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FDDI
FDDI
• Similar to IEEE802.5, but runs on fiber instead of copper.
Physical Properties
– FDDI consist of dual ring.
• Two i...
FDDI
• Concentrator detects the failure of the SAS.
– By using optical bypass, it keeps the ring connected.
• Network adap...
FDDI
Example: 100 Mbps FDDI
– 10 ns for bit time
• Each station 10 bit buffer – waits until buffer half full before
transm...
FDDI
Timed Token Algorithm
• to give a opportunity to the node, to transmit a frame with in a
certain amount of time,
– It...
Provides two class of traffic,
– Synchronous
– Asynchronous
Synchronous:
– Traffic is delay sensitive
– station transmits ...
– If the timer expires, the node suspects a failure
• Then transmits a “claim” frame
• Bid for the TTRT.
• Lowest TTRT- ho...
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FDDI

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Computer Networks - FDDI

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FDDI

  1. 1. FDDI
  2. 2. FDDI • Similar to IEEE802.5, but runs on fiber instead of copper. Physical Properties – FDDI consist of dual ring. • Two independent rings that transmit data in opposite direction. • Second ring is not used during normal operation. But work when primary link fails. – Allows nodes to attach to the network using single cable. • Called as single attachment station (SAS). – Concentrator is used to connect multiple SAS
  3. 3. FDDI • Concentrator detects the failure of the SAS. – By using optical bypass, it keeps the ring connected. • Network adaptor holds some number of bits between input and output interface. – Variable size buffer (never less than 9 bits nor more than 80bits) • Station transmits an amount equal to half the buffer
  4. 4. FDDI Example: 100 Mbps FDDI – 10 ns for bit time • Each station 10 bit buffer – waits until buffer half full before transmitting – station introduces 50 ns delay into TRT • Network size is limited to 500 stations with a maximum distance of 200km. • Uses 4B/5B encoding.
  5. 5. FDDI Timed Token Algorithm • to give a opportunity to the node, to transmit a frame with in a certain amount of time, – It sets an upper bound on TRT (Token Rotation time) observed by any node. – Target Token Rotation time (TTRT) – all node are agree to live with in the TTRT • Each node measures the time between the successive arrival of the token called measured TRT. If measured TRT > TTRT – Token is late and node does not transmit any data. If measured TRT < TTRT – Token is earlier and the node can hold the token for the (TTRT – measured TRT) and transmit data. – down stream station may not be able to transmit.
  6. 6. Provides two class of traffic, – Synchronous – Asynchronous Synchronous: – Traffic is delay sensitive – station transmits data whether token is late or early – Eg., Voice and Video Asynchronous: – Station transmits only if token is early. – Eg., File transfer Token Maintenance – Process of setting TTRT. – Monitor ring to ensure token has not been lost. – Idle time between valid transmissions that a given node experiences is • ring latency + time to transmit a full frame • 2.5 ms maximally sized ring – Each node sets a timer event that fires after 2.5ms.
  7. 7. – If the timer expires, the node suspects a failure • Then transmits a “claim” frame • Bid for the TTRT. • Lowest TTRT- holds the token & inserting a valid token. – After every valid transmission, node resets the timer back to 2.5ms. Frame Format:

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