Fddi and Cddi

C H A P T E R 8 Chapter Goals Provide primer coat in coifion about FDDI technology. Explain how FDDI works. Describe the differences between FDDI and grunter Distributed info interface (CDDI). Describe how CDDI works. lineament Distributed selective information interface Introduction The grapheme Distributed selective information interface (FDDI) specifies a 100-Mbps token-passing, multiple- b mobilize forward LAN employ quality-optic stemma. FDDI is a great deal used as high-velocity backb one technology because of its documentation for high bandwidth and great distances than bullshit.It should be noted that relatively recently, a related copper spec, called Copper Distributed Data port wine (CDDI), has emerged to provide 100-Mbps service oer copper. CDDI is the writ of execution of FDDI protocols over deformed-pair copper wire. This chapter focuses mainly on FDDI judicial admissions and operations, but it also provides a high-level overview of CDDI. FDDI uses dual- environ architecture with traffic on each coterie period in opposite directions (called counter-rotating). The dual sound consist of a primal and a secondary ring.During regulation operation, the main(a) ring is used for info transmission, and the secondary ring remains idle. As will be discussed in detail later in this chapter, the primary purpose of the dual rings is to provide superior reliability and robustness. view 8-1 shows the counter-rotating primary and secondary FDDI rings. Internedeucerking Technologies enchiridion 1-58705-001-3 8-1 Chapter 8 FDDI Transmission Media Fiber Distributed Data larboard discover 8-1 FDDI Uses Counter-Rotating radical and substitute(prenominal) dance bands Primary Secondary FDDI Concentrator WAN StandardsFDDI was developed by the American National Standards Institute (ANSI) X3T9. 5 measurings committee in the mid-1980s. At the time, high-speed engineering work s hold back were beginning to tax the bandwidth of experien ceing local- ara networks (LANs) based on Ethernet and Token hollo. A new LAN media was needed that could easily support these work beams and their new distributed applications. At the same time, network reliability had become an progressively important issue as system managers migrated mission- vituperative applications from large computers to networks.FDDI was developed to engross these needs. After completing the FDDI specification, ANSI submitted FDDI to the International Organization for Standardization (ISO), which created an international transformation of FDDI that is completely compatible with the ANSI standard version. FDDI Transmission Media FDDI uses visual fiber as the primary transmission medium, but it also can run over copper cabling. As mentioned precedent, FDDI over copper is referred to as Copper-Distributed Data Interface (CDDI). Optical fiber has several advantages over copper media.In particular, security, reliability, and carrying into action all ar en hanced with optical fiber media because fiber does not emit galvanic signals. A physical medium that does emit electrical signals (copper) can be tapped and therefore would permit unauthorized access to the selective information that is transiting the medium. In addition, fiber is immune to electrical interference from radio frequency interference (RFI) and electromagnetic interference (EMI). Fiber historically has supported a lot higher bandwidth ( by dint ofput potential) than copper, although recent technological advances have made copper undetermined of transmitting at 100 Mbps.Finally, FDDI allows 2 km between mail services using multi room fiber, and even longer distances using a case-by-case humour. FDDI defines two types of optical fiber single- path and multimode. A mode is a ray of devolve that submits the fiber at a particular angle. Multimode fiber uses LED as the free-generating dodge, while single-mode fiber generally uses lasers. Internetworking Technologies enchiridion 8-2 ct840801 1-58705-001-3 Chapter 8 Fiber Distributed Data Interface FDDI Specifications Multimode fiber allows multiple modes of light to propagate through the fiber.Because these modes of light enter the fiber at different angles, they will 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 used for bondivity within a building or a relatively geographically contained environment. Single-mode fiber allows only one mode of light to propagate through the fiber. Because only a single mode of light is used, modal dispersion is not present with single-mode fiber.Therefore, single-mode fiber is overt of delivering considerably higher performance connectivity over much larger distances, which is why it generally is used for connectivity between buildings and within environments t hat are much geographically dispersed. Figure 8-2 depicts single-mode fiber using a laser light pedigree and multimode fiber using a light emitting diode (LED) light source. Figure 8-2 Light consultations Differ for Single-Mode and Multimode Fibers Laser light source Single mode Multimode LED light source ct840802 FDDI SpecificationsFDDI specifies the physical and media-access portions of the OSI fibre model. FDDI is not in truth a single specification, but it is a collection of four snap off specifications, each with a specific function. Combined, these specifications have the capability to provide high-speed connectivity between upper- form protocols such as TCP/IP and IPX, and media such as fiber-optic cabling. FDDIs four specifications are the Media entrance fee Control (mackintosh), visible Layer Protocol (PHY), Physical-Medium Dependent (PMD), and carry Management (SMT) specifications.The MAC specification defines how the medium is accessed, including physical body in format, token handling, addressing, algorithms for calculating cyclic redundancy cover (CRC) value, and error-recovery mechanisms. The PHY specification defines entropy encoding/decoding procedures, clocking requirements, and framing, among former(a) functions. The PMD specification defines the characteristics of the transmission medium, including fiber-optic colligates, power levels, bit-error rates, optical components, and connectors.The SMT specification defines FDDI lieu configuration, ring configuration, and ring temper features, including station insertion and removal, initialization, fault isolation and recovery, scheduling, and statistics collection. FDDI is connatural to IEEE 802. 3 Ethernet and IEEE 802. 