FDDI

1
FDDI
Seminar on resume writing for CS Students
Presenter Yuri A. Tijerino Ph.D. Date
September 29th, 2003 and October 29th, 2003 (same
info for both seminars) Time 3pm to 5pm Place
Room 151 in the Tanner Building
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Objectives

• Introduce CRC lab
• Understand FDDI
• Understand Token Bus

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Ethernet vs. Token Ring Ethernet Dominance

• Open standard
• Proprietary platforms forced to support
  standards or lose value

FDDI Market 220M 1997, 40M 2001. Fast Ethernet
150/port FDDI 750/port
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Ethernet vs. Token Ring Media Access Control
Methods

• Contention (Ethernet)
• performs better than token passing on low
  utilization LANs
• high utilization - collisions and retransmission
  when 2 stations try to communicate simultaneously
  
• Token passing
• high utilization - superior performance, no
  collisions
• QoS multimedia preference to some applications
• used to control bus in USB, Firewire, and other
  emerging shared media technologies

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Comparison

• FDDI uses 4b/5b NRZI (Non-Return to Zero Invert
  on ones) with 125 Mb/s baud rate to achieve 100
  Mb/s data rate
• 10BaseT Ethernet uses Manchester encoding with 20
  Mb/s baud rate to achieve 10 Mb/s data rate.
  2Volts or 0 volts for logic values. 802.3
• Base Baseband - Baseband signaling simply means
  that Ethernet signals are the only signals
  carried over the media system.
• 100BaseT Ethernet uses 4B/5B with 125 Mbps to
  achieve 100Mbps data rate. 802.3
• MLT3 (Multi-Level Transmission)
• defines 3 levels of voltages 1 volt, 0 volt, -1
  volt
• Binary 1 is transmitted by changing to the
  adjacent voltage
• Binary 0 is transmitted by maintaining the same
  voltage

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Gig Ether

• Copper
• Uses 4 pairs of wires
• 125MHz clock speed
• PAM-5 uses five different voltage levels and
  defines each as a specific 2 bit pattern. 00,
  01, 10, 11. Sends 2 bits each clock cycle
• Fiber
• 8b10B encoding to transmit data enhanced
  version of the 4B5B used in fast Ethernet which
  allows data to be sent in 10-bit groups (2
  overhead bits in each group)

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10Gig Ether

• LAN version parallel transmission through four
  separate fibers using 8b10B coding scheme with
  clock speed of 3.125GHz.
• WAN Version -- Uses 64B66B encoding sends 64
  bits of data with 2 bits of overhead (over SONET)

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Ethernet vs. Token RingResponse Time vs. Load
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Overview

• Token Ring Networks
• PRONET 10Mbps and 80 Mbps rings
• IBM 4Mbps token ring
• 16Mbps IEEE 802.5/token ring
• 100Mbps Fiber Distributed Data Interface (FDDI)

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Basic Idea

• frames flow in one direction upstream to
  downstream
• special bit pattern (token) rotates around ring
• must capture token before transmitting
• release token after done transmitting
• immediate release
• delayed release
• remove your frame when it comes back around
• stations get round-robin service

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Physical Properties of FDDI

• Dual Ring Configuration
• Single and Dual Attachment Stations

Downstream Neighbor
Upstream Neighbor
SAS
Concentrator
SAS
SAS
SAS
SAS
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Characteristics

• Each station imposes a delay (e.g., 50ns)
• Maximum of 500 stations
• Upper limit of 100km (200km of fiber)
• Uses 4B/5B encoding
• Can be implemented over copper (CDDI)

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Timed Token Algorithm

• Token Holding Time (THT) upper limit on how long
  a station can hold the token.
• Token Rotation Time (TRT) how long it takes the
  token to traverse the ring.
• TRT lt ActiveNodes x THT RingLatency
• Target Token Rotation Time (TTRT) agreed-upon
  upper bound on TRT.

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• Algorithm
• each node measures TRT between successive
  arrivals of the token
• if measured TRT gt TTRT, then token is late so
  don't send data
• if measured TRT lt TTRT, then token is early so OK
  to send data
• define two classes of traffic
• synchronous data can always send
• asynchronous data can send only if token is
  early
• worse case 2xTTRT between seeing token
• not possible to have back-to-back rotations that
  take 2xTTRT time

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Token Maintenance

• Lost Token
• no token when initializing ring
• bit error corrupts token pattern
• node holding token crashes
• Generating a Token (and agreeing on TTRT)
• execute when join ring or suspect a failure
• each node sends a special claim frame that
  includes the node's bid for the TTRT
• when receive claim frame, update bid and forward
• if your claim frame makes it all the way around
  the ring
• your bid was the lowest
• everyone knows TTRT
• you insert new token

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• Monitoring for a Valid Token
• should see valid transmission (frame or token)
  periodically
• maximum gap ring latency max frame lt 2.5ms
• set timer at 2.5ms and send claim frame if it
  fires

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Acknowledgements with Token Ring

• Acknowledgement of a frame arrival can be done by
  destination by changing a bit at the tail of a
  frame

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Token Bus

• Uses broadcast channel, but the stations form a
  logical ring (13576824)

• There is a special packet called the token
• a station that has the token is allowed to
  transmit for a time
• when the time is up it passes the token to next
  station in the ring
• a station may only transmit what it has when the
  token arrived. If it has no frames to send then
  it simply passes the token on

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Properties of the Token Bus

• Useful in the real-time application when a
  guaranteed level of service is required
• In heavy loads there is a very good utilization
  since token passing is only a small percentage of
  the traffic and there are no collisions
• In very light loads there are delays caused by
  the token passing
• If a station goes down there is a potential of a
  token being lost. A lost token can be detected
  and can be regenerated by the remaining active
  stations

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Properties of the Token Bus

• The token bus allows priorities. For example,
  high priority can be given to voice packets
• The token bus can allow for quick turnaround on
  acknowledgements. The station that has the token
  allows the recipient to ack before sending the
  next frame
• IEEE 802.4 is a standard for token buses running
  on broadcast channel