on activities and questions have been added at the end of each chapter that
guide students in understanding how to select technologies to build a network that would support an
organization’s business needs. In addition to this overarching change, the thirteenth edition has three
major changes from the twelfth edition:
First, at the end of each chapter, in addition to providing key implications for cyber security that arise | Page 17 | Chapter 11 |
71dc7c223102-2 | from the topics discussed in the chapter, we also introduce Tech Updates. We draw implications that focus
on improving the management of networks and information systems as well as implications for cyber
security of an individual and an organization. Tech Updates offer two cybersecurity topics per chapter that | Page 17 | Chapter 11 |
5049ab7b3718-0 | help students to expand their knowledge of cybersecurity and see how it relates to the material covered in
the chapter.
Second, we have revised Chapter 2 to use a new framework for application architecture that includes
application services.
Third, we have revised the WAN chapter (Chapter 9) to include the rapidly changing WAN environment
and Software Defined Networking.
LAB EXERCISES
www.wiley.com/go/fitzgerald/datacommunications14e
This edition includes an online lab manual with many hands-on exercises that can be used in a
networking lab. These exercises include configuring servers and other additional practical topics.
ONLINE SUPPLEMENTS FOR INSTRUCTORS
www.wiley.com/go/fitzgerald/datacommunications14e
Instructor’s supplements comprise an Instructor’s Manual that includes teaching tips, war stories, and
answers to end-of-chapter questions; a Test Bank that includes true-false, multiple choice, short answer,
and essay test questions for each chapter; and Lecture Slides in PowerPoint for classroom presentations.
All are available on the instructor’s book companion site.
E-BOOK
Wiley E-Text: Powered by VitalSource offers students continuing access to materials for their
course. Your students can access content on a mobile device, online from any Internet-connected
computer, or by a computer via download. With dynamic features built into this e-text, students can
search across content, highlight, and take notes that they can share with teachers and classmates. Readers
will also have access to interactive images and embedded podcasts. Visit
www.wiley.com/go/fitzgerald/datacommunications14e for more information.
ACKNOWLEDGMENTS
Our thanks to the many people who helped in preparing this edition. Specifically, we want to thank the
staff at John Wiley & Sons for their support.
Alan Dennis
Bloomington, Indiana
www.kelley.indiana.edu/ardennis | Page 18 | Chapter 11 |
0e76b4a4b586-1 | Bloomington, Indiana
www.kelley.indiana.edu/ardennis
Alexandra Durcikova
Norman, Oklahoma
http://www.ou.edu/price/mis/people/alexandra_durcikova.html | Page 18 | Chapter 11 |
6150ca05e1f0-0 | PART ONE INTRODUCTION | Page 19 | Chapter 11 |
923d0b06c1d8-0 | CHAPTER 1
INTRODUCTION TO DATA COMMUNICATIONS
This chapter introduces the basic concepts of data communications. It describes why it is important to
study data communications, how data communications fit within the discipline of Management
Information Systems (MIS), and introduces you to the three fundamental questions that this book
answers. Next, it discusses the basic types and components of a data communications network. Also, it
examines the importance of a network model based on layers. Finally, it describes the three key trends in
the future of networking.
OBJECTIVES
Be aware of the three fundamental questions this book answers
Be aware of the applications of data communications networks
Be aware of how data communications fit within the discipline of MIS
Be familiar with the major components of and types of networks
Understand the role of network layers
Be familiar with the role of network standards
Be aware of cyber security issues
Be aware of three key trends in communications and networking
OUTLINE
1.1 Introduction
1.2 Data Communications Networks
1.2.1 Components of a Network
1.2.2 Types of Networks
1.3 Network Models
1.3.1 Open Systems Interconnection Reference Model
1.3.2 Internet Model
1.3.3 Message Transmission Using Layers
1.4 Network Standards
1.4.1 The Importance of Standards
1.4.2 The Standards-Making Process
1.4.3 Common Standards
1.5 Future Trends
1.5.1 Wireless LAN and BYOD
1.5.2 The Internet of Things
1.5.3 Massively Online
1.6 Implications for Cyber Security
Summary | Page 20 | Chapter 11 |
04c54b563141-0 | 1.1 INTRODUCTION
What Internet connection should you use? Cable modem or DSL (formally called Digital Subscriber Line)?
Cable modems are supposedly faster than DSL, providing data speeds of 50 Mbps to DSL’s 1.5–25 Mbps
(million bits per second). One cable company used a tortoise to represent DSL in advertisements. So
which is faster? We’ll give you a hint. Which won the race in the fable, the tortoise or the hare? By the time
you finish this book, you’ll understand which is faster and why, as well as why choosing the right company
as your Internet service provider (ISP) is probably more important than choosing the right
technology.
Over the past decade or so, it has become clear that the world has changed forever due to the third and
fourth Industrial Revolutions. The first Industrial Revolution revolutionized the way people worked at the
end of the 18th century by introducing machines, steam and water power. New companies and industries
emerged, and old ones died off. The second Industrial Revolution in the late 19th century is known for
starting mass production, electricity, and the telephone. The third Industrial Revolution, in the second
half of the 20th century, is revolutionizing the way people work through electronics and information
technology (IT) to automate production.
The fourth Industrial Revolution is currently underway. It builds on the technological advances of the
third Industrial Revolution, but the way it merges the physical, digital, and biological worlds is
unprecedented. It is deeply rooted in the Internet and digitization. Digitization enables us to build a world
where interactions can happen in real time across different continents (think about email, instant
messaging, and exchange of data between different devices). These interactions are possible because of | Page 21 | Chapter 11 |
de6c8e705aa4-1 | messaging, and exchange of data between different devices). These interactions are possible because of
technologies such as cloud, big data, big data analytics, and the Internet of Things. But the technology that
enables all these technologies to communicate is the high-speed data communication network, that is, the
Internet.
Today, the value of a high-speed data communications network is that it brings people together in a way
never before possible. In the 1800s, it took several weeks for a message to reach North America by ship
from England. By the 1900s, it could be transmitted within an hour. Today, it can be transmitted in
seconds. Collapsing the information lag to Internet speeds means that people can communicate and
access information anywhere in the world regardless of their physical location. In fact, today’s problem is
that we cannot handle the quantities of information we receive.
Data communications and networking is a truly global area of study, both because the technology enables
global communication and because new technologies and applications often emerge from a variety of
countries and spread rapidly around the world. The World Wide Web, for example, was born in a Swiss
research lab, was nurtured through its first years primarily by European universities and exploded into
mainstream popular culture because of a development at an American research lab.
One of the problems in studying a global phenomenon lies in explaining the different political and
regulatory issues that have evolved and currently exist in different parts of the world. Rather than attempt
to explain the different paths taken by different countries, we have chosen simplicity instead. Historically,
the majority of readers of previous editions of this book have come from North America. Therefore,
although we retain a global focus on technology and its business implications, we focus mostly on North
America.
This book answers three fundamental questions. | Page 21 | Chapter 11 |
fdb6a1f8ed7d-2 | America.
This book answers three fundamental questions.
First, how does the Internet work? When you access a website using your computer, laptop, iPad, or
smartphone, what happens so that the page opens in your Web browser? This is the focus in Chapters 1–5.
The short answer is that the software on your computer (or any device) creates a message composed in
different software languages (HTTP, TCP/IP, and Ethernet are common) that requests the page you
clicked. This message is then broken up into a series of smaller parts that we call packets. Each packet is
transmitted to the nearest router, which is a special-purpose computer whose primary job is to find the
best route for these packets to their final destination. The packets move from router to router over the
Internet until they reach the Web server, which puts the packets back together into the same message that
your computer created. The Web server reads your request and then sends the page back to you in the
same way—by composing a message using HTTP, TCP/IP, and Ethernet and then sending it as a series of
smaller packets back through the Internet that the software on your computer puts together into the page | Page 21 | Chapter 11 |
f534a39fb39a-0 | you requested. You might have heard a news story that the U.S. or Chinese government can read your
email or see what websites you’re visiting. A more shocking truth is that the person sitting next you at a
coffee shop might be doing exactly the same thing—reading all the packets that come from or go to your
laptop. How is this possible, you ask? After finishing Chapter 5, you will know exactly how this is possible.
Second, how do I design a network? This is the focus of Chapters 6–10. We often think about networks in
four layers. The first layer is the Local Area Network, or the LAN (either wired or wireless), which enables
users like you and me to access the network. The second is the backbone network that connects the
different LANs within a building. The third is the core network that connects different buildings on a
company’s campus. The final layer is connections we have to the other campuses within the organization
and to the Internet. Each of these layers has slightly different concerns, so the way we design networks for
them and the technologies we use are slightly different. Although this describes the standard for building
corporate networks, you will have a much better understanding of how your wireless router at home
works. Perhaps more importantly, you’ll learn why buying the newest and fastest wireless router for your
house or apartment is probably not a good way to spend your money.
Finally, how do I manage my network to make sure it is secure, provides good performance, and doesn’t
cost too much? This is the focus of Chapters 11 and 12. Would it surprise you to learn that most companies
spend between $1,500 and $3,500 per computer per year on network management and security? Yup, we
spend way more on network management and security each year than we spend to buy the computer in | Page 22 | Chapter 11 |
3cc44403b6ef-1 | spend way more on network management and security each year than we spend to buy the computer in
the first place. And that’s for well-run networks; poorly run networks cost a lot more. Many people think
network security is a technical problem, and, to some extent, it is. However, the things people do and
don’t do cause more security risks than not having the latest technology. According to Symantec, one of
the leading companies that sell antivirus software, about half of all security threats are not prevented by
their software. These threats are called targeted attacks, such as phishing attacks (which are emails that
look real but instead take you to fake websites) or ransomware (software apps that appear to be useful but
actually lock your computer and demand a payment to unlock it). Therefore, network management is as
much a people management issue as it is a technology management issue.
Most readers of this book will be taking classes towards their degree in management information systems
(MIS) or a closely related field. How does this book relate to what MIS? Let us explain!
MIS begins with an IT strategy—a plan for buying and/or building IT to help the organization accomplish
its goals. For most companies, this means increasing revenues and/or decreasing costs. Companies must
deploy the right IT to support their business operations. IT has four core capabilities within organizational
settings:
1. Storing and Retrieving Data—Just like humans live in houses, data created by businesses and
societies must live somewhere. The “house” for data is a database. There are many different kinds of
databases, just like many different kinds of houses. The most frequently used database in
organizations is an SQL database.
