physical topology of a network refers to the configuration of cables, computersWritten by Gianfranco Fracassi
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The protocols used with star configurations are usually Ethernet or LocalTalk. Token Ring uses a similar topology, called star-wired ring. Star-Wired Ring A star-wired ring topology may appear (externally) to be same as a star topology. Internally, MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring (See fig. 3). The Token Ring protocol uses a star-wired ring topology. Tree A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 4). Tree topologies allow for expansion of an existing network, and enable schools to configure a network to meet their needs. Advantages of a Tree Topology •Point-to-point wiring for individual segments. •Supported by several hardware and software venders. Disadvantages of a Tree Topology •Overall length of each segment is limited by type of cabling used. •If backbone line breaks, entire segment goes down. •More difficult to configure and wire than other topologies. 5-4-3 Rule A consideration in setting up a tree topology using Ethernet protocol is 5-4-3 rule. One aspect of Ethernet protocol requires that a signal sent out on network cable reach every part of network within a specified length of time. Each concentrator or repeater that a signal goes through adds a small amount of time. This leads to rule that between any two nodes on network there can only be a maximum of 5 segments, connected through 4 repeaters/concentrators. In addition, only 3 of segments may be populated (trunk) segments if they are made of coaxial cable. A populated segment is one which has one or more nodes attached to it . In Figure 4, 5-4-3 rule is adhered to. The furthest two nodes on network have 4 segments and 3 repeaters/concentrators between them. This rule does not apply to other network protocols or Ethernet networks where all fiber optic cabling or a combination of a fiber backbone with UTP cabling is used. If there is a combination of fiber optic backbone and UTP cabling, rule is simply translated to 7-6-5 rule. Considerations When Choosing a Topology: •Money. A linear bus network may be least expensive way to install a network; you do not have to purchase concentrators. •Length of cable needed. The linear bus network uses shorter lengths of cable. •Future growth. With a star topology, expanding a network is easily done by adding another concentrator. •Cable type. The most common cable in schools is unshielded twisted pair, which is most often used with star topologi
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| | What is a Protocol? the communications between computers on a networkWritten by Gianfranco Fracassi
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Token Ring The Token Ring protocol was developed by IBM in mid-1980s. The access method used involves token-passing. In Token Ring, computers are connected so that signal travels around network from one computer to another in a logical ring. A single electronic token moves around ring from one computer to next. If a computer does not have information to transmit, it simply passes token on to next workstation. If a computer wishes to transmit and receives an empty token, it attaches data to token. The token then proceeds around ring until it comes to computer for which data is meant. At this point, data is captured by receiving computer. The Token Ring protocol requires a star-wired ring using twisted pair or fiber optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps. Due to increasing popularity of Ethernet, use of Token Ring in school environments has decreased. FDDI Fiber Distributed Data Interface (FDDI) is a network protocol that is used primarily to interconnect two or more local area networks, often over large distances. The access method used by FDDI involves token-passing. FDDI uses a dual ring physical topology. Transmission normally occurs on one of rings; however, if a break occurs, system keeps information moving by automatically using portions of second ring to create a new complete ring. A major advantage of FDDI is speed. It operates over fiber optic cable at 100 Mbps. ATM Asynchronous Transfer Mode (ATM) is a network protocol that transmits data at a speed of 155 Mbps and higher. ATM works by transmitting all data in small packets of a fixed size; whereas, other protocols transfer variable length packets. ATM supports a variety of media such as video, CD-quality audio, and imaging. ATM employs a star topology, which can work with fiber optic as well as twisted pair cable. ATM is most often used to interconnect two or more local area networks. It is also frequently used by Internet Service Providers to utilize high-speed access to Internet for their clients. As ATM technology becomes more cost-effective, it will provide another solution for constructing faster local area networks. isJustFreeReal Family Freebies free stuff from USA Best Surveys for Cah Rewards Real Free Ringtones and Logos Win Free Prizes with latest free contests
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