1. 1 Performance Results The following are some graphical performance results out of the literature for different ATM switch designs and configurations For more information, see [Tobagi 1990]

2. 2 Input Buffering The first set of performance results is for input buffering (alone) with First Come First Serve (FCFS) service discipline (also known as First In First Out (FIFO)) Suffers from the Head of the Line blocking problem

3. NMaximum Throughput1 20.75 30.6825 40.6553 50.6399 60.6302 70.6234 80.6184 0.5858 Maximum Throughput for Input Buffering

4. NUMBER OF PORTS (N) Maximum Throughput for Input Buffering 020406080100 MAXIMUM ACHIEVABLE THROUGHPUT 0.8 0.5 0.6 0.7

5. 5 Performance of Banyans The next set of performance results is for banyan multistage interconnection networks (NOTE: these are NOT Batcher-banyans) FACT: in a bufferless banyan, throughput T degrades significantly with an increase in N, the number of input ports, due to the blocking problems (path contention and output port contention) T = 40% for N = 32, T = 26% for N = 1024

6. 6 Buffered Banyans Performance of banyans can be improved by adding internal buffers to the switch fabric at places where contention may occur (i.e., at outputs of each 2x2 module) This approach can increase the effective throughput of banyans

7. 7 0.0 0.2 0.4 0.6 0.8 1.0 0.00.20.40.60.81.0 OFFERED LOAD p THROUGHPUT N=2 Throughput for Uniform Traffic (Single Buffered Banyan)

8. 8 0.0 0.2 0.4 0.6 0.8 1.0 0.00.20.40.60.81.0 OFFERED LOAD p THROUGHPUT N=2 Throughput for Uniform Traffic (Single Buffered Banyan) N=4

9. 9 0.0 0.2 0.4 0.6 0.8 1.0 0.00.20.40.60.81.0 OFFERED LOAD p THROUGHPUT N=2 Throughput for Uniform Traffic (Single Buffered Banyan) N=4 N=16

10. 10 0.0 0.2 0.4 0.6 0.8 1.0 0.00.20.40.60.81.0 OFFERED LOAD p THROUGHPUT N=2 Throughput for Uniform Traffic (Single Buffered Banyan) N=4 N=16 N=64

11. 11 0.0 0.2 0.4 0.6 0.8 1.0 0.00.20.40.60.81.0 OFFERED LOAD p THROUGHPUT N=2 Throughput for Uniform Traffic (Single Buffered Banyan) N=4 N=16 N=64 N=1024

12. 12 0.3 0.4 0.5 0.6 0.7 0.8 0.30.40.50.6 0.70.8 OFFERED LOAD p THROUGHPUT B=4 Effect of Buffer Size (N = 64) B=2 B=1 0.91.0

13. 13 0.3 0.4 0.5 0.6 0.7 0.8 0.3 OFFERED LOAD p TROUGHPUT HOL BYPASS Effect of HOL Bypass (N = 64) FIFO (WITH HOL BLOCKING) 0.40.50.6 0.70.8 0.91.0

14. 14 Buffered Banyans: Summary Performance depends on load The more buffers, the better the throughput HOL bypass helps Performance still degrades as N increases, due to blocking effects

15. 15 Shared Memory Switches The next set of performance results looks at buffer managment strategies for shared memory switches In particular, looks at cell loss performance for partitioned versus shared buffering

16. 16 Partitioned Buffers SHARED MEMORY

17. 17 BUFFER SIZE, b (per port) Cell Loss with Partitioned Buffers (  =0.9) -12 -10 -8 -6 -4 -2 020406080 CELL LOSS PROBABILITY N=2 1.0 10

18. 18 BUFFER SIZE, b (per port) Cell Loss with Partitioned Buffers (  =0.9) -12 -10 -8 -6 -4 -2 020406080 CELL LOSS PROBABILITY N=2 N=4 1.0 10

19. 19 BUFFER SIZE, b (per port) Cell Loss with Partitioned Buffers (  =0.9) -12 -10 -8 -6 -4 -2 020406080 CELL LOSS PROBABILITY N=2 N=4 N=8 1.0 10

20. 20 BUFFER SIZE, b (per port) Cell Loss with Partitioned Buffers (  =0.9) -12 -10 -8 -6 -4 -2 020406080 CELL LOSS PROBABILITY N=2 N=4 N=8 1.0 10 N= 

21. 21 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY -12 -10 -8 -6 -4 -2 1.0 10 p=0.70 Cell Loss with Partitioned Buffers (N=)

22. 22 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY -12 -10 -8 -6 -4 -2 1.0 10 p=0.70 0.75 Cell Loss with Partitioned Buffers (N=)