2. Analyzing and Visualizing Data—Managers need to able to make decisions regarding their business,
such as: What is our bestselling product? Which regions bring in the most revenue? Which regions | Page 22 | Chapter 11 |
5ab3bb1fc6be-2 | such as: What is our bestselling product? Which regions bring in the most revenue? Which regions
are losing money? These decisions are made using the data stored in databases. Data is retrieved
from a database and imported to a software like Excel, Tableau, or PowerBI so that these business
questions can be answered using a variety of techniques (e.g., aggregation, conditional aggregation,
and charting).
3. Automating Data Operations—Many business operations are repeated over and over again, such as
calculating the total amount of a items bought at a local store or an e-commerce web site, applying
any discounts, and determining appropriate taxes. To automate these kinds of every day transactions
on data, we have a wide variety of IT we can buy or build using a variety of programming languages.
4. Protecting Data—The first three core capabilities are designed to make it easy to store and access
data. However, this means that an intruder or malicious employee could also access the data.
Therefore, organizations must spend resources to protect their data and ensuring the confidentiality,
integrity, and availability of the data. We will discuss security capability in Chapter 11. | Page 22 | Chapter 11 |
50751c6b5812-0 | FIGURE 1-1 What is MIS?
In order for the IT strategy to implement the core capabilities, data communications and networking
infrastructure must be available. You are using this infrastructure anytime you use the Internet on your
laptop and even your cell phone. MIS core capabilities and the IT strategy rest on a solid infrastructure
(see Figure 1-1). Therefore, understanding how data communications and networking works will enable
you to understand what it takes for a modern organization to stay in business and for you to be able to
work and connect with your family and friends.
MANAGEMENT FOCUS 1-1
Career Opportunities
It’s a great time to be in information technology (IT)! The technology-fueled new economy has
dramatically increased the demand for skilled IT professionals. According to the U.S. Bureau of
Labor Statistics and Career Profiles (http://www.careerprofiles.info), 2 out of 10 fastest growing
occupations are computer network administrator and computer systems analyst, which is expected
to grow by 22% over the next 10 years with an annual median salary of $72,500—not counting
bonuses. There are two reasons for this growth. First, companies have to continuously upgrade their
networks and thus need skilled employees to support their expanding IT infrastructure. Second,
people are spending more time on their mobile devices, and because employers are allowing them to
use these personal devices at work (i.e., BYOD, or bring your own device), the network infrastructure
has to support the data that flow from these devices as well as to make sure that they don’t pose a
security risk. | Page 23 | Chapter 11 |
8b0d9893a51e-0 | With a few years of experience, there is the possibility to work as an information systems manager,
for which the median annual pay is as high as $117,780. An information systems manager plans,
coordinates, and directs IT-related activities in such a way that they can fully support the goals of
any business. Thus, this job requires a good understanding not only of the business but also of the
technology so that appropriate and reliable technology can be implemented at a reasonable cost to
keep everything operating smoothly and to guard against cybercriminals.
Because of the expanding job market for IT and networking-related jobs, certifications become
important. Most large vendors of network technologies, such as the Microsoft Corporation and Cisco
Systems Inc., provide certification processes (usually a series of courses and formal exams) so that
individuals can document their knowledge. Certified network professionals often earn $10,000 to
$15,000 more than similarly skilled uncertified professionals—provided that they continue to learn
and maintain their certification as new technologies emerge.
Sources: http://jobs.aol.com, “In Demand Careers That Pay $100,00 a Year or More”; www.careerpath.com, “Today’s 20 Fastest-
Growing Occupations”; www.cnn.com, “30 Jobs Needing Most Workers in Next Decade,” http://www.careerprofiles.info/top-
careers.html.
By the time you finish this book, you’ll understand how networks work, how to design networks, and how
to manage networks. You won’t be an expert, but you’ll be ready to enter an organization and have an
educated conversation about the role of data communications and networks or move on to more advanced
courses and workshops.
1.2 DATA COMMUNICATIONS NETWORKS
Data communications is the movement of computer information from one point to another by means of
electrical or optical transmission systems. Such systems are often called data communications networks. | Page 24 | Chapter 11 |
f389bb799a30-1 | electrical or optical transmission systems. Such systems are often called data communications networks.
This is in contrast to the broader term telecommunications, which includes the transmission of voice and
video (images and graphics) as well as data and usually implies longer distances. In general, data
communications networks collect data from personal computers and other devices and transmit those
data to a central server that is a more powerful personal computer, minicomputer, or mainframe, or they
perform the reverse process, or some combination of the two. Data communications networks facilitate
more efficient use of computers and improve the day-to-day control of a business by providing faster
information flow. They also provide message transfer services to allow computer users to talk to one
another via email, chat, and video streaming.
TECHNICAL FOCUS 1-1
Internet Domain Names
Internet address names are strictly controlled; otherwise, someone could add a computer to the
Internet that had the same address as another computer. Each address name has two parts, the
computer name and its domain. The general format of an Internet address is therefore
computer.domain. Some computer names have several parts separated by periods, so some
addresses have the format computer.computer.computer.domain. For example, the main university
Web server at Indiana University (IU) is called www.indiana.edu, whereas the Web server for the
Kelley School of Business at IU is www.kelley.indiana.edu.
Since the Internet began in the United States, the American address board was the first to assign
domain names to indicate types of organizations. Some common U.S. domain names are as follows:
EDU for an educational institution, usually a university
COM for a commercial business
GOV for a government department or agency
MIL for a military unit
ORG for a nonprofit organization | Page 24 | Chapter 11 |
b469db1ca758-0 | As networks in other countries were connected to the Internet, they were assigned their own domain
names. Some international domain names are as follows:
CA for Canada
AU for Australia
UK for the United Kingdom
DE for Germany
New top-level domains that focus on specific types of businesses continue to be introduced, such as
the following:
AERO
for aerospace companies
MUSEUM for museums
NAME
for individuals
PRO
for professionals, such as accountants and lawyers
BIZ
for businesses
Many international domains structure their addresses in much the same way as the United States
does. For example, Australia uses EDU to indicate academic institutions, so an address such as
xyz.edu.au would indicate an Australian university.
For a full list of domain names, see www.iana.org/domains/root/db.
1.2.1 Components of a Network
There are three basic hardware components for a data communications network: a server (e.g., personal
computer, mainframe), a client (e.g., personal computer, terminal), and a circuit (e.g., cable, modem) over
which messages flow. Both the server and client also need special-purpose network software that enables
them to communicate.
The server stores data or software that can be accessed by the clients. In client–server computing, several
servers may work together over the network with a client computer to support the business application.
The client is the input–output hardware device at the user’s end of a communication circuit. It typically
provides users with access to the network and the data and software on the server.
The circuit is the pathway through which the messages travel. It is typically a copper wire, although
fiber-optic cable and wireless transmission are becoming common. There are many devices in the circuit
that perform special functions such as switches and routers. | Page 25 | Chapter 11 |
bd68910041d3-1 | that perform special functions such as switches and routers.
Strictly speaking, a network does not need a server. Some networks are designed to connect a set of
similar computers that share their data and software with each other. Such networks are called peer-to-
peer networks because the computers function as equals, rather than relying on a central server to store
the needed data and software.
Figure 1-2 shows a small network that has several personal computers (clients) connected through a
switch and cables (circuit) and wirelessly through a wireless access point (AP). In this network,
messages move through the switch to and from the computers. The router is a special device that
connects two or more networks. The router enables computers on this network to communicate with
computers on the same network or on other networks (e.g., the Internet).
The network in Figure 1-3 has three servers. Although one server can perform many functions, networks
are often designed so that a separate computer is used to provide different services. The file server
stores data and software that can be used by computers on the network. The Web server stores
documents and graphics that can be accessed from any Web browser, such as Internet Explorer. The Web
server can respond to requests from computers on this network or any computer on the Internet. The
mail server handles and delivers email over the network. Servers are usually personal computers (often
more powerful than the other personal computers on the network) but may be mainframes too. | Page 25 | Chapter 11 |
4049247d344e-0 | FIGURE 1-2 Example of a local area network (LAN)
FIGURE 1-3 Network architecture components
There are three computers that make networks what they are. These are the client, the server, and the
router. The client initiates a communication with the server by sending a request to the server. Once the
server receives the request, it processes it, and responds with a response. The router makes this | Page 26 | Chapter 11 |
1a2b13dc5b74-0 | connection possible.
All three devices are computers, and their hardware is pretty much the same—they have a motherboard
with CPU (central processing unit), memory, and some storage space. However, only the client had a
screen, keyboard, and mouse. Why? Are the server and router less deserving? No. Their purpose is not to
receive an input from the user (keyboard or mouse) or display output (screen) but rather to respond to
requests, so they have no need for. Pretty clever, isn’t it!
You probably know that a client can have a variety of client operating systems (e.g., Windows, Mac OS, or
Linux) and application software (e.g., a web browser, outlook). Likewise, a server can have different
operating systems (e.g., Windows, Linux, or z/OS) and application software (e.g., web server software,
Exchange). What do you think is the operating system on a router? It turns out that about 90% of routers
run Cisco IOS (Inter-operating system) that was specifically created for routers. In fact, Cisco IOS is the
second most popular operating system in the world, ahead of Mac and Linux. Interesting, right?
1.2.2 Types of Networks
There are many different ways to categorize networks. One of the most common ways is to look at the
geographic scope of the network. Figure 1-3 illustrates three types of networks: local area networks
(LANs), backbone networks (BNs), and wide area networks (WANs). The distinctions among these are
becoming blurry because some network technologies now used in LANs were originally developed for
WANs, and vice versa. Any rigid classification of technologies is certain to have exceptions.
A local area network (LAN) is a group of computers located in the same general area. A LAN covers a | Page 27 | Chapter 11 |
2069ae518ff2-1 | clearly defined small area, such as one floor or work area, a single building, or a group of buildings. The
upper-left diagram in Figure 1-3 shows a small LAN located in the records building at the former
McClellan Air Force Base in Sacramento. LANs support high-speed data transmission compared with
standard telephone circuits, commonly operating 100 million bits per second (100 Mbps). LANs and
wireless LANs are discussed in detail in Chapter 6.
