a test-bed investigation of qos mechanisms for supporting slas in ipv6 vasilios a. siris and...

A test-bed investigation of QoS mechanisms for

supporting SLAs in IPv6Vasilios A. Siris and Georgios

Fotiadis

University of Crete and FORTHHeraklion, Crete, Greece

[email protected] in part by GRNET, through subcontract in 6NET (IST-2001-32603)

Objectives and motivation Investigate operation and interaction of

QoS mechanisms in IPv6 networks Policing, shaping, queuing

These mechanisms will be used in customer-provider interface

Tuning is important for supporting Service Level Agreements (SLAs) Tuning each in isolation not sufficient

Do they have different performance in IPv6 compared to IPv4?

User-network interface

shaping, class-based queuing

policing class-based queuing

traffic flow

User/customer Provider

QoS mechanisms investigated Cisco Traffic Policing

Committed Access Rate – CAR not supported in IPv6

Cisco Generic Traffic Shaping - GTS Linux Traffic Policing Linux Traffic Shaping

Token Bucket Filter – TBF Linux Class Based Queuing - CBQ

Token bucket algorithm True token bucket (r,b) Shaping includes a buffer

Arriving packet:length L

Token bucket depth: bx

xL?

No, packet isnonconforming

Yes, x=x-L

Token rate r

Implementation differs Mean rate or Committed Information Rate (CIR) Committed Burst Size (Bc) Time interval (=Bc/CIR)

IPv6 test-bed

shaping, class-based queueing

policing

Linux-based router or Cisco 7100/7200

class-based queueing

traffic flow

100 Mbps

RedHat Linux 9.0

RedHat Linux 9.0

TCP traffic generated with Iperf 1.7.0 for Linux RTT < 4 ms

Policing tests topology

policing


TCP traffic

For fixed policing rate, measure aggregate throughput for different burst sizes

Variable policing rates (1/3)

Only Policing (Router),Variable Policing Rate,1 Connection - 3 Flows

0

5

10

15

20

25

30

35

40

45

50

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8

Burst Size (Bc) - Mbits

Ag

g. T

hro

ug

hp

ut

- M

bp

s

10 Mbps

20 Mbps

30 Mbps

40 Mbps

50 Mbps

70 Mbps

Burst size, Bc (Mbits)

Ag

gre

gate

Th

rou

gh

pu

t (M

bp

s)


Aggregate throughput increases with burst size, but is always < policing rate

For higher rates throughput is proportionally smaller Rate = 10 Mbps -> Throughput = 9.7 Rate = 70 Mbps -> Throughput = 46

Experiments for both Cisco & Linux routers gave identical results


Throughput versus burst size exhibits a “knee” at Bc*, which is approximately: If Rate < 40Mbps,

Bc* = 0.6 Mbit + 0.03sec*Rate If Rate > 40Mbps,

Bc* = 1.5 Mbit + 0.01sec*Rate Burst Size > RTT*Rate not sufficient!

Variable number of flows (1/2)

Only Policing (Router),Variable Number of Flows,

Policing Rate = 50Mbps

0

5

10

15

20

25

30

35

40

45

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2


Ag

g. T

hro

ug

hp

ut

- M

bp

s

1 Flow

3 Flows

5 Flows

10 Flows


Ag

gre

gate

Th

rou

gh

pu

t (M

bp

s)

Variable number of flows (2/2)

Optimum burst size (“knee” value) is independent of the number of flows

Aggregate throughput increases with number of flows (multiplexing)

Similar results for Cisco & Linux routers

Interaction of policing & shaping

shaping policing


TCP traffic

For fixed rate & burst size of policer and rate of shaper, measure aggregate throughput for different burst sizes of shaper

Throughput vs. burst size (1/4)

Interaction of Policing and Shaping,Variable Number of Flows,

Shaping (Router1): Rate = 50Mpbs, Buffer Limit = 1000pkts,Policing (Router2): Rate = 50Mbps, Bc = 2Mbits.

