ATM%20Switch%20Architectures

1
ATM Switch Architectures

• Carey Williamson

Department of Computer Science University of
Calgary
2
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

3
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

4
Time Division Switches

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

5
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

6
Shared Memory Switch
Dual Ported Memory
Input Ports
Output Ports
7
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)

8
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)

9
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
10
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

11
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

12
4 x 4 Crossbar Switch
A1
A2
A3
A4
B1
B2
B3
B4
13
4 x 4 Crossbar Switch
A1
A2
A3
A4
B1
B2
B3
B4
14
4 x 4 Crossbar Switch
A1
A2
A3
A4
B1
B2
B3
B4
15
2 x 2 NETWORK
INPUT 0
OUTPUT 0
OUTPUT 1
INPUT 1
16
2 x 2 NETWORK
INPUT 0
OUTPUT 0
OUTPUT 1
INPUT 1
17
2 x 2 NETWORK
INPUT 0
OUTPUT 0
OUTPUT 1
INPUT 1
18
4 x 4 NETWORK
19
8 x 8 NETWORK
20
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)