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.can be lost between two nodes.(Thesignal is at least partially regeneratedPMD (Physical Medium Dependent)by the transceiver at each node.)PMD represents the lowest sublayer sup-Can handle packets from either theported by FDDI.This document specifies theLLC (logical-link control) sublayerrequirements for the optical power sources,of the data-link layer or from thephotodetectors, transceivers, MIC (mediumnetwork layer.interface connector), and cabling.This is theSupports hybrid networks, which canonly optic (as opposed to electrical) levelbe created by attaching a subnetworkand corresponds roughly to the lower parts(for example, a collection of stationsof the physical layer in the OSI Referencearranged in a star or a tree) to the ringModel.through a concentrator.The power source must be able to senda signal of at least 25 microwatts (25 mil-The figure Context and properties oflionths of a watt) into the fiber.The photo-FDDI summarizes this architecture.detector, or light receptor, must be able toFDDI Applications pick up a signal as weak as 2 microwatts.The MIC for FDDI connections serves asThe FDDI architecture can be used for threethe interface between the electrical and opti-types of networks:cal components of the architecture.Thisconnector was specially designed by ANSIIn a backbone network, in which thefor FDDI and is also known as the FDDIFDDI architecture connects multipleconnector.networks.Optical fiber s very highThe cabling specified at this sublayer callsbandwidth makes FDDI ideal for suchfor two rings running in opposite directions.applications.The primary ring is the main transmissionAs a back-end network to connectmedium.A secondary ring provides redun-mainframes, minicomputers, anddancy by making it possible to transmit theperipherals.Again, the high bandwidthdata in the opposite direction if necessary.makes FDDI attractive.When the primary ring is working properly,the secondary ring is generally idle. FDDI (Fiber Distributed Data Interface) 381CONTEXT AND PROPERTIES OF FDDIaContextbNetwork Architectures cElectricaldEthernet, ARCnet, etc.CoaxialeOpticalFDDIfgFDDI PropertieshMedium Multi-mode or single-mode optical fiberiLight source LED or laser operating at approximately 1300 nm wavelengthjEncoding scheme 4B/5B + NRZIkTopology Dual rings, traveling in opposite directionslAccess method Token passing, but with multiple frames allowedmData frame size Maximum of 4500 data bytes plus 8+ bytes for a preamblenLayers PMD optical, PHY, MAC, SMToPerformance Supports transmission speeds of up to 100 MbpsCan provide and maintain a guaranteed bandwidthpSupports up to 1000 nodes on the networkSupports a network span of up to 100 kmqSupports nodes up to 2 km apart with multimode cable; up to 40 km with single-mode cablerVariants FDDI-I and FDDI-IIstPHY (Physical) upper parts of the OSI Reference Modeluphysical layer.The PHY layer mediates between the MACvlayer above and the PMD layer below it.MAC (Media Access Control)Unlike the PMD layer, this is an electronicwlayer.Signal-encoding and signal-decoding The MAC layer defines the frame formatsxschemes are defined at the PHY layer.and also the media-access method used byFunctionally, this corresponds to the the network.This corresponds to the loweryz 382 FDDI (Fiber Distributed Data Interface)part of the OSI Reference Model data-link guarantee a uniform data stream as wouldlayer.The MAC and PHY layers are imple- be required, for example, for voice or certainmented directly in the FDDI chip set.video data.)The MAC layer gets its data from the To handle voice, video, and multimediaLLC sublayer above it.applications in real-time, a uniform data-transmission capability was added in a revi-SMT (Station Management) sion that is generally known as FDDI-II, butthat is officially named hybrid ring controlThe SMT component monitors and manages(HRC) FDDI.This new capability usesthe node s activity.The SMT facility alsocircuit-switching, so that FDDI-II supportsallocates the architecture s bandwidth asboth packet- and circuit-switched services.required.The figure FDDI-I and FDDI-II organiza-There are three elements to the SMTtion shows the major differences betweencomponent:the two versions.The major structural additions to FDDI-IIFrame services generate frames forare a medium access control element capablediagnostics.of dealing with circuit-switched data and aConnection management (CMT)multiplexer capable of passing either packet-controls access to the network.or circuit-switched (that is, data, voice,video, and so on) material to the physicalRing management (RMT) trouble-layer.This hybrid multiplexer (HMUX) getsshoots the network [ Pobierz całość w formacie PDF ]