Computer Networks
| Author | Badie Farah, Rhoda Wilburn |
| Pages | 104-108 |
Page 104
For most businesses in the United States, computers are an essential part of their daily operations. Many businesses have come to rely on their computers to store and track information, communicate with customers and suppliers, design and manufacture products, and more. It is not uncommon for businesses of all sizes to have multiple computers in an office. Often, these computers are connected through networks that allow information to be shared between computers.
A computer network, as defined in the Merriam-Webster dictionary, is "a system of computers, peripherals, terminals, and databases connected by communications lines." In other words, networks are used to connect computers to other computers, as well as to other devices such as printers, scanners, and fax machines. Networks can be used to connect devices in the same building or they can be used to connect devices that are miles apart. Perhaps the most well known network in use today is the Internet. Many individuals and businesses around the world connect to the Internet on a daily basis. Other examples of networks include library card catalogs, the displays of flight arrival and departure times used at airports, and credit card readers at retail stores.
Networks can be set up in a number of different ways depending on the number of devices, the distances between those devices, the transmission speed requirements, and other factors. The most popular configurations, or topologies, include the bus, token ring, star, and star bus topologies.
With a bus configuration, each node is connected sequentially along the network backbone. A node is any device connected to the network, such as a computer, printer, or scanner. Backbone is the term used to describe the main cables to which the network segments are connected. Resistors are placed at each end of the network to ensure that the signal is terminated when it reaches the end. When one node sends information to another node through the network, the information travels along the backbone until it reaches the desired receiving node.
Figure 1
A Bus Topology
With a ring configuration, each node is connected sequentially along the network backbone. However, unlike the bus configuration, the end of the network connects to the first node, forming a circuit. Nodes on a token ring take turns sending and receiving information. In the token ring topology, a token travels along the backbone with the information being sent. The node with the token sends information to the next node along the backbone. The receiving node reads the information addressed to it and then passes the token and any additional information to the next node. This continues until the token and data make it back to the first node in the network.
Figure 2
A Token Ring Topology
With a star configuration, each node is connected to a central hub via network segments. When one node sends information to another node, the information passes through the hub. The hub does not filter or route the information in any way; it simply serves as a connector between network segments.
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Figure 3
A Star Topology
With a star bus configuration, the hubs of multiple star networks are connected together via the backbone. This is the most common network configuration in use.
Figure 4
A Star Bus Topology
A local area network (LAN), as the name implies, is a network that connects devices that are local, or relatively close to each other. Nodes on a LAN are usually in the same building. A wide area network (WAN), on the other hand, is used to connect nodes that could be miles apart. LANs generally transmit data faster than WANs, and they are usually more reliable. Fiber-optic cables are used for both LANs and WANs.
Ethernet is a LAN protocol (i.e., a set of rules that governs communications) developed in the mid-1970s by Bob Metcalfe and David Boggs at Xerox Corporation's Palo Alto Research Center. Today, Ethernet is the most widely used network technology in the world. The original Ethernet used a bus topology and provided for transfer rates of up to 10 million bits per second (Mbps). This Ethernet specification was modified slightly and became the Institute of Electrical and Electronics Engineering (IEEE) 802.3 standard, which helped solidify Ethernet as a widely-recognized, open international standard. The IEEE 802.3 specifies the physical networking interface and lower layers of software usually associated with Ethernet. Vendors ship an estimated total of 300 million Ethernet ports each year.
Although networks using Ethernet protocol generally connect devices over short distances, technological advances now allow Ethernet to connect devices that are miles apart. Ethernet is widely accepted and largely installed because it is simple and efficient and because network interface cards (NIC)...
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