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CS601 - Data Communication - Lecture Handout 44

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Related Content: CS601 - VU Lectures, Handouts, PPT Slides, Assignments, Quizzes, Papers & Books of Data Communication

Token Ring

  • Token Ring allows each station to send one frame per turn
  • Access method: Token passing

Token Ring

Access Control of Token Ring

  • Priority and reservation
    • Each station has a priority code
  • Time limits
    • Token Ring imposes a time limit to keep traffic moving

Monitor Stations

  • One station is designated as a monitor station to handle several problems
  • Monitor station generates a new token when it is lost
  • Monitor station removes recirculating data frames

Token Ring Frame

Token Ring Frame

Implementation

  • Each station in the Token Ring regenerates the frame
  • One disabled or disconnected node could stop the traffic flow around the entire network
    • Each station is connected to an automatic switch

Implementation

Token Ring Switch

Token Ring Switch

Multi station Access Unit (MAU)

  • Individual automatic switches are combined in to a hub
  • One MAU can support up to 8 stations
  • Although it looks like a star, it is in fact a ring

Multi station Access Unit (MAU)

FDDI

  • Fiber Distributed Data Interface standardized by ANSI and the ITU-T
  • 100 Mbps LAN protocol
  • CDDI: Copper version of FDDI
  • Access method: Token passing

FDDI Time Registers

Time registers

  • Values are set when the ring is initialized and do not vary
  • SA (Synchronous Allocation)
  • TTRT (Target Token Rotation Time)
  • AMT (Absolute Maximum Time)

FDDI Timers

Timers

  • Each station contains two timers
  • TRT (Token Rotation Timer) : Incrementing
  • THT (Token Holding Timer) : Decrementing

Station Procedure

Station Procedure

Station Procedure

  • THT is set to the difference between TTRT and TRT
  • THT = TTRT - TRT
  • TRT is reset to zero (TRT = 0)
  • The station sends S-frames during the time in SA
  • The station sends A-frames as long as THT ≥ 0
  • Release the token

Dual Ring (Figure-1)

Dual Ring (Figure-1)

Dual Ring (Figure-2)

Dual Ring (Figure-2)

Summary

  • Token Ring
  • FDDI

Reading Sections

  • Section 12.5, 12.6, 12.7
    “Data Communications and Networking” 4th Edition by Behrouz A. Forouzan