1. A Load-Balanced Switch with an Arbitrary Number of Linecards Isaac Keslassy, Shang-Tse Chuang, Nick McKeown

2. Outline  Hybrid Electro-Optical Switch Fabric  Number of MEMS Switches  TDM Schedule

3. Stanford 100Tb/s Internet Router Goal: Study scalability  Challenging, but not impossible  Two orders of magnitude faster than deployed routers  We will build components to show feasibility 40Gb/s OpticalSwitch Line termination IP packet processing Packet buffering Line termination IP packet processing Packet buffering Electronic Linecard #1 Electronic Linecard #1 Electronic Linecard #625 Electronic Linecard #625 160- 320Gb/s 160Gb/s 160- 320Gb/s 100Tb/s = 640 * 160Gb/s

4. Out R R R R/N In R R R R/N 3 3 1 2 3 3 3 3 3 The Load-Balanced Switch

5. Out R R R R/N In R R R R/N 3 3 1 2 3 3 3 3 3 The Load-Balanced Switch

6. Needed Properties  Scalability  Flexibility  Each linecard spreads its data equally among all linecards.

7. Decomposing the Mesh for Scalability R/8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

8. Decomposing the Mesh for Scalability 2R/4 R R R R 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 TDM WDM

9. Flexibility: When Linecards Fail 2R/4 R R R R 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 TDM WDM

10. Hybrid Architecture: Logical View

11. Hybrid Electro-Optical Architecture

12. Outline  Hybrid Electro-Optical Switch Fabric  Number of MEMS Switches  TDM Schedule

13. Number of MEMS Switches Linecard 1 Linecard 2 Linecard 3 Crossbar Linecard 1 Linecard 2 Linecard 3 R RR R Linecard 1 Linecard 2 Linecard 3 Crossbar Linecard 1 Linecard 2 Linecard 3 Static MEMS Linecard 4 Linecard 3Linecard 4 R R R R R R R R R R R R R R R R R R R R

14. Number of MEMS Switches Linecard 1 Linecard 2 Linecard 3 Crossbar Linecard 1 Linecard 2 Linecard 3 4R/3 2R/3 R/3 Linecard 1 Linecard 2 Linecard 3 Crossbar Linecard 1 Linecard 2 Linecard 3 Static MEMS R R/3 2R/3 R/3 2R/3 R R R R R R R R R R R R

15. Number of MEMS needed for a schedule  L i : number of linecards in group i, 1 ≤ i ≤ G. Group i needs to send to group j:  Assume each group can send upto R to each MEMS. Number of MEMS needed between groups i and j:

16. Number of MEMS needed for a schedule  The number of MEMS needed for group i to send to group j is A ij  The total number of MEMS needed for group i is the sum of the A ij ’s

17. Outline  Hybrid Electro-Optical Switch Fabric  Number of MEMS Switches  TDM Schedule

18. Constraints for the TDM Schedule 1. Within any period of N, each transmitting linecard is connected to each receiving linecard exactly once. 2. (MEMS constraint) In any time-slot, there are at most A ij connections between transmitting group i and receiving group j, where:

19. Example  Assume L 1 =3, L 2 =2, L 3 =1  Then  E.g., at most 2 packets from the first group to the first group at each time-slot

20. Bad TDM Linecard Schedule T+1T+2T+3T+4T+5T+6 Tx LC 1123456 Tx LC 2612345 Tx LC 3561234 Tx LC 4456123 Tx LC 5345612 Tx LC 6234561

21. Good TDM Linecard Schedule T+1T+2T+3T+4T+5T+6 Tx LC 1123456 Tx LC 2512364 Tx LC 3654123 Tx LC 4231645 Tx LC 5465231 Tx LC 6346512

22. Configuration Algorithm 1. Assign connections between groups, so MEMS constraint is satisfied. 2. Assign group connections to specific linecards, so there is exactly one connection per linecard pair in the schedule.

23. 1. TDM Group Schedule T+1T+2T+3T+4T+5T+6 Tx Group A (3 linecards) BAC Tx Group B (2 linecards) ABAB Tx Group C (1 linecard) A

24. 1. TDM Group Schedule T+1T+2T+3T+4T+5T+6 Tx Group ABACBAA Tx Group BABACAC Tx Group CAB

25. 1. TDM Group Schedule T+1T+2T+3T+4T+5T+6 Tx Group ABACBAA BACBAABAC Tx Group BABABACACABABACACABABABAB Tx Group CABCBAA

26. 2. TDM Linecard-to-Group Schedule T+1T+2T+3T+4T+5T+6 Group A Tx LC 1AAABBC Tx LC 2BAAACB Tx LC 3CBBAAA Group B Tx LC 4AAACBB Tx LC 5BCBAAA Group C Tx LC 6ABCBAA

27. 2. TDM Linecard Schedule T+1T+2T+3T+4T+5T+6 Tx LC 1123456 Tx LC 2512364 Tx LC 3654123 Tx LC 4231645 Tx LC 5465231 Tx LC 6346512

28. Conclusion  Introduced the hybrid electro-optical architecture.  Showed that it needs at most L+G-1 MEMS.  Found an algorithm to get a linecard schedule satisfying all the constraints.