Most LANs are connected to a backbone network (BN), a larger, central network connecting several
LANs, other BNs, MANs, and WANs. BNs typically span from hundreds of feet to several miles and
provide very high-speed data transmission, commonly 100–1,000 Mbps. The second diagram in Figure 1-
3 shows a BN that connects the LANs located in several buildings at McClellan Air Force Base. BNs are
discussed in detail in Chapter 7.
Wide area networks (WANs) connect BNs and MANs (see Figure 1-1). Most organizations do not
build their own WANs by laying cable, building microwave towers, or sending up satellites (unless they
have unusually heavy data transmission needs or highly specialized requirements, such as those of the
Department of Defense). Instead, most organizations lease circuits from IXCs (e.g., AT&T, Sprint) and use
those to transmit their data. WAN circuits provided by IXCs come in all types and sizes but typically span
hundreds or thousands of miles and provide data transmission rates from 64 Kbps to 10 Gbps. WANs are
discussed in detail in Chapter 8.
Two other common terms are intranets and extranets. An intranet is a LAN that uses the same | Page 27 | Chapter 11 |
e11d2f5775f6-2 | technologies as the Internet (e.g., Web servers, Java, HTML [Hypertext Markup Language]) but is open to
only those inside the organization. For example, although some pages on a Web server may be open to the
public and accessible by anyone on the Internet, some pages may be on an intranet and therefore hidden
from those who connect to the Web server from the Internet at large. Sometimes, an intranet is provided
by a completely separate Web server hidden from the Internet. The intranet for the Information Systems
Department at Indiana University, for example, provides information on faculty expense budgets, class
scheduling for future semesters (e.g., room, instructor), and discussion forums.
An extranet is similar to an intranet in that it, too, uses the same technologies as the Internet but instead
is provided to invited users outside the organization who access it over the Internet. It can provide access
to information services, inventories, and other internal organizational databases that are provided only to
customers, suppliers, or those who have paid for access. Typically, users are given passwords to gain
access, but more sophisticated technologies such as smart cards or special software may also be required.
Many universities provide extranets for Web-based courses so that only those students enrolled in the
course can access course materials and discussions. | Page 27 | Chapter 11 |
62afdd3e5d40-0 | 1.3 NETWORK MODELS
There are many ways to describe and analyze data communications networks. All networks provide the
same basic functions to transfer a message from sender to receiver, but each network can use different
network hardware and software to provide these functions. All of these hardware and software products
have to work together to successfully transfer a message.
One way to accomplish this is to break the entire set of communications functions into a series of layers,
each of which can be defined separately. In this way, vendors can develop software and hardware to
provide the functions of each layer separately. The software or hardware can work in any manner and can
be easily updated and improved, as long as the interface between that layer and the ones around it
remains unchanged. Each piece of hardware and software can then work together in the overall network.
There are many different ways in which the network layers can be designed. The two most important
network models are the Open Systems Interconnection Reference (OSI) model and the Internet model. Of
the two, the Internet model is the most commonly used; few people use the OSI model, although
understand it is commonly required for network certification exams.
1.3.1 Open Systems Interconnection Reference Model
The Open Systems Interconnection Reference model (usually called the OSI model for short)
helped change the face of network computing. Before the OSI model, most commercial networks used by
businesses were built using nonstandardized technologies developed by one vendor (remember that the
Internet was in use at the time but was not widespread and certainly was not commercial). During the late
1970s, the International Organization for Standardization (ISO) created the Open System Interconnection
Subcommittee, whose task was to develop a framework of standards for computer-to-computer
communications. In 1984, this effort produced the OSI model. | Page 28 | Chapter 11 |
630066a855b1-1 | communications. In 1984, this effort produced the OSI model.
The OSI model is the most talked about and most referred to network model. If you choose a career in
networking, questions about the OSI model will be on the network certification exams offered by
Microsoft, Cisco, and other vendors of network hardware and software. However, you will probably never
use a network based on the OSI model. Simply put, the OSI model never caught on commercially in North
America, although some European networks use it, and some network components developed for use in
the United States arguably use parts of it. Most networks today use the Internet model, which is discussed
in the next section. However, because there are many similarities between the OSI model and the Internet
model, and because most people in networking are expected to know the OSI model, we discuss it here.
The OSI model has seven layers (see Figure 1-4).
Layer 1: Physical Layer
The physical layer is concerned primarily with transmitting data bits (zeros or ones) over a
communication circuit. This layer defines the rules by which ones and zeros are transmitted, such as
voltages of electricity, number of bits sent per second, and the physical format of the cables and
connectors used.
Layer 2: Data Link Layer
The data link layer manages the physical transmission circuit in layer 1 and transforms it into a circuit
that is free of transmission errors as far as layers above are concerned. Because layer 1 accepts and
transmits only a raw stream of bits without understanding their meaning or structure, the data link layer
must create and recognize message boundaries; that is, it must mark where a message starts and where it
ends. Another major task of layer 2 is to solve the problems caused by damaged, lost, or duplicate
messages so the succeeding layers are shielded from transmission errors. Thus, layer 2 performs error | Page 28 | Chapter 11 |
7a734b999759-2 | messages so the succeeding layers are shielded from transmission errors. Thus, layer 2 performs error
detection and correction. It also decides when a device can transmit so that two computers do not try to
transmit at the same time. We say, that data link layer has a local responsibility. | Page 28 | Chapter 11 |
1c0fb952ef95-0 | FIGURE 1-4 Network models. OSI = Open Systems Interconnection Reference
Layer 3: Network Layer
The network layer performs routing. It determines the next computer to which the message should be
sent, so it can follow the best route through the network and finds the full address for that computer if
needed.
Layer 4: Transport Layer
The transport layer deals with end-to-end issues, such as procedures for entering and departing from the
network. It establishes, maintains, and terminates logical connections for the transfer of data between the
original sender and the final destination of the message. It is responsible for breaking a large data
transmission into smaller packets (if needed), ensuring that all the packets have been received,
eliminating duplicate packets, and performing flow control to ensure that no computer is overwhelmed by
the number of messages it receives. Although error control is performed by the data link layer, the
transport layer can also perform error checking. Therefore, transport layer has a global responsibility.
Layer 5: Session Layer
The session layer is responsible for managing and structuring all sessions. Session initiation must arrange
for all the desired and required services between session participants, such as logging on to circuit
equipment, transferring files, and performing security checks. Session termination provides an orderly
way to end the session, as well as a means to abort a session prematurely. It may have some redundancy
built in to recover from a broken transport (layer 4) connection in case of failure. The session layer also
handles session accounting so the correct party receives the bill.
Layer 6: Presentation Layer
The presentation layer formats the data for presentation to the user. Its job is to accommodate different
interfaces on different computers so the application program need not worry about them. It is concerned
with displaying, formatting, and editing user inputs and outputs. For example, layer 6 might perform data | Page 29 | Chapter 11 |
2b0ee964b6c8-1 | compression, translation between different data formats, and screen formatting. Any function (except
those in layers 1 through 5) that is requested sufficiently often to warrant finding a general solution is
placed in the presentation layer, although some of these functions can be performed by separate hardware
and software (e.g., encryption).
Layer 7: Application Layer
The application layer is the end user’s access to the network. The primary purpose is to provide a set of | Page 29 | Chapter 11 |
39b301c0b527-0 | utilities for application programs. Each user program determines the set of messages and any action it
might take on receipt of a message. Other network-specific applications at this layer include network
monitoring and network management.
1.3.2 Internet Model
The network model that dominates current hardware and software is a more simple five-layer Internet
model. Unlike the OSI model that was developed by formal committees, the Internet model evolved from
the work of thousands of people who developed pieces of the Internet. The OSI model is a formal standard
that is documented in one standard, but the Internet model has never been formally defined; it has to be
interpreted from a number of standards. The two models have very much in common (see Figure 1-4);
simply put, the Internet model collapses the top three OSI layers into one layer. Because it is clear that the
Internet has won the “war,” we use the five-layer Internet model for the rest of this book.
Layer 1: The Physical Layer
The physical layer in the Internet model, as in the OSI model, is the physical connection between the
sender and receiver. Its role is to transfer a series of electrical, radio, or light signals through the circuit.
The physical layer includes all the hardware devices (e.g., computers, modems, and switches) and
physical media (e.g., cables and satellites). The physical layer specifies the type of connection and the
electrical signals, radio waves, or light pulses that pass through it. Chapter 3 discusses the physical layer
in detail.
Layer 2: The Data Link Layer
The data link layer is responsible for moving a message from one computer to the next computer in the
network path from the sender to the receiver. The data link layer in the Internet model performs the same
three functions as the data link layer in the OSI model. First, it controls the physical layer by deciding | Page 30 | Chapter 11 |
8a1d1b2a718f-1 | when to transmit messages over the media. Second, it formats the messages by indicating where they start
and end. Third, it detects and may correct any errors that have occurred during transmission. Chapter 4
discusses the data link layer in detail.
Layer 3: The Network Layer
The network layer in the Internet model performs the same functions as the network layer in the OSI
model. First, it performs routing, in that it selects the next computer to which the message should be sent.
Second, it can find the address of that computer if it doesn’t already know it. Chapter 5 discusses the
network layer in detail.
Layer 4: The Transport Layer
The transport layer in the Internet model is very similar to the transport layer in the OSI model. It
performs two functions. First, it is responsible for linking the application layer software to the network
and establishing end-to-end connections between the sender and receiver when such connections are
needed. Second, it is responsible for breaking long messages into several smaller messages to make them
easier to transmit and then recombining the smaller messages back into the original larger message at the
receiving end. The transport layer can also detect lost messages and request that they be resent. Chapter 5
discusses the transport layer in detail.
Layer 5: Application Layer
The application layer is the application software used by the network user and includes much of what
the OSI model contains in the application, presentation, and session layers. It is the user’s access to the
network. By using the application software, the user defines what messages are sent over the network.
Because it is the layer that most people understand best and because starting at the top sometimes helps
people understand better, Chapter 2 begins with the application layer. It discusses the architecture of
network applications and several types of network application software and the types of messages they
generate.
