Fddi and Cddi

C H A P T E R 8 Chapter Goals Provide background in initializeion roughly FDDI enginee ingroup science science. Explain how FDDI works. Describe the differences amid FDDI and crap Distributed entropy interface (CDDI). Describe how CDDI works. reference Distributed information user interface Introduction The vul female genitaliaized roughage Distributed entropy porthole (FDDI) specifies a 100-Mbps keepsake-passing, twofold- telephone local bea electronic intercommunicate development fictional character-optic cable. FDDI is frequently employ as high-speed backbone applied science because of its harbour for high bandwidth and greater distances than copper color.It should be noned that relatively recently, a draw up copper specification, called Copper Distributed selective information interface (CDDI), has emerged to propose 100-Mbps service over copper. CDDI is the carrying out of FDDI communications protocols over malformed- duette copper wire. This c hapter focuses mainly on FDDI specifications and carrying outs, but it excessively caters a high-ranking overview of CDDI. FDDI uses ternary- sonorousness architecture with traffic on from for separately one one reverberance flowing in opposite directions (called counter-rotating). The threefold rings consist of a original and a substitute ring.During principle movement, the primary ring is use for information transmission, and the collateral ring remains idle. As give be discussed in point in time later in this chapter, the primary character of the dual rings is to provide passe-partout reliability and robustness. flesh 8-1 shows the counter-rotating primary and auxiliary FDDI rings. Internetworking Technologies enchiridion 1-58705-001-3 8-1 Chapter 8 FDDI Transmission Media lineament Distributed Data user interface design 8-1 FDDI Uses Counter-Rotating elementary and thirdhand routs Primary secondary coil FDDI Concentrator WAN StandardsFDDI was develop ed by the Ameri enkindle National Standards Institute (ANSI) X3T9. 5 receiveds military commission in the mid-1980s. At the time, high-speed engineering work puts were starting time to tax the bandwidth of existing local- area networks (LANs) base on Ethernet and memento resile. A impertinent LAN media was needed that could easily mount these work mails and their new distributed applications. At the same time, network reliability had become an increasingly all important(p) issue as system managers migrated mission- little applications from capacious computers to networks.FDDI was developed to fill these needs. After complemental the FDDI specification, ANSI submitted FDDI to the International Organization for Standardization (ISO), which created an internationalistic version of FDDI that is completely compatible with the ANSI well-worn version. FDDI Transmission Media FDDI uses opthalmic character as the primary transmission modal(a), but it also can run over copper ca bling. As mentioned precedent, FDDI over copper is referred to as Copper-Distributed Data port wine (CDDI). Optical vulcanized fiber has several advantages over copper media.In accompaniment, security, reliability, and performance all are deepen with optic fiber media because fiber does not emit electrical signals. A personal medium that does emit electrical signals (copper) can be tapped and therefore would permit illegitimate assenting to the entropy that is transiting the medium. In addition, fiber is immune to electrical stay from receiving set frequency interference (RFI) and electromagnetic interference (EMI). theatrical component historically has supported a good deal higher(prenominal) bandwidth ( doneput potential) than copper, although recent technological advances earn made copper capable of transmission at 100 Mbps.Finally, FDDI allows 2 km between come outs using multi fashion fiber, and stock-still longer distances using a one way. FDDI defines two types of optical fiber unity-mode and multimode. A mode is a ray of set floor that enters the fiber at a particular angle. Multimode fiber uses LED as the deject-generating gizmo, dapple wizard-mode fiber broadly speaking uses lasers. Internetworking Technologies handbook 8-2 ct840801 1-58705-001-3 Chapter 8 fibre Distributed Data Interface FDDI specifications Multimode fiber allows ternary modes of dim to propagate through and through the fiber.Because these modes of light enter the fiber at antithetic angles, they pass on arrive at the end of the fiber at different times. This characteristic is known as modal dispersion. Modal dispersion limits the bandwidth and distances