User Generated




1. In the network, data are produced and exchanged according to meticulously defined rules of communication and engagement. These rules are codified in the _________.

Group of answer choices

intermediary device




network link

2. The fiber optic cable uses _____ signal encoding.

Group of answer choices

two-level voltage



multiple-level voltage

on and off

3. Which is an intermediary device designed to facilitate inter-networking?

Group of answer choices



network printer



access point

Question 8 pts

The ____ bit in the TCP header is used to request handshaking.

Group of answer choices






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A Practical Introduction to Enterprise Network and Security Management A Practical Introduction to Enterprise Network and Security Management Bongsik Shin, Ph.D CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2017 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-1-4987-8797-0 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. 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Visit the Taylor & Francis Web site at and the CRC Press Web site at Contents Preface Author Chapter 1: Fundamental Concepts 1.1 Introduction 1.2 Network Elements 1.2.1 Host Client–Server Mode P2P Mode Network Interface Card 1.2.2 Intermediary Device 1.2.3 Network Link 1.2.4 Application 1.2.5 Data/Message 1.2.6 Protocol 1.3 Modes of Communication 1.3.1 Methods of Data Distribution Unicasting Broadcasting Multicasting 1.3.2 Directionality in Data Exchange Simplex Duplex 1.4 Network Topology 1.4.1 Point-to-Point Topology 1.4.2 Bus Topology 1.4.3 Ring Topology 1.4.4 Star (Hub-and-Spoke) Topology 1.4.5 Mesh Topology 1.4.6 Tree (or Hierarchical) Topology 1.5 Classification of Networks 1.5.1 Personal Area Network 1.5.2 Local Area Network 1.5.3 Metropolitan Area Network 1.5.4 Wide Area Network 1.5.5 Rise of Internet of Things 1.6 Subnetwork versus Inter-network 1.7 Measures of Network Performance 1.7.1 Capacity Data Types and Data Rate 1.7.2 Delay 1.7.3 Reliability 1.7.4 Quality of Service 1.8 Numbering Systems 1.8.1 Binary versus Decimal 1.8.2 Binary versus Hexadecimal 1.9 Network Addressing 1.9.1 Characterizing Network Addressing 1.9.2 MAC Address 1.9.3 IP Address 1.9.4 Pairing of MAC and IP Addresses Chapter Summary Key Terms Chapter Review Questions Chapter 2: Architectures and Standards 2.1 Introduction 2.2 TCP/IP versus OSI 2.2.1 Standard Architecture 2.2.2 Standard and Protocol 2.2.3 Protocol Data Unit 2.3 Layer Functions: An Analogy 2.4 Layer Processing 2.5 Application Layer (Layer 5) 2.5.1 HTTP Demonstration 2.5.2 Select Application Layer Protocols 2.6 Transport Layer (Layer 4) 2.6.1 Provision of Data Integrity Error Control Flow Control TCP and Data Integrity UDP and Data Integrity 2.6.2 Session Management Session versus No Session Session Management by TCP TCP Session in Real Setting Additional Notes 2.6.3 Port Management Port Types and Ranges Source versus Destination Port Socket 2.7 Internet Layer (Layer 3) 2.7.1 Packet Creation and Routing Decision Packet Creation Packet Routing Decision 2.7.2 Performing Supervisory Functions 2.8 Data Link Layer (Layer 2) 2.8.1 LAN Data Link Frame and Switching Link Types Technology Standard(s) Single Active Delivery Path Frame’s MAC Addresses 2.8.2 WAN Data Link 2.9 Physical Layer (Layer 1) 2.10 Layer Implementation 2.10.1 Application Layer 2.10.2 Transport and Internet Layers 2.10.3 Data Link and Physical Layers Chapter Summary Key Terms Chapter Review Questions Chapter 3: Intermediary Devices 3.1 Introduction 3.2 Intermediary Devices 3.2.1 Operational Layers 3.2.2 Operating System General Attributes Access to Operating System 3.3 Hub (Multiport Repeater) 3.4 Bridge and Wireless Access Point 3.5 Switch 3.5.1 General Features 3.5.2 Switch Port 3.5.3 Switch Table Switch Table Entries Switch Learning Aging of Entries 3.5.4 Switch Types Nonmanaged versus Managed Switches Store-and-Forward versus Cut-Through Switches Symmetric versus Asymmetric Switches Layer 2 versus Layer 3 Switches Fixed, Stackable, and Modular Switches Power over Ethernet 3.5.5 Security Issues Safeguarding Switch Ports Port Mirroring 3.6 Routers 3.6.1 Two Primary Functions Routing Table Development and Its Update Packet Forwarding 3.6.2 Router Components 3.6.3 Router Ports and Naming 3.6.4 Router Configuration Basic Features Advanced Features 3.7 Switching versus Routing 3.7.1 Data Link Layer versus Internet Layer 3.7.2 Connection-Oriented versus Connectionless 3.7.3 Single Delivery versus Multiple Delivery Paths 3.8 Address Resolution Protocol 3.8.1 Background 3.8.2 ARP Usage Scenarios 3.9 Choice of Intermediary Devices 3.10 Collision versus Broadcast Domains 3.10.1 Collision Domain Collision Domain Types Collision Domain and Network Design CSMA/CD 3.10.2 Broadcast Domain Chapter Summary Key Terms Chapter Review Questions Chapter 4: Elements of Data Transmissions 4.1 Introduction 4.2 Data Transmission Elements 4.2.1 Digital Signaling On/Off Signaling Voltage Signaling 4.2.2 Analog Signaling Properties of Analog Signal Modulation 4.2.3 Signaling Devices Modem and Analog Signaling CSU/DSU and Digital Signaling 4.2.4 Bandwidth and Related Concepts Bandwidth Baseband and Broadband 4.2.5 Synchronous versus Asynchronous Transmissions Asynchronous Transmission Synchronous Transmission 4.2.6 Multiplexing Frequency Division Multiplexing FDM Example: ADSL Time Division Multiplexing TDM Example: T-1 Line Spread Spectrum 4.2.7 Digital Speed Hierarchies Digital Signal Optical Carrier/Synchronous Transport Module 4.3 Networking Media 4.3.1 Propagation Effects Attenuation Distortion 4.3.2 Twisted Pairs UTP versus STP Cable Structure and Categories Twisted-Pair Patch Cable 4.3.3 Optical Fibers Advantages Physical Structure Single Mode versus Multimode Fiber Patch Cable 4.3.4 LAN Cabling Standards 4.4 Structured Cabling 4.4.1 Background 4.4.2 Structured Cabling System Chapter Summary Key Terms Chapter Review Questions Chapter 5: IP Address Planning and Management 5.1 Introduction 5.2 Governance of IP Address Space 5.3 Structure of the IP Address 5.3.1 Binary versus Decimal Value Conversion 5.3.2 Structure of the IP Address 5.4 Classful IP: Legacy 5.4.1 Class A Network 5.4.2 Class B Network 5.4.3 Class C Network 5.5 Classless IP: Today 5.6 Special IP Address Ranges 5.6.1 Loopback Internal Testing of TCP/IP Stack Off-Line Testing of an Application 5.6.2 Broadcasting Limited Broadcasting Directed Broadcasting Security Risk of Directed Broadcasting 5.6.3 Multicasting 5.6.4 Private IP and NAT NAT: One-to-One IP Mapping NAT: Many-to-One IP Mapping Pros and Cons of NAT 5.7 Subnetting 5.7.1 Defining Subnet Boundary (Review) 5.7.2 Subnetwork Addressing 5.8 Subnet Mask 5.8.1 Subnet Mask 5.8.2 Subnetting Address Space 5.8.3 Broadcasting within a Subnet 5.9 Supernetting 5.10 Managing IP Address SPACE 5.10.1 Determining Number of Nodes 5.10.2 Determining Subnets Managing Security with DMZ Subnet Developing IP Assignment Policy Chapter Summary Key Terms Chapter Review Questions Hands-On Exercise: Enterprise IP Management at Atlas Co. Chapter 6: Fundamentals of Packet Routing 6.1 Introduction 6.2 Routing Mechanism 6.3 Routing Table 6.3.1 Background 6.3.2 Routing Table Elements 6.4 Packet Forwarding Decision 6.5 Entry Types of Routing Table 6.5.1 Directly Connected Routes 6.5.2 Static Routes Static Routes of a Router Static Routes of a Host 6.5.3 Dynamic Routes 6.6 Dynamic Routing Protocols 6.6.1 Protocol Categories Interior Gateway Protocols Exterior Gateway Protocols 6.6.2 Delivery of Advertisement 6.6.3 Determination of Dynamic Routes 6.6.4 Security Management 6.6.5 Static versus Dynamic Routing 6.7 Inter-domain Routing 6.8 Perspectives on Packet Routing Chapter Summary Key Terms Chapter Review Questions Chapter 7: Ethernet LAN 7.1 Introduction 7.2 Standard Layers 7.3 Ethernet Frame 7.3.1 Frame Structure 7.3.2 Addressing Modes 7.4 Ethernet LAN Design 7.4.1 Flat versus Hierarchical Design 7.4.2 Access Layer 7.4.3 Distribution and Core Layers 7.4.4 Benefits of Hierarchical Design 7.5 Spanning Tree Protocol 7.5.1 Link Redundancy 7.5.2 Protocols and Mechanism 7.6 Link Aggregation Review Questions 7.7 Virtual LANs (VLANs) 7.7.1 Background: Without VLANs 7.7.2 VLAN Concept 7.8 VLAN Scenarios 7.8.1 Without VLANs 7.8.2 With VLANs Define VLANs on Switches Plan the Range of Trunk and Access Ports Assign Access Ports to VLANs 7.8.3 How VLANs Work 7.8.4 VLAN ID versus Subnet Addressing 7.9 VLAN Tagging/Trunking (IEEE802.1Q) 7.9.1 Background 7.9.2 VLAN Tagging 7.9.3 VLAN Tagging/Untagging Process 7.10 VLAN Types 7.10.1 Default VLAN 7.10.2 Data VLAN Data VLAN and Security 7.10.3 Voice VLAN 7.11 Inter-VLAN Routing 7.11.1 A Router Interface per VLAN Scenario 1 Scenario 2 7.11.2 Sub-Interfaces/Ports (Advanced) 7.12 VLANS and Network Management Chapter Summary Key Terms Chapter Review Questions Chapter 8: Wireless LAN (WiFi) 8.1 Introduction 8.2 Standard Layers and Wireless Cards 8.3 WiFi Setup Modes 8.3.1 Ad Hoc Mode 8.3.2 Infrastructure Mode 8.4 Wireless Access Points 8.4.1 AP in Infrastructure Mode 8.4.2 AP in Non-infrastructure Modes Repeater Mode Bridge Mode 8.5 SSID, BSS, and ESS 8.5.1 Service Set Identifier 8.5.2 BSS versus ESS Basic Service Set Extended Service Set 8.6 Media Access Control 8.6.1 CSMA/CA 8.6.2 RTS/CTS 8.7 WiFi Frames 8.7.1 Data Frame 8.7.2 Management Frame 8.7.3 Control Frame 8.8 WiFi and Radio Frequency 8.8.1 Radio Spectrum Low versus High Radio Frequency Governance Licensed versus Unlicensed Radio 8.8.2 WiFi Channels 8.8.3 Planning Basic Service Sets 8.9 Authentication and Association 8.9.1 Three-Stage Process 8.9.2 Authentication Methods of a Station Open Authentication Pre-shared Key Authentication Authentication Server Additional Notes on Security 8.10 WiFi Standards 8.10.1 IEEE802.11n Throughput Modes 2.4/5.0 GHz Bands Single-User MIMO QoS Support 8.10.2 IEEE802.11ac 5.0 GHz Band Throughput Modes Multi-user MIMO 8.11 WiFi Mesh Network (IEEE802.11s) 8.12 WiFi Home/SOHO Network 8.12.1 DSL/Cable Modem 8.12.2 Wireless Access Router 8.12.3 IP Configuration 8.12.4 Case: Wireless Access Router Configuration Chapter Summary Key Terms Chapter Review Questions Chapter 9: Wide Area Network 9.1 Introduction 9.2 WAN and Enterprise Networks 9.2.1 WAN Connection Scenarios 9.2.2 Service-Level Agreement 9.2.3 CPE versus SPF Demarcation Point 9.2.4 WAN Design Considerations 9.3 Layers of WAN Standards 9.3.1 Physical Layer 9.3.2 Data Link Layer Circuit Switching Packet Switching 9.3.3 Comparison: WAN versus LAN 9.4 IP Addressing for WAN Links 9.4.1 Leased Lines 9.4.2 Packet Switched Data Network One Subnet between Two Locations One Subnet for All Locations 9.5 Physical Layer Options: Leased Lines 9.5.1 T-Carrier/E-Carrier T1 and T3 Circuits 9.5.2 SONET/SDH 9.6 Data Link Standard: Leased Lines 9.6.1 PPP Frame Structure 9.6.2 Router Authentication PAP versus CHAP 9.7 Data Link Standards: PSDN 9.7.1 General Attributes 9.7.2 Virtual Circuits WAN Switch Table PVC versus SVC Access Link Speeds 9.8 Frame Relay 9.8.1 General Characteristics 9.8.2 Frame Structure 9.8.3 Data Link Connection Identifier How DLCI Works FR Switch Table Multiple VCs and DLCIs 9.8.4 Mapping IP Addresses 9.9 Asynchronous Transfer Mode 9.9.1 Background 9.9.2 Cell Switching 9.9.3 Quality of Service 9.10 Carrier Ethernet 9.10.1 Background 9.10.2 Strengths 9.10.3 Service Transport 9.11 Multi-Protocol Label Switching 9.11.1 Labels and Label Information Base 9.11.2 Benefits of MPLS 9.12 Wireless WAN: Cellular Network 9.12.1 General Architecture Cell Base Station Mobile Terminal Switching Office Call Channels 9.12.2 Multiple Access Technologies Frequency Division Multiple Access Time Division Multiple Access Code Division Multiple Access Orthogonal Frequency Division Multiple Access 9.12.3 Generations of Cellular Standards 9.12.4 LTE and Future Long-Term Evolution What Does the Future Hold? Chapter Summary Key Terms Chapter Review Questions Chapter 10: The Internet and Client–Server Systems 10.1 Introduction 10.2 Internet Architecture 