Groups of Layers | Page 30 | Chapter 11 |
1f354ca1c507-0 | The layers in the Internet are often so closely coupled that decisions in one layer impose certain
requirements on other layers. The data link layer and the physical layer are closely tied together because
the data link layer controls the physical layer in terms of when the physical layer can transmit. Because
these two layers are so closely tied together, decisions about the data link layer often drive the decisions
about the physical layer. For this reason, some people group the physical and data link layers together and
call them the hardware layers. Likewise, the transport and network layers are so closely coupled that
sometimes these layers are called the internetwork layers (see Figure 1-4). When you design a
network, you often think about the network design in terms of three groups of layers: the hardware layers
(physical and data link), the internetwork layers (network and transport), and the application layer.
1.3.3 Message Transmission Using Layers
Each computer in the network has software that operates at each of the layers and performs the functions
required by those layers (the physical layer is hardware, not software). Each layer in the network uses a
formal language, or protocol, that is simply a set of rules that define what the layer will do and that
provides a clearly defined set of messages that software at the layer needs to understand. For example, the
protocol used for Web applications is HTTP (Hypertext Transfer Protocol, which is described in more
detail in Chapter 2). In general, all messages sent in a network pass through all layers. All layers except
the physical layer create a new Protocol Data Unit (PDU) as the message passes through them. The
PDU contains information that is needed to transmit the message through the network. Some experts use
the word packet to mean a PDU. Figure 1-5 shows how a message requesting a Web page would be sent on
the Internet. | Page 31 | Chapter 11 |
1ad761bd9b41-1 | the Internet.
FIGURE 1-5 Message transmission using layers. IP = Internet Protocol; HTTP = Hypertext Transfer
Protocol; TCP = Transmission Control Protocol | Page 31 | Chapter 11 |
bf550c38aed9-0 | Application Layer
First, the user creates a message at the application layer using a Web browser by clicking on a link (e.g.,
get the home page at www.somebody.com). The browser translates the user’s message (the click on the
Web link) into HTTP. The rules of HTTP define a specific PDU—called an HTTP packet—that all Web
browsers must use when they request a Web page. For now, you can think of the HTTP packet as an
envelope into which the user’s message (get the Web page) is placed. In the same way that an envelope
placed in the mail needs certain information written in certain places (e.g., return address, destination
address), so too does the HTTP packet. The Web browser fills in the necessary information in the HTTP
packet, drops the user’s request inside the packet, then passes the HTTP packet (containing the Web page
request) to the transport layer.
Transport Layer
The transport layer on the Internet uses a protocol called TCP (transmission control protocol), and it, too,
has its own rules and its own PDUs. TCP is responsible for breaking large files into smaller packets and for
opening a connection to the server for the transfer of a large set of packets. The transport layer places the
HTTP packet inside a TCP PDU (which is called a TCP segment), fills in the information needed by the
TCP segment, and passes the TCP segment (which contains the HTTP packet, which, in turn, contains the
message) to the network layer.
Network Layer
The network layer on the Internet uses a protocol called IP (Internet Protocol), which has its rules and
PDUs. IP selects the next stop on the message’s route through the network. It places the TCP segment
inside an IP PDU, which is called an IP packet, and passes the IP packet, which contains the TCP segment, | Page 32 | Chapter 11 |
ff6dbeb754fa-1 | which, in turn, contains the HTTP packet, which, in turn, contains the message, to the data link layer.
Data Link Layer
If you are connecting to the Internet using a LAN, your data link layer may use a protocol called Ethernet,
which also has its own rules and PDUs. The data link layer formats the message with start and stop
markers, adds error checks information, places the IP packet inside an Ethernet PDU, which is called an
Ethernet frame, and instructs the physical hardware to transmit the Ethernet frame, which contains the IP
packet, which contains the TCP segment, which contains the HTTP packet, which contains the message.
Physical Layer
The physical layer in this case is network cable connecting your computer to the rest of the network. The
computer will take the Ethernet frame (complete with the IP packet, the TCP segment, the HTTP packet,
and the message) and send it as a series of electrical pulses through your cable to the server.
When the server gets the message, this process is performed in reverse. The physical hardware translates
the electrical pulses into computer data and passes the message to the data link layer. The data link layer
uses the start and stop markers in the Ethernet frame to identify the message. The data link layer checks
for errors and, if it discovers one, requests that the message be resent. If a message is received without
error, the data link layer will strip off the Ethernet frame and pass the IP packet (which contains the TCP
segment, the HTTP packet, and the message) to the network layer. The network layer checks the IP
address and, if it is destined for this computer, strips off the IP packet and passes the TCP segment, which
contains the HTTP packet and the message, to the transport layer. The transport layer processes the
message, strips off the TCP segment, and passes the HTTP packet to the application layer for processing. | Page 32 | Chapter 11 |
e72693efdc9b-2 | The application layer (i.e., the Web server) reads the HTTP packet and the message it contains (the
request for the Web page) and processes it by generating an HTTP packet containing the Web page you
requested. Then the process starts again as the page is sent back to you.
The Pros and Cons of Using Layers
There are three important points in this example. First, there are many different software packages and
many different PDUs that operate at different layers to successfully transfer a message. Networking is in
some ways similar to the Russian matryoshka, nested dolls that fit neatly inside each other. This is called | Page 32 | Chapter 11 |
e35107a1af15-0 | encapsulation, because the PDU at a higher level is placed inside the PDU at a lower level so that the
lower-level PDU encapsulates the higher-level one. The major advantage of using different software and
protocols is that it is easy to develop new software, because all one has to do is write software for one level
at a time. The developers of Web applications, for example, do not need to write software to perform error
checking or routing, because those are performed by the data link and network layers. Developers can
simply assume those functions are performed and just focus on the application layer. Similarly, it is
simple to change the software at any level (or add new application protocols), as long as the interface
between that layer and the ones around it remains unchanged.
Second, it is important to note that for communication to be successful, each layer in one computer must
be able to communicate with its matching layer in the other computer. For example, the physical layer
connecting the client and server must use the same type of electrical signals to enable each to understand
the other (or there must be a device to translate between them). Ensuring that the software used at the
different layers is the same as accomplished by using standards. A standard defines a set of rules, called
protocols, that explain exactly how hardware and software that conform to the standard are required to
operate. Any hardware and software that conform to a standard can communicate with any other
hardware and software that conform to the same standard. Without standards, it would be virtually
impossible for computers to communicate.
Third, the major disadvantage of using a layered network model is that it is somewhat inefficient. Because
there are several layers, each with its own software and PDUs, sending a message involves many software
programs (one for each protocol) and many PDUs. The PDUs add to the total amount of data that must be | Page 33 | Chapter 11 |
70f7b9080072-1 | sent (thus increasing the time it takes to transmit), and the different software packages increase the
processing power needed in computers. Because the protocols are used at different layers and are stacked
on top of one another (take another look at Figure 1-5), the set of software used to understand the
different protocols is often called a protocol stack.
1.4 NETWORK STANDARDS
1.4.1 The Importance of Standards
Standards are necessary in almost every business and public service entity. For example, before 1904,
fire hose couplings in the United States were not standard, which meant a fire department in one
community could not help in another community. The transmission of electric current was not
standardized until the end of the nineteenth century, so customers had to choose between Thomas
Edison’s direct current (DC) and George Westinghouse’s alternating current (AC).
The primary reason for standards is to ensure that hardware and software produced by different vendors
can work together. Without networking standards, it would be difficult—if not impossible—to develop
networks that easily share information. Standards also mean that customers are not locked into one
vendor. They can buy hardware and software from any vendor whose equipment meets the standard. In
this way, standards help to promote more competition and hold down prices.
The use of standards makes it much easier to develop software and hardware that link different networks
because software and hardware can be developed one layer at a time.
1.4.2 The Standards-Making Process
There are two types of standards: de jure and de facto. A de jure standard is developed by an official
industry or a government body and is often called a formal standard. For example, there are de jure
standards for applications such as Web browsers (e.g., HTTP, HTML), for network layer software (e.g., | Page 33 | Chapter 11 |
2a235f6608c8-2 | IP), for data link layer software (e.g., Ethernet IEEE 802.3), and for physical hardware (e.g., V.90
modems). De jure standards typically take several years to develop, during which time technology
changes, making them less useful.
De facto standards are those that emerge in the marketplace and are supported by several vendors but
have no official standing. For example, Microsoft Windows is a product of one company and has not been
formally recognized by any standards organization, yet it is a de facto standard. In the communications
industry, de facto standards often become de jure standards once they have been widely accepted. | Page 33 | Chapter 11 |
74fc8a44cb98-0 | The de jure standardization process has three stages: specification, identification of choices, and
acceptance. The specification stage consists of developing a nomenclature and identifying the problems to
be addressed. In the identification of choices stage, those working on the standard identify the various
solutions and choose the optimum solution from among the alternatives. Acceptance, which is the most
difficult stage, consists of defining the solution and getting recognized industry leaders to agree on a
single, uniform solution. As with many other organizational processes that have the potential to influence
the sales of hardware and software, standards-making processes are not immune to corporate politics and
the influence of national governments.
International Organization for Standardization
One of the most important standards-making bodies is the International Organization for Standardization
(ISO), which makes technical recommendations about data communication interfaces (see www.iso.org).
ISO is based in Geneva, Switzerland. The membership is composed of the national standards
organizations of each ISO member country.
International Telecommunications Union-Telecommunications Group
The International Telecommunications Union-Telecommunications Group (ITU-T) is the
technical standards-setting organization of the United Nations International Telecommunications Union,
which is also based in Geneva (see www.itu.int). ITU is composed of representatives from about 200
member countries. Membership was originally focused on just the public telephone companies in each
country, but a major reorganization in 1993 changed this, and ITU now seeks members among public- and
private-sector organizations who operate computer or communications networks (e.g., RBOCs) or build
software and equipment for them (e.g., AT&T).
American National Standards Institute
The American National Standards Institute (ANSI) is the coordinating organization for the U.S.
national system of standards for both technology and nontechnology (see www.ansi.org). ANSI has about | Page 34 | Chapter 11 |
ce4fdeaeb561-1 | 1,000 members from both public and private organizations in the United States. ANSI is a standardization
organization, not a standards-making body, in that it accepts standards developed by other organizations
and publishes them as American standards. Its role is to coordinate the development of voluntary national
standards and to interact with the ISO to develop national standards that comply with the ISO’s
international recommendations. ANSI is a voting participant in the ISO.
