1

On Maximum Rate Control of Weighted Fair Scheduling

Jeng Farn Lee

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Outline Introduction Related Work WF2Q with maximum rate control Simulations Conclusions

3

Introduction Current service disciplines provided

minimum performance guarantees, but not maximum rate constraint

Max-Rate Control is needed Control lease line’s maximum services rate Restrict specific applications’ total traffics to

enforce some management policies

4

Introduction (cont’d) Ban over-provisioning in a link-sharing

environment (e.g. WF2Q) Stabilize the throughput to smooth media

streaming in order not to overflow receiving buffers or cause packet drop

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GPS GPS (Generalized Processor Sharing)

A fluid system traffic is infinitely divisible all the traffic streams can receive service

simultaneously Each session i is assigned a fixed real-valued

positive parameter i

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GPS (cont’d)

session is idle after time 10

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Virtual Clock Implementation of PGPS Virtual clock is a clock to keep a

normalized time as a standard reference for all sessions/packets.

jBii

jj tVtV

V

)()(

0)0(

11

8

Two-Stage Rate-Control Service Model

Regulator 1

Regulator 2

Regulator N

one regulator for each ofthe N sessions

Rate Controller

Regulated Traffic

Output

Scheduler

Iutput

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Two-Stage Rate-Control Service Model (cont’d)

Drawbacks When move packets from regulator queue to eligible

queue Timer

the system must use one interrupt to change the status per packet Time-framing (system accuracy v.s. time granularity) Event-Driven (high uncertainty)

It still needs to modify the scheduling algorithm to distribute the excess bandwidth to other sessions

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Policer-Based Rate-Control Service Model

Scheduler

OutputPolicer

conformingpackets

Input

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Policer-Based Rate-Control Service Model (cont’d) Drawbacks

Token bucket Token buffer allows traffic exceed the maximum

rate Leaky bucket

Not allow traffic burst

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Simulation environment ns2

Version : ns-allinone2.1b6 WFQ patch 1.1a1 We implement of policer-based rate-control

service model and WF2Q-M topology n1 n2 R1S1

10Mbps,2ms

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Traffic pattern UDP Exponential ON/OFF traffic The packet size of ON period : exponential

distribution with mean (1000, 950 and 900 bytes) The maximum rate of the session is 4Mbps

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Traffic pattern

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70

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Token bucket with r = 4Mbps, B=0.25Mb

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70

Loss rate : 0.211%Over max rate rate : 12.96%

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Leaky bucket r=4Mbps

0

0.5

1

1.5

2

0 10 20 30 40 50 60 70

Loss rate : 58.89%

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Wf2q-m buffer size 0.25Mb

00.5

11.5

22.5

33.5

44.5

0 10 20 30 40 50 60 70

Loss rate : 0.219%

18

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GPS-M An extension of GPS A session can be “normal” session or “maximum

rate constrained” session. If a maximum rate constrained has shared bandwidth greater than the maximum rate, It receives the maximum rate; GPS-M distributes the excess bandwidth to others

weightily WF2Q-M use the same link sharing principle as

GPS-M

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GPS-MResource Allocation

ex. 10 packets per second, reserved bandwidth 5:2.5:1.25:1.25

GPS and GPS-M52.5

1.251.25

GPS

52.52.5

GPS-M

433

Max Rate=4

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Features of WF2Q-M Merge packet eligible time into virtual starting

time Only the packets have started receiving service in

GPS-M can be selected for transmission Adjust the ticking rate of the system virtual clock

to distribute the excess bandwidth from saturated queues to other sessions

Use the same real clock/virtual clock ratio to transfer real clock for packets of saturated queues to virtual clock

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Virtual Clock Adjustment

)(

)()(

0)0(

tratiotVtV

V

)()(

)(

)()( *

*

Bj

Bkk

Bjj

Bkk

Bjj

j

p

p

PC

C

ratio(t)=

23

Marge eligible time into virtual starting time

The virtual starting and finishing times of packets of Bp(p)

)(/

}}),(max{

),max(

1

11

tratioPL

SF

FeVS

PLeae

i

kik

ik

i

ki

ki

ki

i

kik

iki

ki

)(/

}),(max{ 1

tratioPL

SF

FaVS

i

kik

ik

i

ki

ki

ki

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WF2Q-M: Virtual Times

CL

S

FaV

others

tratioPL

S

FaV

i

kik

i

ki

ki

i

kik

i

ki

ki

*F

}),(max{S

)(/F

}),(max{S

(p)Bfor

ki

1ki

ki

1ki

p

25

Simulationsns2

Version : ns-allinone2.1b6 WFQ patch 1.1a1 WF2Q and WF2Q-M

topologyn1 n2 n3 n4

S1

S2

S3

S4

R1

R3

R2

R4

10Mbps,2ms10Mbps,

2ms

10Mbps,2ms

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Simulations (cont’d) Data sending rate : 5Mbps

Packet size : Uniform(100,1500) bytes Data type : UDP Maximum rate of session 3 is 3Mbps

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Simulation Result (WF2Q)

time (sec)

0 2 4 6 8 10 12 14

thro

ughp

ut (M

bps)

0

1

2

3

4

5

6

S1 reserved bandwidth 10%S2 reserved bandwidth 15%S3 reserved bandwidth 25%S4 reserved bandwidth 50%

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Simulation Result (WF2Q-M)

time (sec)

0 2 4 6 8 10 12 14

Thro

ughp

ut (M

bps)

0

1

2

3

4

5

6

S1 reserved bandwidth 10%S2 reserved bandwidth 15%S3 reserved bandwidth 25%S4 reserved bandwidth 50%

Maximum rate is 3Mbps

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Conclusions we propose a new service discipline WF2Q-M

guarantee minimum service rates as WF2Q provide maximum service rate constraint merge packet eligible time into its virtual starting time

to reduce complexity virtual clock adjustment allows the sharing of excess

bandwidth to non saturated sessions WF2Q-M performance is bounded by a fluid reference

mode

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Thank You!

Jeng Farn Leekunimi@iis.sinica.edu.tw