The Concurrent Matching Switch Architecture Bill Lin (University of California, San Diego) Isaac Keslassy (Technion, Israel)

IEEE INFOCOM, Barcelona, April 23-29, Motivation  Traffic demands expected to grow, driven in part by increasing broadband adoption  10x increase in broadband subscription in just last 3 years, already over 100 million subscribers  Gbps fiber to homes emerging (GPON, GEPON, EPON, BPON …)  Larger routers needed for consolidation  Operators need scalable routers that provide good performance

IEEE INFOCOM, Barcelona, April 23-29, Limitations of Previous Routers  Output-Queueing (OQ) Switch  Well-known to provide good performance, but scalability hampered by need for internal N speedup  Crossbar Switches, using Input-Queueing (IQ) or Combined Input-Output Queueing (CIOQ)  Huge body of literature, but scalability hampered by need for centralized scheduling and arbitrary per- packet switch configurations

IEEE INFOCOM, Barcelona, April 23-29, Limitations of Previous Routers  Load-Balanced Routers  No centralized scheduler  Scalable fixed configuration switch fabric in optics  Guarantees 100% throughput  100 Tb/s design with 160 Gb/s linecards shown  But packets may be delivered “out-of-order”

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R/N R R R Basic Load-Balanced Router R/N In Linecards A1 A2 A3 B1 C1 C2 B1 B2 C1

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R/N R R R Basic Load-Balanced Router R/N In Linecards A1 A2 A3 B1 C1 C2 B1 B2 C1 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 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

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R/N R R R Basic Load-Balanced Router R/N In Linecards A1 A2 A3 B1 C1 C2 B1 B2 C1 Out of Order !

IEEE INFOCOM, Barcelona, April 23-29, Packet Ordering Problem  Out-of-order packet delivery is undesirable (e.g. bad for TCP)  Previous techniques (e.g. EDF, UFS, FOFF)  Accumulate and delay packets at input/middle ports  And/or delay and re-order packets at middle/output ports  However, these techniques are unsatisfactory because they add substantial delays

IEEE INFOCOM, Barcelona, April 23-29, Impact on Avg. Delay (N = 128, uniform traffic) Basic Load-Balanced UFS FOFF Significant Delay

IEEE INFOCOM, Barcelona, April 23-29, Concurrent Matching Switch (CMS)  Basic idea  Retain load-balanced router structure and scalability of a fixed optical mesh, no dynamic reconfiguration  Instead of packets, load-balance “request tokens” to N parallel “schedulers”  Each scheduler independently solves its own matching  Packets delivered in order based on matching results Goal is to provide much lower average delay than accumulation-based methods for ensuring packet order while retaining 100% throughput and scalability

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Architecture Linecards A1 B1 C1 C2 C1 B2 C2 Retain Fixed Configuration Meshes BUT move packet buffers to INPUT A2 A3 A4

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Architecture Linecards A1 B1 C1 C2 C1 B2 C2 A2 A3 A Add N 2 Token Counters

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Arrival Phase Linecards A1 C1 C2 C1 C2 A2 A3 A B1 B2 A1 A2 B1 B2 C2 C3 C4

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Arrival Phase Linecards A1 C1 C2 C1 C2 A2 A3 A B1 B2 B1 B2 C2 C3 C4 A1 A2

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Arrival Phase Linecards A1 C1 C2 C1 C2 A2 A3 A B1 B2 A1 A2 B1 B2 C2 C3 C4

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Arrival Phase Linecards A1 C1 C2 C1 C2 A2 A3 A B1 B2 A1 A2 B1 B2 C2 C3 C4

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Matching Phase Linecards A1 C1 C2 A2 A3 A B1 B2 A1 A2 B1 B2 C1 C2 C1 C2 C3 C4

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Matching Phase Linecards A1 C1 C B1 A2 A3 A4 B1 A1 A2 C1 B1 B2 C2 C1 C2 C3 C4

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Matching Phase Linecards A1 C1 C B1 A2 A3 A4 B1 B2 C3 C4 A1 A2 C1 B1 C1 B2 C2

IEEE INFOCOM, Barcelona, April 23-29, Out R R R R R R Departure Phase Linecards A1 C1 C B1 A2 A3 A4 B1 B2 C3 C4 A1 A2 C1 B1 C1 B2 C2

IEEE INFOCOM, Barcelona, April 23-29, Distributed Operation  All linecards operate in parallel in a fully distributed manner  Arrival, matching, and departure phases overlap in a pipeline manner

IEEE INFOCOM, Barcelona, April 23-29, Main Ideas  Each middle linecard acts as a “micro-router” with 1/N th of the arrival traffic  Therefore, it gets N time slots to think about the schedule, time complexity amortized by a factor of N  If each micro-router can guarantee 100% throughput, so can the overall switch  Each micro-router can work the way that it wants, leveraging huge body of existing work on scheduling CMS provides a new way of aggregating routers together. Therefore, provides a new way of thinking about scaling routers.

IEEE INFOCOM, Barcelona, April 23-29, Practicality  Well-studied randomized approximations to Maximum Weighted Matching have been shown to achieve very good results [Tassiulas 1998] [Giaccone, Prabhakar & Shah, 2003]  These algorithms only require O(N) complexity using sequential hardware, but can provide 100% throughput guarantees with no speedup and good delay results  Amortized over N time slots, CMS with these scheduling algorithms can achieve  O(1) time complexity (independent of switch size)  100% throughput  Good delay results  Packet ordering

IEEE INFOCOM, Barcelona, April 23-29, Experimental Results (N = 128, uniform traffic) Basic Load-Balanced UFS FOFF CMS Difference of N time slots for matching phase

IEEE INFOCOM, Barcelona, April 23-29, Conclusions  CMS is scalable  Leverages scalability of fixed optical meshes  Fully distributed  Can achieve O(1) time complexity  CMS achieves good performance  Guarantees 100% throughput  Guarantees packet ordering  Experimentally achieves low packet delays  CMS provides new way of thinking about scaling routers and connects huge body of existing literature on scheduling to load-balanced routers

Thank You