A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams. Two very common types of networks include:
You may also see references to a Metropolitan Area Networks (MAN), a Wireless LAN (WLAN), or a Wireless WAN (WWAN). Local Area NetworkA Local Area Network (LAN) is a network that is confined to a relatively small area. It is generally limited to a geographic area such as a writing lab, school, or building. Computers connected to a network are broadly categorized as servers or workstations. Servers are generally not used by humans directly, but rather run continuously to provide "services" to the other computers (and their human users) on the network. Services provided can include printing and faxing, software hosting, file storage and sharing, messaging, data storage and retrieval, complete access control (security) for the network's resources, and many others. Workstations are called such because they typically do have a human user which interacts with the network through them. Workstations were traditionally considered a desktop, consisting of a computer, keyboard, display, and mouse, or a laptop, with with integrated keyboard, display, and touchpad. With the advent of the tablet computer, and the touch screen devices such as iPad and iPhone, our definition of workstation is quickly evolving to include those devices, because of their ability to interact with the network and utilize network services. Servers tend to be more powerful than workstations, although configurations are guided by needs. For example, a group of servers might be located in a secure area, away from humans, and only accessed through the network. In such cases, it would be common for the servers to operate without a dedicated display or keyboard. However, the size and speed of the server's processor(s), hard drive, and main memory might add dramatically to the cost of the system. On the other hand, a workstation might not need as much storage or working memory, but might require an expensive display to accommodate the needs of its user. Every computer on a network should be appropriately configured for its use. On a single LAN, computers and servers may be connected by cables or wirelessly. Wireless access to a wired network is made possible by wireless access points (WAPs). These WAP devices provide a bridge between computers and networks. A typical WAP might have the theoretical capacity to connect hundreds or even thousands of wireless users to a network, although practical capacity might be far less. Nearly always servers will be connected by cables to the network, because the cable connections remain the fastest. Workstations which are stationary (desktops) are also usually connected by a cable to the network, although the cost of wireless adapters has dropped to the point that, when installing workstations in an existing facility with inadequate wiring, it can be easier and less expensive to use wireless for a desktop. See the Topology, Cabling, and Hardware sections of this tutorial for more information on the configuration of a LAN. Wide Area NetworkWide Area Networks (WANs) connect networks in larger geographic areas, such as Florida, the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of global network. Using a WAN, schools in Florida can communicate with places like Tokyo in a matter of seconds, without paying enormous phone bills. Two users a half-world apart with workstations equipped with microphones and a webcams might teleconference in real time. A WAN is complicated. It uses multiplexers, bridges, and routers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN. Advantages of Installing a School NetworkUser access control. Modern networks almost always have one or more servers which allows centralized management for users and for network resources to which they have access. User credentials on a privately-owned and operated network may be as simple as a user name and password, but with ever-increasing attention to computing security issues, these servers are critical to ensuring that sensitive information is only available to authorized users. Information storing and sharing. Computers allow users to create and manipulate information. Information takes on a life of its own on a network. The network provides both a place to store the information and mechanisms to share that information with other network users. Connections. Administrators, instructors, and even students and guests can be connected using the campus network. Services. The school can provide services, such as registration, school directories, course schedules, access to research, and email accounts, and many others. (Remember, network services are generally provided by servers). Internet. The school can provide network users with access to the internet, via an internet gateway. Computing resources. The school can provide access to special purpose computing devices which individual users would not normally own. For example, a school network might have high-speed high quality printers strategically located around a campus for instructor or student use. Flexible Access. School networks allow students to access their information from connected devices throughout the school. Students can begin an assignment in their classroom, save part of it on a public access area of the network, then go to the media center after school to finish their work. Students can also work cooperatively through the network. Workgroup Computing. Collaborative software allows many users to work on a document or project concurrently. For example, educators located at various schools within a county could simultaneously contribute their ideas about new curriculum standards to the same document, spreadsheets, or website. Expensive to Install. Large campus networks can carry hefty price tags. Cabling, network cards, routers, bridges, firewalls, wireless access points, and software can get expensive, and the installation would certainly require the services of technicians. But, with the ease of setup of home networks, a simple network with internet access can be setup for a small campus in an afternoon. Requires Administrative Time. Proper maintenance of a network requires considerable time and expertise. Many schools have installed a network, only to find that they did not budget for the necessary administrative support. Servers Fail. Although a network server is no more susceptible to failure than any other computer, when the files server "goes down" the entire network may come to a halt. Good network design practices say that critical network services (provided by servers) should be redundant on the network whenever possible. Cables May Break. The Topology chapter presents information about the various configurations of cables. Some of the configurations are designed to minimize the inconvenience of a broken cable; with other configurations, one broken cable can stop the entire network. Security and compliance. Network security is expensive. It is also very important. A school network would possibly be subject to more stringent security requirements than a similarly-sized corporate network, because of its likelihood of storing personal and confidential information of network users, the danger of which can be compounded if any network users are minors. A great deal of attention must be paid to network services to ensure all network content is appropriate for the network community it serves.