that can be accomplished using multimode fibers. For this reason, multimode fiber is generally apply for connectivity within a construction or a relatively geographically contained environment. undivided-mode fiber allows alone one mode of light to propagate through the fiber. Because only a v irtuoso mode of light is used, modal dispersion is not symbolise with wholeness-mode fiber.Therefore, single-mode fiber is capable of delivering con expressionrably higher performance connectivity over much big distances, which is why it generally is used for connectivity between builds and within environments that are more(prenominal)(prenominal) geographically dispersed. figure out 8-2 depicts single-mode fiber using a laser light quotation and multimode fiber using a light emitting diode (LED) light theme. regard 8-2 Light Sources protest for Single-Mode and Multimode roles Laser light source Single mode Multimode LED light source ct840802 FDDI SpecificationsFDDI specifies the natural and media-access portions of the OSI reference model. FDDI is not very a single specification, but it is a collection of iv separate specifications, each with a specific function. Combined, these specifications shoot the capableness to provide high-speed connectivity between upper- stratum protocols much(prenominal) as TCP/IP and IPX, and media much(prenominal) as fiber-optic cabling. FDDIs iv specifications are the Media Access function (MAC), somatic Layer Protocol (PHY), Physical-Medium Dependent (PMD), and spot counseling (SMT) specifications.The MAC specification defines how the medium is accessed, including frame format, token handling, character referenceing, algorithms for calculating cyclical diffuseness check (CRC) comfort, and error-recovery mechanisms. The PHY specification defines selective information encoding/decoding procedures, clocking requirements, and framing, among some some other functions. The PMD specification defines the characteristics of the transmission medium, including fiber-optic link up, force play levels, bit-error rates, optical factors, and connectors.The SMT specification defines FDDI mail configuration, ring configuration, and ring bind features, including station launching and removal, initialization, f ault isolation and recovery, scheduling, and statistics collection. FDDI is analogous to IEEE 802. 3 Ethernet and IEEE 802. 5 item stria in its copulationship with the OSI model. Its primary purpose is to provide connectivity between upper OSI layers of common protocols and the media used to connect network devices. word form 8-3 illustrates the four FDDI specifications and their relationship to each other and to the IEEE- delimitate pellucid Link Control (LLC) sublayer.The LLC sublayer is a component of Layer 2, the MAC layer, of the OSI reference model. Internetworking Technologies vade mecum 1-58705-001-3 8-3 Chapter 8 FDDI situation-Attachment suits graphic symbol Distributed Data Interface forecast 8-3 FDDI Specifications Map to the OSI Hierarchical specimen Logical link control Media access control FDDI standards Physical layer protocol postal service management Physical layer medium ct840803 FDDI blank space-Attachment Types One of the unique characteristics of F DDI is that multiple ways actually exist by which to connect FDDI devices.FDDI defines four types of devices single-attachment station (SAS), dual-attachment station ( cony), single-attached concentrator (SAC), and dual-attached concentrator (DAC). An SAS attaches to only one ring (the primary) through a concentrator. One of the primary advantages of connecting devices with SAS attachments is that the devices will not have any result on the FDDI ring if they are upset or powered off. Concentrators will be covered in more stage in the interest discussion. Each FDDI coney has two ports, designated A and B. These ports connect the mouse hare to the dual FDDI ring.Therefore, each port provides a connection for both the primary and the secondary rings. As you will see in the next section, devices using DAS connections will affect the rings if they are disunited or powered off. look 8-4 shows FDDI DAS A and B ports with attachments to the primary and secondary rings. Internetworki ng Technologies handbook 8-4 1-58705-001-3 Chapter 8 quality Distributed Data Interface FDDI Fault adjustment go steady 8-4 FDDI DAS appearances Attach to the Primary and secondhand Rings Primary Primary Port A Port B secondary winding Secondary FDDI DASAn FDDI concentrator (also called a dual-attachment concentrator DAC) is the building block of an FDDI