10.2.1 Internet Service Provider National ISPs Regional/Local ISPs ISP Network Architecture 10.2.2 Internet Exchange Point 10.2.3 Autonomous System 10.2.4 World Wide Web and Search Engine World Wide Web Deep Web 10.3 VPN for Secure Communications 10.3.1 Technology Background VPN Technology 10.3.2 Benefits of VPN Cost-Effectiveness Accessibility and Scalability Flexibility 10.3.3 Risks of VPN Reliability Security 10.3.4 Types of VPN Remote-Access VPN Site-to-Site VPN 10.3.5 VPN Standards 10.3.6 IP Security Tunnel Mode Transport Mode 10.3.7 Secure Socket Layer Broad Acceptance VPN Implementation SSL and Internet Commerce 10.3.8 IPSec versus SSL 10.4 IPv6 (IP Next Generation) 10.4.1 Background 10.4.2 IP Packet Structure 10.4.3 IP Addressing Subnet Address Bits Host Address Bits 10.4.4 Address Abbreviation 10.4.5 IPv6 versus IPv4 Standards 10.4.6 Transition Approaches Dual IP Stacks within a Node Direct Address Conversion Packet Tunneling 10.5 Client–Server Applications 10.5.1 Domain Name System Domain and Name Resolution Domain Hierarchy DNS Architecture Host DNS File 10.5.2 Dynamic Host Configuration Protocol The Process View 10.6 Server Virtualization 10.6.1 Traditional Computing Model 10.6.2 Virtualization Concept 10.6.3 Virtualization Approaches Hosted Virtualization Hypervisor-Based Virtualization 10.6.4 Shared Infrastructure 10.6.5 Summary: Benefits Realized Chapter Summary Key Terms Chapter Review Questions Chapter 11: Cybersecurity: Threats 11.1 Introduction 11.2 Malicious Codes: Malware 11.2.1 Virus 11.2.2 Worm 11.2.3 Trojan 11.2.4 Bot 11.2.5 Other Malware Types 11.2.6 Malware Issues 11.3 Password Cracking 11.3.1 Brute Force Method 11.3.2 Dictionary Method 11.4 Spoofing 11.4.1 Source Address Spoofing IP Spoofing MAC Spoofing 11.4.2 Email Spoofing 11.4.3 Web (or HTTP) Spoofing 11.5 Denial of Service 11.5.1 Pinging and SYN Requests Pinging SYN Requests 11.5.2 Distributed DOS 11.5.3 MAC Address Flooding 11.6 Packet Sniffing 11.6.1 Packet Sniffing with Wireshark 11.7 Port Scanning 11.7.1 Port Scanning with Zenmap 11.8 Social Engineering 11.9 Man-in-the-Middle 11.9.1 MITM with Bogus DHCP Server 11.10 Spam 11.11 Poisoning 11.11.1 ARP Poisoning (ARP Spoofing) 11.11.2 DNS Poisoning (DNS Spoofing) 11.12 Zero-Day Attack 11.13 WiFi Threats 11.13.1 Wardriving 11.13.2 Denial of Service 11.13.3 Rogue AP 11.13.4 MITM Chapter Summary Key Terms Chapter Review Questions Chapter 12: Cybersecurity: Defenses 12.1 Introduction 12.2 Security Requirements and Solutions 12.2.1 Security Requirements Confidentiality (Privacy) Data Integrity Authentication Access Control/Authorization Availability 12.2.2 Technology Solutions 12.3 Principles in Architecting Defense 12.3.1 Layering 12.3.2 Limiting 12.3.3 Simplicity 12.4 Firewall 12.4.1 Firewall and DMZ Separating Firewall and Border Router 12.4.2 Firewall Functions and Management Firewall Functions Managing Firewall 12.4.3 Stateless versus Stateful Filtering Stateless Filtering Stateful Filtering 12.5 Access Control List 12.5.1 How Many ACLs? 12.5.2 ACL Filtering versus Packet Routing 12.6 Cryptography 12.6.1 Cryptography System Basic Components How It Works 12.6.2 Symmetric-Key Cryptography 12.6.3 Asymmetric-Key Cryptography How It Works Pros and Cons 12.6.4 Hybrid Approach 12.6.5 Hashing Cryptography 12.7 Digital Signature 12.8 Digital Certificate 12.8.1 Digital Certificate 12.8.2 Certificate Authority 12.9 Security Protocol 12.9.1 WiFi Security Standards Wired Equivalent Privacy WiFi Protected Access (WPA and WPA2) Enterprise Mode versus Personal Mode Chapter Summary Key Terms Chapter Review Questions Glossary Acronyms Index Preface This book is written for those who study or practice information technology, management information systems (MIS), accounting information systems (AIS), or computer science (CS). It is assumed that readers are exposed to computer networking and security subjects for the first time. Computer networking and cybersecurity are challenging subjects, partly because of the constant rise and fall of related technologies and IT paradigms. As the title implies, much focus of this book is on providing the audience with practical, as well as, theoretical knowledge necessary to build a solid ground for a successful professional career. If used for a class, the book of 12 chapters contains just about right amount of coverage for a semester or quarter. It balances introductory and fairly advanced subjects on computer networking and cybersecurity to effectively deliver technical and managerial knowledge. Although the writing is moderately dense, utmost attempts have been made on explaining sometimes challenging concepts in a manner that readers can follow through, with careful reading. The book is designed to offer impactful, hands-on learning experience without relying on a computer lab. First, each chapter comes with practical exercise questions. In the class setting, they are good as individual or group assignments. Many of them are based on simulated or real cases, and take advantage of actual industry products and systems for a reader to better relate theories to practice. Second, there are a number of information-rich screen shots, figures, and tables in each chapter carefully constructed to solidify concepts and thus enhance visual learning. In addition to the thorough technical details, managerial issues including, enterprise network planning, design, and management are embedded throughout the book from the practitioner’s perspective to assist balanced learning. Besides, bearing in mind of the critical importance of security in today’s enterprise networks, implications of network design and management on enterprise security are discussed whenever appropriate. Lastly, to further reinforce knowledge in security management, two chapters are dedicated to introduce fundamentals of cybersecurity in terms of threat types and defense techniques. Author Bongsik Shin is a professor of management information systems at San Diego State University. He earned a Ph.D. from the University of Arizona and was an assistant professor at the University of Nebraska at Omaha before joining San Diego State University. He has taught computer network & cybersecurity management, business intelligence (data warehousing & data mining, statistics), decision support systems, electronic commerce, and IT management & strategy. Especially, he has been teaching computer networking and cybersecurity continuously over 20 years. His academic activities in pursuit of teaching and research excellence have been funded by more than 25 internal and external grants. His recent research efforts have been all about cybersecurity on subjects related to cyber threat intelligence, ransomware, authentication & access control and countermeasures of phishing. Recently, his team, he as the principal investigator, has been awarded a grant by the US Department of Defense to conduct research on “Actionable Intelligence-Oriented Cyber Threat Modeling.” He has published more than 30 articles in such high impact journals as MIS Quarterly; IEEE Transactions on Engineering Management; IEEE Transactions on Systems, Man, and Cybernetics; Communications of the ACM; Journal of Association for Information Systems; European Journal of Information Systems; Journal of Management Information Systems; Information Systems Journal; Information & Management; and Decision Support Systems. In 2016, he served as a conference cochair of the Americas Conference on Information Systems, one of the three largest MIS conferences with attendees from 40+ countries. 1 Fundamental Concepts 1.1 Introduction By definition, the computer network represents a collection of wired and wireless communication links through which computers and other hardware devices exchange data (or messages). A network can be either as small as the one installed in a house or as big as the Internet that literally covers the entire planet. The size of a particular network, thus, reflects the size of the place (e.g., building, campus) where it is installed. In recent days, the wireless and wired network links have become the arteries of organizations (e.g., companies, universities) and the society, revolutionizing every facet of our life by facilitating resource (e.g., storage) sharing and exchange of data (e.g., texts, videos, music) in an unprecedented manner. Throughout this book, the two terms “data” and “message” are used synonymously. Because of the rapid advancement of information and communication technologies (ICTs), more electronic and mobile devices are being attached to the computer network. Among them are digital smart phones, high-definition Internet protocol televisions (IPTVs), music and video game players, tablets such as iPads, electronic appliances, and control and monitoring systems (e.g., security cameras, closed-circuit televisions (CCTVs), traffic signals). The rapid increase of various digital devices is transforming the network into a more dynamic, diversified, and, at the same time, more vulnerable platform. Besides the digital computer network, there are also other traditional network platforms that existed long before the digital revolution. They include radio/TV broadcasting networks and public switched telephone networks. The traditional networks are, however, not the focus of this book. Although traditional networks and digital computer networks started off on separate platforms, their convergence has been taking place. For instance, nowadays, more voice calls are digitized and transported over the Internet. Think of the popularity of Internet call services such as Skype, Vonage, and Google Voice. The convergence is accelerating as the computer network has become stable in handling both non-realtime (e.g., email, web browsing) and real-time (e.g., voice, live video) traffic. The prevalence of computer networks, meanwhile, poses a great deal of cybersecurity threats to individuals, organizations (e.g., businesses, universities), and governments. The threats are getting stealthier and sophisticated, inflicting more grave consequences on victims than ever before. Aggressors and organized crimes have mounted various cybersecurity attacks, and numerous ill-prepared individuals and public/private organizations have suffered dearly. Amid the constant news of cybersecurity breaches, adequate preparations including threat monitoring and prevention have become essential in the design and operation of computer networks. This chapter covers the fundamental concepts of computer networking. Main objectives of this chapter are to learn the following: Key elements of a computer network Methods used by network nodes to distribute data Directionality in data propagation Network topologies focusing on physical layouts Classification of networks in terms of their scope Subnetwork versus inter-network Key measures of network performance Binary, decimal, and hexadecimal numbering systems Addressing methods: Internet protocol (IP) and media access control (MAC) 1.2 Network Elements A computer network is made up of various hardware and software components including hosts, intermediary devices, network links (or communication links), applications, data, and protocols. Figure 1.1 demonstrates a simple network in which two hosts (i.e., a personal computer (PC) and a server) exchange data produced by applications (e.g., web browser, web server) in accordance with a protocol over the two network links joined by an intermediary device. Each of the constituents is briefly explained. 