b9820806 黃冠智
Post on 24-Feb-2016
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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• Soft-real-time constraints(300 ms latency)
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)
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
• OLDI(Online Data Intensive) architecture• DCTCP(Datacenter TCP)• D3(Deadline Driven Delivery) Protocol• D2TCP(Deadline-Aware Datacenter TCP)– Congestion avoidance algorithm
• Simulation• Q&A
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
• OLDI(Online Data Intensive) architecture• DCTCP(Datacenter TCP)• D3(Deadline Driven Delivery) Protocol• D2TCP(Deadline-Aware Datacenter TCP)– Congestion avoidance algorithm
• Simulation• Q&A
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
D3 Protocol
• Challenges– Requires custom switch ASICs (high cost low vol)– Cannot coexist with legacy TCP
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
• OLDI(Online Data Intensive) architecture• DCTCP(Datacenter TCP)• D3(Deadline Driven Delivery) Protocol• D2TCP(Deadline-Aware Datacenter TCP)– Congestion avoidance algorithm
• Simulation• Q&A
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
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
Congestion avoidance algorithm
• ≤ 𝛼 1 and therefore, ≤ 1𝑝• d > 1 (near-deadline flows incur lower penalty)• d < 1 (far-deadline flows incur higher penalty)• d = 1 behavior matches DCTCP
Determining d
• 𝑇𝑐 is the time needed for a flow to complete transmitting• D is the time remaining until its deadline expires
• OLDI(Online Data Intensive) architecture• DCTCP(Datacenter TCP)• D3(Deadline Driven Delivery) Protocol• D2TCP(Deadline-Aware Datacenter TCP)– Congestion avoidance algorithm
• Simulation• Q&A
Simulation
TCP DCTCP D3 D2TCP
Background flows discuss
Missed deadline under tight deadline
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