23. 23 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY -12 -10 -8 -6 -4 -2 1.0 10 p=0.70 0.75 0.80 Cell Loss with Partitioned Buffers (N=)

24. 24 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY -12 -10 -8 -6 -4 -2 1.0 10 0.85 p=0.70 0.75 0.80 Cell Loss with Partitioned Buffers (N=)

25. 25 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY -12 -10 -8 -6 -4 -2 1.0 10 0.90 0.85 p=0.70 0.75 0.80 Cell Loss with Partitioned Buffers (N=)

26. 26 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY p=0.95 -12 -10 -8 -6 -4 -2 1.0 10 0.90 0.85 p=0.70 0.75 0.80 Cell Loss with Partitioned Buffers (N=)

27. 27 Shared Buffers SHARED MEMORY

28. 28 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY N=16 -12 -10 -8 -6 -4 -2 1.0 10 Cell Loss with Shared Buffers (  =0.9)

29. 29 BUFFER SIZE, b (per port) 01020304050 CELL LOSS PROBABILITY N=16 -12 -10 -8 -6 -4 -2 1.0 10 N=32 Cell Loss with Shared Buffers (  =0.9)

30. 30 Shared Memory: Summary Shared buffers provide much lower cell loss than partitioned buffers, for uniform input traffic (Note: the opposite may be true for non-uniform traffic!) For partitioned, cell loss gets worse with larger N, while for partitioned it gets better

31. 31 Sunshine Switch The final set of graphs looks at the performance of the Sunshine switch Sunshine switch is based on a Batcher banyan design, but with recirculation lines and with the use of multiple banyans in parallel to accommodate multiple cells destined to the same output port

32. 32 Batcher-Banyan Switching Fabric RECIRCULATING QUEUE MM BATCHER SORTER TRAP NETWORK CONCENTRATOR IN 1 IN N... BANYAN ROUTING NETWORK M+N N

33. 33 SUNSHINE SWITCH ARCHITECTURE DELAY M M BATCHER SORTER TRAP NETWORK CONCENTRATOR IN 1 IN N... M+N... M+N... M+N SELECTOR BANYAN 1 BANYAN K... OUT 1 OUT N...

34. 34 0.0 M/N CELL LOSS RATIO Cell Loss in Sunshine Switch (K=1) p=0.4 -10 10 -8 10 -6 10 -2 10 -4 10 0 0.20.40.60.8 Uniform Traffic N = 128 Single Banyan (K=1)

35. 35 0.0 M/N CELL LOSS RATIO Cell Loss in Sunshine Switch (K=1) p=0.6 p=0.4 -10 10 -8 10 -6 10 -2 10 -4 10 0 0.20.40.60.8 Uniform Traffic N = 128 Single Banyan (K=1)

36. 36 0.0 M/N CELL LOSS RATIO Cell Loss in Sunshine Switch (K=1) p=0.8 p=0.6 p=0.4 -10 10 -8 10 -6 10 -2 10 -4 10 0 0.20.40.60.8 Uniform Traffic N = 128 Single Banyan (K=1)

37. 37 0.0 M/N CELL LOSS RATIO p=1.0 Cell Loss in Sunshine Switch (K=1) p=0.8 p=0.6 p=0.4 -10 10 -8 10 -6 10 -2 10 -4 10 0 0.20.40.60.8 Uniform Traffic N = 128 Single Banyan (K=1)

38. 38 0.00.10.20.30.40.5 M/N CELL LOSS RATIO K=1 -10 10 -8 10 -6 10 -2 10 -4 10 0 Uniform Traffic N = 128 p = 1.0 Cell Loss in Sunshine Switch (K>1)

39. 39 0.00.10.20.30.40.5 M/N CELL LOSS RATIO K=2 K=1 -10 10 -8 10 -6 10 -2 10 -4 10 0 Uniform Traffic N = 128 p = 1.0 Cell Loss in Sunshine Switch (K>1)

40. 40 0.00.10.20.30.40.5 M/N CELL LOSS RATIO K=2 K=1 K=3 -10 10 -8 10 -6 10 -2 10 -4 10 0 Uniform Traffic N = 128 p = 1.0 Cell Loss in Sunshine Switch (K>1)

41. 41 0.00.10.20.30.40.5 M/N CELL LOSS RATIO K=2 K=4 K=1 K=3 -10 10 -8 10 -6 10 -2 10 -4 10 0 Uniform Traffic N = 128 p = 1.0 Cell Loss in Sunshine Switch (K>1)

42. 42 Sunshine Switch: Summary Sunshine switch was designed and prototyped at Bellcore Multiple banyans provide parallel routing paths to accommodate multiple cells destined for the same output port Recirculation handles the “overflows” Very promising switch design