1.2.1 Host In this book, the host is defined as a data-producing entity attached to a network, and it has been primarily a computer. Oftentimes, hosts are also called end devices, end systems, or end stations. They are capable of accepting user inputs (e.g., keyboarding, video feeds from a camera), processing them, generating outputs in the form of 1s and 0s, and storing them. The outputs can be digitized texts, sounds, images, videos, or any other multimedia contents that can be transported over the computer network. Figure 1.1 Key elements of a computer network. The host is generally a source or a destination of data in transit, and it has been predominantly a general-purpose or high-performance computer (e.g., PC, laptop, mainframe, supercomputer). Because of continuous addition of nontraditional computing and communication devices to the network, host types are much more diversified these days. They include smart phones, personal digital assistants (PDAs), video game consoles, home electronics and appliances, and other peripheral devices, such as, network-enabled printers, copiers, and fax machines. When hosts exchange data over a network, their relationship is in one of two modes: client–server or peer-topeer (P2P) (see Figure 1.2). Figure 1.2 Client–server versus P2P networking. Client–Server Mode In the client–server mode, a host acts as a dedicated client or server. The client host takes advantage of resources (e.g., files, storage space, databases, web pages, central processing unit (CPU) processing) offered by servers. The server host generally has high-performance capacity to quickly respond to resource requests from client hosts. In the early days, many programs (e.g., Microsoft Outlook for email) installed in the client host were tailored to a particular server application (e.g., Microsoft Exchange). However, the web browser (e.g., Firefox, Google Chrome) has changed it all. The browser has become an application that allows a client host to communicate with many different server applications (e.g., email, database, web servers) over the network. This one client (web browser) to many server applications has benefitted individuals and organizations tremendously. Above all, using the “thin” client in which a client host only needs a web browser to take advantage of resources available from various servers, organizations can control IT spending and save efforts necessary to maintain programs on client hosts. P2P Mode In P2P networking, each participating host on a network behaves as both a client and a server in sharing resources with other hosts. As an example, by joining P2P filesharing sites such as, anyone can download multimedia files available from other participating computers (client mode) and, at the same time, allow others to copy files available in his/her hard drive (server mode) over the Internet. As another example of the P2P technology, today’s operating systems such as Windows support P2P networking among nearby computers, especially through the WiFi technology called WiFi Direct. Exercise 1.1 1. It is generally agreed that the client–server approach has several advantages over P2P computing. Explain why in terms of the following aspects. Search the Internet if necessary. a. Easier to protect server resources such as data b. Better accessibility to server resources c. Easier to back up server resources d. More cost-effective in maintaining and upgrading server programs (or applications) e. Easier to add server resources to meet growing demands 2. Create a simple private P2P network and conduct file swapping. For this, form a team of two students each with his/her own computer. Then, create a P2P network by connecting the two computers on WiFi. P2P requires additional configuration (e.g., creation of a workgroup on Windows). Once the configuration is complete, exchange files over the P2P network. If necessary, conduct Internet search to learn the setup procedure. Network Interface Card To access a network, the host should be equipped with at least one network interface card (NIC), which is an electronic circuit board. Also called an adaptor or a local area network (LAN) card, the NIC is generally built into a computer these days, and it converts host-generated binary data (e.g., emails) into signals (e.g., electronic currents, lights, radio signals) and releases them to the network. The NIC also accepts signals arriving over the network, restores original data, and forwards them to the host’s CPU for processing. Figure 1.3 NIC cards for (a) Ethernet and (b) WiFi. (From Many user computers have two NICs these days: one for cabled Ethernet LAN and the other for Wireless (or WiFi) LAN to enable both wired and wireless networking as needed. Figure 1.3 illustrates NIC cards for Ethernet and WiFi. It can be observed that an Ethernet NIC has one or more ports that allow physical connectivity of a computer to the wired network, but the wireless NIC (WNIC) has one or more antennas for radio communications. Wireless NICs in universal serial bus (USB) are also popular. Each NIC comes with a unique address, called a physical or MAC address (to be explained). 1.2.2 Intermediary Device Depending on the size, a network can have many different intermediary devices that conduct functions necessary to relay data between the source and destination hosts. Intermediary devices do not produce user data, but transport them in an effective, reliable, and secure manner. Among the frequently used intermediary devices are modems, firewalls, multiplexers, channel service unit (CSU)/data service unit (DSU), hubs (or multiport repeaters), switches, routers, bridges, and wireless access points. Their functional details are explained in other chapters, mainly in Chapter 3. Hubs, bridges, wireless access points, and switches provide hosts (e.g., clients, servers) with inter-connectivity “within” a network segment called a subnetwork (or subnet). In contrast, the router is used to tie different network segments (or subnetworks). The data-forwarding activity (e.g., email delivery between two nodes) taking place within a subnetwork boundary is termed as intra-networking and that across two or more subnetworks joined by routers is called inter-networking (see Figure 1.4). In other words, hubs, bridges, wireless access points, and switches are intra-networking devices, and routers are inter-networking devices. More on intra- networking versus inter-networking is explained in Section 1.6. Figure 1.4 Intra-networking and inter-networking devices. Intermediary devices are distinct from each other in many different ways. For example, some devices (e.g., hubs) transmit data in the half-duplex mode, whereas others (e.g., switches, routers) transmit data in the full-duplex mode (for more details, see Section 1.3.2). Some devices are hardware-driven in performing their primary functions, while others rely more on their software capability. Software-enabled devices generally use a higher level of intelligence to conduct networking functions than their hardware-enabled counterparts. Intermediary devices are also different in their processing speeds, in their capacity of data filtering and security provision, and in the addressing mechanism used to move data. As with the host, an intermediary device also has one or more internal network cards with built-in ports (or interfaces) to tie wireless or wired network segments. Because of the critical importance of intermediary devices in computer networking, Chapter 3 is dedicated to cover their structural and functional features in detail. The term “network node” is used throughout the book as an inclusive concept that refers to an intermediary device or a host. Network nodes = Intermediary devices + Hosts (end devices). 1.2.3 Network Link The network link is a wired (or guided) or wireless (or unguided) connection that enables data exchange between network nodes. Various communication media have been used to form a link. Copper wires (e.g., twisted pairs, coaxial cables) and optical fibers made of extremely pure glass or plastic are the predominant wired transmission media these days. The earth’s atmosphere becomes the medium of wireless communications. Data are transported in the form of various signals through the guided and unguided media: electronic signals through copper wires and coaxial cables, light signals through optical fibers, and radio/microwave signals in the atmosphere. Details on the media and communication signals are explained in Chapter 4. The network link can be either an access link or a trunk link. While the access link provides direct connectivity between a host (end station) and an intermediary device, the trunk link interconnects intermediary devices (e.g., router–router, router–switch, switch–switch), resulting in the extension of network span. The trunk link is a point-topoint connection, and it generally carries traffic that comes from multiple access links. When two hosts exchange data through two or more intermediary devices, they take one or more trunk links to complete the end-to-end data delivery (see Figure 1.5). Although trunk links are not necessary to create a small-scale network such as the one shown in Figure 1.1, most organizations rely on them to create an enterprise network. Figure 1.5 Access links versus trunk links. Exercise 1.2 The hypothetical enterprise network of an organization shown in Figure 1.6 covers one main office and two remotely located branch offices. Each office has its own LAN, and the three LANs are interconnected by routers (R1, R2, and R3) over the three wide area network (WAN) links leased from a WAN service provider. Figure 1.6 A hypothetical enterprise network. 1. 2. 3. 4. 5. 6. 7. How many hosts does each LAN contain? How many intermediary devices does each LAN contain? How many access links and trunk links are there in each LAN? What is the total number of access links and trunk links? How many network nodes are there in the enterprise network? What intermediary devices are used for intra-networking in each LAN? What intermediary device is used for inter-networking? 1.2.4 Application The application (e.g., MS Outlook, web browser) represents a software program developed to support a specialized user task (e.g., email exchange, web surfing). Numerous applications have been introduced to support various tasks over the computer network. Many of them are designed to improve communications, which include those of email (e.g., Outlook, Thunderbird), instant messaging (e.g., Yahoo Messenger), and voice & video (e.g., Skype, Google Voice). Also, the web browser has become an extremely popular application on which countless online services (e.g., social networking, online banking, e-commerce, cloud computing) are offered over the Internet. Applications can be characterized from different angles, and their individual and organizational usage has important implications on the design of computer networks because of the close relevance between application types and requirements of network performance. For instance, the majority of user applications need to be supported by the following: Predictable or guaranteed network reliability (e.g., financial transactions) Predictable or guaranteed network capacity/speed (e.g., videoconferencing) Little or no network delay/latency (e.g., audio conferencing, video streaming) Reasonable network responsiveness (though not real time) (e.g., web browsing, instant messaging) Figure 1.7 Transmission of discrete data units over a computer network. 1.2.5 Data/Message Applications produce data (or messages) that need to be transported over the network. The data may be real-time or interactive audios/videos, or such static contents as web pages and emails. In computer networking, data produced are packaged in discrete data units and are delivered to the destination one by one. As a simple demonstration, imagine a network-enabled conversation between two persons and observe how their dialog is packaged into discrete data units and gets delivered (see Figure 1.7). The general name of each data unit is packet. Each packet contains source data and additional overhead information necessary for its delivery, such as source and destination addresses. To better visualize the relationship between source data and a packet, think of a letter (as source data) contained in an envelope with mailing addresses (as a packet). 