A Scalable Switch for Service Guarantees

1. A Scalable Switch for Service Guarantees Bill Lin (University of California, San Diego) Isaac Keslassy (Technion, Israel)

2. Motivation • Scalability: Traffic demands growing, driven in part by increasing broadband adoption • 10x increase in broadband subscription in just last 3 years, already over 100 million subscribers • 1.25-2.4 Gbps fiber to homes emerging (GPON, GEPON, EPON, BPON …) • Service Guarantees: Operators need bandwidth partitioning capabilities • Provide guaranteed rates in service-level agreements • Enable logical partitioning of converged networks • Traffic engineering in general

3. Router Wish List • Scalable in line rates and number of linecards • e.g. R = 160 Gbps (new packet every 2ns), thousands of linecards, petabit capacity • No centralized scheduler • No per-packet dynamic switch reconfigurations • Low complexity linecards • Provide performance guarantees • 100% throughput guarantee • Service guarantees • No packet reordering

4. Existing Architectures • Output-Queueing (OQ) Switch • Well-known rate guarantees possible with Weighted Fair Queueing or Deficit Round-Robin scheduling • But OQ switches require speedup of N • Crossbar Switches, using Input-Queueing (IQ) or Combined Input-Output Queueing (CIOQ) • OQ emulation possible • But expensive centralized scheduling and per-packet dynamic switch reconfigurations • Birkhoff-von Neumann decomposition • If traffic matrix known, can provide rate guarantees with distributed scheduling, but still requires per-packet dynamic switch reconfigurations

5. Existing Architectures (cont’d) • Load-Balanced Switches • Chang et al., “Load balanced Birkhoff-von Neumann switches, Part I: one-stage buffering”, Computer Communications, 2002 • Keslassy et al., “Scaling Internet routers using optics”, ACM SIGCOMM 2003 • A key idea: fixed configuration uniform meshes in optics, no dynamic switch reconfigurations • Showed 100 Tb/s load-balanced router with R = 160 Gbps and N = 640 linecards • Showed 100% throughput for “best effort” traffic, but no service guarantees

6. This Talk • Presents the Interleaved Matching Switch (IMS) • Like a load-balanced switch, use fixed configuration uniform meshes, implemented with an optical fabric • No arbitrary per-packet switch reconfiguration • Can emulate any IQ or CIOQ switch • Can emulate a Birkhoff-von Neumann switch • If traffic matrix known, can ensure 100% throughput, service guarantees, and packet ordering • Show we can use O(1) distributed online scheduling

7. Generic Load-Balanced SwitchUsing Fixed Configuration Uniform Meshes Linecards Linecards Linecards In Out R R R/N R/N 1 2 3 R/N R/N R/N R/N R/N In Out R/N R R R/N R/N R/N R/N R/N R/N R/N In Out R/N R R R/N R/N

8. Generic Load-Balanced SwitchUsing Fixed Configuration Uniform Meshes Linecards Linecards Linecards In Out R R R/N R/N R/N R/N 1 R/N R/N R/N In Out R/N R R R/N R/N 2 R/N R/N R/N R/N R/N In Out R/N R R R/N R/N 3

9. Generic Load-Balanced SwitchUsing Fixed Configuration Uniform Meshes Linecards Linecards Linecards In Out R R R/N R/N R/N R/N • Many Fabric Options (any spreading device) • Space: Full uniform mesh • Wavelength: Static WDM • Time: Round-robin switches Just need fixed uniform rate channels at R/N No dynamic switch reconfigurations R/N R/N R/N In Out R/N R R R/N R/N R/N R/N R/N R/N R/N In Out R/N R R R/N R/N

10. From Load-Balanced Switch Linecards Linecards Linecards In Out R R R/N R/N R/N R/N R/N R/N R/N In Out R/N R R R/N R/N R/N R/N R/N R/N R/N In Out R/N R R R/N R/N

11. To Interleaved Matching Switch Add coordination slots in MIDDLE Linecards Linecards Linecards Out R R R/N R/N R/N R/N Move main packet buffers to INPUT R/N R/N R/N Out R/N R R R/N R/N R/N R/N R/N R/N R/N Out R/N R R Retain Fixed Configuration Meshes R/N R/N

12. How It Works • IMS works by emulating an IQ or CIOQ crossbar switch, but without per-packet dynamic switch reconfigurations (will show how centralized scheduling can be avoided later)

13. How It Works Linecards Linecards Linecards Out R R R/N R/N A2 A1 A A1 R/N R/N A2 A1 R/N R/N R/N Out R/N R R B1 B R/N R/N B2 B1 B2 B1 R/N R/N R/N R/N R/N Out R/N R R C2 C1 C C2 C1 R/N R/N C2 C1

