BIC Control for Fast Long-Distance Networks

paper written byInjong Rhee, Lisong Xu & Khaled Harfoush (2004)

Presented by Jonathan di Costanzo (2009/02/18)

Outline

Motivation

◦Origin of the problem ◦Response Function of TCP

Existing protocolsBIC-TCPConclusion

2/23

Origin of the problem – TCP strenghExtremely reliable (ACK notification)Many high-speed networks (>10Gbps)90% of datatransmission

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NLSURFnet

GENEVA

UKSuperJANET4

ABILENE

ESNET

CALREN

ItGARR-B

GEANT

NewYork

FrRenater

STAR-TAP

STARLIGHT

Origin of the problem – TCP Weakness

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The instantaneous throughput of TCP is controlled by a variable cwnd,

TCP transmits approximately a cwnd number of packets per RTT (Round-Trip Time).

Time (RTT)Slow start Congestion avoidance

Packet loss Packet loss Packet losscwnd

Packet loss TCP

cwnd = cwnd + 1 cwnd = cwnd * (1-1/2)

5

Origin of the problem – TCP Weakness

Packet loss

Time (RTT)Congestion avoidance

Packet loss Packet losscwnd

Slow start

Packet loss

A TCP connection with 1250-Byte packet size and 100ms RTT is running over a 10Gbps link (assuming no other connections, and no buffers at routers)

100,000 10Gbps

50,000 5Gbps

1.4 hours 1.4 hours 1.4 hours

TCP

bigdecrease

slowincrease

Response Function

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Response function of TCP is the average throughput of a TCP connection in terms of the packet loss probability, the packet size, and the round-trip time.

5.02.1

pRTTMSSR

R : Average Throughput MSS: Packet Size RTT: Round-Trip Time P : Packet Loss Probability

Response Function of TCP is :

Response Function

7

1,0E+01

1,0E+02

1,0E+03

1,0E+04

1,0E+05

1,0E+06

1,0E-10 1,0E-09 1,0E-08 1,0E-07 1,0E-06 1,0E-05 1,0E-04 1,0E-03 1,0E-02Packet Loss Probability

Thro

ughp

ut (M

bps)

TCP

10Gbps requires a packet loss rate of 10-10, or correspondingly a link bit error rate of at most 10-10,

Assuming 1250-Byte packet size, and 100ms RTT

Outline

Motivation

Existing protocols

◦AIMD◦HSTCP◦STCP

BIC-TCPConclusion

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High-Speed Protocols

A new protocol is needed◦More aggressive about increasing transmission

speeds (scalability)◦Able to work simultaneously with TCP

Advanced TCP◦AIMD (Additive Increase Multiplicative Decrease)◦HSTCP (High-Speed TCP)◦STCP (Scalable TCP)

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10

AIMD AIMD increases cwnd by a larger number, say 32, instead of 1 per RTT. After a packet loss, AIMD decreases cwnd by 1/8, instead of 1/2

Packet loss

Time (RTT)Slow start Congestion avoidance

Packet loss Packet losscwnd

Packet loss

cwnd = cwnd + 1

cwnd = cwnd + 32

cwnd = cwnd * (1-1/2)

cwnd = cwnd * (1-1/8)

TCP

11

AIMD – Response Function

1,0E+01

1,0E+02

1,0E+03

1,0E+04

1,0E+05

1,0E+06

1,0E-07 1,0E-06 1,0E-05 1,0E-04 1,0E-03 1,0E-02

Packet Loss Probability

Thro

ughp

ut (M

bps)

TCP

AIMD5.02.1

pRTTMSSR TCP:

5.05.15

pRTTMSSR AIMD:

The throughput of AIMD is always about 13 times larger than that of TCP

12

AIMD – Response Function

1,0E+01

1,0E+02

1,0E+03

1,0E+04

1,0E+05

1,0E+06

1,0E-07 1,0E-06 1,0E-05 1,0E-04 1,0E-03 1,0E-02

Packet Loss Probability

Thro

ughp

ut (M

bps)

TCP

AIMD

Bandwidth Scalable Bandwidth Scalability

The ability to achieve 10Gbps with a reasonable packet loss probability NOT TCP

Friendly TCP-Friendliness

The ability to share bandwidth with TCP connections on low-speed networks

STCP & HSTCP – RTT unfairness RTT unfairness between 2 flows Numerical definition :

= ratio between the average throughputs

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14

STCP STCP adaptively increases cwnd, and decreases cwnd by 1/8.

Packet loss

Time (RTT)Slow start Congestion avoidance

Packet loss Packet losscwnd

Packet loss

cwnd = cwnd + 1

cwnd = cwnd + 0.01*cwndcwnd = cwnd * (1-1/2)

cwnd = cwnd * (1-1/8)

TCP

15

HSTCP HSTCP adaptively increases cwnd, and adaptively decreases cwnd. The larger the cwnd, the larger the increment, and the smaller the

decrement.