1.2.6 Protocol A host application (e.g., web browser, email program) produces and exchanges data/messages according to a protocol, which contains a collection of detailed communication rules. For this, an application has a particular protocol built into it (e.g., Hypertext Transfer Protocol [HTTP] embedded in the browser). The application produces outgoing data and interprets incoming data strictly based on the set of communication rules defined by the built-in protocol. There are two types of communication rules: Syntactic rules: Rules regarding the format of a message in its construction Semantic rules: Rules concerned with the meaning or interpretation of a message For example, if a computer user enters into a web browser’s Uniform Resource Locator (URL), the browser produces a simple request message according to the built-in HTTP. Here, the request message has syntax similar to GET/HTTP/1.1 Host: so that the target host ( server) can understand/interpret its meaning (or semantics). The semantics of the above statements is “Please send me the main page of using HTTP, version 1.1.” The request message thus produced is then dispatched to the target server. Certain protocols are standardized so that hardware and software vendors can incorporate them into their own products. For example, HTTP is a standard protocol adopted by all web browsers (e.g., Firefox, Internet Explorer, Chrome) and web servers (e.g., Apache, Microsoft IIS). There are also numerous proprietary protocols developed by vendors exclusively for their own commercial products (e.g., the protocol embedded in Skype or Yahoo Messenger). Important standard protocols are introduced throughout the book. 1.3 Modes of Communication This section explains methods utilized by network nodes to distribute data and the directionality of data exchanges. 1.3.1 Methods of Data Distribution The methods of data distribution between network nodes are primarily unicasting, broadcasting, and multicasting (see Figure 1.8). Unicasting In unicasting, data exchange takes place between a single source and a single destination node identified by their unique addresses. The destination may be located within the same network of the source or separated from the source across multiple networks. It was explained that the co-location of the source and the destination within a subnetwork takes intra-networking for data delivery. When the source and the destination are in different subnetworks, data delivery requires inter-networking (for more details, see Section 1.6). Normally, the majority of messages produced by a user application are exchanged in this mode. Figure 1.8 Multicasting, broadcasting, and unicasting. Broadcasting Broadcasting results in the flooding of data from one node to all the other nodes within a network. In fact, we have been enjoying the broadcasting service daily by tuning into radio or TV channels. From satellites or earth stations, radio and TV companies broadcast signals that carry various contents (e.g., music, drama, reality shows). Such broadcasting is also widely used by computer networks for various reasons. A prevalent example is WiFi. Multicasting Multicasting from a data source results in its concurrent delivery to a selected group of destinations. We have been using multicasting services extensively. For example, numerous online sites provide multimedia streaming for live news, music, TV programs, movies, online gaming, and SNS videos over the Internet. These services rely on a multicasting protocol so that a server can stream multimedia contents to requesting clients concurrently. With the growing popularity of such on-demand multimedia services, usage of multicasting will only grow. Although the demonstration in Figure 1.8 is only between hosts, intermediary nodes including switches and routers also take advantage of them to advertise supervisory information or to exchange information necessary to perform scheduled and unscheduled network control functions. 1.3.2 Directionality in Data Exchange Data flows between two network nodes can be one of the three types in directionality: simplex, half-duplex, and full-duplex (see Figure 1.9). Simplex In simplex transmission, data flow is in only one direction. Radio and TV broadcasting services are good examples. This mode of communications also exists between computers and their input devices (e.g., keyboard, mouse). The simplex transmission, however, is not a prevalent mode in the computer network. Duplex In the duplex mode, data flows both ways between two network nodes, and thus each node has the capability of sending and receiving data. Duplex transmissions are either half-duplex or full-duplex. Figure 1.9 (a) Simplex, (b) half-duplex, and (c) full-duplex transmissions. Half-duplex: In this mode, only one party is allowed to transmit data at a time, and the other party should wait until its turn. For a good analogy, imagine the two-way traffic flow on a single-lane railway. Another well-known example is the walkietalkie, a portable radio device that communicators take turns for speaking. Although used in the early generation of computer networking (e.g., hubs), it has been largely replaced by more effective full-duplex communications these days. Full-duplex: In full-duplex mode, data flows in both directions simultaneously between two network nodes. For this, there are generally two separate channels established for a link (or circuit): one channel for each direction. It is like having double lanes for two-way traffic. The traditional telephone system has been using full duplex, so that two communicators on a circuit can talk and listen simultaneously. Most computer networks take advantage of the full-duplex technology these days. 1.4 Network Topology Network topology is defined as the physical layout of a network, a design approach utilized to interconnect network nodes (i.e., intermediary devices and hosts). The logical layout concept also exists, but here we focus more on the physical arrangement of network nodes and links. The physical layout of a network can be understood in terms of relationships between intermediary devices and hosts, between hosts, or between intermediary devices. Many different topologies including bus, star, ring, mesh, tree (or hierarchy), and hybrid (e.g., bus–star) have been in use to arrange network nodes. Each topology has its own strengths and weaknesses, and the design process of an enterprise network should factor in various elements unique to its organizational circumstance. These include characteristics of locations (e.g., number of locations, degree of their distribution), users (e.g., number of users), hosts (e.g., type and number of on-site hosts), applications (e.g., importance of reliability in message delivery), and security conditions. 1.4.1 Point-to-Point Topology As the simplest topology, point-to-point establishes a direct connection between two nodes. There may be only two end nodes directly linked or more than two nodes between two end nodes making it an extended point-to-point connection (see Figure 1.10). A point-to-point link can have permanent and dedicated capacity as in the case of the phone line between a house and a telephone company. Or, it can be dynamically constructed and dismantled as needed. This dynamic formation occurs more often in the form of extended point-to-point topology. For example, a long-distance or an international call between two remote locations requires dynamic circuit formation through multiple telephone switches. Figure 1.10 (a) Point-to-point and (b) extended point-to-point topologies. 1.4.2 Bus Topology In the bus topology, end stations are directly connected to a half-duplex common line, with a terminator device at each end of the line absorbing data remaining in the network (see Figure 1.11). Communications between any two stations, therefore, should be made via the backbone medium. Using the common-line approach practically results in broadcasting of data in which transmissions from a station reach all the other stations on the network, although there is only one intended receiver. This topology therefore allows only a single station to release data at a time to avoid transmission collisions. Figure 1.11 Bus topology (LAN example). Because of its structural simplicity, the bus topology works well for small networks. However, it is subject to traffic congestions when a network grows with more stations attached. The early generation of Ethernet LAN was running on bus, but its usage has mostly disappeared these days due to inherent limitations including unnecessary data broadcasting and difficulties in cabling (e.g., installing a main line inside the ceiling). Figure 1.12 Ring topology: (a) LAN and (b) WAN. 1.4.3 Ring Topology In the ring topology, nodes are attached to a backbone ring that may be a copper wire or an optical fiber. Depending on the technology standard, a network can have a single-ring or a dual-ring architecture that affords redundancy and thus higher survivability from link failures (see Figure 1.12). The ring network has technological advantages in handling high-volume traffic in a reliable manner. This topology is also adequate in constructing long-haul networks. Despite the technological advancement and availability of ring-based standards for LANs such as token ring and fiber distributed data interface (FDDI), their acceptance has been dwarfed by more cost-effective Ethernet that runs on star (or extended star) topology. Ring topology, however, remains a popular choice in creating a high-speed WAN backbone with fiber optics (for more details, see Chapter 9). 1.4.4 Star (Hub-and-Spoke) Topology In the star topology, host stations are connected to a central intermediary device (see Figure 1.13). The topology has several advantages. Above all, the topology makes it easy to add and remove a host station from a network and also to locate node or cable problems. It is also relatively simple to add more stations to a network. Ethernet LANs mostly run on this topology these days. With Ethernet being a dominant wired LAN standard, there are many equipment options (e.g., cabling, ports, connection speeds) with competitive pricing. As a disadvantage, the intermediary device becomes a single point of failure that can bring down a network. Figure 1.13 Star (hub-and-spoke) topology: (a) LAN and (b) WAN. An enterprise can also adopt a star to interconnect distributed LANs with WAN connections. In this case, the network node placed at the hub location (e.g., main office) mediates traffic between any other locations. Observe that the WAN topology is determined by the relationship among intermediary devices, such as, routers rather than those between hosts and an intermediary device. 1.4.5 Mesh Topology Figure 1.14 (a) Full mesh and (b) partial mesh topology (WAN examples). The mesh topology is an arrangement in which all possible connections between network nodes are directly linked (see Figure 1.14). This makes a mesh network very reliable through extra redundancies in which one inoperable node does not drag down the entire network. The mesh network can be a sound option when the number of nodes is relatively small. For example, for three network nodes, only three connections are required, but if there are four nodes, it will take six direct links. As more devices or locations are attached to a network, the number of direct connections increases exponentially, making full mesh less practical in terms of operational costs. The partial-mesh topology uses less links (thus less cost burden) than full-mesh topology but more links than star (hub-and-spoke), making a network less vulnerable to link failures with the redundancy. 