Computer Networks PDF

The learning objectives are: 7.1 Describe computer networks and their pros and cons. 7.2 Explain the different ways networks are defined. 7.3 Describe the types of transmission media used in networks. 7.4 Describe the basic hardware devices necessary for networks. 7.5...

The learning objectives are: 7.1 Describe computer networks and their pros and cons. 7.2 Explain the different ways networks are defined. 7.3 Describe the types of transmission media used in networks. 7.4 Describe the basic hardware devices necessary for networks. 7.5 Describe the type of software necessary for networks. 7.6 Summarize the broadband options available to access the Internet. 2 Additional learning objectives are: 7.7 Summarize how to access the Internet wirelessly. 7.8 Explain what should be considered before creating a home network. 7.9 Describe how to set up a home network. 7.10 Describe the potential problems with wireless networks and the means to avoid them. 7.11 Describe how to secure wireless home networks. 3  A computer network is simply two or more computers that are connected via software and hardware so that they can communicate with each other. Each device connected to a network is referred to as a node. A node can be a computer, a peripheral such as a printer or game console, or a network device such as a router. 4  There are several benefits to having computers networked: Sharing an Internet connection: A network lets you share the high-speed Internet connection coming into your home. Sharing printers and other peripherals: Networks let you share printers and other peripheral devices. Sharing files: You can share files between networked computers without having to use portable storage devices to transfer the files. Common communications: Computers running different operating systems can communicate on the same network. The major disadvantage of networks is the setup time. 5  The following terms help us understand how data moves through networks. Data transfer rate (bandwidth) is the maximum speed data can be transmitted. Throughput is the actual speed data is transferred. Data transfer rate and throughput are usually measured in megabits per second (Mbps) and gigabits per second (Gbps). 6 Networks can be classified by distance. A personal area network (PAN) is used for communication among devices close to one person. A local area network (LAN) is a network in which the nodes are located within a small geographical area. A home area network (HAN) is a specific type of LAN located in a home. A metropolitan area network (MAN) is a large network designed to provide access to a specific geographical area, such as an entire city. A wide area network (WAN) spans a large physical distance. 7 Networks can be classified by levels of administration. In a client/server network, a client is a computer on which users accomplish tasks and make requests, whereas the server is the computer that provides information or resources to the client computers. In a peer-to-peer (P2P) network, each node connected on the network can communicate directly with every other node on the network. 8 Networks can be classified by the protocols used. Ethernet Developed by the Institute of Electrical and Electronics Engineers (IEEE). This applies to wireless and wired networks. The ability of current devices to use earlier standards in addition to the current standard is known as backward compatibility. 9  In order to function, all networks must include: A means of connecting the nodes on the network—cables or wireless technology. Special hardware devices that allow the nodes to communicate with each other and to send data. Software that allows the network to run. 10  Transmission media establish a communications channel between the nodes on a network. They can be either wireless or wired. 11  Wired networks can use the following media: UTP cable: twisted copper wires surrounded by a plastic jacket. Coaxial cable: single copper wire surrounded by layers of plastic. Fiber-optic cable: plastic or glass fibers. 12  Each node needs a network adapter. An integrated network adapter is referred to as a network interface card. A broadband connection requires a modem, which translates the signal into digital and back again. Data is sent in bundles called packets. Network navigation devices facilitate and control the flow of data. A router transfers packets of data between two or more networks. A switch acts like a traffic signal on a network. 13  Because home networks are P2P networks, they need operating system software that supports P2P networking. As opposed to P2P networks, the nodes on a client/sever network don’t communicate directly with each other; rather, they communicate through a centralized server. Communicating through a server is more efficient in a network with a large number of nodes, but it requires more complex software. Therefore, servers on client/server networks have specialized network operating system (NOS) software installed. 14  One of the main reasons for setting up a network is to share an Internet connection. Some businesses and large organizations have a dedicated connection to the Internet, but other businesses and homeowners purchase Internet access from Internet service providers (ISPs). ISPs might be specialized providers. Broadband is the preferred way to access the Internet, but in some situations cellular or dial-up access might be necessary. 15  Broadband is often referred to as high-speed Internet. This high rate of access is in contrast to dial-up Internet access. The standard wired broadband technologies in most areas are cable, DSL, and fiber-optic service. Satellite Internet is used mostly in rural or mountain areas. 