1. MASCON: A Single IC Solution to ATM Multi-Channel Switching With Embedded Multicasting Ali Mohammad Zareh Bidoki April 2002

2. Table of Contents Crossbar switch MASCON architecture MASCON properties MASCON modules Backpressure and fault tolerance MASCON problems

3. Crossbar switch fabric N2N2

4. High level diagram of MASCON Loss packet Output R Buffer N MMRNRPCN ACFGACFG

5. MASCON Properties Fully Shared Buffer Internally Non-blocking Multicasting Fault Tolerance Cell base (for ATM)

6. MASCON Properties Multi-Channeling Any number of consecutive outputs can be grouped It is software configurable Cell sequence integrity over the port of each output channel group being preserved

7. MASCON Properties We can construct MIN (Multistage Interconnected Network) It has Backpressure Mechanism (Using two Thresholds for QOS) Its Architecture is very regular (so its implementation in ASIC is simpler)

8. OGN (output group number) Shows the number of output group 00001000 shows that GN =3 Only one bit can be zero There are N OGN that each is N bits (for N*N switch)

9. RGN(Request Group Number) Shows the destinations of packet By OGN) If RGN=00001101 then fan-out is three (to outputs 0,2,3) It is in header of cell (set by lookup engine)

10. MASCON Architecture 11111111 10000000 00000010 00101000 11111111 10001000 00000010 01001000 10000001 00000010 FIFO 01 02 04 04 04 20 40 80 Output GN Concentrator X-bar Multicast X-bar Input cells Dropped cells

11. MASCON Properties By using crossbar architecture: High integration density in Integrated Circuits Ease of synchronization High performance Modularity Fault tolerance

12. MMRN (Multicast Multichannel Routing Network) Routing & copying cells Connection management Its includes N*R(N+1) MMRN-MX points Sin CI RGNout S out RGNin MMRN MX OGNin OGNout

13. MMRN

14. X_Point in MMRN Each X-point has inputs: OGNin,RGNin,Sin(status in) outputs : OGNout, RGNout, Sout Connection state latched as the connection indicator once per cell time

15. X_point function Start OGNout=OGNin If Sin=0 and RGNin=OGNin CI=1 Modify RGNin RGNout=RGNin Else CI=0 Sout=Sin RGNout=RGNin END

16. RPCN (Recirculation path Concentrator Network)

17. Saving Area in RPCN Since we do not need the upper an lower diagonals we save R 2 X-point Since the original area is (N+R)*R we save R/(N+R) For R=3N we save 75 percent of area

18. ACFG(Assigned Cell Flag Generator) Outputs: “1” at rows for which the input is an assigned cell “0” in the case of an unassigned (null)cell

19. RPCN Function Sin CI ACF out S out ACF in CX Start If Sin=0 and ACFin=1 CI=1 Sout=1 ACFout=0 else CI=0 Sout=Sin ACFout=ACfin END

20. MASCON characteristics It is internally non-blocking and buffer efficient No cells are lost when there is a path Since computation of paths are done using combinational logic simultaneously at all cross point: The processing headers is done in a parallel and distributed manner

21. Cell sequence integrity Loss packet R Buffer MMRNRPCN ACFGACFG E3 b5 e4 a3 b4 d3 C2 c3 d2 e1 b3 A2 b2 c1 A1 b1 d1 E4 b5 e3 d3 b4 a3 c3 c2 b3 c1 d2 c1 b2 a2 d1 b1 a1 A1 b1 d1 A2 b2 c1 d2 e1 b3 c2 A3 b4 d3 e3 B5 e4 c3

22. Performance Evaluation performance of MIN with output grouping is better than without output grouping. Connections using groups use share resource so gain performance advantage

23. Output Grouping 16*16 switch

24. Traffic Flow Control and Monitoring

25. Backpressure mechanism To prevent excess cell loss due to bursty traffic To decide to generate a backpressure signal to upstream modules MASCON monitors the buffers occupancy of its shared buffer and compares it with thresholds (configurable by software) It implement by counting ACFG flags in Backpressure Signal Control Unit(BSCU)

26. Backpressure Backpressure signal send to upstream modules or input buffers If upper threshold is less than or equal to R(buffer capacity)-N then no cell loss can be occur

27. Traffic Monitoring Cells dropped from each input channel at the RPCN are counted in a 8 bit Cell Loss Counter(CLC) All of parameters are software configurable via CPU interface Unit (CIU)

28. Backpressure in detail

29. Fault Tolerance Some faults in Look up tables Software control Physical transmission of signals There may be invalid RGN

30. Implementation Using 9 byte routing tag it scales to 40Gb/s (3 stages, 4 MASCON modules in each stage- MIN) Use 64 bytes internal cell format Supports 16 channel at 622 Mb/s per channel Use two ASICs per module Clock is 51.84 MHz

31. Byte interleaving (two 310 Mb/s)

32. MIN

33. Another Advantage of multi-channel switching is the reduced memory requirement for self routing If N=16 For three state single group N-2N-4N For three state 8 channel per group 2-4-4N

34. Implementation in ASIC Implementation MMRN and RPCN X-points and as standard cells For MMRN X-point 74 equivalent gates For RPCN X-point 23 equivalent gates Use pipeline, cut through in which the path computation is done in half a cell time By 0.5 micron CMOS technology,the ASIC has 370k gates and 479 pin BGA

35. MMRN Implementation Results Switch SizeNumber of gatesSystem clockCell time clockStart of cell clock 8 *83970222.0 MHz33.4 MHz36.2 MHz 4 * 41164284.2 MHz88.1 MHz211.5 MHz

36. Speed How we can increase the speed? How we can decrease crossbars? What is bottle neck in MASCON?

37. Fariness in MASCON(Starvation) Data,RGN Sout Sin Gin token MX OR DFF OR...

38. There is big cross-point in MASCON In each time only N CX are using. We can decrease them by using DFG graphs. Wave front arrays

39. Can we change it to IP switch? Cell base or not. 41.5% are one cell If use cell base (fragments packet to cells). Cell loss IP cells guarantee Can we use MIN ?

40. N Independent FIFO Memory N 2 1..... 1 23 Simulation showed the throughput will decrease to 60%.

41. Q & A

42. Thank You! Ali Mohammad Zareh Bidoki