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FDDI (Fiber Distributed Data Interface)

FDDI (Fiber Distributed Data Interface). Standardized by ASI and ITU-T (ITU-T X.3. FDDI (Fiber Distributed Data Interface). Data rate – 100 Mbps Access method – token passing CDDI – copper version. S-frames – synchronous (real time data) A-frame – asynchronous (not real time).

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FDDI (Fiber Distributed Data Interface)

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  1. FDDI (Fiber Distributed Data Interface) Standardized by ASI and ITU-T (ITU-T X.3

  2. FDDI (Fiber Distributed Data Interface) Data rate – 100 Mbps Access method – token passing CDDI – copper version S-frames – synchronous (real time data) A-frame – asynchronous (not real time)

  3. Access Method • TIME REGISTERS • Synchronous allocation (SA) • Target token rotation time (TTRT) • Absolute maximum time (AMT) • Access is limited by time • Priority – real time data • Steps • A station captures the token • Send S-frames first • Any remaining time may then be used to send A-frames

  4. Time Registers Synchronous Allocation (SA) • Length of time allowed for S-frames • Different for each station • Ring initialization Target Token Rotation Time (TTRT) • Average time required for a token to circulate around the ring exactly once • Absolute Maximum Time (AMT) • Twice the TTRT • To avoid monopolizing the network

  5. Timers Token Rotation Timer (TRT) • Runs continuously • Measures the actual time taken by the token to complete a cycle • Incrementing or (decrementing) TRT Token Holding Timer (THT) • Begins running as soon as the token is received • Shows how much time remains for sending asynchronous frames • Decrementing or (incrementing ) THT

  6. Station Procedure • Set the values of timers • THT = TTRT – TRT • TRT = 0 • Sends synchronous data • Sends asynchronous data as long as the value of THT is positive

  7. FDDI Example ASSUMPTIONS: • TTRT = 30 time units • Traveling token from one station to another = 1 time unit • Each station is allowed to send 2 S-frames per turn • Each station has a lot of A-frames to send

  8. Figure 12-22 FDDI Example Round 0 – The token travels around the ring: each station sets its TRT timer to 0

  9. FDDI Example Figure 12-22-continued

  10. FDDI Encoding Figure 12-23 NRZ-I

  11. 4B/5B Encoding None of the five bit patterns start with more than one zero Transforms each 4-bit data into a 5-bit unit that contains no more than two consecutive 0s

  12. 4B/5B Encoding Unused five-bit codes are used for control

  13. FDDI Layers Figure 12-24

  14. Figure 12-25 FDDI Frames Each frame is preceded by 16 idle symbols (1111), a total of 64 bits ED – Full byte in token frame, T control code(s) FS – same to that of token ring SD – J and K control codes FC – Identify the frame type

  15. Figure 12-26 Physical Medium Dependent Layer Dual Ring – secondary ring make s FDDI self-healing

  16. FDDI Ring Failure Figure 12-27

  17. FDDI Nodes Figure 12-28 MIC – Media Interface Connector Three Types of Nodes SAS – Single Attachment Station DAS – Dual Attachment Station DAC – Dual Attachment Concentrator

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