16  To access the Internet wirelessly at home, you need to establish WiFi on your home network by using a router. When away from home, you can find a mobile hotspot. Mobile broadband connects you to the Internet through 4G or 5G access. You must have a wireless Internet service provider. An Internet connectivity plan is known as a data plan. 17  One of the first things you should do to evaluate your network is list all the devices you’re using. For a home network to run most efficiently and to provide the fastest experience, it’s best that all network nodes use the latest Ethernet standard. If your router is provided by your ISP and it’s an older standard, you should consider having your ISP provide you with a new router. 18  Apple has designed routers that are optimized for working with Apple computers. Windows machines can also connect to an AirPort router, so it’s a great choice for households with both Apples and PCs. The AirPort Express router can be used for home networks to support devices running iOS, macOS, and Windows. A switch acts like a traffic signal on a network. 19  There are specialized home networking devices. Network-attached storage (NAS) devices are specialized devices designed to store and manage network data. NAS devices provide centralized data storage and access. Home network servers are specialized devices designed to store and share files across the network. A network-ready device (or Internet-ready device) can be connected directly to a network through either a wired or wireless connection. 20  The maximum range of Wi-Fi 4 or Wi-Fi 5 wireless devices is about 350 feet. As you go farther away from your router, the speed (throughput) decreases. Walls, floors, and large metal objects (such as refrigerators) are the most common sources of interference with wireless signals. Place an access point in the location where the original Wi-Fi signal becomes weaker. Use a wireless range extender to repeat or amplify the wireless router signal. 21  There are various issues and methods for securing your wireless network: Use encryption and security protocols. Change network name service set identifier (SSID). Disable SSID broadcast. Change the default password. Create a passphrase. 22  Additional methods for securing your wireless network: Implement media access control. Limit signal range. Keep router firmware up to date. Disable remote access. 23 By accessing your router, you can configure the security protocols available on your router and change the SSID. 24 25  Cybercrime is any criminal action perpetrated primarily through the use of a computer. Cybercriminals are individuals who use computers, networks, and the Internet to perpetrate crime. Four common categories of complaints received were FBI-related scams, identity theft, nonauction/non-delivery of merchandise, and advance fee fraud. Although the top four complaints all relate to some type of fraud, other complaints received involved equally serious matters such as computer intrusions—hacking—child pornography, and blackmail. 2  Identity theft occurs when a thief steals personal information and poses as you. It is the most financially damaging cybercrime for individuals. Types of scams include: Counterfeiting credit and debit cards Requesting changes of address Opening new credit cards Obtaining medical services Buying a home in your name and then reselling the house 3  A hacker is most commonly defined as anyone who unlawfully breaks into a computer system. There are numerous types of hackers: White-hat hackers break into systems for nonmalicious reasons such as to test system security vulnerabilities or to expose undisclosed weaknesses. Black-hat hackers break into systems to destroy information or for illegal gain. Grey-hat hackers illegally break into systems to flaunt their expertise or to attempt to sell their services in repairing security breaches. A packet analyzer (sniffer) is a program deployed by hackers that looks at (or sniffs) each packet as it travels on the Internet. A keylogger is a program that captures all keystrokes made on a computer. 4  A Trojan horse is a program that appears to be something useful or desirable but does something malicious in the background without your knowledge. Backdoor programs and rootkits are programs that allow hackers to gain access to your computer and take almost complete control of it without your knowledge. 5  A computer that a hacker controls is referred to as a zombie. Zombies are often used to launch denial-of-service attacks on other computers. In a denial-of-service attack, legitimate users are denied access to a system because a hacker is repeatedly making requests of that system through a computer the hacker has taken over as a zombie. A computer can handle only a certain number of requests for information at one time. When it is flooded with requests, it shuts down and refuses to answer any requests for information, even if the requests are from a legitimate user. A distributed denial-of-service (DDoS) attack launches DoS attacks from more than one zombie at the same time. A botnet is a large group of software running on zombie computers. 6  Exploit kits are software programs that run on servers searching for vulnerabilities. Logical ports are virtual, not physical, communications paths. 7  A virus is a program that attaches to a computer program to spread to other computers. Its main purpose is to replicate itself and copy its code into as many other host files as possible. Secondary objectives range from displaying annoying messages on the computer screen to destroying files or the contents of entire hard drives. Viruses can be destructive. Smartphones and tablets can be infected with viruses. 8  Viruses can come in many types: Boot-sector viruses replicates themselves onto a hard drive’s master boot record. A logic bomb is a virus that is triggered when certain logical conditions are met, such as opening a file or starting a program a certain number of times. A time bomb is a virus that is triggered by the passage of time or on a certain date. Worms work independently of host file execution and are much more active in spreading themselves. Script and macro viruses are a series of commands that are executed without one’s knowledge. E-mail viruses use the address book in the victim’s e-mail system to distribute themselves. When encryption or ransomware viruses infect a computer, they run a program that searches for types of data files and compresses them. You then receive a message that asks you to send payment to an account if you want to receive the program to decrypt your files. 