Network Communications Standards Today’s networks connect terminals, devices, and computers from many different manufacturers across many types of networks, such as wide area, local area, and wireless. For the different devices on various types of networks to be able to communicate, the network must use similar techniques of moving data through the network from one application to another. To alleviate the problems of incompatibility and ensure that hardware and software components can be integrated into any network, various organizations such as ANSI and IEEE (pronounced I triple E) propose, develop, and approve network standards. A network standard defines guidelines that specify the way computers access the medium to which they are attached, the type(s) of medium used, the speeds used on different types of networks, and the type(s) of physical cable and/or the wireless tech- nology used. A standard that outlines characteristics of how two network devices communicate is called a protocol. Hardware and software manufacturers design their products to meet the guidelines specified in a particular standard, so that their devices can communicate with the network. The following sections discuss some of the more widely used network communications standards for both wired and wireless networks including Ethernet, token ring, TCP/IP, 802.11 (Wi-Fi), Bluetooth, UWB, IrDA, RFID, WiMAX, and WAP. ETHERNET Ethernet is a network standard that specifies no central computer or device on the network (nodes) should control when data can be transmitted; that is, each node attempts to trans- mit data when it determines the network is able to receive communications. If two computers on an Ethernet network attempt to send data at the same time, a collision occurs, and the computers must attempt to send their messages again. Ethernet is based on a bus topology, but Ethernet networks can be wired in a star pattern. The Ethernet standard defines guidelines for the physical configuration of the network, e.g., cabling, network cards, and nodes. Today, Ethernet is the most popular LAN standard because it is relatively inexpensive and easy to install and maintain. Ethernet networks often use cables to transmit data. TOKEN RING The token ring standard specifies that computers and devices on the network share or pass a special signal, called a token, in a unidirectional manner and in a preset order. A token is a special series of bits that function like a ticket. The device with the token can transmit data over the network. Only one token exists per network. This ensures that only one computer transmits data at a time. Token ring is based on a ring topology (although it can use a star topology). The token ring standard defines guidelines for the physical configuration of a network. Some token ring networks connect up to 72 devices. Others use a special type of wiring that allows up to 260 connections. TCP/IP Short for Transmission Control Protocol/Internet Protocol, TCP/IP is a network standard, specifically a protocol, that defines how messages (data) are routed from one end of a network to the other. TCP/IP describes rules for dividing messages into small pieces, called packets; providing addresses for each packet; checking for and detecting errors; sequencing packets; and regulating the flow of messages along the network. TCP/IP has been adopted as a network standard for Internet communications. Thus, all hosts on the Internet follow the rules defined in this standard. Internet communications also use other standards, such as the Ethernet standard, as data is routed to its destination. When a computer sends data over the Internet, the data is divided into packets. Each packet contains the data, as well as the recipient (destination), the origin (sender), and the sequence information used to reassemble the data at the destination. Each packet travels along the fastest individual available path to the recipient’s computer via communications devices called routers. 802.11 (WI-FI) Developed by IEEE, 802.11 also known as Wi-Fi (wireless fidelity) and wireless Ethernet, is a series of network standards that specifies how two wireless devices communicate over the air with each other. Using Wi-Fi, computers or devices that have the appropriate wireless capa- bility communicate via radio waves with other computers or devices. The Wi-Fi standard uses tech- niques similar to the Ethernet standard to specify how physically to configure a wireless network. Most of today’s computers and many personal mobile devices, such as smart phones and handheld game consoles, are Wi-Fi enabled.
