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 (Cont’d)
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
INPUT 1 AF
OUTPUT 1
S/P
FIFO
P/S
OUTPUT 2
INPUT 2
S/P AF
FIFO
P/S
TIME DIVISION BUS
...
...
...
...
...
...
INPUT N
OUTPUT N
S/P AF
FIFO
P/S

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 1 2 3

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)