FDDI

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FDDI

• supervised by D. Hasan Abbas
• Achieved by Susan Alshgree

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FDDIFiber Distributed Data Interfase

• FDDI
• Today we shall to study about
• 1- FDDI technology
• 2- Components of FDDI
• 3- FDDI characteristics
• 4- FDDI access method
• 5- FDDI OSI model

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FDDI Technology

• The Fiber Distributed Data Interface (FDDI) is a
  high-speed LAN using ring topology with a data
  rate of 100 Mbps. FDDI support high bandwidth and
  greater distances than copper .

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FDDI Technology

• FDDI uses dual-ring architecture with traffic on
  each ring flowing in opposite directions (called
  counter-rotating). The dual rings consist of a
  primary and a secondary ring. During normal
  operation, the primary ring is used for data
  transmission, and the secondary ring remains
  idle. The secondary ring is used for backup in
  the case of primary breakdown

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FDDI Technology

• One of most important features of FDDI is its use
  of optical-fiber transmission for media . the
  main advantage of using fiber optic over copper
  wiring is security because there is no
  electrical signal on the media to tap.

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FDDI Technology

• FDDI allows up to 1000 stations to be connected
  to the ring, with a maximum ring circumference of
  200 km .
• Next figure shows the counter-rotating primary
  and secondary FDDI rings.

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FDDI Technology
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Components of FDDI

• The components of FDDI are a fiber-optic , a
  concentrator (ring) , and the stations connected
  to the concentrator

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Components of FDDI

• There are two types of stations used in FDDI
• 1-Dual Attachment Station (DAS) or class A DAS
  is attached to both rings and has two ports to
  connect to the ring , one connected to the
  primary ring and other to the secondary ring
• 2- Single Attachment Station (SAS) or class B
  SAS attaches to the primary ring

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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
  wrapped, the dual-ring topology becomes a
  single-ring topology

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Dual Ring

• Data continues to be transmitted on the FDDI ring
  without performance impact during the wrap
  condition.
• Next figures illustrate the effect of a ring
  wrapping in FDDI

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Dual Ring
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Dual Ring

• When a single station fails, as shown in previous
  Figure, 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.

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Dual Ring
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Dual Ring

• When a cable failure occurs, as shown in previous
  Figure, devices on either side of the cable
  fault wrap. Network operation continues for all
  stations.

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Dual Ring

• 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 independent rings that are
  incapable of communicating with each other

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Why haven't companies converted Ring to Ethernet
and Token FDDI ?

• First, the cost of FDDI interfaces has been 5-10
  times more than Ethernet interfaces, and 3-5
  times more than Token Ring interfaces. Also, FDDI
  concentrators have also been expensive.
• Second, 100Mbps throughput has not been needed
  until recent years.

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FDDI Characteristics

• FDDI LAN operations offer several advantages over
  Ethernet and Token Ring LANs.

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FDDI Characteristics

• First FDDI will provide 100Mbps of data
  throughput. FDDI also offers a redundancy feature
  which is not available on Ethernet or Token Ring.

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FDDI Characteristics

• Second equipment can be connected to the FDDI
  ring with two interfaces Both interfaces are
  active and are continuously passing Management
  Packets. The primary ring passes data packets
  during normal operation. If one interface or set
  of interface cables is taken out of service, the
  other interface will go into a "loop" state which
  allows the equipment to remain part of the ring.

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FDDI Characteristics

• Third FDDI also provides a method for connecting
  equipment to the ring over long distances. The
  maximum distances between pieces of equipment
  operating on the ring is 2kmeters using multimode
  fiber and 20kmeters using single-mode fiber.

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Single-Mode and Multimode Fibers
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FDDI Characteristics

• Fourth FDDI also allows all pieces of equipment
  operating on the ring to have an equal amount of
  time to transmit data. This results in high
  throughput without data collisions.

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FDDI Characteristics

• A final feature offered with FDDI is distributed
  management. FDDI is a LAN with Station ManagemenT
  (SMT), The function of s SMT is ring control,
  ring initialization, station insertion and
  station remove.

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Comparison of basic characteristics
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FDDI Access Method

• FDDI uses token passing as an access method
  similar to the IEEE 802.5 token ring any station
  want to transmit information holds the token and
  then transmits the information and when it finish
  it realizes the token in the ring

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FDDI Access Method

• The length of time a station holds the token is
  called synchronous allocation time (SAT) and this
  time is variable for each station . The
  allocation of this time to each station is
  achieved by station management

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FDDI bit transmission

• FDDI uses light pulses to transmit
  information from source to destination . A bit
  can have two values one or zero . FDDI determines
  bit change by the state of the light on the
  receiver side . The receiver takes a sample of
  light every eight nanoseconds. If the light has
  changed since the last sample then a one is
  received . If there is no change in the light
  then a zero is received

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FDDI OSI model
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FDDI OSI model

• Layers 1 and 2 of the OSI model are divided into
  4 sub layers in an FDDI packet. The Physical
  layer is divided into the Physical Media
  Dependent (PMD) and Physical Access Control (PHY)
  sub layers.

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FDDI OSI model

• The PMD layer indicates the type of cabling which
  can be used on a FDDI interface. Current cabling
  types include multimode fiber (MMF), single mode
  fiber (SMF) and copper (CDDI).

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FDDI OSI model

• The PHY sublayer is responsible for several
  functions. The most important functions include
  clock recovery and encoding. The clock recovery
  function will synchronize the workstation with
  the incoming signal. This is used to prevent
  packet loss in a workstation due to
  synchronization problems

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FDDI OSI model

• The Data Link layer is divided into the Media
  Access Control (MAC) and Logical Link Control
  (LLC) sub layers.

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FDDI OSI model

• The MAC layer also performs several functions. It
  is responsible for address checking, error
  detection (CRC).

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FDDI OSI model

• The LLC layer is used to encapsulate OSI layers
  3-7 into the LLC data transfer format. This is
  the same LLC function used on Ethernet and Token
  Ring LANs

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FDDI Frame Format

• The FDDI frame format is similar to the format of
  a Token Ring frame.
• Next Figure shows the frame format of an FDDI
  data frame and token.

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FDDI Frame Format
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FDDI Frame Fields

• PreambleGives a unique sequence that prepares
  each station for an upcoming frame.
• Start delimiterIndicates the beginning of a
  frame

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FDDI Frame Fields

• Frame controlIndicates the size of the address
  fields and whether the frame contains
  asynchronous or synchronous data, among other
  control information.

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FDDI Frame Fields

• 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

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FDDI Frame Fields

• 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.

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FDDI Frame Fields

• 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.

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FDDI Frame Fields

• 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.

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Summary

• -Fiber Distributed Data Interface (FDDI) is a
  high-speed LAN with a data rate of 100 100Mbps
  using dual ring topology and optical fiber as
  transmission media . FDDI is applied in network
  backbone

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Summary

• -Fiber Distributed Data Interface uses two
  fiber-optical rings , one primary ring for data
  transmission and a secondary ring for back up in
  the case of failure of primary ring

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Summary

• - FDDI uses token passing as its access method .
  The FDDI frame format similar to the token ring
  frame format

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Summary

• - A Dual Attachment Station (DAS) is connected
  to the primary and secondary rings
• - A Single Attachment Stations (SAS) is
  connected only to the primary ring

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References

• 1-Network Communications Technology
• 2-http//en.wikipedia.org/wiki/fiber_distributed_d
  ata_interface
• 3-http//www.cisco.com/univercd/cc/td/doc/cisintwk
  /ito_doc/fddi.htm