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Chapter 1: Networking BasicsIn this chapter, we'll introduce you to the basic concept of computer networking, and we'll begin by giving you a background history of networking. We'll then introduce you to the two current methods of networking-peer-to-peer and client/server-and with these concepts in mind, we'll show you the industry standard for networking-the OSI model.
We'll then introduce you to the various forms networks can appear in, known as network topologies. We'll also show you how these forms are implemented in LANs, MANs, and WANs.
You'll build on the previous concepts by learning about all of the various components and hardware devices used in networks, and you'll then learn how networks communicate with these devices and other networks using network protocols. We'll then define the standards that dictate how these devices and media are implemented in networks, known as the ISO 8802 specifications.
Following these discussions, you'll learn about how all of these concepts are controlled by the network operating system. Finally, you'll learn about the various tools and methodologies employed by network technicians to troubleshoot common network challenges.
A Brief History of Networking
In 1957, the Soviet Union launched Sputnik, an unmanned satellite that orbited the planet for three months before falling back to Earth. This technology prompted the United States, in 1958, to form the Advanced Research Projects Agency (ARPA) to develop advanced communications by means of the computer.
Eleven years later in 1969, ARPA focused on implementing a network of computers that could span large geographical distances. A four-node network called ARPANET was created, with locations at UCLA, the Stanford Research Institute (SRI), the University of California Santa Barbara, and the University of Utah. On October 29, 1969, history was made when the first data packets were sent across a network. Charley Kline at UCLA attempted to log in (gain access) to a computer located at SRI. The login attempt caused a system crash as the letter G in the word LOGIN was typed. This minor drawback was overcome, and the data packets were sent. To grasp how this technology affects all of us today, a discussion of the elements of a network is in order.
Elements of Networking
To understand the concept of networking, consider for a moment the following analogy. You wish to talk to a friend who lives far away-say, in another country. You pick up the telephone and dial the number. After a series of rings, your friend picks up the phone and says, "Hello?"You greet your friend and begin a conversation. After your conversation is completed, you both say," Goodbye" and hang up your respective phones. What you've just participated in is a networking communication, which is what millions of computer systems around the globe do every day.
This analogy outlines, in simple terms, three of the core components of computer networking:
The telephone represents the hardware component. It's an electronic device with a specific purpose. However, it isn't necessary for your friend to have an exact duplicate of your telephone for the transmission to occur. The same holds true for computer networks. It's possible in networking for an Apple PowerBook G3 to communicate with an IBM AS/400 Server (a large, powerful computer) and for that IBM to communicate with a Compaq Presario. This is referred to as platform independence. In computer terms, a platform refers to a type of computer system.
Now consider the greeting portion of your telephone call. When your friend answered the phone and said "Hello," he was using what's referred to as a protocol, which is nothing more than a method or standard of communication. If, for example, the person who answered the phone had said "Hej," you would probably have sat there baffled at this greeting (because you don't speak Danish) and terminated the communication by hanging up the phone. For two computers to communicate, they must speak the same language or protocol. Otherwise, the data that's being presented by one computer is unrecognizable by the receiving computer.
Finally, let's consider the media portion of our analogy. When you pick up your phone, you hear a dial tone that indicates the device is ready to initiate a communication sequence. As you dial the number, a series of electronic pulses is sent down the copper wire from your phone, through the wall, out of your house, and through a series of relays that forward the pulses around the world to your friend's telephone, causing it to ring.
Along the communication path, these electronic pulses are transformed into pulses of light that are carried along fiber-optic cables and then converted back into electronic pulses that are carried along the copper wire to your friend's telephone.
In computer networks, each computer sends its data along a form of media that carries the signals. So these signals can be converted from one media type to another, allowing computers to use dissimilar forms of media while communicating. Thanks to further advancements in technology, it's now possible for computer systems to communicate through the air without the need of a physical media. This is known as wireless communication.
In its purest sense, networking is defined as the communication of two separate computers using a defined protocol over a form of media. The purpose of these networks is to share resources, whether the resources are data (such as a document) or devices (such as a printer).
In today's world, the term networking encompasses a broad range of technologies and methods. Computers are now able to not only communicate across relatively short distances, such as from room-to-room, but across entire continents, even from planet to planet. To understand how these communications take place, let's continue our discussion on the basic elements of a network.
Now that you have a sense of how a network operates, we can begin to define the elements that make up a network. Looking back at our telephone analogy; two people participated in the communication-you and your friend. Think of these positions as points at each end of a line. Along that line, or communication path, there existed points (the relays) that forwarded the electronic pulses to the next relay in the path. Also on that path were devices that converted the electronic pulses to pulses of light that traveled down fiberoptic cables. These, too, were points along that path. In computer networks, each of these points is referred to as a node, which can be a computer (you and your friend would each be a node) or any device along the path that moves the communication along. With that concept in mind, we can now begin to discuss two standard types of networks-peer-to-peer networks and client/server networks.
Using the telephone analogy, a peer-to-peer network allows a conversation, or information exchange, between two individuals. An important element to point out is that at the beginning of the phone call, the person receiving the call is responsible for allowing the communication to start. For example, if the receiver of the phone call doesn't want to speak with the person who made the call, the receiver of the call simply hangs up the phone. The receiver makes this determination after the caller identifies himself. Furthermore, if the receiver does wish to talk to the caller, she simply needs to continue the conversation.
In networking terms, this process is called authentication. In a peer-to-peer network, each node in the network is responsible for authenticating all incoming requests for information. This is accomplished by assigning a password to each resource associated with any given computer. For example, let's say Bob would like to access a file on another computer on the network. In a peer-to-peer model, Bob is prompted to supply a password each time he attempts to access that file over the network. Furthermore, if Bob wants to access a file on a different computer, he's prompted to supply a different password assigned to that file. It becomes readily apparent that trying to maintain passwords for each separate resource on a large network is quite cumbersome. In response to this dilemma, a new model of networking was introduced-the client/server model.
The major drawback of the peer-to peer model is its lack of centralized administration. Network administrators essentially have two choices: keep all of the passwords the same for all resources (creating a serious lack of security), or maintain a list of the passwords and update the list when changes occurred. To solve this problem, the client/server model was introduced. In this model, all usernames are stored centrally on one computer. Each user, then, has a unique password that allows the user to access the network. To allow a user to access a resource on the network, the network administrator need only add that user's name to the list of allowed users. When that user attempts to access the resource, her username is compared with that list, and access is granted or denied.
Using our telephone analogy, this is like placing an operator-assisted call. The caller dials the operator and requests that a connection be made between her and her friend. Before making the connection, the operator contacts her friend and verifies that the friend would like to receive the connection. If the receiver accepts the request, the connection is made and the conversation can take place. However, if the receiver doesn't wish to accept the call, the operator denies the connection request of the caller.
As you can see, the client/server model lends itself well to a large-scale network with thousands of users and resources. The process of allowing access to a resource on a network is referred to as sharing, and two types of resource sharing exist: share-level and user-level...