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EXAM OBJECTIVES IN THIS CHAPTER
WHAT IS A NETWORK? 2
LOGICAL NETWORKING TOPOLOGIES 14
PHYSICAL NETWORKING MODELS 24
NETWORK TYPES 31
Networks have been around for many years, long before the first home computer was ever designed or created. Other forms of networking have been around since the dawn of time. Today, designing, planning, implementing, deploying, and managing computer networks is somewhat of a never-ending journey into technology as it develops and integrates, standardizes and grows. It's amazing to see where the computer networks are today from just 15 years ago. Now, more than ever, computer networks are relied upon to produce not only data in the form of files or connectivity to a printer for printing, but also everything from surfing the Internet securely to making a call from New York to Tianjin, works off of the power of a network. Wired to wireless, satellites in the sky to home PC networks allow two computers in your home to share the Internet at the same time. This is all done through networking. The wonderful world of networking is colorful, exciting, and is growing each and every day. Routers, switches, and other infrastructure devices are deployed every day from companies such as Cisco, Juniper, Nortel, and 3Com to name a few. So who deploys them? Who plans, designs, and leads the way for all of this equipment to be planned, purchased, implemented, and managed? Each and every day technology grows more and more complicated, and it evolves as we do.
By the end of this chapter, you will have learned what a network is, and you will start to build upon the initial concepts you need to develop to become a network technician, as well as to pass the Network+ exam. In this chapter, we cover a brief history on the development of networks, as well where they originated from and where they are heading. We also cover the fundamental terminology you absolutely must know to perform your duties as a network technician and to pass the CompTIA Network+ exam.
We cover network models such as centralized and decentralized, the differences between a local area network (LAN) and a wide area network (WAN). Network topologies such as bus, ring, mesh, and star are covered, as well as a discussion on wired and wireless networks.
We then cover the Institute of Electrical and Electronics Engineers (IEEE), which is a standards committee aimed at making things in networking standardized, and easier to support and maintain. We cover in detail the most common standards, testable on the exam. Finally, we cover Requests for Comments (RFCs), a common source for networking professionals to get the definitive source on networking knowledge. So let us start from the very beginning, what exactly is a network anyway?
WHAT IS A NETWORK?
Even someone who's new to computers has experienced the basic concept of networking; it is the difference between standing alone or being part of a group. Networks are systems that are interconnected in some way and provide a method of communication. If you think of your own experiences, you've probably networked with groups of colleagues, and perhaps discussed how you're planning on taking the Network+ exam. Doing so provided a method of sharing information and possibly opened avenues to accessing important resources. Computers are the same; they can be standalone, or part of a network.
A computer network exists when two or more machines are connected together, thereby allowing them to share data, equipment, and other resources. Using a combination of software and hardware the computers gain added functionality, including the ability to:
* Transfer data between machines.
* Save and access files on the same hard disks or other storage devices.
* Share printers, scanners, modems, and other peripheral devices.
* Allow messages to be exchanged via e-mail, instant messaging, and other technologies.
Although networks may provide similar functions, they can be as different from one another as groups of people. Networks are characterized by a number of factors, which we'll discuss later in this chapter and throughout this book. Some of the elements that will define your network and make it different from others include:
* Hardware, such as network interface cards (NIC) or network adapters, that allow computers to transmit and receive data across the network; or routers, switches, and hubs that passes the data to other computers or networks.
* Media, which consists of cables or wireless technologies that carry the data across the network.
* Protocols, which are sets of rules that control how the data is sent between computers. The most popular of these is the protocol used on the Internet, Transmission Control Protocol/Internet Protocol (TCP/IP), while other protocols used on networks include IPX/SPX and AppleTalk.
* Topology, which is shape of the network. It defines how the network is designed and describes how computers are connected together (discussed later in this chapter).
* Network type, which defines the size of the network and its scale within a geographical area (discussed later in this chapter).
* Network model, which determines the levels of security available to the network, and the components needed to connect the computers together (discussed later in this chapter).
* Access, which determines who can use the network and how, and if features of the network are available for private or public use.
* Network operating systems (NOS), such as Windows, NetWare, and Linux. A NOS may be used on a server, which is a computer that provides services to numerous computers, and/or installed on computers that are used by individual users of the network. In some cases, such as with Novell NetWare, additional software may need to be installed on computers that use the server, who are referred to as clients.
* Other software and services, such as whether the network provides access to internal Web sites, e-mail, databases, and so forth.
As you can imagine, these factors influence the design of networks, so they aren't consistently the same. Networks may use different protocols, topologies, and other elements that make them unique. This means that you can look at two networks in two different homes or businesses, and they can be completely different from one another.
