A Load Balanced Switch with an Arbitrary Number of Linecards

1. A Load Balanced Switch with an Arbitrary Number of Linecards I.Keslassy, S.T.Chuang, N.McKeown ( CSL, Stanford University ) Comp 629, Rice University - Presented by Animesh Nandi Some slides adapted from authors

2. Motivation • Internet traffic growth -> Need for faster routers • Approaches 1) Single stage Crossbar switch with central scheduler : Scheduler bottlenecks in memory speed & power dissipation 2) Distributed Multistage switching fabrics : unpredictable throughput 3) Need for architecture that is scalable in terms of memory speed, power requirements and which has predictable throughput.

3. Load Balanced Router Architecture

4. Simple Crossbar Switch Outputs 1 2 N Even if arrival is uniform, 100 % throughput not achieved

5. Fixed Equal-rate switch using multiple VOQs per input Guarantees 100% throughput if arrival is uniform

6. Load Balancing Switch at Front End

7. Three Stages in single Linecard

8. Using Optics for Switching

9. Guaranteeing 100% throughput and preventing packet missequencing N FIFO queues Load Balan- cing Equi- rate switching

10. Handling Linecard Failures Required Switching rate = R/2, instead of R/N R 1 R VOQ 1 R 2 R VOQ 2 VOQ N VOQ N Desired switching rate could becoming arbitrarily high, resulting in Lack of intermediate paths between end-to-end linecards

11. Hybrid Architecture

12. Number of MEMS Switches R R 4R/3 Linecard 1 Crossbar Crossbar Linecard 1 L1 = 2 R R Linecard 2 Linecard 2 R R Linecard 3 Crossbar Crossbar Linecard 3 2R/3 2R/3 L2 = 1 R/3 N = Σ Li = 3 StaticMEMS 2R/3 R R Linecard 1 Crossbar Crossbar Linecard 1 2R/3 R 2R/3 R Linecard 2 Linecard 2 R/3 R R Linecard 3 Crossbar Crossbar Linecard 3 2R/3

13. Number of MEMS needed between a pair of groups • Li: 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:

14. Number of MEMS needed for a schedule • The number of MEMS needed for group i to send to group j is Aij • The total number of MEMS needed for group i is the sum of the Aij’s • The maximum number of MEMS needed =

15. Finding a schedule within a frame on N time slots Time slots N = 7 Linecards L1 = 3 L2 = 2 L3 = 2 Switch configuration at time-slot 1

16. Finding a schedule within a frame on N time slots Time slots N = 7 Linecards L1 = 3 L2 = 2 L3 = 2 Constraint 1 : Linecard 1 should send to N different linecards in N slots

17. Finding a schedule within a frame on N time slots Time slots N = 7 Linecards L1 = 3 L2 = 2 L3 = 2 Constraint 2 : In a particular timeslot, a linecard should be configured to receive only from a particular linecard

18. Finding a schedule within a frame on N time slots Time slots A11 = 2 Constraint fails in time-slot 1 : MEM switches used = 3 Constraint satisfied In time-slot 7 Linecards Switch configuration at time-slot 1 Constraint 3 : Number of connections between group I to group j in a particular time-slot is Li * Lj / N

19. L-L -> L-G -> G-G schedule A A A B B C C L-G schedule L-L schedule A A B B B A C G-G schedule

20. Linecard Schedule Algorithm • Solving for a valid G-G schedule by satisfying MEMS constraint • Given the valid G-G schedule, construct a valid L-G and then a valid L-L schedule

21. Algorithmic Complexity Placement of linecards was chosen randomly with maximum of N = 640 linecards , L = 16 linecards per group , G = 40 groups Conclusion : We need to precompute schedules for effective real-time router reconfiguration

22. 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.