14. How It Works Crossbar Switch Interleaved Matching Switch Linecards XBAR Linecards Linecards Linecards Linecards Out Out R R R R R R A2 A1 A2 A1 R/N R/N A1 A1 R/N R/N A2 A1 A2 A1 R/N R/N Out Out R R R R R R B1 B1 R/N R/N B2 B1 B2 B1 R/N R/N B2 B1 B2 B1 R/N R/N Out Out R/N R/N R R R R R R C2 C1 C2 C1 C2 C1 C2 C1 R/N R/N C2 C1 C2 C1 R/N R/N

15. How It Works R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N Crossbar Switch Interleaved Matching Switch Linecards XBAR Linecards Linecards Linecards Linecards Out Out R R R R R R A2 A1 A2 A1 A1 A1 A2 A1 A2 A1 Out Out R R R R R R B1 B1 B2 B1 B2 B1 B2 B1 B2 B1 Out Out R R R R R R C2 C1 C2 C1 C2 C1 C2 C1 C2 C1 C2 C1

16. How It Works R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N Crossbar Switch Interleaved Matching Switch Linecards XBAR Linecards Linecards Linecards Linecards Out Out R R R R R R B1 A2 A1 A2 A1 B1 A1 A1 C1 A2 A2 A1 Out Out R R R R R R C1 B2 B1 B2 B1 B2 B1 B2 B1 Out Out R R R R R R A1 C2 C1 C2 C1 C2 C2 C2 C1 C2 C1

17. How It Works R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N Crossbar Switch Interleaved Matching Switch Linecards XBAR Linecards Linecards Linecards Linecards Out Out R R R R R R B1 B1 A2 A1 A2 A1 A1 • Differences with crossbar switch • No dynamic switch reconfigurations • Departure times delayed by 2N time slots, Ntime slots per mesh, otherwise same sequence • Packet transfers initiated at each time slot to next MIDDLE linecard in round-robin order A1 A2 A2 Out Out R R R R R R R C1 C1 B2 B1 B2 B1 B2 B1 B2 B1 Out Out R R R R R R R A1 A1 C2 C1 C2 C1 C2 C2 C2 C1 C2 C1

18. How It Works R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N Crossbar Switch Interleaved Matching Switch Linecards XBAR Linecards Linecards Linecards Linecards Out Out R R R R R R A2 A1 A2 A1 A1 A1 A2 A2 Out Out R R R R R R R B2 B1 B2 B1 B2 B1 B2 B1 Out Out R R R R R R R C2 C1 C2 C1 C2 C2 C2 C1 C2 C1

19. How It Works R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N Crossbar Switch Interleaved Matching Switch Linecards XBAR Linecards Linecards Linecards Linecards Out Out R R R R R R A1 A2 A2 A1 A1 A2 A2 Out Out R R R R R R R B1 A1 B2 B2 B1 B2 B1 B2 B1 C1 Out Out R R R R R R R C1 C2 C1 C2 C1 C2 C2 C2 C2

20. How It Works R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N R/N Crossbar Switch Interleaved Matching Switch Linecards XBAR Linecards Linecards Linecards Linecards Out Out R R R R R R A2 A2 A1 A1 A2 A2 Out Out R R R R R R R B2 B2 B2 B1 B2 B1 Crossbar MATCHINGS are INTERLEAVED across MIDDLE linecards (analogous to memory interleaving) Out Out R R R R R R R C2 C1 C2 C1 C2 C2 C2 C2

21. IQ and CIOQ Switch Emulation • An IMS can emulate any IQ or CIOQ switch.

22. When Traffic Matrix is Known • When traffic matrix is known, can perform Birkhoff-von Neumann decompositionoffline • Given anyadmissibletraffic matrix • Can decompose into a series of permutation matrices ( ) such thatwhere

23. Example • Consider following example: • Use weighted fair queueing to schedule each permutation matrix proportionally to its corresponding weight

24. Distributed Storage and Scheduling • Distributed storage: each input linecard only stores its corresponding “rows” • Distributed scheduling: each input linecard only responsible for scheduling its own VOQs • O(1) time/hardware complexity: use deficit round-robin scheduling (many efficient variants)

25. Birkhoff-von Neumann Emulation • If traffic matrix known, an IMS can guarantee 100% throughput and guaranteed flow rates when combined with Birkhoff-von Neumann decomposition and online fair scheduling

26. Frame-Based Decomposition • If traffic matrix  can be converted to an integer matrix by multiplying by an integerF, then  can be decomposed into F permutations • Known decomposition algorithms (if Fis integer multiple of N ) • Birkhoff-von Neumann: O( N3.5 ) • Slepian-Duguid: O( N3 ) • New efficient formulation using edge-coloring • O( N2 log N)

27. Conclusions • Scalability • IMS leverages scalability of fixed optical meshes • If traffic matrix known, distributed online scheduling can achieve O(1) time and hardware complexity • Emulation • IMS can emulate any IQ or CIOQ switch under same speedup and matching • Guarantees • If traffic matrix known, can ensure 100% throughput, service guarantees, and packet ordering via Birkhoff-von Neumann switch emulation • For integer matrices, new edge coloring formulation

28. Thank You