Performance of TCP/IP with MEDF Scheduling€¦ · Iub TNL P(W>t) Waiting Time (W) ... Level of...

University of WürzburgDept. of Distributed SystemsProf. Dr. P. Tran-Gia

Performance of TCP/IP with MEDF Scheduling

4. Würzburger Workshop “IP Netzmanagement, IP Netzplanung und Optimierung”

Rüdiger Martin, Michael Menth, Vu Phan-GiaUniversity of Würzburg, Germany

[martin|menth|phan]@informatik.uni-wuerzburg.de

University of WürzburgDistributed Systems

Rüdiger Martin


Motivation

> Best effort traffic only in today’s InternetNo prioritization

> Static Priority (SP) for high priority Transport Service Class (TSC)Starvation of low priority traffic

> Differentiated Services Architecture (DiffServ) implements appropriate per hop behavior to differentiate between TSCs

Common recommendations:– Weighted Round Robin (WRR)– Deficit Round Robin (DRR)– …

Fixed share of bandwidth for different TSCs


Rüdiger Martin


Motivation

Anticipated traffic mix:

TCP trafficsources TSChigh

TCP trafficsources TSClow

Destinations TSChigh

DestinationsTSClow

TSChigh

1

TSClow

3

:

Fixed bandwidth share TSChigh:TSClow = 2:3 (class based)

Bandwidth per flow TSChigh:TSClow 2:1


Rüdiger Martin


Motivation

Current traffic mix:

TSChigh

2

Fixed bandwidth share TSChigh:TSClow = 2:3 (class based)

Bandwidth per flow TSChigh:TSClow 1:1



: TCP trafficsources TSClow

DestinationsTSClowTSClow

3


Rüdiger Martin


Motivation

> Problem:Conventional scheduling algorithms:

– No priority– Starvation of low priority flows– Fixed bandwidth shares

Knowledge of traffic mix required to provision adequate Quality of Service

Is there a way to introduce traffic-mix-independentper-flow-prioritization?


Rüdiger Martin


Modified Earliest Deadline First (MEDF)

> MEDF descriptionOne queue per TSCPackets equipped with a time stamp

– Deadline=ArrivalTime+MTSC– Delay advantage: Mhigh=0, Mlow >0,

Scheduling decision– Take packet with the earliest deadline among all queues

> Difference to EDFSimple implementation, no searching / sorting required

Scheduling

TSChigh

TSClow


Rüdiger Martin


Modified Earliest Deadline First

4

1

6

2

Packet No.Arrival Time

Mhigh = 0, Mlow = 1

TSClowPackets

TSChighPackets

5

2

6

2

4

1

3

1

1

0

0

0

2

11

1 2

2

1

01

4

1

3

12

2

MEDF6

2

5

2

2

1

3

2

4

2

0

1

1

1

Packet No.Modified Deadline

0 1 2 3 4 5 6 Time Slot

ME

DF

Packet No.Arrival Time

20 1 Time Slot


Rüdiger Martin


MEDF: Service Differentiation in the UTRAN

> UMTS Terrestrial Access Network (UTRAN)

PSTN

Iur

Core Network

Internet

UE

RNC RNC

UMSC

NodeB

SGSN

NodeB NodeB NodeB NodeB NodeB

Iub

IubRNC

NodeB

Rural coverage: using leased lines causes extensive operating

costs.Optimization required!


Rüdiger Martin


Model of the Transport Network Layer (TNL)

Speech64 Kbit/s CSD

64 Kbit/s PSD

Stringent TSCS

cheduling

Tolerant TSC

Segm

entation

RNC NodeB

Iub

TNLP(W>t)

Waiting Time (W)Delay Budget (DB)

p

P(W>DB) ≤ p!

ptolerant = 10-2

pstringent = 10-4

QoS Requirements


Rüdiger Martin


Performance of MEDF Scheduling in the UTRAN

0,55

0,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

5:0 4:1 3:2 2:3 1:4 0:5

Traffic Mix Ratio CSD:PSD

Max

imum

Lin

k U

tiliz

atio

n

SP

FIFO

MEDF, Mtolerant =0.75 DB

0,55

0,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

5:0 4:1 3:2 2:3 1:4 0:5


Max

imum

Lin

k U

tiliz

atio

n

SP

FIFO


0,55

0,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

5:0 4:1 3:2 2:3 1:4 0:5


Max

imum

Lin

k U

tiliz

atio

n

SP

FIFO


0,55

0,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

5:0 4:1 3:2 2:3 1:4 0:5


Max

imum

Lin

k U

tiliz

atio

n

SP

FIFO


WRR(4:1)

