Objective 5. Describe Networks and Define Network Terms

As discussed earlier, computers and the various peripherals that are connected to them are called hardware. However, connecting one computer to another creates a network. Networks consist of two or more connected computers plus the various peripheral devices that are attached to them. Each object connected to a network, whether it is a computer or a peripheral device, is known as a node. Some of the benefits of computer networks include the ability to share resources (such as printers and scanners) and software, and improved communication and data sharing. Computers can be connected to a network in several ways. They can use existing telephone wires or power lines, or use coaxial, UTP, or fiber-optic cable. Networks can also be wireless, in which case they use radio waves instead of wires or cables to connect.

---

A computer network that connects computers reasonably close together, such as within a home or in a small office or business, is called a local area network (LAN). Usually these networks are contained within a single building or group of adjacent buildings. If the network begins to cover a larger geographic area or begins to include other networks, it becomes a wide area network (WAN). An example of this is the network used by Penn State University. Penn State has many campuses located across the state of Pennsylvania. Because the different campuses are connected through a WAN, students and teachers are able to use a computer in one location and access files or resources located at any of the other campuses, wherever they might be located. Both LANs and WANs can be wired or wireless. Wired LANs might use phone lines or cable connections, while wired WANs might use phone lines, satellites, or special leased lines, known as T-1 or T-3 lines, for high-speed communication. Did you realize the Internet is actually the largest network of all because it connects computers all over the globe?

Networks can be configured in several ways. There are two main categories: peer-to-peer and client/server. Peer-to-peer or P2P networks are most commonly found in homes and small businesses. In a peer-to-peer network, each node on the network can communicate with every other node. Peer-to-peer networks are relatively easy to set up, but tend to be rather small. This makes them ideal for home use, although not as desirable in the workplace. If a network has more than ten nodes, it is generally best to use the client/server network instead. Remember that a node can be a computer, printer, scanner, modem, or any other peripheral device that can be connected to a computer. Therefore, it isn't difficult to find more than ten nodes in an office or business setting. Client/server networks typically have two different types of computers. The client computer is the one most people directly interact with. This is the computer used at your desk or workstation to write letters, send e-mail, produce invoices, or perform any of the many tasks that can be accomplished with a computer. In contrast, the server computer is typically kept in a secure location and is used to manage network resources. Sometimes servers are dedicated and are assigned specific tasks. For instance, a Web server is used to deliver Web pages, a file server is used to store and archive files, and a print server manages the printing resources for the network.

Network topology describes the different types of network architecture used for client/server networks. Just as there are different sizes and styles of buildings that are designed for different purposes, networks are designed to be physically configured and connected in different ways. The three most common layouts are explained in the following list. Figure 1.27 shows an example of each of these layouts, while Figure 1.28 discusses the advantages and disadvantages of each of these topographies.

---

Figure 1.27.

Figure 1.28. Advantages and Disadvantages of Bus, Ring, and Star Topologies

(This item is displayed on page 218 in the print version)

Topology	Advantages	Disadvantages
Bus	Uses a minimal amount of cabling Easy, reliable, and inexpensive to install	Breaks in the cable can disable the network Large numbers of users will greatly decrease performance because of high volumes of data traffic
Ring	Allocates access to the network fairly Performance remains acceptable even with large numbers of users	Adding or removing nodes disables the network Failure of one computer can bring down the entire network Problems in data transmission can sometimes be difficult to find
Star	Failure of one computer does not affect other computers on the network Centralized design simplifies trouble-shooting and repairs Easy to add additional computers or network segments as needed (high scalability) Performance remains acceptable even with large numbers of users	Requires more cable and is often more expensive than a bus or ring topology The switch is a central point of failure. If it fails, all computers connected to that switch are affected

• Bus topology connects each node to a single, central high-speed line known as a bus. No server is used, and, although it is possible for each node to communicate with all the others, they can only do so one at a time. If one computer or device is sending over the network, all the others must wait till the transmission is complete before they can begin. Because this is an inexpensive and easy way to connect, this topology is often found in peer-to-peer networks.
• Ring topology, sometimes known as token-ring topology, connects each node to the next, forming a loop or a circle. The data that's sent is passed from node to node, traveling around the circle in only one direction. A token travels around the ring until one of the nodes is ready to send a transmission. The node then holds the token until the transmission is finished, preventing any of the other devices from sending until the token is released to make its way around the circle again. This type of topology gives each device an equal chance of being able to send data and prevents one node from doing all the communicating.
• Star topology is the most frequent networking style used for businesses. It offers a high degree of flexibility. Each node is connected to a special device known as a switch, which is centrally located. Each node must go through the switch to communicate with the others. If something happens to one node, the others are still able to communicate.

Objective 6 Identify Safe Computing Practices