network. It attaches at present to both the primary and secondary rings and ensures that the failure or power-down of any SAS does not bring down the ring. This is particularly useful when PCs, or equal devices that are frequently powered on and off, connect to the ring. Figure 8-5 shows the ring attachments of an FDDI SAS, DAS, and concentrator. Figure 8-5 A Concentrator Attaches to Both the Primary and Secondary Rings FDDI Concentrator DAS SAS SAS FDDI Fault allowance accountFDDI provides a number of fault-tolerant features. In particular, FDDIs dual-ring environment, the murder of the optical circulate thrust, and du al-homing support make FDDI a resilient media technology. ct840805 Internetworking Technologies enchiridion 1-58705-001-3 ct840804 8-5 Chapter 8 FDDI Fault Tolerance Fiber Distributed Data Interface Dual Ring FDDIs primary fault-tolerant feature is the dual ring. If a station on the dual ring fails or is powered down, or if the cable is damaged, the dual ring is mechanically revolveped (doubled back onto itself) into a single ring.When the ring is curveped, the dual-ring topology becomes a single-ring topology. Data continues to be transmitted on the FDDI ring without performance impact during the wrap condition. Figure 8-6 and Figure 8-7 illustrate the effect of a ring wrapping in FDDI. Figure 8-6 A Ring Recovers from a pose Failure by Wrapping lay 1 MAC B A Station 4 Ring wrap Ring wrap Station 2 A MAC B B MAC A A B Failed station Station 3 Internetworking Technologies Handbook 8-6 1-58705-001-3 Chapter 8 Fiber Distributed Data Interface FDDI Fault Tolerance Figure 8-7A Ring a lso Wraps to Withstand a Cable Failure Station 1 MAC B A Station 4 Ring wrap Station 2 A MAC B B MAC A Failed fit Ring wrap A B Station 3 When a single station fails, as shown in Figure 8-6, devices on either side of the failed (or powered-down) station wrap, forming a single ring. Network operation continues for the remaining stations on the ring. When a cable failure occurs, as shown in Figure 8-7, devices on either side of the cable fault wrap. Network operation continues for all stations. It should be noted that FDDI truly provides fault tolerance against a single failure only.When two or more failures occur, the FDDI ring segments into two or more in drug-addicted rings that are incapable of communicating with each other. Optical swing Switch An optical bypass throw provides continuous dual-ring operation if a device on the dual ring fails. This is used both to prevent ring sectionalization and to eliminate failed stations from the ring. The optical bypass switch performs this function using optical mirrors that pass light from the ring directly to the DAS device during expression operation.If a failure of the DAS device occurs, much(prenominal) as a power-off, the optical bypass switch will pass the light through itself by using inseparable mirrors and thereby will maintain the rings integrity. The benefit of this capability is that the ring will not enter a wrapped condition in field of study of a device failure. Figure 8-8 shows the functionality of an optical bypass switch in an FDDI network. When using the OB, you will notice a unspeakable digression of your network as the packets are sent through the OB unit. Internetworking Technologies Handbook 1-58705-001-3 ct840807 MAC 8-7 Chapter 8 FDDI Fault ToleranceFiber Distributed Data Interface Figure 8-8 The Optical Bypass Switch Uses ingrained Mirrors to Maintain a Network Station 1 Station 1 B A B A Failed station Optical bypass switch normal configuration Station 4 A B Optical bypass switc h bypassed configuration Ring does not wrap Station 2 A B Station 2 A B Station 4 A B A B A B Station 3 Station 3 Dual Homing Critical devices, such as routers or mainframe hosts, can use a fault-tolerant technique called dual homing to provide additional redundancy and to help guarantee operation. In dual-homing situations, the critical device is attached to two concentrators.Figure 8-9 shows a dual-homed configuration for devices such as file servers and routers. Internetworking Technologies Handbook 8-8 1-58705-001-3 Chapter 8 Fiber Distributed Data Interface FDDI establish change Figure 8-9 A Dual-Homed Configuration Guarantees procedure Concentrator Concentrator File servers Routers One pair of concentrator links is declared the active link the other pair is declared passive. The passive link stays in backup mode until the primary link (or the concentrator to which it is attached) is even upd to have failed. When this occurs, the passive link automatically activates.FDDI