1.4.6 Tree (or Hierarchical) Topology In the tree topology, nodes are joined in a hierarchical fashion in which the one on top becomes a root node (see Figure 1.15). There are two or more levels in the hierarchy with the number of nodes increasing at the lower level, making the overall structure like a Christmas tree. The tree structure is highly effective when many nodes (or locations) have to be interconnected using reduced direct links. This topology has been a popular choice among telephone service providers in constructing a backbone network to cover a large geographical area. Figure 1.15 Tree/hierarchical topology: (a) LAN and (b) WAN. The tree approach is also frequently used for an enterprise network in which a large number of end stations are interconnected through a hierarchy of intermediary devices. For example, the LAN of a building may be star-based on each floor. Then, the multiple star networks from different floors can be linked to higher-speed devices to form a bigger LAN that covers the entire building. This topology shares strengths inherent to the star network such as ease of network management and expansion. When a network has a tree structure, intermediary devices (e.g., switches) located at the higher level generally handle more traffic and thus should be more powerful (e.g., faster forwarding rate) than those at the lower level. When it comes to actual implementations, many corporate networks adopt a hybrid solution that combines more than one topology. Taking a simple example, each direct link between two nodes in star, mesh, or tree topology becomes an instance of the point-to-point connection. 1.5 Classification of Networks In terms of coverage scope, computer networks are generally classified into four different types: personal area networks (PANs), LANs, metropolitan area networks (MANs), and WANs. Each type has widely accepted standard technologies. 1.5.1 Personal Area Network The PAN represents a small network whose coverage is typically a few meters or less. It has been popularized by the introduction of such wireless standards as Bluetooth, WiFi Direct, Zigbee, and more recently near-field communication (NFC). For instance, NFC represents a set of short-range—generally up to 2 in. (or 4 cm)—networking technologies for small data sharing. NFC-enabled portable devices read tags or do credit card transactions through such tap-and-pay systems as Apple Pay and Google Wallet. As another popular standard of the short-range PAN, Bluetooth builds a network organized around an individual and thus allows devices located in close proximity (e.g., generally up to 10 m) to exchange data without hard wiring. Figure 1.16 illustrates the usage of Bluetooth to interconnect computing and electronic devices in a wireless setting. 1.5.2 Local Area Network The LAN, in general, covers a relatively confined area to interconnect hosts located within the physical boundary of an organization or a company, making it larger than the personal area network in coverage. Size of the LAN varies considerably as it is determined by the size of an organization. For example, if a company occupies only a single floor of a building, the firm’s LAN is limited to that floor. If an organization uses all floors of a building, its LAN covers the entire building. Figure 1.16 Bluetooth-enabled personal area networks. A bigger network that interconnects multiple buildings within a university or a corporate campus is also a LAN. The oversized LAN is generally termed as a campus LAN or a campus area network. The campus LAN’s extended scale makes its design and operations more challenging than smaller LANs. To create a campus LAN, smaller networks (e.g., one in a building) are joined by high-speed intermediary devices (e.g., core routers or switches) in a hierarchical structure of multiple layers (see the tree topology in Figure 1.15). As a simple example, imagine a relatively small-scale campus LAN of two buildings, each with a fast core switch and two workgroup switches that attach computers to the LAN (see Figure 1.17). The actual campus LAN can be significantly more complex than the example. Details of LAN technologies are covered in Chapters 7 and 8 focusing on the dominant Ethernet and WiFi standards. As said, there is no one-size-fits-all definition of the LAN especially in its size, and therefore, readers should interpret the term in its usage context. Lastly, as a LAN is installed within an organization’s boundary, the organization fully controls it, making any changes (e.g., updates, maintenance) as needed. Figure 1.17 An illustration of campus LAN. 1.5.3 Metropolitan Area Network The MAN is generally designed to cover a good-sized city, being considerably larger in its geographical span than the LAN. The MAN is used to interconnect LANs through land-based or wireless standards within a metropolitan area. In general, common carriers (or telecom carriers) such as telephone service providers (telcos) and Internet service providers (ISPs) have the ownership of the MAN infrastructure, and corporate clients subscribe to the MAN service to access the Internet and other WANs. Figure 1.18 An illustration of MAN. Figure 1.18 demonstrates a hypothetical MAN of a common carrier around the Boston metropolitan area, with high-speed cabling (e.g., 10 Gb/s) and fast intermediary devices. It shows that through the MAN, the three client-site LANs are interconnected and also send data to the Internet and to the carrier’s WAN platform. In the past, WAN standards (e.g., Frame Relay) were technology choices for the MAN infrastructure. However, because of the popularity of Ethernet as a LAN standard, the Ethernet-based technology called Metro-Ethernet has become a preferred choice for the MAN platform. Besides, WiMax (or WirelessMAN) has been introduced as a broadband standard for wireless MAN service. 1.5.4 Wide Area Network The WAN is designed to cover a state, a nation, or an international territory (see Figure 1.19). It interlinks LANs including campus networks, MANs, and even smaller WANs. To tie its geographically distributed LANs, a client organization (e.g., university, company) creates its own private WAN connections by subscribing to the WAN service available from telecom carriers (e.g., China Telecom, Verizon, Vodafone). These companies install and maintain their private WAN infrastructure to commercially offer WAN services to individual and organizational clients. Figure 1.19 WAN links and an enterprise network. Separate from the carrier-owned private WAN infrastructure, the Internet has become an extremely popular platform for WAN connections as well. The Internet itself is the largest global network that no single company or nation has an exclusive ownership on. For example, a telecom carrier has its own Internet infrastructure, but it makes up just a small fraction of the global Internet backbone. With its ubiquity (covers the entire planet), flexibility (connect any time and any place), and cost advantage (substantially cheaper than the private WAN service), the Internet has become an extremely popular option for WAN connections these days. The enterprise network spans an organization to facilitate communications among employees, departments, workgroups, and other entities. An organization’s units may be housed in one building or several buildings at a location, distributed in multiple locations throughout a region, or dispersed nationally or globally. Reflecting the structural diversity of organizations, an enterprise network can be of any combination of one or more PANs, LANs, and MAN/WAN connections (see Figure 1.19). Chapter 9 explains popular WAN services available from telecom carriers, and Chapter 10 covers the architectural details of the Internet, another extremely popular WAN platform these days. 1.5.5 Rise of Internet of Things Because of the prevalence of PANs, LANs, MANs, and WANs, a new paradigm called Internet of things (IoT) is unfolding. IoT is not a type of network/networking technology, but it represents a new development (or paradigm) in which numerous devices (e.g., cars, appliances, gadgets, electronics, mobile devices, security monitoring devices, health devices) automatically detect each other and communicate seamlessly to perform a host of tasks over wired/wireless networks and the Internet. Surely, the various network types explained earlier are keys that will bring IoT to reality, although its full-swing may be years away. The following scenario demonstrates how the emerging IoT paradigm is going to fundamentally transform the society through transparent and automated connectivity among numerous computing and non-computing devices. Exercise 1.3 Year 2025 in San Diego: Laura is a marketing manager of a large business insurance firm. Her daily schedule is loaded with both personal routines and job-related activities. Today, she has to wake up at 6 am. There is an early morning meeting at downtown, and also a business flight to Los Angeles is scheduled at 12 pm. While her car self-drives to the downtown location, it warns that the brake pads are wearing thin and the tire pressure is low. Her car transmits the information to her maintenance shop for a biannual assessment and report. At one point, her car cautions that the shortest path originally suggested has a sudden traffic jam caused by an accident and chooses an alternative path. It also senses weather conditions, adjusts internal temperature and humidity, activates the sun blind, and controls influx of polluted air. After the brief meeting at downtown, she is on the road again for a short trip to Los Angeles to meet a key business partner. The electronic ticket purchased days ago is in her Apple watch. When she enters the Lindberg airport, the watch initiates communications with the airport’s customer support system by sending the ticket information. It suggests the nearest entrance gate as well as a close parking lot for the flight. At the boarding gate, she taps her watch to the kiosk for boarding. While flying, she checks the delivery status of the Xbox game she ordered 2 days ago. Her son has been asking for it for his birthday gift. Tracking the postal office database indicates that the game has been delivered to her office. Using her watch, she also checks her son’s current location and health conditions. Although he is with a caring nanny, Laura worries about her son who suffers from asthma. He wears a wrist device for remote diagnosis and monitoring by her family doctor. On arriving in Los Angeles, she is directed by her watch to pick a reserved rental car equipped with a smart chip that records usage time, location, travel distance, and other information for automated billing to the corporate account. After a short meeting with her boss to report the outcome of the Los Angeles trip, she heads back home with her son’s Xbox game. It has been a long day for Laura. On the way home, she drops by a nearby grocery store. When she grabs a shopping cart, its attached display greets her recognizing her membership and shows special discount items of the day. She also picks up an advertisement paper that has a full list of products in promotion. By placing her watch close to a particular product code, more details are displayed. Prior to shopping, she connects her home network to check the availability of food items and their condition. Using the check, the watch automatically develops a recommended shopping list. As the watch knows Laura’s precise location in the store, it plots ideal routing through the store, saving her precious time in searching for shopping items. With her busy schedule, she realizes that she might have to sign up for the grocery store’s auto-replenishment service that links her home network to the store’s tracking system. When Laura arrives home, information and data stored in her watch and the notebook computer are auto-synchronized with the home network’s central server. Laura’s health information (e.g., pulse rates) gathered by the watch’s smart sensors is also synchronized with the home server’s health assistant. Tonight, the health assistant analyzes gathered data and recommends her to see a doctor after spotting abnormality in her pulsation for the past 3 days. With Laura’s nodding, the health assistant makes an appointment with her family doctor’s reservation system and transmits health data for the doctor’s review. When she replenishes groceries in the refrigerator, product information including their expirations is passed on to the central server. It is already 10 o’clock. Before going to bed, she reads arrived messages including automatic diagnosis of her son’s condition and an electronic report from the auto maintenance shop. Class Discussion 1. Discuss where and how PAN, LAN, MAN, and WAN technologies are used to realize IoT. 2. In the scenario, can you identify new business opportunities (called business models) that do not exist today? What about existing business models that may become less relevant or even obsolete in the future because of technology advancement? 