On the Necessity of Time-based Updates in SDN

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Tal Mizrahi Technion Israel Institute of Technology Research Track Session Part 1 ONS2015: http://bit.ly/ons2015sd ONS Inspire! Webinars: http://bit.ly/oiw-sd Watch the talk (video) on ONS Content Archives: http://bit.ly/ons-archives-sd
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  • 1. On the Necessity of Time-based Updates in SDN Tal Mizrahi, Yoram Moses Technion – Israel Institute of Technology Open Networking Summit (ONS) March 2014
  • 2. Accurate Time in Distributed Applications • Mobile backhaul • Power substations • Industrial automation • Automotive networks • Audio/video bridging • High frequency trading • Google’s ‘Spanner’ • … On the Necessity of Time-based Updates in SDN 2
  • 3. Time-based Network Updates Our approach: switches/routers use accurate time – Coordinated network updates – Minimize packet loss / temporary anomalies during updates 3On the Necessity of Time-based Updates in SDN Controller switch switch switch switch
  • 4. Time-based Updates in SDN • One of the key benefits of SDN: Dynamic path allocation based on network load • Claim: time is an essential tool in path allocation 4 Controller switch switch switch switch On the Necessity of Time-based Updates in SDN
  • 5. The Flow-swapping Scenario 5 A B C D S1 S2 S3 S4 S5 All links @ 10 Gbps On the Necessity of Time-based Updates in SDN
  • 6. The Flow-swapping Scenario 6 A B C D S1 S2 S3 S4 S5 F1 F2 4 4 On the Necessity of Time-based Updates in SDN
  • 7. The Flow-swapping Scenario Problem: add new flow BD @ 2 Gbps 7 A B C D S1 S2 S3 S4 S5 F1 F2 4 4 F3 F4 5 5 5+4=9 5+4=9 On the Necessity of Time-based Updates in SDN 10G capacity 9G traffic
  • 8. The Flow-swapping Scenario 8 A B C D S1 S2 S3 S4 S5 F1 F2 F3 F4 4+4=8 5+5=10 4 45 5 After flow-swapping: On the Necessity of Time-based Updates in SDN
  • 9. The Flow-swapping Scenario 9 A B C D S1 S2 S3 S4 S5 F1 F2 F3 F4 5 5 4 4 F5 2 After flow-swapping: Flow swapping: S2 and S3 should be updated ~ simultaneously. On the Necessity of Time-based Updates in SDN
  • 10. A B C D S1 S2 S3 S4 S5 F1 F2 4 4 F3 F4 5 5 5+4=9 5+4=9 The Flow-swapping Scenario 10 Before flow-swapping: Flow swapping: S2 and S3 should be updated ~ simultaneously. On the Necessity of Time-based Updates in SDN
  • 11. The Flow-swapping Scenario 11 A B C D S1 S2 S3 S4 S5 F1 F2 4 4 F3 F4 5 5+5+4=14 5 S2 updated first:  Flow swapping: S2 and S3 should be updated ~ simultaneously. On the Necessity of Time-based Updates in SDN 10G capacity 14G traffic
  • 12. Goal: prove that flow-swaps are inevitable regardless of the controller’s route allocation policy. 12On the Necessity of Time-based Updates in SDN ... ... d o1 o2 on q1 q2 qm c c c s The Lossless Flow Allocation Problem
  • 13. The Lossless Flow Allocation Problem • Special case of multi-commodity flow (MCF). • We analyze it as a two-players game. 13 ... ... d o1 o2 on q1 q2 qm c c c s Source • Progressively adds flows. • Goal: force the controller to swap. Controller • Configures a path for each flow. • Goal: guarantee a path assignment. On the Necessity of Time-based Updates in SDN
  • 14. The Swap Theorem 14 ... ... d o1 o2 on q1 q2 qm c c c s On the Necessity of Time-based Updates in SDN Theorem: There exists a strategy Ss for the source that forces the controller to perform an n-way swap.
  • 15. Controller switch switch switch switch Conclusion • Flow-swaps are inevitable – Existing approaches for consistent network updates do not address flow-swaps • Time and synchronized clocks are optimal for this task • Time-based solutions are useful for many tasks in SDN • A time extension for OpenFlow is under discussion by the ONF Extensibility WG 15On the Necessity of Time-based Updates in SDN
  • 16. THANKS ! 16On the Necessity of Time-based Updates in SDN Controller switch switch switch switch
  • 17. BACKUP SLIDES 17On the Necessity of Time-based Updates in SDN
  • 18. C D S1 S2 after before S3 S4 Example: Multicast Reconfiguration Time Extension to OpenFlow 18 • Update S3 and then S4  S1 is temporarily disconnected. • Update S4 and then S3  S1 temporarily receives two copies of each packet.
  • 19. C D S1 S2 after before S3 S4 Example: Multicast Reconfiguration Time Extension to OpenFlow 19 Solution: update S3 and S4 at the same time.
  • 20. Example: Port Rate Reconfiguration 20 Switch Switch OpenFlow Configuration Point Both switches are configured to change the port rate at time T. On the Necessity of Time-based Updates in SDN Physical layer updates with short transition period.
  • 21. Example: Path Reconfiguration 21 Switch 2 Switch 1 Switch 3 Switch 4 Flow A Flow A path 1 path 2 All switches are updated at (T-, T+ ). On the Necessity of Time-based Updates in SDN
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