Despite this, there are similarities that will exist between different networks. In all cases, a computer is configured to use the network (either by configuring its operating system (OS) or installing client software) and has a device capable of transmitting and receiving data, such as a network adapter or modem. Using a protocol like TCP/IP, it communicates with other computers, and sends data over media (i.e. cables or wireless) to a device (i.e. hub, router, or switch) that will send the data to its destination (i.e. another computer or device, such as a printer). Although the specifics may vary greatly, the basic aspects of a network remain the same.
What Is an Internetwork?
Just as computers can be connected together, so can networks. An internetwork exists when two or more networks that are connected together. By connecting networks together, different businesses or locations can share data between their systems.
Internetworks are particularly important in organizations where sharing data is vital to its ability to function or operate effectively. For example, the police may have a network of computers in their cars, which connects to a network of computers located in police stations. If you're pulled over by the police, the officer may check your license plate number on the computer in his or her car. This computer would connect to a server used by the network of cars, and then pass along the request to a server on a different network that's used by other members of the organization, such as a records department. If additional information was requested, the request might also be sent to networks belonging to state/provincial or federal police. By internetworking these different systems, the police can determine if the car is stolen, if it was used to commit a crime, or if the owner is wanted or believed dangerous.
As you've probably guessed from the name, the largest internetwork is the Internet. The Internet originated as a Department of Defense (DOD) project in 1969, when the cold war was still going on between the West and the former Union of Soviet Socialist Republics (USSR). Under the direction of the DOD's Advanced Research Projects Agency (ARPA), the goal was to create a network that could withstand a nuclear attack. If any part of ARPANet was destroyed, the other parts of it would continue to function. Initially connecting four universities (University of California Los Angeles (UCLA), Stanford Research Institute, University of California Santa Barbara, and University of Utah), it allowed researchers and government to exchange information and quickly grew to include other organizations. Using the TCP/IP protocol suite that ARPA developed, additional computers and networks were added over the years, until finally in 1990, ARPANet was disbanded and removed from the Internet. Today, hundreds of millions of computers and networks connect to the Internet, making it a fundamental method of communication and data exchange.
Internetworks and the Internet aren't to be confused with intranets. Intranets use the same technologies and features of the Internet, such as Internet browsers, Web sites, and so on. This allows users of a network to view documents, distribute data, share employee information, access shared databases, online programs, and other components that are needed or wanted by an organization. The major difference between an intranet and the Internet is that an intranet is used internally. Although the Internet allows the public to view Web pages and other resources, intranets are private and available to employees of a company.
A Brief History on Networking and Communications
Although the Network+ exam won't quiz you on the history, it is nevertheless important to understand past achievements and how we've reached our present state of technology. The history of networking and communications is rich and complex, stretching over a hundred years in the past, with massive changes in the later part of the twentieth century. By looking at these changes, you will see the development of OSes, hardware, and innovations that are still used today.
Early Telecommunications and Computers
Telecommunications got its start in 1870s in Brantford Ontario, when Alexander Graham Bell developed the idea of a telephone. After the first successful words were sent over the device on March 10, 1876, a revolution of communication began. Within decades of its conception, millions of telephones were sold, with operators connecting people using manual circuit switching. This method of calling the operator to have them connect you to another party was routine until the mid-twentieth century, when mechanical and electronic circuit switching became commonplace. These events would have a massive impact on the innovation of computers, even though they wouldn't be invented until 60 years after Bell's first successful phone call.
Although arguments could be made as to whether ancient devices (such as the abacus) could be considered a type of computer, the first computer that could be programmed was developed by a German engineer named Konrad Zuse. In 1936, Zuse created the Z1, a mechanical calculator that was the first binary computer. Zuse continued making innovations to his design, and five years later had reached the point where the Z3 was able to accept programming. Although the next version of his computer would use punch cards to store programs, Zuse used movie film to store programming and data on the Z3 due to a supply shortage of paper during World War II. Just as his computers evolved, so did his programming skills. Zuse's achievements also extended to creating the first algorithmic programming language called Plankalkül, which later was used to create the first computer chess game.
During this same time, John Atanasoff and Clifford Berry developed what is acknowledged to be the first electronic-binary computer. Created at the University of Iowa, the initial prototype acquired this team a grant that allowed them to build their 700 pound final product, containing more than 300 vacuum tubes and approximately one mile of wire. Because the war prevented them from completing a patent on their computer, the computer was dismantled when the physics department needed storage space that was being used by the machine. The distinction of being first initially went to John Mauchly and J. Presper Eckert for their Electrical Numerical Integrator And Calculator (ENIAC I) computer, until a 1973 patent infringement case determined Atanasoff and Berry were the first.
Excerpted from CompTIA Network+ Certification Study Guide Exam N10-004 2E by Robert J. Shimonski. Copyright © 2009 by Elsevier, Inc.. Excerpted by permission of Elsevier Science.
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