0

5

10

15

20

25

30

35

40

45

50

0 0.2

0.4

0.6

0.8

1 1.2

1.4

1.6

1.8

2 2.2

2.4

2.6

2.8

3 3.2

3.4

3.6

3.8

4 4.2

4.4

4.6

4.8

5 5.2


Ag

g. T

hro

ug

hp

ut

- M

bp

s

1 Flow

3 Flows

5 Flows

10 Flows

No Shaping (1 Flow)

No Shaping (3 Flows)




Ag

gre

gate

Th

rou

gh

pu

t (M

bp

s)

Shaping at LinuxPolicing at Cisco


Appropriate shaper burst size can lead to significant throughput increase Throughput is always higher with shaping Setting burst size of shaper = burst size of

policer not always optimal Low throughput for very small burst sizes

Due to overflow at shaper’s queue But also, very large burst size gives low

throughput Very large burst sizes allow large bursts

which lead to multiple drops at the policer


For larger # of flows there is larger range of burst sizes that achieve maximum throughput




0

10

20

30

40

50

60

0 0.2

0.4

0.6

0.8

1 1.2

1.4

1.6

1.8

2 2.2

2.4

2.6

2.8

3 3.2

3.4

3.6

3.8

4 4.2

4.4

4.6

4.8

5 5.2


Ag

g. T

hro

ug

hp

ut

- M

bp

s

1 Flow

3 Flows

5 Flows

10 Flows

No Shaping (1 Flow)




Shaping at LinuxPolicing at Linux


Ag

gre

gate

Th

rou

gh

pu

t (M

bp

s)

No qualitative difference when using two Linux or Linux & Cisco routers

Throughput vs. shaping rate (1/2)


Shaping (Router1): Bc = 2Mbits, Buffer Limit = 1000pkts,Policing (Router2): Rate = 50Mbps, Bc = 2Mbits.

0

5

10

15

20

25

30

35

40

45

50

44 46 48 50 52 54 56 58 60 62

Shaping Rate - Mbps

Ag

g.

Th

rou

gh

pu

t -

Mb

ps

1 Flow

3 Flows

5 Flows

No Shaping (1 Flow)



Shaping Rate (Mbps)

Ag

gre

gate

Th

rou

gh

pu

t (M

bp

s)

Shaping at LinuxPolicing at CiscoPolicing rate

Throughput vs. shaping rate (2/2)

Throughput maximum for shaping rate a little higher than policing rate

Very high shaping rates leads to throughput degradation, due to bursts that are allowed by the shaper

Delay jitter tests (1/3)

Policing/Shaping tests showed there is a range of shaper burst sizes for which throughput is maximized

Which burst size is best?

Answer: consider delay

Delay jitter tests (2/3)Interaction of Policing and Shaping,


0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2


Ave

rag

e Ji

tter

- m

s

1 Flow

Burst Size, Bc (Mbit)

Ag

gre

gate

Th

rou

gh

pu

t (M

bp

s)

Delay jitter tests (3/3)

Jitter decreases when burst size increases

Optimal burst size is one for which delay jitter is smallest, but is in the range of values that maximize throughput

Interaction of Policing and Class Base Queuing

class-based queuing

policing


TCP traffic

For fixed rate & burst size of policer and rate of CBQ, measure aggregate throughput for different maxburst values

Variable maxburst at CBQ (1/2)

Interaction of CBQ and Policing,CBQ (Router1): Rate = 50Mpbs

Policing (Router2): Rate = 50Mbps, Bc = 2Mbits,

0

10

20

30

40

50

60

0 50 100 150 200 250

Maxburst - packets

Th

rou

gh

pu

t -

Mb

ps

5 Flows

maxburst (packets)

Ag

gre

gate

Th

rou

gh

pu

t (M

bp

s)

CBQ at LinuxPolicing at Cisco

Variable maxburst at CBQ (2/2)

Maximum throughput achieved with appropriate maxburst value

Low throughput for small maxburst Large maxburst values do not

result in throughput degradation maxburst has different effect than

burst size in shaping CBQ performs traffic smoothing

Conclusions and outlook Interaction of QoS mechanisms is

important for effectively supporting SLAs In the presence of policing, shaping can

increase aggregate throughput Must appropriately set shaping parameters

Tuning of parameters should consider throughput & delay

Similar behavior with Cisco/Linux, IPv6/IPv4

Further research directions: Experiments in wide area (larger RTT) Experiments in wireless networks

A test-bed investigation of QoS mechanisms for

supporting SLAs in IPv6Vasilios A. Siris and Georgios

Fotiadis

University of Crete and FORTHHeraklion, Crete, Greece

[email protected] in part by GRNET, through subcontract in 6NET (IST-2001-32603)

a test-bed investigation of qos mechanisms for supporting slas in ipv6 vasilios a. siris and...

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