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A Scalable Switch for Service Guarantees

This presentation discusses the Interleaved Matching Switch (IMS), a breakthrough in scalable switching technology that addresses the growing demand for bandwidth driven by widespread broadband adoption. It highlights key features like guaranteed service rates and packet ordering, utilizing fixed configuration uniform meshes to avoid the complexity of per-packet dynamic switch reconfigurations. The IMS can emulate complex input-output queued switches while ensuring 100% throughput and upholding service-level agreements, making it suitable for high-capacity, performance-demanding scenarios.

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A Scalable Switch for Service Guarantees

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  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

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