Packet loss

Time (RTT)Slow start Congestion avoidance

Packet loss Packet losscwnd

Packet loss

cwnd = cwnd * (1-1/2)

cwnd = cwnd * (1-dec(cwnd))

cwnd = cwnd + 1

cwnd = cwnd + inc(cwnd)TCP

16

STCP & HSTCP – Response Functions

1,0E+01

1,0E+02

1,0E+03

1,0E+04

1,0E+05

1,0E+06

1,0E-07 1,0E-06 1,0E-05 1,0E-04 1,0E-03 1,0E-02

Packet Loss Probability

Thro

ughp

ut (M

bps)

TCP

AIMD

HSTCP

STCP

835.012.0

pRTTMSSR HSTCP:

pRTTMSSR 08.0

STCP:

Bandwidth Scalable

TCP Friendly

HSTCP and STCP are both bandwidth scalable and TCP friendly

Outline

MotivationExisting protocols

BIC-TCP◦RTT fairness◦Protocol design◦Binary increase search◦Response Function / RTT fairness

Conclusion17/23

18

RTT fairness

◦Differents session different RTT We want a fair bandwidth allocation

◦RTT fairness index = throughout ratio of two flows with ≠ RTTs

19

RTT fairness

dpc

RTTMSSR

For a protocol with the following response function, where c and d are protocol-related constants.

1

2

RTTRTT

The RTT Fairness Index (or the throughput ratio of two flows) networks is

For low-speed networks

d

RTTRTT

11

1

2For high-speed networks

◦Low speed networks same RTT fairness◦High speed networks same RTT fairness

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RTT fairnessGeneral response function

◦ RTT fairness dpc

RTTMSSpR )(

d

RTTRTT

11

1

2

1,E+01

1,E+02

1,E+03

1,E+04

1,E+05

1,E+06

1,E-07 1,E-06 1,E-05 1,E-04 1,E-03 1,E-02

Packet Loss Probability

Pack

ets/

RTT

TCP

AIMD

HSTCP

STCP

2

1

2:

RTTRTTAIMD

56,5

1

2:

RTTRTTHSTCP

1

2:RTTRTTSTCP

21

RTT fairness Throughout ratio of two flows on a 2.5Gbps Link Throughout ratio of two flows on a 2.5Gbps Link

When the network capacity increases, the RTT fairness become worse

Inverse RTT Ratio 1 3 6

AIMD 1.11 6.68 22.03

HSTCP 1.01 29.19 107.90

STCP 1.01 127.23 389.13

64.9719.050.95

best

worse

STCP & HSTCP – RTT unfairness

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80ms

160ms

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Protocol Design

1,0E+01

1,0E+02

1,0E+03

1,0E+04

1,0E+05

1,0E+06

1,0E-07 1,0E-06 1,0E-05 1,0E-04 1,0E-03 1,0E-02

Packet Loss Probability

Thro

ughp

ut (M

bps)

TCPAIMDHSTCPSTCPBIC

TCP Fairness

Scalability, RTT Fairness

24

BIC adaptively increase cwnd, and decrease cwnd by 1/8

Packet loss

Time (RTT)Slow start Congestion avoidance

Packet loss Packet losscwnd

Packet loss

cwnd = cwnd + 1

cwnd = cwnd + f(cwnd, history)

cwnd = cwnd * (1-1/2)

cwnd = cwnd * (1-1/8)

TCP

25

Binary increase search◦The problem is to know how to adjust the cwnd

Throughput (cwnd/RTT) vs. Available bandwidth

◦Linear search ?

0

32

64

96

128

160

192

224

256

0 50 100 150 200 250Time (RTT)

cwnd

Linear Search

Available Bandwidth

26

Binary increase search◦The problem is to know how to adjust the cwnd

Throughput (cwnd/RTT) vs. Available bandwidth

◦Binary search ?

0

32

64

96

128

160

192

224

256

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (RTT)

cwnd

Linear Search

Binary Search with Smax and Smin

Smin

Smax

Wmax

Wmin

inc = (Wmin+Wmax)/2 – cwndSmin > inc > Smaxcwnd = cwnd + inc

Binary increase search

27

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Response Function

1,E+01

1,E+02

1,E+03

1,E+04

1,E+05

1,E+06

1,E-07 1,E-06 1,E-05 1,E-04 1,E-03 1,E-02

Packet Loss Probability

Pack

ets/

RTT

TCPAIMDHSTCPSTCPBIC

Bandwidth scalability

RTT Fairness

TCP-Friendliness

29

RTT fairness

Inverse RTT Ratio 1 3 6

BIC 1 12 38

AIMD 1 6 22

HSTCP 1 29 107

STCP 1 127 389

Throughput ratio of two flows with different RTTs on a 2.5Gbps link

Outline

MotivationExisting protocolsBIC-TCP

Conclusion

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31

ConclusionQuick summary

AIMD HSTCP STCP BIC

Scalability TCP-Friendliness RTT Fairness

32

Conclusion• Further works : CUBIC

32

0

64

128

192

256

320

384

448

512

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time (RTT)

cwnd

3max KtCWCwnd

Any questions ?

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