MANAGEMENT FOCUS 1-2
How Network Protocols Become Standards
There are many standards organizations around the world, but perhaps the best known is the
Internet Engineering Task Force (IETF). IETF sets the standards that govern how much of the
Internet operates.
The IETF, like all standards organizations, tries to seek consensus among those involved before
issuing a standard. Usually, a standard begins as a protocol (i.e., a language or set of rules for
operating) developed by a vendor (e.g., HTML). When a protocol is proposed for standardization, the
IETF forms a working group of technical experts to study it. The working group examines the
protocol to identify potential problems and possible extensions and improvements, and then issues a
report to the IETF.
If the report is favorable, the IETF issues a Request for Comment (RFC) that describes the
proposed standard and solicits comments from the entire world. Most large software companies
likely to be affected by the proposed standard prepare detailed responses. Many “regular” Internet
users also send their comments to the IETF.
The IETF reviews the comments and possibly issues a new and improved RFC, which again is posted
for more comments. Once no additional changes have been identified, it becomes a proposed
standard. | Page 34 | Chapter 11 |
b19e9d9531d8-0 | Usually, several vendors adopt the proposed standard and develop products based on it. Once at
least two vendors have developed hardware or software based on it and it has proven successful in
operation, the proposed standard is changed to a draft standard. This is usually the final
specification, although some protocols have been elevated to Internet standards, which usually
signifies mature standards not likely to change.
The process does not focus solely on technical issues; almost 90% of the IETF’s participants work for
manufacturers and vendors, so market forces and politics often complicate matters. One former
IETF chairperson who worked for a hardware manufacturer has been accused of trying to delay the
standards process until his company had a product ready, although he and other IETF members
deny this. Likewise, former IETF directors have complained that members try to standardize every
product their firms produce, leading to a proliferation of standards, only a few of which are truly
useful.
Sources: “How Networking Protocols Become Standards,” PC Week, March 17, 1997; “Growing Pains,” Network World, April 14,
1997.
MANAGEMENT FOCUS 1-3
Keeping Up with Technology
The data communications and networking arena changes rapidly. Significant new technologies are
introduced and new concepts are developed almost every year. It is therefore important for network
managers to keep up with these changes.
There are at least three useful ways to keep up with change. First and foremost for users of this book
is the website for this book, which contains updates to the book, additional sections, teaching
materials, and links to useful websites.
Second, there are literally hundreds of thousands of websites with data communications and
networking information. Search engines can help you find them. A good initial starting point is the | Page 35 | Chapter 11 |
5c0efe87405c-1 | networking information. Search engines can help you find them. A good initial starting point is the
telecom glossary at http://www.atis.org. Three other useful sites are http://www.zdnet.com,
http://www.networkcomputing.com, and http://www.zdnet.com.
Third, there are many useful magazines that discuss computer technology in general and networking
technology in particular, including Network Computing, Info World, Info Week, and CIO Magazine. | Page 35 | Chapter 11 |
d70ea1d79d1c-0 | FIGURE 1-6 Some common data communications standards. HTML = Hypertext Markup Language;
HTTP = Hypertext Transfer Protocol; IMAP = Internet Message Access Protocol; IP = Internet Protocol;
LAN = Local Area Network; MPEG = Motion Picture Experts Group; POP = Post Office Protocol; TCP =
Transmission Control Protocol
Institute of Electrical and Electronics Engineers
The Institute of Electrical and Electronics Engineers (IEEE) is a professional society in the
United States whose Standards Association (IEEE-SA) develops standards (see www.standards.ieee.org).
The IEEE-SA is probably most known for its standards for LANs. Other countries have similar groups; for
example, the British counterpart of IEEE is the Institution of Electrical Engineers (IEE).
Internet Engineering Task Force
The Internet Engineering Task Force (IETF) sets the standards that govern how much of the
Internet will operate (see www.ietf.org). The IETF is unique in that it doesn’t really have official
memberships. Quite literally anyone is welcome to join its mailing lists, attend its meetings, and comment
on developing standards. The role of the IETF and other Internet organizations is discussed in more detail
in Chapter 8; also, see the box entitled “How Network Protocols Become Standards.”
1.4.3 Common Standards
There are many different standards used in networking today. Each standard usually covers one layer in a
network. Some of the most commonly used standards are shown in Figure 1-6. At this point, these models
are probably just a maze of strange names and acronyms to you, but by the end of the book, you will have | Page 36 | Chapter 11 |
6be45f861a0b-0 | a good understanding of each of these. Figure 1-6 provides a brief road map for some of the important
communication technologies we discuss in this book.
For now, there is one important message you should understand from Figure 1-6: For a network to
operate, many different standards must be used simultaneously. The sender of a message must use one
standard at the application layer, another one at the transport layer, another one at the network layer,
another one at the data link layer, and another one at the physical layer. Each layer and each standard is
different, but all must work together to send and receive messages.
Either the sender and receiver of a message must use the same standards or, more likely, there are devices
between the two that translate from one standard into another. Because different networks often use
software and hardware designed for different standards, there is often a lot of translation between
different standards.
1.5 FUTURE TRENDS
The field of data communications has grown faster and become more important than computer
processing itself. Both go hand in hand, but we have moved from the computer era to the communication
era. Three major trends are driving the future of communications and networking.
1.5.1 Wireless LAN and BYOD
The rapid development of mobile devices, such as smartphones and tablets, has encouraged employers to
allow their employees to bring these devices to work and use them to access data, such as their work
email. This movement, called bring your own device, or Bring Your On Device (BYOD), is a great way
to get work quickly, saves money, and makes employees happy. But BYOD also brings its own problems.
Employers need to add or expand their Wireless Local Area Networks (WLANs) to support all these new
devices.
Another important problem is security. Employees bring these devices to work so that they can access not | Page 37 | Chapter 11 |
e7a87890302a-1 | Another important problem is security. Employees bring these devices to work so that they can access not
only their email but also other critical company assets, such as information about their clients, suppliers,
or sales. Employers face myriad decisions about how to manage access to company applications for
BYOD. Companies can adopt two main approaches: (1) native apps or (2) browser-based technologies.
Native apps require an app to be developed for each application that an employee might be using for
every potential device that the employee might use (e.g., iPhone, Android, Windows). The browser-
based approach (often referred to as responsive design using HTML5) doesn’t create an app but rather
requires employees to access the application through a Web browser. Both these approaches have their
pros and cons, and only the future will show which one is the winner.
What if an employee loses his or her mobile phone or tablet so that the application that accesses critical
company data now can be used by anybody who finds the device? Will the company’s data be
compromised? Device and data loss practices now have to be added to the general security practices of the
company. Employees need to have apps to allow their employer to wipe their phones clean in case of loss
so that no company data are compromised (e.g., SOTI’s MobiControl). In some cases, companies require
the employee to allow monitoring of the device at all times, to ensure that security risks are minimized.
However, some argue that this is not a good practice because the device belongs to the employee, and
monitoring it 24/7 invades the employee’s privacy.
1.5.2 The Internet of Things
Telephones and computers used to be separate. Today voice and data have converged into unified
communications, with phones plugged into computers or directly into the LAN using Voice over Internet | Page 37 | Chapter 11 |
f33910b95e52-2 | communications, with phones plugged into computers or directly into the LAN using Voice over Internet
Protocol (VoIP). Vonage and Skype have taken this one step further and offer telephone service over the
Internet at dramatically lower prices than traditional separate landline phones, whether from traditional
phones or via computer microphones and speakers.
Computers and networks can also be built into everyday things, such as kitchen appliances, doors, and
shoes. In the future, the Internet will move from being a Web of computers to also being an Internet of
Things (IoT), as smart devices become common, that creates the Network of Things (NoT) where all | Page 37 | Chapter 11 |
5d885c517b3e-0 | this interaction between IoT devices will happen seamlessly, without human intervention. And you might
already be asking Alexa or Siri for advice on where to eat, lock, and unlock your apartment, turn on/off
your lights, or change the thermostat setting. For this to happen, Alexa/Siri must be able to communicate
with your lock or thermostat without any intervention from you.
Google is a leading innovator in the IoT world. It entered the IoT playground with the Nest thermostat.
Google has also been developing a self-driving car that not only passes a standard driving test but also has
fewer collisions than cars driven by humans. Other car developers are also developing autonomous
vehicles. | Page 38 | Chapter 11 |
f9384d5af2ed-0 | FIGURE 1-7 A security robot on the IOT
IoT technologies are not restricted to consumer use. To the contrary, they are used in many places such as
manufacturing, process automation, decision analytics, and smart electrical grids. However, the
underlying principle of all the applications is that IoT devices are connected to the Internet either through
wired or wireless Ethernet. Figure 1-7 shows an IOT device that we encountered in a mall in Boston. It is
semi-autonomous security robot, meaning it can be controlled by a human or set to roam its environment. | Page 39 | Chapter 11 |
750b039d2ba8-0 | Ten years ago, network managers would never have thought about the need to manage robots over their
networks.
1.5.3 Massively Online
You have probably heard of massively multiplayer online games, such as World of Warcraft, where you
can play with thousands of players in real time. Well, today not only games are massively online.
Education is massively online. Edx, Khan Academy, Lynda.com, or Code Academy have websites that offer
thousands of education modules for children and adults in myriad fields to help them learn. Your class
very likely also has an online component. You may even use this textbook online and decide whether your
comments are for you only, for your instructor, or for the entire class to read. In addition, you may have
heard about massive open online courses, or MOOC. MOOC enable students who otherwise wouldn’t have
access to elite universities to get access to top knowledge without having to pay the tuition. These classes
are offered by universities, such as Stanford, UC Berkeley, MIT, UCLA, Carnegie Mellon, and of course,
Indiana University, free of charge and for no credit (although at some universities, you can pay and get
credit toward your degree).
Politics has also moved massively online. President Obama reached out to the crowds and ordinary voters
not only through his Facebook page but also through Reddit and Google Hangouts. President Trump’s use
of Twitter is unprecedented. He can directly reach millions of followers—a strategy that paid off in the
2016 elections. Finally, massively online allows activists to reach masses of people in a very short period of
time to initiate change. Examples of use of YouTube videos or Facebook for activism include the Arab
Spring, Kony 2012, or the use of sarin gas in Syria.