Up to 10% more utilization

by MEDF

SP: Static PriorityFIFO: First-In First-OutWRR(n:m): Weighted Round Robin with Weights (n:m)


Rüdiger Martin


Motivation

> Features of MEDF (verified for the UTRAN application)

Best performanceDegree of prioritization of stringent TSC over tolerant TSC on the packet level

independent of the current traffic mix

Can MEDF be used to introduce traffic-mix-independent per-flow-prioritization?


Rüdiger Martin


MEDF: Single Link Simulation Environment

> TCP adapts its rate to Packet loss ploss ( space priority)Round Trip Time RTT ( time priority MEDF)

> Network Simulator 2

> Classical dumbell topology to isolate MEDF characteristics




DestinationsTSClow


Rüdiger Martin


MEDF Analysis: Traffic Mix

1

1,5

2

2,5

3

3,5

4

4,5

0 64 128 192 256

Nor

mal

ized

Ban

dwid

th R

atio

(TS

Chi

gh:n

high

)(TS

Clo

w:n

low)

Number of Users

nhigh:nlow = 1:3

nhigh:nlow = 1:1

nhigh:nlow = 3:1

Mlow = 0.5s

)erFlow(TSCBandwidthP)erFlow(TSCBandwidthP

RatioBandwidth Normalized

low

high=

=

Number of users

=Level of network congestion

^

Slight differences due to influence of buffer space:

full buffer sharing

MEDF offers traffic-mix-independent per-flow-prioritization


Rüdiger Martin


MEDF Analysis: Mlow parameter

0

2

4

6

8

10

12

14

128 640 1152 1664 2176

Ban

dwid

th R

atio

TS

Chi

gh: T

SC

low

Bandwidth [Kbit/s]

Mlow = 0 = FIFO^Mlow = 0.1s

Mlow = 0.5s

Mlow = 1.0s

Mlow = 1.5s

Sufficient capacity available

Increase due to -Less competition for resources-Decreasing RTT Mlow relatively larger


Rüdiger Martin


MEDF: Multi-Link Simulation Environment

Cross Traffic

Router A Router B

Router C

Router D

BW BW’ = 2*BW

BW




DestinationsTSClow

TCP cross trafficsources TSChigh

TCP cross trafficsources TSClow

Destinations crosstraffic TSChigh

Destinations crosstraffic TSClow


Rüdiger Martin


MEDF Analysis: Multiple Links

05

101520253035404550

0 64 128 192 256

Ban

dwid

th R

atio

TS

Chi

gh: T

SC

low

Number of Users

Mlow = 1.0s

3 links

2 links

1 link

Relative delay advantage increases with the number of links


Rüdiger Martin





DestinationsTSClow


Rüdiger Martin


MEDF Analysis: Buffer Space Priority

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0 64 128 192 256

FIFO full sharing

FIFO space priority

Mlow = 0.5s space priority

Mlow = 0.5s full sharing

Ban

dwid

th R

atio

TS

Chi

gh: T

SC

low

Number of Users

Space priority slightly prefers TSChigh

Space priority prohibits the typical decrease of

the bandwidth ratio


Rüdiger Martin


Summary

> Problem

Conventional scheduling disciplines:– No prioritization or starvation or fixed bandwidth shares per

TSC or– traffic mix required for adequate QoS provisioning (not

available)

> Solution

MEDF – traffic-mix-independent per-flow-prioritization in TCP/IP

networks– Single parameter: delay advantage Mlow


Rüdiger Martin


Conclusion

> Results

Effective prioritization of TCP trafficImpact of delay advantage Mlow

Comparison with buffer management strategies

> MEDF

Simple and parameterizable prioritization in TCP/IP networks without starvationApplication in Differentiated Services network


Rüdiger Martin


Q&A

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Performance of TCP/IP with MEDF Scheduling€¦ · Iub TNL P(W>t) Waiting Time (W) ... Level of...

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