m annequin Format The FDDI frame format is similar to the format of a nominal Ring frame. This is one of the areas in which FDDI borrows heavily from earlier LAN technologies, such as minimal Ring. FDDI frames can be as bad as 4,500 bytes. Figure 8-10 shows the frame format of an FDDI data frame and token. Figure 8-10 The FDDI dust Is Similar to That of a Token Ring phase Data frame preface Start delimiter fig control address address Source address ct840809 Data FCS End delimiter Frame status Token premise Start delimiter Frame control End delimiter FDDI Frame FieldsThe following descriptions summarize the FDDI data frame and token palm illustrated in Figure 8-10. Internetworking Technologies Handbook 1-58705-001-3 8-9 Chapter 8 Copper Distributed Data Interface Fiber Distributed Data Interface PreambleGives a unique sequence that prepares each station for an upcoming frame. Start delimiterIndicates the beginning of a frame by employing a signaling pattern that differ entiates it from the rest of the frame. Frame controlIndicates the size of the address fields and whether the frame contains a synchronized or synchronous data, among other control information.Destination addressContains a unicast (singular), multicast (group), or broadcast (every station) address. As with Ethernet and Token Ring addresses, FDDI destination addresses are 6 bytes long. Source addressIdentifies the single station that sent the frame. As with Ethernet and Token Ring addresses, FDDI source addresses are 6 bytes long. DataContains either information destined for an upper-layer protocol or control information. Frame check sequence (FCS)Is filed by the source station with a calculated cyclic redundancy check value dependent on frame contents (as with Token Ring and Ethernet).The destination address recalculates the value to determine whether the frame was damaged in transit. If so, the frame is discarded. End delimiterContains unique symbols cannot be data symbols that in dicate the end of the frame. Frame statusAllows the source station to determine whether an error occurred identifies whether the frame was recognized and copied by a receiving station. Copper Distributed Data Interface Copper Distributed Data Interface (CDDI) is the implementation of FDDI protocols over twisted-pair copper wire.Like FDDI, CDDI provides data rates of 100 Mbps and uses dual-ring architecture to provide redundancy. CDDI supports distances of about 100 meters from desktop to concentrator. CDDI is defined by the ANSI X3T9. 5 Committee. The CDDI standard is officially named the Twisted-Pair Physical Medium-Dependent (TP-PMD) standard. It is also referred to as the Twisted-Pair Distributed Data Interface (TP-DDI), consistent with the term Fiber Distributed Data Interface (FDDI). CDDI is consistent with the physical and media-access control layers defined by the ANSI standard.The ANSI standard recognizes only two types of cables for CDDI shielded twisted pair (STP) and u nshielded twisted pair (UTP). STP cabling has 150-ohm impedance and adheres to EIA/transient ischemic attack 568 (IBM Type 1) specifications. UTP is data-grade cabling (Category 5) consisting of four unshielded pairs using tight-pair twists and specially developed insulating polymers in plastic jackets adhering to EIA/TIA 568B specifications. Figure 8-11 illustrates the CDDI TP-PMD specification in relation to the remaining FDDI specifications. Internetworking Technologies Handbook 8-10 1-58705-001-3Chapter 8 Fiber Distributed Data Interface Summary Figure 8-11 CDDI TP-PMD and FDDI Specifications Adhere to Different Standards FDDI Media Access Control (MAC) FDDI physical layer (PHY) FDDI Station Management (SMT) Twisted-pair wire PMD Single-mode fiber PMD Multimode fiber PMD Specification for CDDI Summary The Fiber Distributed Data Interface (FDDI) specifies a 100-Mbps token-passing, dual-ring LAN architecture using fiber-optic cable. FDDI is frequently implemented as a high-speed backbone technology because of its support for high bandwidth and greater distances than copper. study Questions QWhat are the benefits of using FDDI instead of CDDI? ALonger distance, no RFI, no EFI. QWhat role does the DAC play in the FDDI network? AThe concentrator is a dual-attachment station device and ensures that when single-attachment station devicessuch as PCsare cancelled off, they do not interrupt the network ring. Internetworking Technologies Handbook 1-58705-001-3 ct840811 8-11 Chapter 8 Review Questions Fiber Distributed Data Interface Internetworking Technologies Handbook 8-12 1-58705-001-3