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B9820806 黃冠智

B9820806 黃冠智. Outline. OLDI(Online Data Intensive) architecture DCTCP(Datacenter TCP) D3(Deadline Driven Delivery) Protocol D2TCP(Deadline-Aware Datacenter TCP) Congestion avoidance algorithm Simulation Q&A. OLDI application. Tree-based structure, divide-and-conquer algo

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B9820806 黃冠智

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  1. B9820806 黃冠智

  2. Outline • OLDI(Online Data Intensive) architecture • DCTCP(Datacenter TCP) • D3(Deadline Driven Delivery) Protocol • D2TCP(Deadline-Aware Datacenter TCP) • Congestion avoidance algorithm • Simulation • Q&A

  3. OLDI application • Tree-based structure, divide-and-conquer algo • Soft-real-time constraints(300 ms latency)

  4. OLDI application • Problems： • Maintain deadline will affect respond quality • Fan-in burst cause congestive packet drops and TCP retransmits • Sols: • Over-provision the network link bandwidths(high cost) • increase the network’s time budget(degrades respond quality)

  5. OLDI application • Datacenter network also carry background flow which push control information and data to the node • Long-lived flows cause switch buffer to high utilization • Package drop feedback • Fair-share protocol

  6. OLDI(Online Data Intensive) architecture • DCTCP(Datacenter TCP) • D3(Deadline Driven Delivery) Protocol • D2TCP(Deadline-Aware Datacenter TCP) • Congestion avoidance algorithm • Simulation • Q&A

  7. DCTCP • AQM(Active Queue Management) scheme • Using CE(Congestion Encountered) bit to control transmission rate • ECN does not have suffice to solve fan-in burst problem • Aggregates one-bit ECN feedback and multiple RTTs to form multiple-bit metric

  8. OLDI(Online Data Intensive) architecture • DCTCP(Datacenter TCP) • D3(Deadline Driven Delivery) Protocol • D2TCP(Deadline-Aware Datacenter TCP) • Congestion avoidance algorithm • Simulation • Q&A

  9. D3 Protocol • The bandwidth request for the next RTT is piggybacked on the data packets of the current RTT • Switch grant as much of the request as possible • Far-deadline requests arriving slightly ahead of near-deadline requests

  10. D3 Protocol • Challenges • Requires custom switch ASICs (high cost low vol) • Cannot coexist with legacy TCP

  11. The DC Network Protocol Should • Meet OLDI deadlines, especially in fan-in-burst-induced congestion • Achieve high bandwidth for background flows • Work with existing switch hardware • Be able to coexist with legacy TCP

  12. OLDI(Online Data Intensive) architecture • DCTCP(Datacenter TCP) • D3(Deadline Driven Delivery) Protocol • D2TCP(Deadline-Aware Datacenter TCP) • Congestion avoidance algorithm • Simulation • Q&A

  13. D2TCP • Meet OLDI deadlines, especially in fan-in-burst-induced congestion • Deadline-aware • Achieve high bandwidth for background flows • Work with existing switch hardware • Be able to coexist with legacy TCP

  14. Congestion avoidance algorithm • 𝑓 is the fraction of packets that were marked with CE bits in the most recent window • 𝑔 is the weight given to new samples • d is the deadline imminence factor • P is the penalty function applied to the window size • W is congestion window

  15. Congestion avoidance algorithm • 𝛼 ≤ 1 and therefore, 𝑝≤ 1 • d > 1 (near-deadline flows incur lower penalty) • d < 1 (far-deadline flows incur higher penalty) • d = 1 behavior matches DCTCP

  16. Determining d • 𝑇𝑐 is the time needed for a flow to complete transmitting • D is the time remaining until its deadline expires

  17. OLDI(Online Data Intensive) architecture • DCTCP(Datacenter TCP) • D3(Deadline Driven Delivery) Protocol • D2TCP(Deadline-Aware Datacenter TCP) • Congestion avoidance algorithm • Simulation • Q&A

  18. Simulation

  19. TCP DCTCP D3 D2TCP

  20. Background flows discuss

  21. Missed deadline under tight deadline

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