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Frame of

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Each wavelength channel organized into a series of frames, each of which into timeslots. ... Performance determined by number of timeslots per frame (N) ... – PowerPoint PPT presentation

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Title: Frame of


1
WDM links
Concentrator
Packet from a host
Lower bit-rate host interface (e.g. Gig-Ethernet)
Frame of time slots
TSOBS Concept
  • Time Sliced Optical Burst Switching (TSOBS)
  • Eliminates the need for expensive wavelength
    conversion by switching data in the time domain.
  • Each wavelength channel organized into a series
    of frames, each of which into timeslots.
  • A few wavelength channels are reserved to carry
    control information (Burst Header Cells).
  • TSOBS routers can potentially be
    cost-competitive with electronic routers.

Statistical Multiplexing Performance
  • Performance determined by number of timeslots
    per frame (N)
  • With single timeslot length packets, good
    performance achieved at 64 timeslots/frame.
  • As the average number of timeslots/frame
    increases, performance degrades.
  • For good performance, we need 128-256
    timeslots/frame.

2
TSOBS Router Design
OTSI Design
  • TSOBS Router Design
  • Each wavelength channel is demultiplexed and
    switched independently.
  • Uses high-speed crossbars to switch data into
    timeslots.
  • Each router is equipped with a few regeneration
    ports to regenerate signals as necessary.
  • OTSIs use fiber delay lines to provide the time
    domain switching.
  • OTSIs use WDM for the delay lines, thus sharing
    the cost of fiber among the wavelengths.
  • SYNCs synchronize data to a common timing
    reference using a structure similar to OTSIs.

Optical Time Slot Interchanger Design
  • Nonblocking OTSIs provide the best performance,
    however they are significantly more expensive.
  • Key performance criteria
  • Num. of switching operations per timeslot
  • Scheduling complexity of timeslots
  • Number of delay lines (size of crossbar)
  • Natural choice of delay values for blocking
    OTSIs 1, 2, 3,, N/2 timeslots.
  • Blocking OTSIs give good performance using at
    most 3 switching operations for most timeslots.

1 Time Sliced Optical Burst Switching,
J.Ramamirtham and J. Turner, Proceedings of
INFOCOM 2003, April 2003.
3
Component Cost Requirements
  • Cost/Gbps changes linearly with cost of
    crossbars and multiplexors.
  • Cost of the system scales linearly with number
    of wavelengths.
  • The cost of the fiber is not a big factor for a
    large number of wavelengths.
  • Above estimates are for a system with 16
    input/output fibers, 128 wavelengths per fiber,
    and 128 timeslots per frame.

1 µs Timeslot
Synchronizer Design
  • A timeslot has a guard time with a minimum guard
    time for switching operations.
  • For a system with 1 µs timeslots each having 100
    ns guard times and 20 ns minimum guard time, the
    900 ns long data can be placed anywhere in a 960
    ns period.

Minimum guard time20ns
960 ns
Data900ns
  • Two parameters affect the cost
  • Precision difference between successive delay
    values (60 ns)
  • Range maximum delay it provides
  • By operating with links synchronized to timeslot
    boundaries instead of frame boundaries, the range
    can be reduced.
  • For a network with 1 µs timeslots each having 100
    ns guard times, the synchronizer can be operated
    with a precision-to-range ratio of 110.

Incoming Signals
Passive Coupler
Optical Crossbar
Optical Crossbar
Optical Crossbar
  • Two switching stages delay lines of 1, 2,,
    ??S?-1 followed by ??S?, 2??S?,, (??S? -1) ??S?.
  • Two switching operations needed.
  • Two crossbars of size ??S? x ??S?
  • Good for moderate number of delay values.
  • One delay line for each delay value, 1, 2,, S
    (S range-precision ratio)
  • One switching operation needed.
  • Good for small number of delay values.

Department of Computer Science And Engineering
4
Design Issues for Time Sliced Optical Burst
Routers
Jeyashankher Ramamirtham, Jonathan Turner jai,
jst _at_arl.wustl.edu Washington University in St.
Louis
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