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