9  Viruses can be classified by the methods they take to avoid detection: A polymorphic virus changes its code to avoid detection. Most polymorphic viruses infect a particular type of file. A multipartite virus is designed to infect multiple file types in an effort to fool the antivirus software that is looking for it. Stealth viruses temporarily erase their code from the files where they reside and hide in the active memory of the computer. 10  Malware is software that has a malicious intent. Adware displays unsponsored advertisements. Spyware is an unwanted program that downloads with other software from the Internet and runs in the background. Spyware transmits information about you. Many spyware programs use tracking cookies. A keystroke logger program monitors keystrokes. 11  Spam is unwanted or junk e-mail. A spam filter is an option you can select in your e-mail account that places known or suspected spam messages into a special folder. 12  Cookies are small text files that some websites automatically store on your hard drive when you visit them. Companies use this information to determine the traffic flowing through their website and the effectiveness of their marketing strategy. Cookies do not go through your hard drive in search of personal information. The main concern is that advertisers will use this information indiscriminately, thus invading your privacy. Cookies pose no security threat because it is virtually impossible to hide a virus or malicious software program in a cookie. 13  Social engineering is any technique using social skills to generate human interaction with the purpose of luring individuals to reveal sensitive information. Pretexting involves creating a scenario that sounds legitimate. 14  Phishing lures Internet users to reveal personal information. Pharming occurs when malicious code is planted on your computer. These guidelines help to avoid such schemes: Never reply directly to any e-mail asking for personal information. Don’t click on a link in an e-mail. Check with the company asking for information. Never give personal information over the Internet unless you know the site is secure. Use phishing filters. Use Internet security software that’s constantly being updated. 15  Scareware is a type of malware that downloads onto your computer and tries to convince you that your computer is infected with a virus or other type of malware. You’re then directed to a website where you can buy fake removal or antivirus tools that provide little or no value. Scareware is a social engineering technique because it uses people’s fear of computer viruses to convince them to part with their money. 16  A firewall is a software program or hardware device designed to protect computers from hackers. Both Windows and macOS include reliable firewalls. Windows Firewall displays the status of a firewall. 17 Antivirus protection is included in comprehensive Internet security packages such as Norton Security Suite or Trend Micro Internet Security. 18  Firewalls can be configured so that they filter out packets sent to specific logical ports in a process known as packet filtering. Firewalls can also be configured to completely refuse requests from the Internet asking for access to specific ports in a process known as logical port blocking. Firewalls use a process called network address translation to assign internal IP addresses on a network. 19  Antivirus software is specifically designed to detect viruses and protect your computer and files from harm. Symantec, Trend Micro, and Avast are among the companies that offer highly rated antivirus software packages. 20  A virus signature is a portion of the virus code that’s unique to a particular computer virus. Quarantining involves placing virus in a secure area so it won’t spread to other files. During inoculation, key attributes about your computer files are recorded and keep stats in secure place. 21  Many viruses exploit weaknesses in operating systems. This type of attack, known as a drive-by download, affects almost 1 in 1,000 web pages. To combat these threats, make sure your OS is up to date and contains the latest security patches. 22  You should create strong passwords—ones that are difficult for hackers to guess. Typically they should be at least eight characters and use uppercase, lowercase, numeric, and symbol characters. 23  A biometric authentication device is a device that reads a unique personal characteristic such as a fingerprint or the iris pattern in your eye and converts it to a digital code. Because no two people have the same biometric characteristics, these devices provide a high level of security. Other biometric devices, including voice authentication and facial recognition systems, are now widely offered in notebook computers, tablets, and smartphones. This figure shows Windows Hello, which brings facial recognition for login to laptops and mobile devices that have an integrated camera. 24  Every day we face a wide array of tasks. Some tasks are complex. These tasks require creative thought and human touch. But some tasks are candidates for automation with computers—automation achieved through programming. This includes: Tasks that are repetitive. Those that work with electronic information. Those that follow a series of clear steps. 2  A career in programming offers many advantages: Jobs are plentiful. Salaries are strong. Telecommuting is often easy to arrange. If you can’t find an existing software product to accomplish a task, programming is mandatory. Macros can execute a complicated sequence of steps with a single command. 