Transcript D2TCP

B9820806 黃冠智
Outline
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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
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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
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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-inburst-induced congestion
• Achieve high bandwidth for background flows
• Work with existing switch hardware
• Be able to coexist with legacy TCP
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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-inburst-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, 𝑝≤ 1
• 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
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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