5 Token doughnut in its relationship 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. Figure 8-3 garnishs the four FDDI specifications and their relation ship to each other and to the IEEE-defined lucid Link Control (LLC) sublayer.The LLC sublayer is a component of Layer 2, the MAC layer, of the OSI reference model. Internetworking Technologies Handbook 1-58705-001-3 8-3 Chapter 8 FDDI come out-Attachment Types Fiber Distributed Data Interface Figure 8-3 FDDI Specifications symbolise to the OSI Hierarchical Model Logical link stamp down Media access control FDDI standards Physical layer protocol shoes management Physical layer medium ct840803 FDDI Station-Attachment Types One of the unique characteristics of FDDI 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 ( das), 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 e very effect on the FDDI ring if they are split or powered off. Concentrators will be covered in more detail in the following discussion. Each FDDI DAS has two ports, designated A and B. These ports connect the DAS to the dual FDDI ring.Therefore, each port provides a connective 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 disconnected or powered off. Figure 8-4 shows FDDI DAS A and B ports with attachments to the primary and secondary rings. Internetworking Technologies Handbook 8-4 1-58705-001-3 Chapter 8 Fiber Distributed Data Interface FDDI stain Tolerance Figure 8-4 FDDI DAS Ports Attach to the Primary and Secondary baskets Primary Primary Port A Port B Secondary Secondary FDDI DASAn FDDI concentrator (also called a dual-attachment concentrator DAC) is the building block of an FDDI network. It attaches nowadays to both the primary and secondary rings and ensures that the fa ilure or power-down of any SAS does not bring down the ring. This is particularly useful when PCs, or identical 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 ToleranceFDDI provides a number of fault-tolerant features. In particular, FDDIs dual-ring environment, the effectuation of the optical get around switch, and dual- domiciliate support make FDDI a resilient media technology. ct840805 Internetworking Technologies Handbook 1-58705-001-3 ct840804 8-5 Chapter 8 FDDI Fault Tolerance Fiber Distributed Data Interface treble 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 automatically wrapped (doubled back onto itself) into a single ring.When the ring is wra pped, 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 Station Failure by Wrapping Station 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 also Wraps to put out a Cable Failure Station 1 MAC B A Station 4 Ring wrap Station 2 A MAC B B MAC A Failed outfit Ring wrap A B Station 3 When a single station fails, as shown in Figure 8-6, devices on every side of the failed (or powered-down) station wrap, forming a single ring. engagement operation continues for the rest 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 adjustment against a single failure only.When two or more failures occur, the FDDI ring segments into two or more independent rings that are incompetent of communicating with each other. Optical ring road Switch An optical bypass switch provides continuous dual-ring operation if a device on the dual ring fails. This is used both to prevent ring segmentation and to decease 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 normal operation.If a failure of the DAS device occurs, such as a power-off, the optical bypass switch will pass the light through itself by using internal mirrors and thereby will maintain the rings integrity. The benefit of this capability is that the ring will not enter a wrapped condition in case of a device failure. Figure 8-8 shows the functionalit y of an optical bypass switch in an FDDI network. When using the OB, you will notice a tremendous 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 Internal 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 switch 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 main stray 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 Technol ogies Handbook 8-8 1-58705-001-3 Chapter 8 Fiber Distributed Data Interface FDDI flesh Format Figure 8-9 A Dual-Homed Configuration Guarantees Operation Concentrator Concentrator consign servers Routers One pair of concentrator links is declared the active link the other pair is declared passive. The passive link stays in rilievo mode until the primary link (or the concentrator to which it is attached) is determined to have failed. When this occurs, the passive link automatically activates.FDDI range Format The FDDI frame format is similar to the format of a Token Ring frame. This is one of the areas in which FDDI borrows heavily from earlier LAN technologies, such as Token Ring. FDDI frames can be as large as 4,500 bytes. Figure 8-10 shows the frame format of an FDDI data frame and token. Figure 8-10 The FDDI Frame Is Similar to That of a Token Ring Frame Data frame Preamble Start delimiter Frame control refinement address Source address ct840809 Data FCS End delimiter Frame t erm Token Preamble 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 eon that prepares each station for an upcoming frame. Start delimiterIndicates the beginning of a frame by employing a signaling pattern that differentiates it from the rest of the frame. Frame controlIndicates the size of the address fields and whether the frame contains a coexistent or synchronous data, among other control information.Destination addressContains a unicast (singular), multicast (group), or penetrate (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 sour ce addresses are 6 bytes long. DataContains either information destine for an upper-layer protocol or control information. Frame flake 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 indicate 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 concentra tor. 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 unprotected twisted pair (UTP). STP cabling has 150-ohm impedance and adheres to EIA/TIA 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 Dist ributed 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. revue 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 glowering off, they do not interrupt the network ring. Internetworking Technologies Handbook 1-58705-001-3 ct840811 8-11 Chapter 8 Review Questions Fi ber Distributed Data Interface Internetworking Technologies Handbook 8-12 1-58705-001-3