3  Generally speaking, a system is a collection of pieces working together to achieve a common goal. Your body, for example, is a system of muscles, organs, and other groups of cells working together. An information system includes data, people, procedures, hardware, and software that help in planning and decision making. Information systems help run an office and coordinate online-purchasing systems and are behind database-driven applications used by Amazon and Netflix. 4  There are six steps in a system development life cycle (SDLC) model. Corporations form a development committee to evaluate proposals. Analysts explore the problem, develop a program specification, define user requirements, and recommend a plan of action. A plan using flowcharts and data-flow diagrams helps programmers. Program development begins next. Testing and installing the program ensure it works properly. Program performance is monitored to determine whether the program is meeting the needs of end users. 5  Programming is the process of translating a task into commands that a computer uses to perform a task. Program development life cycle (PDLC) is the process of moving through the stages a project goes through from development to deployment. 6  The problem statement is the starting point of programming. It provides a clear description of tasks to be performed. It helps the programmer understand goals of programming. The goal of a good problem statement is to have programmers interact with users in these three areas: Data is the raw input that users have at the start of the job. Information is the result needed at the end of the problem. Method is the process of converting inputs into proper outputs. 7  Error handling describes what the program should do if the input is invalid. A testing plan lists specific input numbers expected to be entered by users and lists output values that a program would return for those input values. 8  An algorithm is a set of steps that describe what a program must do to complete its task. Algorithms can be represented through flowcharts. They provide visual representations of patterns. Pseudocode is a text-based approach to documenting an algorithm. 9 Flowcharts use symbols to provide a visual representation of the patterns the algorithm. This figure shows the flowcharting symbols. 10  Algorithms include decision points, which are places where the program must choose from a list of actions based on the value of a certain input. Binary decisions are questions that can be answered with either yes (true) or no (false). With loops, when a question is asked, i the answer is yes, actions are performed. Once the actions have finished, the question is asked again, creating a loop. When the answer is no, the algorithm moves to the first step that follows the loop. 11  Top-down design is an approach in which a problem is broken into a series of high-level tasks. In this figure: A. The top-down design is applied to the highest level of tasks in our parking garage example, B. The tasks are further refined into subtasks, and C. Subtasks are refined into a sequence of instructions—an algorithm. 12  In object-oriented analysis, programmers first identify all the categories of inputs the program is meant to solve. These categories are called classes. An important aspect of object-oriented design is that it leads to reusability. Inheritance means that a new class can automatically pick up all the data and methods of an existing class and then can extend and customize those to fit its own specific needs. The original class is called the base class, and the new, modified class is called the derived class. Programmers may need to create several different examples of a class. Each of these examples is an object. As seen in the figure, John Doe, Jane Doe, and Bill McGillicutty are Employee objects (specific examples of the Employee class). 13  Translating an algorithm into a programming language is called coding. Once programmers create an algorithm, they select the best programming language for the problem and then translate the algorithm into that language. Translating an algorithm into a programming language is the act of coding. Once programmers have an algorithm, they identify the key pieces of information the algorithm uses to make decisions. Then they convert the algorithm into computer code in a specific programming language. 14  A programming language is a kind of “code” for the set of instructions the CPU knows how to perform. Computer programming languages use special words and strict rules so that programmers can control the CPU without having to know all of its hardware details. There are five generations of languages. 15  Portability is the capability to move a solution from one type of computer to another. Variables are the input and output a program manipulates. Variable declarations tell the system to allocate space in RAM. Comments are added to explain the purpose of a section of code. 16  Compilation is the process by which code is converted into machine language—the language the CPU can understand (1s and 0s). A compiler is a program that understands both the syntax of the programming language and the exact structure of the CPU. An interpreter translates the source code into an intermediate form, line by line. Each line is executed as it’s translated. The finished program runs faster than an interpreter. 17  An integrated development environment (IDE) is a developmental tool that helps programmers write and test their programs. 