1.6 Subnetwork versus Inter-network Building on the explanation of intermediary devices in Section 1.2.2, the relationship among network, subnetwork (or subnet), and inter-network (or internet) is further clarified. The network is a loosely defined term whose scope covers a variety of settings (e.g., personal surrounding, house, university campus, country). Section 1.5 classified it in terms of PAN, LAN, MAN, and WAN. Depending on how it is designed, a network can be a subnetwork or an inter-network (i as a lowercase letter) with multiple subnetworks joined by one or more routers. Remember that the internetwork is a generic term and thus differs from the Internet (I as an uppercase letter), the largest network on the planet (the architectural details of which are explained in Chapter 10). Figure 1.20 is a simple demonstration of a LAN in which two subnetworks are tied by a router to become an inter-network. When two computers exchange data across the two subnetworks, the data-forwarding process (or activity) is called “internetworking.” As related, the difference between intra-networking and inter-networking was explained in Figure 1.4 in which a subnetwork contains several intermediary devices (e.g., switches, wireless access points) for intra-networking. In summary, Figure 1.20 is a scenario in which the network is a LAN that is also an inter-network with two subnetworks. Figure 1.20 Scenario 1: A company’s network. Figure 1.21 Scenario 2: A company’s network. Figure 1.21 is another scenario of a company network composed of two remotely located office LANs joined by a WAN link. In that setup, each LAN is a subnetwork because delivering messages within the LAN boundary does not need router’s help. This differs from Figure 1.20 in which one LAN consists of two subnetworks. Additionally, the WAN connection is considered a subnetwork, although it may be 3000 miles long! As a result, the company’s enterprise network becomes an internetwork with three subnetworks. These two simple scenarios highlight fluid relationships among the boundaries of the LAN/WAN, subnetwork, and inter-network. Exercise 1.4 1. Refer to Figure 1.6 and answer the following questions: a. How many subnetworks are there in each LAN? b. If PC1 in LAN1 sends a file to a printer in LAN1, is this internetworking? c. If PC1 in LAN1 sends a request message to a server in LAN3, is this inter-networking? d. If PC1 in LAN1 connects to an IP Phone in LAN1, is this internetworking? e. If PC2 and a server in LAN3 exchange messages, is this inter-networking? 2. Figure 1.22 is a small corporate network installed in a building. It has three switches connected to the border router with built-in firewall capability to prevent intrusions from the Internet. Disregarding the connection between the firewall router and the Internet: a. How many LANs are there? b. How many subnetworks are there? c. If PC1 sends a message to the email server, is this inter-networking? Figure 1.22 A hypothetical corporate network. d. If PC1 sends a message to the file server, is this inter-networking? e. What is the intermediary device used for intra-networking? 1.7 Measures of Network Performance Network performance to effectively propagate host-produced data is a critical issue, and much consideration should be given to optimize it during the stages of network planning, design, implementation, maintenance, and upgrade. There is no shortage of stories that underscore the importance of adequate network performance, especially as networks move more real-time (e.g., voice calls, video streaming, online gaming) and mission-critical (e.g., financial transactions, electronic commerce) data these days. Many of the applications demand a certain degree of “guaranteed” performance regardless of circumstances (e.g., traffic congestion). A number of measures are being used to reflect such network performance from different angles, and those of capacity (or speed), delay (or latency), and reliability are among the most important ones. 1.7.1 Capacity Table 1.1 Metrics of Storage versus Network Capacity Storage/Memory Capacity KB (Kilobyte) = 1000 bytes Network Capacity in Data Rate Kbps (kilobits/s) = 1000 bits/s MB (Megabyte) = 1 million bytes Mbps (Megabits/s) = 1 million bits/s GB (Gigabyte) = 1 billion bytes Gbps (Gigabits/s) = 1 billion bits/s TB (Terabyte) = 1 trillion bytes Tbps (Terabits/s) = 1 trillion bits/s PB (Petabyte) = 1 quadrillion bytes Pbps (Petabits/s) = 1 quadrillion bits/s Network capacity (or speed) is gauged by the metrics of data rate. Data rate is about how fast data flow in one direction from point A to point B (not the combined speed of both directions). Not to confuse between byte and bit metrics (1 byte is generally 8 bits) in which byte metrics are primarily for data storage or memory capacity, not network capacity. Table 1.1 summarizes metrics of data storage/memory capacity and network capacity as increasing factors of bits per second (bps). Table 1.2 Data Rates for Audio and Video Contents Type of Content Audio (MP3 encoding) Quality Level Data Rate Telephone sound quality 8 Kbps AM sound quality 32 Kbps FM sound quality 96 Kbps CD sound quality 224–320 Kbps Video (MPEC2 encoding) DVD quality HDTV quality 5 Mbps 15 Mbps Data Types and Data Rate Depending on the type of data to be propagated, required data rate differs considerably in which plain texts take up the smallest capacity followed by audio and video. Much of the network traffic these days is in the multimedia format that combines text, sound, image, and video. To put things in perspective, Table 1.2 summarizes data rate necessary to transport audio and video data at different quality levels. MP3 and MPEC2 are popular compression standards used to encode audio and video data. Exercise 1.5 Refer to Table 1.2. The data rate (in each direction) necessary for a digitized telephone call is 8 Kbps. This means that a two-way full-duplex call between two parties takes 16 Kbps. How many calls can be made concurrently with the data rate necessary to transport just one HDTV channel? Channel Capacity and Throughput: A network’s transmission capacity can be measured in terms of both Channel Capacity and Throughput. Channel Capacity: It is the maximum theoretical data rate of a link and is oftentimes referred to as bandwidth or rated speed. Strictly speaking, channel capacity in data rate is a digital concept, and bandwidth is an analog concept (more accurate technical definition of bandwidth is explained in Chapter 4). However, they are directly correlated—the bigger the bandwidth of a link, the bigger the channel capacity; thus, practitioners use them interchangeably. Throughput: It refers to actual data rate of a link. As a more realistic speed of a network link, it is usually slower than channel capacity due to a number of technical and circumstantial reasons including the effect of link distance, transmission interferences, and internal/external noises. For instance, popular WiFi standards such as 802.11n and 802.11ac can transmit at several hundred Mbps (see Chapter 8). However, its actual throughput gets substantially lower as the distance between two communicating nodes is increased. 1.7.2 Delay Delay (or latency) represents the amount of time a network link takes to deliver data between any two nodes and is usually in milliseconds (or 1000th of a second). Delay can be measured in both one-way trip and round trip (e.g., a request and response cycle) between two points. For example, as shown in Figure 2.13 in Chapter 2, the ping utility program that tests if a particular target node is reachable gauges latency based on a round trip. In the figure, the ping request was issued four times by the source host, and all of them were replied by the target host ( with a round-trip latency of 26–29 ms. When computers exchange data, there are various delay sources. Imagine a hypothetical situation in which a person downloads the main page of She/he will certainly experience delay until the web page is displayed on the browser. Among the sources of delay are Propagation delay: It takes time for the signal carrying the web page to travel between two remotely located hosts. Delay at hosts: The source host should internally process the user request before releasing it to the Internet. This includes conversion of the request into a packet (to be explained in Chapter 2) and then to an electronic signal (to be explained in Chapter 4) for propagation. When the request arrives at the destination host (i.e., server), it also performs similar internal processing to ultimately produce a response packet and convert it to a signal for delivery. Delay at intermediary devices: An intermediary device (e.g., router, switch) mediates data transmissions between hosts, and the message forwarding requires its own internal processing including the lookup of a reference table (e.g., routing table, switch table) and subsequent forwarding path decision. Also, when messages arrive at a port continuously, they are temporarily placed in a queue before processing, inevitably resulting in queuing delay. Delay is especially a sensitive issue when a network is used by time-sensitive applications. In fact, because of the ever-growing popularity of real-time or near-realtime multimedia applications such as video-on-demand, videoconferencing, and online gaming, more messages need to be propagated with little delay and oftentimes with guaranteed performance. 1.7.3 Reliability This performance dimension is about a network’s capacity to convey data in a stable manner. The reliability of data delivery is mildly or severely affected (1) when there are corrupted or lost data in the middle of their transmissions and (2) when a network experiences interruptions (e.g., node failures, link failures). Corrupted or lost data: Data corruption or loss takes place in different magnitudes. It can be as small as a bit change (e.g., from 0 to 1) or as big as the moderation or loss of entire bit streams. There are a number of sources that trigger the reliability problem. Among them are network node crash caused by certain forces; physical damage or cut of cabling; overflow of a network node’s buffer space; power interruption or surge; and internal and external noises triggered by such factors as signal interference due to lightning, industrial noise, and cross talk. Network unavailability: A network becomes unavailable when there is a node or link failure. Just as a computer crashes, an intermediary device can fail for several reasons including overloading, a system bug in its built-in software, power interruption, succumbing to a malicious attack (e.g., denial-of-service attack), and operational mismanagement. Also, the network link can be a source of trouble when it is accidentally damaged or when cabling between a node and a link is unstable. When a network itself becomes unavailable either entirely or partially due to the node or link fault, this limits network accessibility. 