So what started as a game with thousands of people being online at the same time is being reinvented for | Page 40 | Chapter 11 |
48d7fbe44cac-1 | good use in education, politics, and activism. Only the future will show what humanity can do with what
massively online has to offer.
What these three trends have in common is that there will be an increasing demand for professionals who
understand development of data communications and networking infrastructure to support this growth.
There will be more and more need to build faster and more secure networks that will allow individuals
and organizations to connect to resources, probably stored on cloud infrastructure (either private or
public). This need will call not only for engineers who deeply understand the technical aspects of networks
but also for highly social individuals who embrace technology in creative ways to allow business to achieve
a competitive edge through utilizing this technology. So the call is for you who are reading this book—you
are in the right place at the right time!
1.6 IMPLICATIONS FOR CYBER SECURITY
At the end of each chapter, we provide key implications for cyber security that arise from the topics
discussed in the chapter. We draw implications that focus on improving the management of networks and
information systems as well as implications for cyber security of an individual and an organization.
There are three key implications for management from this chapter. First, networks and the Internet
change almost everything. Computer networks and the Internet are designed to quickly and easily move
information from distant locations and to enable individuals inside and outside the firm to access
information and products from around the world. However, this ease of doing work on the Internet makes
it also easy for cyber criminals to steal files from your computer or to put files on your computer (such as
viruses or malware). Understanding how computer networks and the Internet work and how computers
communicate via networks is the first step toward defending your own computer and the computers on a
company’s network.
Second, today’s networking environment requires that a wide variety of devices could connect. Employees’ | Page 40 | Chapter 11 |
5e1f3b505f6b-2 | Second, today’s networking environment requires that a wide variety of devices could connect. Employees’
use of their own devices under BYOD policies increases security risks, as does the move to the IoT. Several
security experts say that IoT doesn’t stand for Internet of Things; it stands for Internet of Targets.
Individuals and companies have to balance BYOD and IoT risks and rewards to create a useful and secure
computing infrastructure.
Third, as the demand for network services and network capacity increases, so too will the need for secure
storage and server space and secure transfer of data. Finding efficient ways to securely store all the | Page 40 | Chapter 11 |
efd4bae3d1a6-0 | information we generate will open new market opportunities. Today, Google has almost a million Web
servers (see Figure 1-8). If we assume that each server costs an average of $1,000, the money large
companies spend on storage is close to $1 billion. Capital expenditure of this scale is then increased by
money spent on power and staffing. One way companies can reduce this amount of money is to store their
data using cloud computing. The good news is that more and more cloud providers meet or exceed
government required security measures for data storage and transfer.
FIGURE 1-8 One server farm with more than 1,000 servers
SUMMARY
Introduction The information society, where information and intelligence are the key drivers of
personal, business, and national success, has arrived. Data communications is the principal enabler
of the rapid information exchange and will become more important than the use of computers
themselves in the future. Successful users of data communications, such as Wal-Mart, can gain
significant competitive advantage in the marketplace.
Network Definitions A LAN is a group of computers located in the same general area. A BN is a
large central network that connects almost everything on a single company site. A metropolitan area
network (MAN) encompasses a city or county area. A wide area network (WAN) spans city, state, or
national boundaries.
Network Model Communication networks are often broken into a series of layers, each of which
can be defined separately, to enable vendors to develop software and hardware that can work
together in the overall network. In this book, we use a five-layer model. The application layer is the
application software used by the network user. The transport layer takes the message generated by
the application layer and, if necessary, breaks it into several smaller messages. The network layer
addresses the message and determines its route through the network. The data link layer formats the | Page 41 | Chapter 11 |
3e082cbb1a3c-1 | addresses the message and determines its route through the network. The data link layer formats the
message to indicate where it starts and ends, decides when to transmit it over the physical media, and
detects and corrects any errors that occur in transmission. The physical layer is the physical
connection between the sender and receiver, including the hardware devices (e.g., computers,
terminals, and modems) and physical media (e.g., cables and satellites). Each layer, except the | Page 41 | Chapter 11 |
dfa25c05f8bb-0 | physical layer, adds a Protocol Data Unit (PDU) to the message.
Standards Standards ensure that hardware and software produced by different vendors can work
together. A de jure standard is developed by an official industry or a government body. De facto
standards are those that emerge in the marketplace and are supported by several vendors but have no
official standing. Many different standards and standards-making organizations exist.
Future Trends At the same time as the use of BYOD offers efficiency at the workplace, it opens up
the doors for security problems that companies need to consider. Our interactions with colleagues
and family will very likely change in the next 5–10 years because of the Internet of Things (IoT),
where devices will interact with each other without human intervention. Finally, massively online not
only changed the way we play computer games but also showed that humanity can change its history.
KEY TERMS
American National Standards Institute (ANSI)
application layer
attacks
backbone network (BN)
Bring Your On Device (BYOD)
browser-based
cable
circuit
client
cyber security
data link layer
extranet
file server
hardware layers
Institute of Electrical and Electronics Engineers (IEEE)
International Telecommunications Union-Telecommunications Group (ITU-T)
Internet Engineering Task Force (IETF)
Internet model
Internet of Things (IoT)
Internet service provider (ISP)
internetwork layers
intranets
layers
local area network (LAN)
mail server
Native apps
network layer
Network of Things (NoT)
Open Systems Interconnection Reference model (OSI model) | Page 42 | Chapter 11 |
c28fb3d815ce-0 | OSI model
peer-to-peer networks
physical layer
Protocol Data Unit (PDU)
protocol stack
protocol
Request for Comment (RFC)
router
server
Standards
switch
transport layer
Web server
wide area networks (WANs)
wireless access point
QUESTIONS
1. How can data communications networks affect businesses?
2. How do data communications networks support the four core capabilities of MIS?
3. Discuss three important applications of data communications networks in business and personal use.
4. How do LANs differ from WANs and BNs?
5. What is a circuit?
6. What is a client?
7. What is a server?
8. What is a router?
9. There are three computers that make the Internet work. Name them and describe their similarities
and differences.
10. Why are network layers important?
11. Describe the seven layers in the OSI network model and what they do.
12. Describe the five layers in the Internet network model and what they do.
13. Explain how a message is transmitted from one computer to another using layers.
14. Describe the three stages of standardization.
15. How are Internet standards developed?
16. Describe two important data communications standards-making bodies. How do they differ?
17. What is the purpose of a data communications standard?
18. Discuss three trends in communications and networking.
19. Why has the Internet model replaced the OSI model?
20. In the 1980s, when we wrote the first edition of this book, there were many, many more protocols in
common use at the data link, network, and transport layers than there are today. Why do you think
the number of commonly used protocols at these layers has declined? Do you think this trend will | Page 43 | Chapter 11 |
276ca8d04908-0 | continue? What are the implications for those who design and operate networks?
21. The number of standardized protocols in use at the application layer has significantly increased since
the 1980s. Why? Do you think this trend will continue? What are the implications for those who
design and operate networks?
22. How many bits (not bytes) are there in a 10-page text document? Hint: There are approximately 350
words on a double-spaced page. We need 8 bits to encode each character.
23. What are three current cyber security issues we face on the Internet?
24. What is the Internet of Things (IoT)? What are the benefits and risks of IoT?
EXERCISES
A. Investigate the latest cyber security threats. What services and/or data were affected by these threats?
What was done to recover from this situation?
B. It turns out that not all industries are equally sensitive to cyber-attacks. There are multiple industries
that belong to the “critical infrastructure.” Investigate which industries belong to the critical
infrastructure, why are they part of it, and what laws govern this group of industries regarding cyber
security.
C. Discuss the issue of communications monopolies and open competition with an economics instructor
and relate his or her comments to your data communication class.
D. Find a college or university offering a specialized degree in telecommunications or data
communications and describe the program.
E. Investigate the IoT. What IoT devices are you most interested in? Why?
F. Investigate the networks in your school or organization. Describe the important LANs and BNs in use
(but do not describe the specific clients, servers, or devices on them).
G. Visit the Internet Engineering Task (IETF) website (www.ietf.org). Describe one standard that is in
the RFC stage. | Page 44 | Chapter 11 |
fbb74639092f-1 | the RFC stage.
H. Discuss how the revolution/evolution of communications and networking is likely to affect how you
will work and live in the future.
I. Investigate the pros and cons of developing native apps versus taking a browser-based approach.
MINICASES
I. Global Consultants John Adams is the chief information officer (CIO) of Global Consultants (GC),
a very large consulting firm with offices in more than 100 countries around the world. GC is about to
purchase a set of several Internet-based financial software packages that will be installed in all of
their offices. There are no standards at the application layer for financial software but several
software companies that sell financial software (call them group A) use one de facto standard to
enable their software to work with one another’s software. However, another group of financial
software companies (call them group B) use a different de facto standard. Although both groups have
software packages that GC could use, GC would really prefer to buy one package from group A for one
type of financial analysis and one package from group B for a different type of financial analysis. The
problem, of course, is that then the two packages cannot communicate and GC’s staff would end up
having to type the same data into both packages. The alternative is to buy two packages from the
same group—so that data could be easily shared—but that would mean having to settle for second
best for one of the packages. Although there have been some reports in the press about the two
groups of companies working together to develop one common standard that will enable software to
work together, there is no firm agreement yet. What advice would you give Adams?
II. Atlas Advertising Atlas Advertising is a regional advertising agency with offices in Boston, New
York, Providence, Washington, D.C., and Philadelphia. (1) Describe the types of networks you think | Page 44 | Chapter 11 |
2301b83dea36-0 | they would have (e.g., LANs, BNs, WANs) and where they are likely to be located. (2) What types of
standard protocols and technologies do you think they are using at each layer (e.g., see Figures 1-3
and 1-5)?
III. Consolidated Supplies Consolidated Supplies is a medium-sized distributor of restaurant supplies
that operates in Canada and several northern U.S. states. They have 12 large warehouses spread
across both countries to service their many customers. Products arrive from the manufacturers and
are stored in the warehouses until they are picked and put on a truck for delivery to their customers.
The networking equipment in their warehouses is old and is starting to give them problems; these
problems are expected to increase as the equipment gets older. The vice president of operations, Pat
McDonald, would like to replace the existing LANs and add some new wireless LAN technology into
all the warehouses, but he is concerned that now may not be the right time to replace the equipment.
