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.History group Permits filtering and storing of statisticsaccording to user-defined parameters and time intervals.Configuration group Defines standard configurationparameters for probes that includes such parameters asnetwork address, serial line information, and SNMP trapdestination information.RMON II is focused more on helping network managersunderstand traffic flow for the purpose of capacity planning REPEATERS 301rather than for the purpose of physical troubleshooting.Thecapability to identify traffic levels and statistics by applica-tion has the potential to greatly reduce the time it takes totroubleshoot certain problems.Without tools that can pin-point which software application is responsible for gobblingup a disproportionate share of the available bandwidth, net-work managers can only guess.Often it is easier just toupgrade a server or a buy more bandwidth, which inflatesoperating costs and shrinks budgets.SummaryApplying remote monitoring and statistics-gatheringcapabilities to Ethernet and Token Ring environments viathe RMON MIB offers a number of benefits.The availabil-ity of critical wireless and wired networks is maximized,since remote capabilities allow for timely problem resolu-tion.With the capability to resolve problems remotely,operations staff can avoid costly travel to troubleshootproblems on site.With the capability to analyze data col-lected at specific intervals over a long period of time, inter-mittent problems can be tracked down that normallywould go undetected and unresolved.And with RMON II,these capabilities are enhanced and extended up to theapplications level across the enterprise.See alsoWireless Management ToolsREPEATERSREPEATERSArepeater is a device that extends the inherent distance lim-itations of various transmission media, including wirelesslinks, by boosting signal power so that it stays at the samelevel regardless of the distance it must travel.As such, the 302 REPEATERSrepeater operates at the lowest level of the Open SystemsInterconnection (OSI) reference model the Physical Layer(Figure R-3).Repeaters are necessary because signal strength weakenswith distance: The longer the path a signal must travel, theweaker it gets.This condition is known as signal attenua-tion. On a telephone call, a weak signal will cause low vol-ume, interfering with the parties ability to hear each other.In cellular networks, when a mobile user moves beyond therange of a cell site, the signal fades to the point of discon-necting the call.In the LAN environment, a weak signal canresult in corrupt data, which can substantially reducethroughput by forcing retransmissions when errors aredetected.When the signal level drops low enough, thechances of interference from external noise increase, render-ing the signal unusable.Repeaters also can be used to link different types of net-work media fiber to coaxial cable, for example.Often LANsare interconnected in a campus environment by means ofrepeaters that form the LANs into connected network seg-Source Station Destination Station7 Application Application 7Presentation Presentation6 6Session Session5 54 Transport Transport 43 Network Network 3Repeater2 Data Link Data Link 21 Physical Physical Physical Physical 1Ethernet EthernetFigure R-3 Repeaters operate at the Physical Layer of the OSI referencemodel. REPEATERS 303ments.The segments may employ different transmissionmedia thick or thin coaxial cable, twisted-pair wiring, oroptical fiber.The cost of media converters is significantlyless than full repeaters and can be used whenever media dis-tance limitations will not be exceeded in the network.Hubs or switches usually are equipped with appropriatemodules that perform the repeater and media conversionfunctions on sprawling LANs
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Tematy
IndexBloom's Period Studies Harold Bloom The Harlem Renaissance (2003)
Patricia Richard Busy Hands, Images of the Family in the Northern Civil War Effort (2003)
William Blum Killing Hope, US Military and CIA Interventions Since World War II (2003)
Quentin W. Fleming Project Procurement Management Contracting, Subcontracting, Teaming (2003)
Characterization of Cereals and Flours G. Kaletunc, K. Breslauer (Marcel Dekker, 2003) WW
Philip D. Morgan Diversity and Unity in Early North America (2003)
Wheeler Secure Programming for Linux and UNIX HOWTO (2003)
Michael Mastering UNIX Shell Scripting (Wiley, 2003)
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Brooks, Terry Jerle Shannara 01 Ilse Witch