One popular use of the Wi-Fi standard is in hot spots that offer mobile users the ability to connect to the Internet with their Wi-Fi enabled wireless computers and devices. Many homes and small businesses also use Wi-Fi to network computers and devices together wirelessly. BLUETOOTH Bluetooth is a standard, specifically a protocol, that defines how two Bluetooth devices use short-range radio waves to transmit data. To communicate with each other, Bluetooth devices often must be within about 10 meters (about 33 feet) but can be extended to 100 meters with additional equip- ment. Examples of Bluetooth devices can include desktop computers, notebook computers, handheld computers, smart phones, PDAs, headsets, microphones, digital cameras, and printers. UWB UWB, which stands for ultra-wideband, is a network standard that specifies how two UWB devices use short-range radio waves to communicate at high speeds with each other. For optimal com- munications, the devices should be within 2 to 10 meters (about 6.5 to 33 feet) of each other. Examples of UWB uses include wirelessly transferring video from a digital video camera, printing pictures from a digital camera, downloading media to a portable media player, or displaying a slide show on a projector. IRDA Some computers and devices use the IrDA specification to transmit data wirelessly to each other via infrared (IR) light waves. Infrared requires a line-of-sight transmission; that is, the sending device and the receiving device must be in line with each other so that nothing obstructs the path of the infrared light wave. RFID RFID (radio frequency identification) is a standard, specifically a protocol, that defines how a network uses radio signals to communicate with a tag placed in or attached to an object, an animal, or a person. The tag consists of an antenna and a memory chip that contains the information to be transmitted via radio waves. Through an antenna, an RFID reader reads the radio signals and trans- fers the information to a computer or computing device. Readers can be handheld or embedded in an object such as a doorway or tollbooth. WIMAX WiMAX (Worldwide Interoperability for Microwave Access), also known as 802.16, is a newer network standard developed by IEEE that specifies how wireless devices communicate over the air in a wide area. Using the WiMAX standard, computers or devices with the appropriate WiMAX wireless capability communicate via radio waves with other computers or devices via a WiMAX tower. The WiMAX tower, which can cover up to a 30-mile radius, connects to the Internet or to another WiMAX tower. Two types of WiMAX specifications are fixed wireless and mobile wireless. With fixed wire- less WiMAX, a customer accesses the Internet from a desktop computer at home or other permanent location. Mobile wireless WiMAX, by contrast, enables users to access the WiMAX network with mobile computers and mobile devices such as smart phones. The WiMAX standard provides wireless broadband Internet access at a reasonable cost over long distances to business and home users. The WiMAX standard, similar to the Wi-Fi stan- dard, connects mobile users to the Internet via hot spots. The next generation of game consoles also plans to support the WiMAX standard.
WAP The Wireless Application Protocol (WAP) is a standard, specifically a protocol, that specifies how some mobile devices such as smart phones can display the content of Internet services such as the Web, e-mail, and chat rooms. For example, users can check weather, sports scores, and headline news from their WAP-enabled smart phone. To display a Web page on a smart phone, the phone should contain a microbrowser. WAP uses a client/server network. The wireless device contains the client software, which connects to the Internet access provider’s server. |
What do you call the connection of computers that allows them to communicate with each other?
Pos Terkait
Copyright © 2024 ketiadaan Inc.