He has read several technology forecasts that suggest there will be dramatic improvements in
networking speeds over the next few years, especially in wireless technologies. He has asked you for
advice about upgrading the equipment. Should Consolidated Supplies replace all the networking
equipment in all the warehouses now, should it wait until newer networking technologies are
available, or should it upgrade some of the warehouses this year, some next year, and some the year
after, so that some warehouses will benefit from the expected future improvements in networking
technologies?
IV. Asia Importers Caisy Wong is the owner of a small catalog company that imports a variety of
clothes and houseware from several Asian countries and sells them to its customers over the Web and
by telephone through a traditional catalog. She has read about the convergence of voice and data and | Page 45 | Chapter 11 |
d5a98a96f82d-1 | by telephone through a traditional catalog. She has read about the convergence of voice and data and
is wondering about changing her current traditional, separate, and rather expensive telephone and
data services into one service offered by a new company that will supply both telephone and data over
her Internet connection. What are the potential benefits and challenges that Asia Importers should
consider in making the decision about whether to move to one integrated service?
TECH UPDATES
In every chapter, we will offer couple ideas to investigate.
Topic A: From ARPANET To NoT: What Happened to the Internet?
What started as a secret military project in the 1960s, grew to the largest network of interconnected
computers known as the Internet, which is changing into the largest network of interconnected devices
that (at the time they were discovered) were not meant to talk to each other. Discuss the history of the
Internet (ARPANET) and the future of it (NoT).
Topic B: A Brief History of Cyber Attacks
We all heard about modern ransomware that encrypts every file on your computer and you must pay a
ransom (in bitcoin, of course!) to get these files unencrypted, or phishing attacks (emails that pretend to
be real) that ask you to download a file or click on link and can cause lot of harm to you and your data.
But, when did this start? What was the evolution of attacks on the Internet? How did individuals,
business, and governments respond to these attacks? What is the current citation with cyber-attacks?
Deliverables
Your job will be to prepare a presentation/video (7–10 minutes long) that addresses the topic and
provides information on the following items:
1. Title Slide
2. Short description of topic
3. Main players—these could be people, processes, software, hardware, etc. | Page 45 | Chapter 11 |
e9ebe5e71d2f-2 | 3. Main players—these could be people, processes, software, hardware, etc.
4. How it works—use lot of pictures and be as technical as possible; create this part as a tutorial so that
your audience can follow along | Page 45 | Chapter 11 |
0781c1dc936c-0 | 5. How does it relate to material covered in class so far (and in the future)
6. Additional material/books/links where to learn more about this topic
7. Credits
8. List of References
9. Memo addressed to your professor describing all of the above information
HANDS-ON ACTIVITY 1A
Internet as We Know It Today
We think about access to the Internet as a daily normal. We check our email, news, chat with friends and
family, and do shopping on the Internet. The objective of this activity is for you to experience this
convergence.
1. Investigate the history of the Internet at http://www.vox.com/a/internet-maps that shows you a
history of the Internet through maps.
2. See how many people are using the Internet in your state/country at
https://www.akamai.com/us/en/resources/visualizing-akamai/real-time-web-monitor.jsp?
tab=traffic&theme=dark.
3. See the cyber security attacks in progress on information systems connected to the Internet by
clicking on the Attacks tab at https://www.akamai.com/us/en/resources/visualizing-akamai/real-
time-web-monitor.jsp?tab=attacks&theme=dark.
Deliverable
Deliverable Write a one-page summary of the history and current state of the Internet. What was the most
surprising thing you learned during your investigation?
HANDS-ON ACTIVITY 1B
Seeing the PDUs in Your Messages
We talked about how messages are transferred using layers and the different PDUs used at each layer. The
objective of this activity is for you to see the different PDUs in the messages that you send. To do this, we’ll
use Wireshark, which is one of the world’s foremost network protocol analyzers and is the de facto | Page 46 | Chapter 11 |
76fc8cf02723-1 | standard that most professional and education institutions use today. It is used for network
troubleshooting, network analysis, software and communications protocol development, and general
education about how networks work.
Wireshark enables you to see all messages sent by your computer, as well as some or all of the messages
sent by other computers on your LAN, depending on how your LAN is designed. Most modern LANs are
designed to prevent you from eavesdropping on other computer’s messages, but some older ones still
permit this. Normally, your computer will ignore the messages that are not addressed for your computer,
but Wireshark enables you to eavesdrop and read messages sent to and from other computers.
Wireshark is free. Before you start this activity, download and install it from https://www.wireshark.org.
1. Start Wireshark.
2. Click on Capture and then Interfaces. Click the Start button next to the active interface (the one that
is receiving and sending packets). Your network data will be captured from this moment on.
3. Open your browser and go to a Web page that you have not visited recently (a good one is
www.iana.org).
4. Once the Web page has loaded, go back to Wireshark and stop the packet capture by clicking on
Capture and then Stop (the hot key for this is Ctrl + E). | Page 46 | Chapter 11 |
7256ff20eac9-0 | 5. You will see results similar to those in Figure 1-9. There are three windows below the tool bar:
a. The top window is the Packet List. Each line represents a single message or packet that was
captured by Wireshark. Different types of packets will have different colors. For example, HTTP
packets are colored green. Depending on how busy your network is, you may see a small number
of packets in this window or a very large number of packets.
b. The middle window is the Packet Detail. This will show the details for any packet you click on in
the top window.
c. The bottom window shows the actual contents of the packet in hexadecimal format, so it is
usually hard to read. This window is typically used by network programmers to debug errors.
6. Let’s take a look at the packets that were used to request the Web page and send it to your computer.
The application layer protocol used on the Web is HTTP, so we’ll want to find the HTTP packets. In
the Filter toolbar, type http and hit enter.
FIGURE 1-9 Wireshark capture
7. This will highlight all the packets that contain HTTP packets and will display the first one in Packet
Detail window. Look at the Packet Detail window in Figure 1-8 to see the PDUs in the message we’ve
highlighted. You’ll see that it contains an Ethernet II Frame, an IP packet, a TCP segment, and an
HTTP packet. You can see inside any or all of these PDUs by clicking on the +box in front of them. In
Figure 1-8, you’ll see that we’ve clicked the +box in front of the HTTP packet to show you what’s
inside it.
Deliverables | Page 47 | Chapter 11 |
e1cce0645035-1 | inside it.
Deliverables
1. List the PDU at layers 2, 3, and 4 that were used to transmit your HTTP GET packet.
a. Locate your HTTP GET packet in the Packet List and click on it.
b. Look in the Packet Detail window to get the PDU information.
2. How many different HTTP GET packets were sent by your browser? Not all the HTTP packets are
GET packets, so you’ll have to look through them to answer this question. | Page 47 | Chapter 11 |
cd928447495f-0 | 3. List at least five other protocols that Wireshark displayed in the Packet List window. You will need to
clear the filter by clicking on the “Clear” icon that is on the right of the Filter toolbar. | Page 48 | Chapter 11 |
cd17c1d7da51-0 | PART TWO FUNDAMENTAL CONCEPTS | Page 49 | Chapter 11 |
09c04aba2d66-0 | CHAPTER 2
APPLICATION LAYER
The application layer (also called layer 5) is the software that enables the user to perform useful work. The
software at the application layer is the reason for having the network because it is this software that
provides the business value. This chapter focuses on the four fundamental types of application
architectures used at the application layer (host-based, client-based, client–server, cloud-based), plus a
fifth legacy architecture (peer-to-peer). It then looks at the Internet and the primary software application
packages it enables: the Web, email, and Telnet.
OBJECTIVES
Understand host-based, client-based, client–server, and cloud-based application architectures
Understand how the Web works
Understand how email works
Be aware of how Telnet and instant messaging work
OUTLINE
2.1 Introduction
2.2 Application Architectures
2.2.1 Host-Based Architectures
2.2.2 Client-Based Architectures
2.2.3 Client–Server Architectures
2.2.4 Cloud Computing Architectures
2.2.5 Peer-to-Peer Architectures
2.2.6 Choosing Architectures
2.3 World Wide Web
2.3.1 How the Web Works
2.3.2 Inside an HTTP Request
2.3.3 Inside an HTTP Response
2.4 Electronic Mail
2.4.1 How Email Works
2.4.2 Inside an SMTP Packet
2.4.3 Attachments in Multipurpose Internet Mail Extension
2.5 Other Applications
2.5.1 Telnet
2.5.2 Videoconferencing
2.6 Implications for Cyber Security
Summary | Page 50 | Chapter 11 |
4b3b20b723c2-0 | 2.1 INTRODUCTION
Network applications are the software packages that run in the application layer. You should be quite
familiar with many types of network software, because it is these application packages that you use when
you use the network. In many respects, the only reason for having a network is to enable these
applications.
In this chapter, we first discuss five basic architectures for network applications and how each of those
architectures affects the design of networks. Because you probably have a good understanding of
applications such as the Web and word processing, we will use those as examples of different application
architectures. We then examine several common applications used on the Internet (e.g., Web, email) and
use those to explain how application software interacts with the networks. By the end of this chapter, you
should have a much better understanding of the application layer in the network model and what exactly
we meant when we used the term protocol data unit in Chapter 1.
2.2 APPLICATION ARCHITECTURES
In Chapter 1, we discussed how the three basic components of a network (client computer, server
computer, and circuit) worked together. In this section, we will get a bit more specific about how the client
computer and the server computer can work together to provide application software to the users. An
application architecture is the way in which the functions of the application layer software are spread
among the clients and servers in the network.
The work done by any application program can be divided into five general functions. The first is data
storage. Most application programs require data to be stored and retrieved, whether it is a small file such
as a memo produced by a word processor or a large database such as an organization’s accounting
records. The second function is data access logic, the processing required to access data, which often
means database queries in SQL (structured query language). The third function is the application logic | Page 51 | Chapter 11 |
4b6a393a2034-1 | means database queries in SQL (structured query language). The third function is the application logic
(sometimes called business logic), which also can be simple or complex, depending on the application.