18  Debugging is the process of running the program over and over to find and repair errors and to make sure the program behaves in the way it should. A complete testing plan includes sample inputs that exercise all the error handling required as well as all the processing paths. Logical errors in the problem are caught when the program executes. Runtime errors include issues like dividing by zero. 19  In internal testing, a group uses the program in every possible way. In external testing, people like those who will use the software work with it. Before commercial release, software is often provided in a beta version to test sites or to interested users. Releasing to other manufacturers is called release to manufacturers (or RTM). Documentation is created. Finally, the product is in general availability (or GA) and can be purchased by the public. 20  One quick way to determine which languages are popular is to examine job postings for programmers. As of this presentation, the languages most in demand include C/C++ and Java. In specific industries, certain languages tend to dominate the work. A good introductory programming course will emphasize many skills and techniques. You should find a course that emphasizes design, algorithm development, debugging techniques, and project management. 21  A programming team considers several factors before selecting the language it will use for a specific project: Space available, Speed required, Organizational resources available, and Type of target application. Visual programming languages, like Scratch and App Inventor, use graphical blocks to represent control elements and variables. Programming consists of clicking together these blocks to define program behavior. 22  Java and C# were developed to collect information from networked computers. They are architecture neutral. C# competes with Java. Objective C is the language most often used to program applications to run under macOS. It’s an object-oriented style of language. Swift is a new programming language introduced by Apple for developing for iOS and macOS. 23  A database is a collection of related data that can be stored, sorted, organized, and queried. Database advantages include that they manage large amounts of data efficiently, they enable information sharing, and they promote data integrity. Data integrity ensures that the data contained in the database is accurate and reliable. 2  Flat databases are often represented as a list or simple table. Flat databases can lead to several problems: Duplicate data or data redundancy Data inconsistency Inappropriate data Incomplete data 3 This figure shows examples of data redundancy and data inconsistency. 4  Relational databases operate by organizing data into various tables based on logical groupings. In relational databases, a link between tables that defines how the data is related is referred to as a relationship. The common field in one table is linked to the common field in another table. There are three types of relationships that can be created: One-to-many One-to-one Many-to-many 5 This figure shows tables linked to each other using a one-to-many relationship and a one-to-one relationship. 6 A database management system (DBMS) is the software that allows a computer to perform database functions. The four main operations are: Storing and defining data Viewing (or browsing), adding, deleting, and modifying data Querying (extracting) data Outputting data 7  Data is stored in a database in: Fields: categories into which a database organizes data. Records: a group of related fields. Tables: a group of related records. 8  Data (field) types indicate what kind of data is stored in the field. The following are the available field types: Short Text Long Text Number, Large Number, and Currency Date/Time Yes/No Calculated OLE Object Hyperlink 9 Field properties help to define field data. Three common field properties are: Field size, which defines the maximum number of characters a field can hold. The default value is what is used unless the user enters another value. A caption enables you to display the field name in a more meaningful or readable manner. 10 The figure shows some of the data types and field properties. 11  When creating a table, the use of primary keys is very important. A primary key is a field in the table that uniquely identifies a record. In related tables, the common field that is linked to a primary key in one table is called the foreign key in the linked table. Referential integrity ensures that relationships between tables remain constant and guarantees the quality of the data in the database. It’s useful, especially for large databases, to access the data dictionary (or the database schema). The attributes that define the data in the data dictionary are metadata: data that describes other data. 12  Input forms are used to control how new data is entered into a database. 13  Data validation is the process of ensuring that data entered into a field meets specified guidelines. A range check ensures that the data entered into the field falls within a certain range of values. A field constraint is a property that must be satisfied for an entry to be accepted into the field. A completeness check ensures that all required fields have been completed. A consistency check compares the values of data in two or more fields to see if those values are reasonable. An alphabetic check confirms that only textual characters are entered in a field. A numeric check confirms that only numbers are entered in the field. 14  Displaying the tables on-screen and browsing through all the data is an option with most databases. You can easily sort data into ascending or descending order. 15  There are two ways to display only those records that match particular criteria: Use a filter. Use a query. The figure shows the results of a query. 16  How is data output? The most common form of output for any database is a viewable (or printable) electronic report. The data in a database can be transferred to another software application. 17  Data mining is the process by which data are analyzed and investigated, trying to spot patterns and trends. The main reason businesses mine data is to understand their customers better. 18  Data mining techniques include: Anomaly detection Association or affinity grouping Classification Clustering Estimation Visualization 19