1.7.4 Quality of Service A concept closely associated with the dimensions of network performance is quality of service (QoS). QoS represents the capability of a network in guaranteeing performance in terms of link capacity, latency, and reliability. It is particularly germane to the carrier’s WAN (including the Internet) service offered to business clients (e.g., e-commerce stores). In early days, QoS was not such a critical issue for WAN connections as network applications were not that sophisticated and mission critical. However, as more computer programs perform business functions vital to organizations over the network, the ability of WAN to guarantee network performance has become an essential requirement. For example, and entirely rely on the Internet for business transactions, and even a few minutes of service disruption means millions of dollars in lost revenue. When a carrier offers QoS to a client organization, its network should be able to provide the client with the level of “promised” performance regardless of circumstances (e.g., traffic congestion). Of course, the QoS-guaranteed network service is costlier than the non-QoS service to client organizations. A carrier can use such techniques as data prioritization and dedication of link capacity to enhance service quality. Businesses, however, may not need such QoS provision if their WAN links are used mainly for general applications (e.g., emails, web surfing). 1.8 Numbering Systems In this section, three different numbering systems (i.e., binary, decimal, and hexadecimal) used to represent numeric values in networking are reviewed. Although they are used altogether, there is a preference of one system over the others depending on the usage context. As we are already aware of, network nodes process various data types (e.g., texts, images, videos) in binary of 0s and 1s. Table 1.3 Numbering Systems Numbering System Number of Digits Digits in Base Binary 2 0 and 1 Decimal 10 0 through 9 Hexadecimal 16 0 through 9, A, B, C, D, E, and F (in which A = 10, B = 11, C = 12, D = 13, E = 14, F = 15) Note: Hexadecimal values are indicated by either 0x prefix or h suffix. For example, 0x3256 means that 3256 is hexadecimal. Data in binary, however, are hard for human beings to comprehend, and thus both decimal (with 10-base) and hexadecimal (with 16-base) numbering systems are also utilized for better readability. With 16 base, hexadecimal is more efficient than decimal in expressing binary combinations. As such, translation between binary and decimal and that between binary and hexadecimal become the fundamental knowledge in studying computer networking, especially network addressing. Table 1.3 summarizes three numbering systems and their base digits. 1.8.1 Binary versus Decimal The translation between binary and decimal is explained based on the unit of 8 bits as it becomes the building block of 32-bit IP addresses. For example, an IP address of is equivalent to 01111011. 00101101. 00111000. 01011001. The binary– decimal conversion is demonstrated using an example of 8-bit binary (01011010) and its equivalent decimal (90) values. 1. Binary (01011010) to decimal (90) conversion a. First, determine the decimal position value of each binary bit using the power-of-two computation. b. Once decimal position values are in place, add up the decimal values of nonzero binary positions. In the example, the summation of 64, 16, 8, and 2 becomes 90. Initial binary combination (8 bits) 0 1 Power of two 27 26 25 24 Decimal position values 128 64 32 16 Add decimal values of nonzero binary positions 0 1 64 1 0 1 0 23 22 21 20 8 4 2 +16 +8 +2 1 = 90 2. Decimal (90) to binary (01011010) conversion Decimal Position Values 128 64 32 16 a. Find the largest decimal position value 128 [64] 32 16 that is ≤90 b. Obtain the remainder value 1 4 2 1 32 [16] 8 4 2 1 Difference between 26 and 16 = 10 e. Find the largest decimal position value that is less than or equal to the remainder 128 64 value 10 f. Obtain the remainder value 8 4 2 Difference between 90 and 64 = 26 c. Find the largest decimal position value that is less than or equal to the remainder 128 64 value 26 d. Obtain the remainder value 8 32 16 [8] 4 2 1 Difference between 10 and 8 = 2 g. Find the largest decimal position value that is less than or equal to the remainder 128 64 value 2 32 16 8 4 [2] 1 h. Obtain the remainder value. As the Difference between 2 and 2 = 0 remainder becomes 0, stop here. i. Binary numbers corresponding to the parenthesis values above are 1s and the 0 others are 0s. 1 0 1 1 0 1 0 Notes: 01011010 (8 bits) is identical to 1011010 (7 bits). The demonstration is based on the 8-bit combination. Exercise 1.6 1. Convert decimal values 38, 110, 192, and 255 to their 8-bit binary counterparts. 2. Translate the following 8-bit binary blocks to their corresponding decimal values. 01100001 11110110 11100011 10100010 1.8.2 Binary versus Hexadecimal In computer networking, hexadecimal digits are used to represent MAC (or physical) addresses (see Section 1.2.1). Each MAC address is 48 bits (see Section 1.9.2), and they are converted to 12 hexadecimal digits (thus, each hex digit is equivalent to 4 bits). The following demonstration focuses on the conversion between a hexadecimal digit and its equivalent 4 binary bits. The conversion takes nothing but the translation between a hexadecimal’s decimal value and its corresponding 4 bits. For example, the hexadecimal digit “A” is equivalent to decimal “10,” which in turn translates into 1010 in binary using the same conversion method in Section 1.8.1. The conversion is summarized as follows: Hexadecimal Decimal Binary A → 10 → 1010 A ← 10 ← 1010 To translate a binary bit “stream” into its corresponding hexadecimal values, the bit stream should be divided into 4-bit blocks first. Then, convert each 4-bit unit into its corresponding decimal value and subsequently find its hexadecimal equivalence. Recall that A = 10, B = 11, C = 12, D = 13, E = 14, and F = 15. As an example, for the binary bit stream of 10010110100010101101, 1. Creation of 4-bit blocks: 10010110100010101101 becomes 1001.0110.1000.1010.1101. 2. Conversion of each block into a decimal value: 1001.0110.1000.1010.1101 becomes 3. Conversion of each decimal value into a hexadecimal equivalence: becomes 0x968AD. Exercise 1.7 1. Convert 0x17AB to its binary counterpart. 2. Convert the following hex digits to binary bits with each hex digit representing 4 binary bits. 0xABCDEF 0x34A57 0x12DF01 0x78ADC 3. Convert the binary stream “10110110100011100001” to hex with each hex digit representing 4 binary bits. 4. If the physical address of a computer’s network card (NIC) is 001001100111100010101011010111000100100010001101, What is its corresponding hexadecimal address? 1.9 Network Addressing Just as postal addresses are necessary to deliver snail mails, network nodes transport data relying on standardized address information. So, allocation of addresses to hosts and intermediary devices, their configuration, and management are activities fundamental to adequate operations of a computer network. In this section, network addresses currently in use are characterized in terms of permanency, accessibility, and privacy dimensions. 1.9.1 Characterizing Network Addressing Permanency (temporary vs. permanent) Network addresses can be either temporary (or dynamic) or permanent (or static). The temporary address is dynamically assigned to a station, and it can be reclaimed and reassigned to another station, if unused for a certain period of time (e.g., 24 h). Such temporary address is typically allocated to a user device (as a related concept, refer to the DHCP standard in Chapters 2 and 10). The permanent address, meanwhile, is either printed on a node’s network card (e.g., MAC address) by the device manufacturer or manually set up (e.g., IP address) on a computer system. In general, server computers and intermediary devices are given one or more permanent IP addresses. Accessibility (local vs. global) Addresses can be either locally or globally recognized. Locally recognized addresses are only used within a subnetwork to move data for intra-networking. The MAC address printed on a host’s network card (NIC) is an example. In contrast, globally recognized addresses are used to transport data beyond the subnetwork boundary, thus for inter-networking and global reach. The IP address belongs to this type. Privacy (public vs. private) IP addresses are divided into public and private addresses. Packets containing public addresses can be forwarded to the destination host over the Internet. In contrast, the private address, as the term implies, is used only within an organization or a home network. In other words, the packet with a private address is deliverable to a destination node located within the same organizational or home network boundary, but not outside. The usage of private addresses offers heightened security as internal nodes are invisible from outside. Many organizations rely on private IP addresses to protect their internal networks and also to be flexible in address allocation to internal hosts and intermediary devices (more details are given in Chapter 5). The two different address schemes used concurrently for computer networking are MAC and IP addresses. 1.9.2 MAC Address The NIC of a computer has at least one MAC address assigned to it. The MAC address is also known as a physical or hardware address because it is permanently printed on an NIC and thus cannot be changed (although it can be spoofed or masked using software). The NIC for Ethernet or WiFi as the two most dominant LAN standards uses an MAC address of 48 bits, which is burned into the NIC’s read only memory (ROM). When a node is started, its MAC address is copied into the NIC’s random access memory (RAM) to enable the node’s networking function. As stated, the 48-bit MAC address is presented to people as 12 hexadecimal digits, each digit representing 4 binary bits. The MAC address in hex is generally written in one of the three formats: 01-35-A7-BC-48-2D: (two hex digits separated by “-”) 01.35.A7.BC.48.2D: (two hex digits separated by “.”) 01A7BC.482D: (four hex digits separated by “.”) Out of the 12 hexadecimal digits, the first 6 become an organizationally unique identifier (OUI). The OUI indicates an NIC card’s manufacturer and is assigned by Institute of Electrical and Electronics Engineers (IEEE), a leading standard-setting organization responsible for LAN standards (e.g., Ethernet, WiFi). The remaining six digits represent a combination uniquely allocated to each NIC. With this allocation scheme, no two NICs should share the same MAC address. Exercise 1.8 Conduct Internet search to locate OUIs of technology powerhouses including Cisco, Apple, Intel, and Microsoft. Observe how many different OUIs are owned by each company. 1.9.3 IP Address The IP address is a global standard necessary for a network node to exchange data with any other nodes. As explained, the temporary IP address is dynamically allocated to a host station whenever it issues a request and therefore has an expiration. In contrast, the permanent IP address allocated to a host (e.g., server) stays with it so that the host performs the intended service functions without interruptions. Whereas, the MAC address is a physical address, the IP address is a logical address because it is not bound to a node physically. Two different IP standards are used concurrently: IPv4 (version 4) and IPv6 (also known as IP next generation or IPng). The IPv4 address consists of 32 bits that are translated into a combination of 4 decimal values (e.g., The IP address is composed of network and host identity parts. For example, in, 172.232 and 53.8 may represent the network and host identities, respectively. Chapter 5 covers IPv4 addressing. The adoption of more advanced IPv6 addressing, with 128 bits for an address, is growing, and the future clearly belongs to it. Some of the fundamentals of the IPv6 addressing scheme are explained in Chapter 10. 