In-Market Experiments: The Science of Placing Small Bets Fast
FAST TCP: design and experiments
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Transcript of FAST TCP: design and experiments
Cheng Jin David Wei Steven Low
http://netlab.caltech.edu
FAST TCP:design and experiments
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
Packet & flow level
ACK: W W + 1/W
Loss: W W – 0.5W
Packet level
Reno TCP
Flow level
Equilibrium
Dynamics
packets
(Mathis formula)
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.
Problem: binary signal
TCP
oscillation
Solution: multibit signal
FAST
stabilized
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)
Solution: estimate target FAST
Slow Start
FAST Conv
Equil
Loss Rec
Scalable to any w*
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
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
Architecture
~ RTT timescaleAck timescale
~ Ack timescale
DataControl
WindowControl
Burstiness Control
Estimation
TCP Protocol Processing
Architecture
Each component designed independently upgraded asynchronously
DataControl
WindowControl
Burstiness Control
Estimation
TCP Protocol Processing
Dynamic sharing: 3 flowsFAST Linux
HSTCP STCP
Steady throughput
FAST Linux
throughput
loss
queue
STCPHSTCP
30min
Room for mice !
HSTCP
Aggregate throughput
small window800pkts
largewindow
8000
Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts
Fairness
Jain’s index
HST
CP ~
Ren
oDummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts
Stability
Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts
stable indiverse
scenarios
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
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
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