ATM Switch Architectures

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ATM Switch Architectures

• Carey Williamson

Department of Computer Science University of
Calgary
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Introduction

• ATM switches are categorized based on internal
  architectural characteristics
• Example shared memory switch
• Two key features of a switch design are the
  switch fabric and the buffer organization

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A Classification Scheme

• ATM switch designs can be classified as
  time-division or space-division switches
• Time-division switches all cells pass through a
  common point within the switch en route to their
  output points, but do so at different times
• Space-division switches all cells pass through
  the switch at the same time, but do so on
  different paths

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Time Division Switches

• The two most common types of time division
  switches are the shared memory switch and the
  shared medium switch

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Time Division Switches (Contd)

• Shared memory switch there is a common internal
  buffer in the switch, through which all cells
  pass en route to their output ports
• Shared medium switch there is a common bus in
  the switch, over which all cells must pass en
  route to their output ports

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Shared Memory Switch
Dual Ported Memory
Input Ports
Output Ports
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Shared Memory Switch

• All incoming cells multiplexed into a single
  stream (common memory)
• Organized into output queues per output port
• Cells retrieved sequentially
• Central controller and memory bandwidth must be
  very fast (at least N times input port
  speed)

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Shared Medium Switch

• All incoming cells multiplexed across a common
  medium (bus)
• Cells processed one at a time
• Bus must be very fast (at
  least N times input port speed)

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SHARED-MEDIUM PACKET SWITCH
OUTPUT 1
INPUT 1
AF
FIFO
S/P
OUTPUT 2
INPUT 2
S/P
AF
P/S
FIFO
TIME DIVISION BUS
...
...
...
...
...
...
INPUT N
OUTPUT N
S/P
AF
FIFO
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Space Division Switches

• Space division switches provide multiple
  concurrent paths from the input ports to the
  output ports
• Cells coming in on different input ports and
  heading to different output ports can proceed
  through the switch simultaneously on these
  separate paths, without interfering with each
  other

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Space Division Switches

• There are many examples of space division
  switches
• Crossbar switches
• Multistage interconnection networks (MINs)
• Banyan, Batcher-Banyan, Benes
• delta, omega, perfect shuffle
• Hypercube switches

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4 x 4 Crossbar Switch
A1
A2
A3
A4
B1
B2
B3
B4
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4 x 4 Crossbar Switch
A1
A2
A3
A4
B1
B2
B3
B4
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4 x 4 Crossbar Switch
A1
A2
A3
A4
B1
B2
B3
B4
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2 x 2 NETWORK
INPUT 0
OUTPUT 0
OUTPUT 1
INPUT 1
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2 x 2 NETWORK
INPUT 0
OUTPUT 0
OUTPUT 1
INPUT 1
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2 x 2 NETWORK
INPUT 0
OUTPUT 0
OUTPUT 1
INPUT 1
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4 x 4 NETWORK
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8 x 8 NETWORK
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Summary

• There is an extensive (and exhausting) set of
  literature on ATM switch architectures
• Much of the real research activity took place
  five or more years ago
• Most vendors have based their ATM switching
  products on the well-established good designs
  (e.g., banyan-based or shared memory)