1.9.4 Pairing of MAC and IP Addresses To be able to exchange data over the network, a host station (e.g., PC, tablet, smartphone) needs a pair of MAC and IP addresses. Figure 1.23 illustrates the one-toone pairing (or binding) of MAC and IP addresses. In the case of intermediary devices, the pairing relationship is a little different and will be explained in Chapter 3. Figure 1.23 Pairing of MAC and IP addresses. It is natural to raise a question of why a host needs the pairing of an MAC and an IP. A rather simple answer is that MAC is for intra-networking and IP is for inter- networking. In other words, within a subnetwork, the MAC address of a destination host is all it takes in delivering a message from a source station. When a packet has to cross multiple subnetworks (for inter-networking) before reaching the ultimate destination, its IP address needs to be continuously referenced by the router(s) on the way. The somewhat complex logic behind the concurrent usage of both addressing systems is explained in Chapters 2 and 3. Exercise 1.9 1. Search the MAC and IP addresses of your smartphone. It might have two MACs: one for WiFi and the other for Bluetooth. 2. Smartphones come with a unique International Mobile Equipment Identifier (IMEI). Search the IMEI of your smartphone. What is it and how is it different from the MAC/IP address? What can you do with the IMEI in protecting the device? (Search the Internet for answers.) 3. Find out the MAC and IP addresses of your computer by typing ipconfig/all for Windows and ifconfig for Linux/Unix at the command prompt. Figure 1.24 IP configuration of a host station (MS Windows). As shown in Figure 1.24, today’s computers are generally equipped with two MAC addresses, one for Ethernet NIC and the other for WiFi NIC. At one point, only the MAC address in usage is associated with the host’s IP address. On the basis of Figure 1.24, answer the following questions: a. b. c. d. e. What is the computer’s current IP address? How many NICs and MAC addresses the host station has? What are their MAC addresses and why there is more than one MAC address? Who are the manufacturers of the NICs? It shows that the WiFi LAN’s MAC address is bound to the IP address What does that mean? Other items shown in Figure 1.24 including auto-configuration, subnet masks, default gateway, DHCP servers, and DNS servers are explained throughout the book. Chapter Summary A computer network is made up of various hardware and software components including hosts, intermediary devices, network links (or communication links), applications, data (or messages), and network protocols. Data communications between network nodes are primarily in the forms of unicasting, broadcasting, and multicasting. Data flows between two network nodes can be simplex (i.e., one-way only), halfduplex (i.e., two ways but one way at a time), and full-duplex (i.e., two ways concurrently). Network topology refers to the layout of network nodes and links, a design approach utilized to interconnect intermediary devices and hosts. Among the different topologies are point-to-point, bus, star (or hub-and-spoke), ring, mesh, and tree (or hierarchy). Computer networks are generally classified into four types in terms of their coverage scope: PANs, LANs, MANs, and WANs. The subnetwork is a network segment formed when intermediary devices including hubs, bridges, wireless access points, and switches interconnect host computers. The router is used to tie different subnetworks to form an internet. The primary dimensions of network performance include capacity (or speed), delay (or latency), and reliability. As related, QoS represents a network’s ability in guaranteeing such performance. Three different numbering systems (i.e., binary, decimal, and hexadecimal) are used in networking, and a particular numbering system is preferred over the others depending on the usage context. Network nodes transport data relying on standardized address information, and MAC and IP addresses are used concurrently. Key Terms access link application binary bits per second (bps) Bluetooth broadcasting bus topology campus network capacity channel capacity circuit switching client–server computing command-line interface data rate decimal delay duplex end device end station end system enterprise network full-duplex half-duplex hexadecimal (HEX) hierarchical topology host hub-and-spoke topology ifconfig intermediary device internet internet Internet of Things (IoT) inter-networking intra-networking IP address ipconfig IPv4 IPv6 latency local area network (LAN) logical address MAC address mesh topology message metropolitan area network (MAN) multicasting near-field communication (NFC) network network interface card (NIC) network link network node networking device organizationally unique identifier (OUI) peer-to-peer computing permanent (or static) address personal area network (PAN) physical address point-to-point topology protocol quality of service (QoS) random access memory (RAM) read only memory (ROM) reliability ring topology semantic rule simplex star topology subnetwork (subnet) syntactic rule temporary (or dynamic) address throughput topology tree topology trunk link unicasting wide area network (WAN) WiFi WiFi Direct wireless NIC (WNIC) Zigbee Chapter Review Questions 1. The ________ represents the layout of network nodes and links. A. network node B. network domain C. network topology D. network architecture E. network blueprint 2. Choose an ACCURATE statement regarding the relationship between hosts, intermediary devices, and network nodes. A. Hosts are intermediary devices. B. Hosts are also called networking devices. C. Intermediary devices include network nodes and hosts. D. An intermediary device is either a network node or a host. E. Network nodes include intermediary devices and hosts. 3. Which topology is used widely when network redundancy is important to prepare for node or link failures? A. point-to-point B. partial mesh C. star D. bus E. hub-and-spoke 4. Star topology is also known as A. ring B. partial mesh C. full mesh D. bus E. hub-and-spoke 5. Which is an access link? A. router–router link B. switch–switch link C. switch–router link D. web server–switch link E. hub–switch link 6. The organizationally unique identifier (OUI) is an element of ________. A. MAC addresses B. public addresses C. IP addresses D. global addresses E. local addresses 7. The throughput of a network A. represents the speed guaranteed by a service provider. B. describes the strength of a signal. 8. 9. 10. 11. 12. 13. C. is interchangeably used with rated speed. D. represents the maximum capacity of its cabling. E. represents its actual speed. Messages (or data) are produced and exchanged according to meticulously defined rules of communication. These rules are implemented in ________. A. protocols B. messages C. network links D. applications E. data Choose an INCORRECT statement regarding the network link. A. Copper wires and optical fibers are popular wired media these days. B. Network links are divided into access and trunk links. C. Creating a computer network needs to have at least one trunk link. D. The access link provides connectivity between a host and an intermediary device. E. The trunk link interconnects intermediary devices. The campus network is a type of ________. A. local area network B. metropolitan area network C. personal area network D. wide area network E. wireless network What is the binary correspondence of hex digits “B301”? A. 1110001100000001 B. 1011001100000001 C. 1001001100010001 D. 1011001100101001 E. 1011001100100101 Select an ACCURATE statement on network addressing. A. MAC addresses of a university’s PCs are the same in their first six hex digits. B. The primary usage of the MAC address is for inter-networking. C. The IPv4 address is longer in its length than the MAC address. D. An IP address should be permanently assigned to a host station. E. A host station should have an MAC and an IP address for networking. Which is TRUE regarding the MAC address? A. It is a permanent address. B. It is stored in a computer’s RAM in eight hex digits. C. It is dynamically provided by a designated server to requesting stations. D. It is determined by a computer’s operating system. 14. 15. 16. 17. 18. 19. 20. E. Two computers can own the same MAC address. Which three terms are used interchangeably as metrics of network performance? A. channel capacity, bandwidth, throughput B. channel capacity, throughput, flow C. reliability, accuracy, availability D. channel capacity, bandwidth, rated speed E. reliability, accuracy, latency When the nearby laptop, wireless mouse and keyboard, smart phone, and digital camera exchange data, a ________ standard is used: A. WAN (wide area network) B. PAN (personal area network) C. NFC (near-field communication) D. LAN (local area network) E. MAN (metropolitan area network) Which is a legitimate MAC address? A. ab-01-cd-ef-23-45 B. ab-01-cd-ef-23-4 C. ab-01-cd-ef-23 D. ab-01-cd-ef-2 E. ab-01-cd-ef Switches within a network are interconnected by ________. A. access links B. peer-to-peer links C. trunk links D. channel links E. internet links Network nodes include ________. A. intra-networking and inter-networking devices B. intermediary devices and end stations C. intermediary devices and network links D. intermediary devices and networking devices E. end devices and network links Which is NOT NECESSARILY an accurate description of the intermediary device? A. It has at least one built-in network card. B. It also becomes a network node. C. It always operates in the full-duplex mode. D. It relies on network addressing to exchange data. E. It operates for either intra-networking or inter-networking. Which is a right sequence of data rate metrics from the smallest to the largest? A. Kbps—Mbps—Pbps—Gbps—Tbps 21. 22. 23. 24. 25. B. Tbps—Pbps—Kbps—Mbps—Gbps C. Kbps—Gbps—Mbps—Tbps—Pbps D. Kbps—Mbps—Gbps—Tbps—Pbps E. Kbps—Mbps—Gbps—Pbps—Tbps There are many websites that offer audio or video streaming of TV programs and movies over the Internet. These services generally rely on the ________ technology. A. unicasting B. anycasting C. multicasting D. broadcasting E. dualcasting The three main sources of network latency (or delay) include A. propagation delay, delay at hosts, and delay of server processing. B. propagation delay, delay at hosts, and delay at intermediary devices. C. delay at intermediary devices, delay at hosts, and delay of client processing. D. delay of application processing, propagation delay, and delay at hosts. E. delay of server processing, delay at intermediary devices, and delay at hosts. The primary dimensions of network performance include ________. A. delay, cost, and reliability B. capacity, reliability, and accessibility C. capacity, reliability, and cost D. delay, capacity, and reliability E. reliability, delay, and accessibility The following message is produced by the web browser according to the ________. “GET/HTTP/1.1 Host:” A. semantic rule B. lexicon rule C. syntactic rule D. message rule E. link rule Which statement CORRECTLY describes network topology? A. Tree: All network nodes are either a hub or a spoke. B. Bus: All network nodes are directly connected. C. Hierarchy: Host stations are linked to a main transmission line. D. Star: All locations connect to a central site, and thus the network is susceptible to a single point of failure. E. Full mesh: It is a cost-effective approach in creating a highly reliable network with redundancy. 2 Architectures and Standards 2.1 Introduction This chapter explains network architecture, layers, standard and protocol, and their relationships. These concepts are highly abstract and can pose a considerable challenge to comprehension. Nonetheless, they are fundamental to computer networking and hence have been introduced in the early part of this book. You are encouraged to go through an entire chapter several times to get a better grasp of the concepts and their relationships. First of all, communications between network nodes demand the precise execution of a number of predefined functions (or activities). If just one of the functions is not properly performed, nodes will either misunderstand or be unable to understand each other. These functions can be grouped by their similarities. The standard architecture in comput...
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