Cheng Jin David Wei Steven Low FAST TCP: design and experiments.
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Transcript of Cheng Jin David Wei Steven Low FAST TCP: design and experiments.
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Cheng Jin David Wei Steven Low
http://netlab.caltech.edu
FAST TCP:design and experiments
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Performance at large windows
capacity = 155Mbps, 622Mbps, 2.5Gbps, 5Gbps, 10Gbps; 100 ms round trip latency; 100 flowsJ. Wang (Caltech, June 02)
ns-2 simulation
10Gbps
27%
txq=100 txq=10000
95%1G
Linux TCP Linux TCP FAST
19%
average utilization
capacity = 1Gbps; 180 ms round trip latency;1 flowC. Jin, D. Wei, S. Ravot, etc (Caltech, Nov 02)
DataTAG Network:CERN (Geneva) – StarLight (Chicago) – SLAC/Level3 (Sunnyvale)
txq=100
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Packet & flow level
ACK: W W + 1/W
Loss: W W – 0.5W
Packet level
Reno TCP
Flow level
Equilibrium
Dynamics
packets
(Mathis formula)
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Difficulties at large window
Equilibrium problem Packet level: AI too slow, MI too drastic. Flow level: requires very small loss
probability. Dynamic problem
Packet level: must oscillate on a binary signal.
Flow level: unstable at large window.
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Problem: binary signal
TCP
oscillation
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Solution: multibit signal
FAST
stabilized
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Problem: no target
ACK: W W + 1/W
Loss: W W – 0.5W
Reno: AIMD (1, 0.5)
ACK: W W + a(w)/W
Loss: W W – b(w)W
ACK: W W + 0.01
Loss: W W – 0.125W
HSTCP: AIMD (a(w), b(w))
STCP: MIMD (1/100, 1/8)
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Solution: estimate target FAST
Slow Start
FAST Conv
Equil
Loss Rec
Scalable to any w*
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Packet level
ACK: W W + 1/W
Loss: W W – 0.5W
Reno AIMD(1, 0.5)
ACK: W W + a(w)/W
Loss: W W – b(w)W
HSTCP AIMD(a(w), b(w))
ACK: W W + 0.01
Loss: W W – 0.125W
STCP MIMD(a, b)
RTT
baseRTT W W :RTT FAST
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FAST TCP
Flow level Understood and Synthesized first.
Packet level Designed and implemented later.
Design flow level equilibrium & stability Implement flow level goals at packet level
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Architecture
~ RTT timescaleAck timescale
~ Ack timescale
DataControl
WindowControl
Burstiness Control
Estimation
TCP Protocol Processing
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Architecture
Each component designed independently upgraded asynchronously
DataControl
WindowControl
Burstiness Control
Estimation
TCP Protocol Processing
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Dynamic sharing: 3 flowsFAST Linux
HSTCP STCP
Steady throughput
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FAST Linux
throughput
loss
queue
STCPHSTCP
30min
Room for mice !
HSTCP
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Aggregate throughput
small window800pkts
largewindow
8000
Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts
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Fairness
Jain’s index
HST
CP ~
Ren
oDummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts
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Stability
Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts
stable indiverse
scenarios
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Open issues
network latency estimation route changes, dynamic sharing does not upset stability
small network buffer at least like TCP adapt on slow timescale, but how?
TCP-friendliness friendly at least at small window tunable, but how to tune?
reverse path congestion
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What can FAST do?
Networks that support large windows Long latency High bandwidth
Networks experience moderate packet losses
HTTP traffic Low-bandwidth networks and LANs
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Acknowledgments Caltech
Bunn, Choe, Doyle, Newman, Ravot, Singh, J. Wang UCLA
Paganini, Z. Wang CERN
Martin SLAC
Cottrell Internet2
Almes, Shalunov Cisco
Aiken, Doraiswami, Yip Level(3)
Fernes LANL
Wu