The fourth function is the presentation logic (sometimes called the user interface), the presentation of
information to the user and the acceptance of the user’s commands. The fifth function is services logic,
which is the provision of services to other applications (e.g., application program interfaces (API)). This is
like the user interface, but enables other application software packages to make requests, rather than
users. Not every application has services logic. These five functions—data storage, data access logic,
application logic, presentation logic, and services logic—are the basic building blocks of any application.
TECHNICAL FOCUS 2-1
Cloud Computing Deployment Models
When an organization decides to use cloud-based architecture, it needs to decide on which
deployment model will it use. There are three deployment models from which to choose:
Private cloud As the name suggests, private clouds are created for the exclusive use of a single
private organization. The cloud (hardware and software) would be hosted by the organization in
a private data center. This deployment model provides the highest levels of control, privacy, and
security. This model is often used by organizations needing to satisfy regulations posed by
regulators, such as in the financial and health-care industries.
Public cloud This deployment model is used by multiple organizations that share the same
cloud resources. The level of control is lower than in private clouds, and many companies are
concerned with the security of their data. However, this deployment model doesn’t require any
upfront capital investment, and the selected service can be up and running in a few days. Public
clouds are a good choice when a lot of people in the organization are using the same application. | Page 51 | Chapter 11 |
29d92f559e2e-2 | Because of this, the most frequently used software as a service (SaaS) is email. For example,
many universities have moved to this model for their students. | Page 51 | Chapter 11 |
8f1eaa221720-0 | Community cloud This deployment model is used by organizations that have a common
purpose. Rather than each organization creating its own private cloud, organizations decide to
collaborate and pool their resources. Although this cloud is not private, only a limited number of
companies have access to it. Community clouds are considered to be a subset of public clouds.
Therefore, community clouds realize the benefits from cloud infrastructure (such as speed of
deployment) with the added level of privacy and security that private clouds offer. This
deployment model is often used in the government, health care, and finance industries,
members of which have similar application needs and require a very high level of security.
Sometimes an organization will choose to use only one of these deployment models for all its
cloud-based applications. This strategy is called a pure strategy, such as a pure private cloud
strategy or a pure public cloud strategy. In other cases, the organization is best supported by a
mix of public, private, and community clouds for different applications. This strategy is called a
hybrid cloud strategy. A hybrid cloud strategy allows the organization to take advantage of
the benefits that these different cloud deployment models offer. For example, a hospital can use
Gmail for its email application (public cloud) but a private cloud for patient data, which require
high security. The downside of a hybrid cloud strategy is that an organization has to deal with
different platforms and cloud providers. However, the truth is that this strategy offers the
greatest flexibility, so most organizations eventually end up with this strategy.
There are many ways in which these five functions can be allocated between the client computers and the
servers in a network. There are four fundamental application architectures in use today. In host-based
architectures, the server (or host computer) performs virtually all of the work. In client-based
architectures, the client computers perform most of the work. In client–server architectures, the | Page 52 | Chapter 11 |
1e59e3a77dff-1 | work is shared between the servers and clients. In cloud-based architectures, the cloud provides services
(software, platform, and/or infrastructure) to the client. Although the client–server architecture is the
dominant application architecture, cloud-based architecture is becoming the runner-up because it
offers rapid scalability and deployability of computer resources.
2.2.1 Host-Based Architectures
The very first data communications networks developed in the 1960s were host-based, with the server
(usually a large mainframe computer) performing all functions. The clients (usually terminals) enabled
users to send and receive messages to and from the host computer. The clients merely captured
keystrokes, sent them to the server for processing, and accepted instructions from the server on what to
display (see Figure 2-1).
This very simple architecture often works very well. Application software is developed and stored on the
one server along with all data. If you’ve ever used a terminal or Citrix Receiver, you’ve used a host-based
application. There is one point of control, because all messages flow through the one central server. In
theory, there are economies of scale, because all computer resources are centralized (but more on cost
later).
There are two fundamental problems with host-based networks. First, the server must process all
messages. As the demands for more and more network applications grow, many servers become
overloaded and unable to quickly process all the users’ demands. Prioritizing users’ access becomes
difficult. Response time becomes slower, and network managers are required to spend increasingly more
money to upgrade the server. Unfortunately, upgrades to the mainframes that are usually the servers in
this architecture are “lumpy.” That is, upgrades come in large increments and are expensive (e.g.,
$500,000); it is difficult to upgrade “a little.” | Page 52 | Chapter 11 |
b863f3e76138-0 | FIGURE 2-1 Host-based architecture
2.2.2 Client-Based Architectures
In the late 1980s, there was an explosion in the use of personal computers. Today, more than 90% of most
organizations’ total computer processing power now resides on personal computers, not in centralized
mainframe computers. Part of this expansion was fueled by a number of low-cost, highly popular
applications such as word processors, spreadsheets, and presentation graphics programs. It was also
fueled in part by managers’ frustrations with application software on host mainframe computers. Most
mainframe software is not as easy to use as personal computer software, is far more expensive, and can
take years to develop. In the late 1980s, many large organizations had application development backlogs
of 2–3 years; that is, getting any new mainframe application program written would take years. New York
City, for example, had a 6-year backlog. In contrast, managers could buy personal computer packages or
develop personal computer-based applications in a few months.
With client-based architectures, the clients are personal computers on a LAN, and the server is usually
another personal computer on the same network. The application software on the client computers is
responsible for the presentation logic, the application logic, and the data access logic; the server simply
stores the data (Figure 2-2). There is no services logic.
This simple architecture often works very well. If you’ve ever used a word processor and stored your
document file on a server (or written a program in Visual Basic or C that runs on your computer but stores
data on a server), you’ve used a client-based architecture.
The fundamental problem in client-based networks is that all data on the server must travel to the client
for processing. For example, suppose the user wishes to display a list of all employees with company life | Page 53 | Chapter 11 |
00c20cc8eb52-1 | insurance. All the data in the database (or all the indices) must travel from the server where the database
is stored over the network circuit to the client, which then examines each record to see if it matches the
data requested by the user. This can overload the network circuits because far more data are transmitted
from the server to the client than the client actually needs.
2.2.3 Client–Server Architectures
Most applications written today use client–server architectures. Client–server architectures attempt to
balance the processing between the client and the server by having both do some of the logic. In these
networks, the client is responsible for the presentation logic, whereas the server is responsible for the data
access logic and data storage. The application logic may either reside on the client, reside on the server, or | Page 53 | Chapter 11 |
b24435aeb2ed-0 | be split between both.
Figure 2-3 shows one example, with the presentation logic and application logic on the client, and services
logic, application logic, data access logic and data storage on the server. In this case, the client software
accepts user requests and performs the application logic that produces database requests that are
transmitted to the server. The server software accepts the database requests, performs the data access
logic, and transmits the results to the client. The client software accepts the results and presents them to
the user.
When you used a Web browser to get pages from a Web server, you used a client–server architecture.
Likewise, if you’ve ever written a program that uses SQL to talk to a database on a server, you’ve used a
client–server architecture.
FIGURE 2-2 Client-based architecture
FIGURE 2-3 Two-tier thick client client–server architecture
For example, if the user requests a list of all employees with company life insurance, the client would
accept the request, format it so that it could be understood by the server and transmit it to the server. On
receiving the request, the server searches the database for all requested records and then transmits only
the matching records to the client, which would then present them to the user. The same would be true for
database updates; the client accepts the request and sends it to the server. The server processes the update
and responds (either accepting the update or explaining why not) to the client, which displays it to the
user.
One of the strengths of client–server networks is that they enable software and hardware from different | Page 54 | Chapter 11 |
c4a206255238-0 | vendors to be used together. But this is also one of their disadvantages, because it can be difficult to get
software from different vendors to work together. One solution to this problem is middleware, software
that sits between the application software on the client and the application software on the server.
Middleware does two things. First, it provides a standard way of communicating that can translate
between software from different vendors. Many middleware tools began as translation utilities that
enabled messages sent from a specific client tool to be translated into a form understood by a specific
server tool.
The second function of middleware is to manage the message transfer from clients to servers (and vice
versa) so that clients need not know the specific server that contains the application’s data. The
application software on the client sends all messages to the middleware, which forwards them to the
correct server. The application software on the client is therefore protected from any changes in the
physical network. If the network layout changes (e.g., a new server is added), only the middleware must be
updated.
There are literally dozens of standards for middleware, each of which is supported by different vendors
and provides different functions. Two of the most important standards are Distributed Computing
Environment (DCE) and Common Object Request Broker Architecture (CORBA). Both of these standards
cover virtually all aspects of the client–server architecture but are quite different. Any client or server
software that conforms to one of these standards can communicate with any other software that conforms
to the same standard. Another important standard is Open Database Connectivity (ODBC), which
provides a standard for data access logic.
Two-Tier, Three-Tier, and n-Tier Architectures
There are many ways in which the application logic can be partitioned between the client and the server.
The example in Figure 2-3 is one of the most common. In this case, the server is responsible for the data | Page 55 | Chapter 11 |
7c5fc8ce47c7-1 | and the client, the application and presentation. This is called a two-tier architecture, because it uses
only two sets of computers, one set of clients and one set of servers.
A three-tier architecture uses three sets of computers, as shown in Figure 2-4. In this case, the
software on the client computer is responsible for presentation logic, an application server is responsible
for the services logic and application logic, and a separate database server is responsible for the data
access logic and data storage.
n-tier architecture uses more than three sets of computers. In this case, the client is responsible for
presentation logic, a database server is responsible for the data access logic and data storage, and the
services logic and application logic are spread across two or more different sets of servers. Figure 2-5
shows an example of an n-tier architecture. The client uses the Web browser (presentation logic). The
Web server that responds to the user’s requests, either by providing Hypertext Markup Language (HTML)
pages and graphics (application logic) or by sending the request to the application server that perform
various tasks (services logic and application logic). The database server stores all the data (data access
logic and data storage). Each of these four components is separate, making it easy to spread the different
components on different servers and to partition the application logic on two different servers. | Page 55 | Chapter 11 |
a5603135c084-0 | FIGURE 2-4 Three-tier thin client client–server architecture
FIGURE 2-5 The n-tier thin client client–server architecture
The primary advantage of an n-tier client–server architecture compared with a two-tier architecture (or a
three-tier compared with a two-tier) is that it separates the processing that occurs to better balance the
load on the different servers; it is more scalable. In Figure 2-5, we have three separate servers, which | Page 56 | Chapter 11 |
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