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 1.Set the values of timers a.THT = TTRT – TRT b.TRT = 0 2.Sends synchronous data 3.Sends asynchronous data as long as the value of THT is positive

7. FDDI Example ASSUMPTIONS: 1.TTRT = 30 time units 2.Traveling token from one station to another = 1 time unit 3.Each station is allowed to send 2 S-frames per turn 4.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. Figure 12-22-continued FDDI Example

10. Figure 12-23 FDDI Encoding NRZ-I

11. 4B/5B Encoding None of the five bit patterns start with more than one zero Data SequenceEncoded Sequence 000011110 000101001 001010100 001110101 010001010 010101011 011001110 011101111 Transforms each 4-bit data into a 5-bit unit that contains no more than two consecutive 0s Data SequenceEncoded Sequence 100010010 100110011 101010110 101110111 110011010 110111011 111011100 111111101

12. 4B/5B Encoding Control SymbolEncoded Sequence Q (Quiet)00000 I (Idle)11111 H (Halt)00100 J (used in start delimiter) 11000 K (used in start delimiter) 10001 T (used in end delimiter) 01101 S (Set)11001 R (Reset)00111 Unused five-bit codes are used for control

13. Figure 12-24 FDDI Layers

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

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

16. Figure 12-27 FDDI Ring Failure

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