Advanced Computer Networks 1

Providing Guaranteed Services Without Per Flow Management

By: Ion Stoica, Hui Zhang

Presented by: Sanjeev R. Kulkarni

Advanced Computer Networks 2

Outline

• Problems with the current QoS architectures

• Stateless Core Architecture(SCORE)– Dynamic Packet State– Core Jitter Virtual Clock Algorithm– Admission Control

• Implementation details

• Extensions to IPv6

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Current QoS architectures

• Integrated Services

• Differentiated Services

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Integrated Services

• All Routers maintain per-flow state

• State– Control Plane

• Admission Control: per flow signaling

– Data Plane• Classifier: per flow flow-ids

• scheduler: per flow scheduling algorithm parameters

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Integrated Services

• All Routers maintain per-flow state

• State– Control Plane

• Admission Control: per flow signaling

– Data Plane• Classifier: per flow flow-ids

• scheduler: per flow scheduling algorithm parameters

• Scalability??

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Jitter Virtual Clock

• For each packet– eligible time – deadline

• Scheduling done in the order of the deadline

– e1i,j = a1

i,j

– eki,j = max ( ak

i,j + gki,j-1, dk-1

i,j)

– dki,j = ek

i,j + lki/ri

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Core-routers and Edge routers

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Differentiated Services

• A small number of traffic classes

• Only Edge routers maintain per flow state

• Control Plane• Admission Control: per flow signaling

• Data Plane• Classifier: per class classification

• Scheduler: per class scheduling

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Differentiated Services

• A small number of traffic classes

• Only Edge routers maintain per flow state

• Control Plane• Admission Control: per flow signaling

• Data Plane• Classifier: per class classification

• Scheduler: per class scheduling

• Quality of QoS??

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Stateless Core Solution

• Idea similar to DiffServ

• Only Edge Routers maintain per flow state

• Dynamic Packet State (DPS) is inserted into each packet by edge routers

• Core routers update DPS and schedule packets accordingly

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DPS

Ingress

Egress

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How it works

a

b

c

d

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How it works

a

b

c

d

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How it works

a

b

c

d

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How it works

a

b

c

d

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How it works

a

b

c

d

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How it works

a

b

c

d

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How it differs from DiffServ

• DPS versus Per Hop Behavior (PHB)– DPS is dynamic– Routers change DPS and schedule packets

based on the DPS state– DPS change mirrors a Core-Jitter Virtual Clock

scheduling

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Core Jitter Virtual Clock

– eki,j = max ( ak

i,j + gki,j-1, dk-1

i,j)

• The main culprit is dk-1i,j

• Introduce a slack variable such that – ak

i,j + gki,j-1 + > dk-1

i,j

ik =max (0, i

k-1 + (lik-1 - li

k)/ri - (ei,1

k - ei,1k-1 - li

k-1/ri)/(h-1) )

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Example

a

b

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Example

a

b

ea1 da

1

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Example

a

b

ga1

ea1 da

1

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Example

a

b eb1 db

1

ea1 da

1

ga1

ga1

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Example

a

b

ea1 da

1

eb1 db

1

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Example

a

b

ea1 ea

2

eb1 db

1

da2

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Example

a

b

ea2

eb1 db

1

da2

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Example

a

b

ea2

eb1

db1

da2

ga1

gb1

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The algorithm

• Parameter Initialization by Ingress Routers

• Core routers examine the parameters and modify g

• Egress Routers strip the packet of these labels

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Admission Control

s r

d

cb

a

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Admission ControlResv

s r

d

cb

a

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Admission Control

1

s r

d

cb

a

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Admission Control

s r

d

cb

a

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Admission Control

s r

d

cb

a

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Admission Control

s r

d

cb

a

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Admission Control

3

s r

d

cb

a

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Admission Control

Resvs r

d

cb

a

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Admission Control

• Each core router maintains an upper bound R on the Total Bandwidth reserved

• Local Admission Control– Accept if R + ri < C

• Periodically they run an algorithm that contains the deviation between the actual B/w reserved and R.

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Recalibration Algorithm

• Packet state b

• Add all b values on each packet arrival

• Periodically they update based on

R = min ( R, RD/(1-f) + Rnew )

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Implementation

0 31157

18

IPv4 Header TOS11

Frag Offset

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Implementation

0 31157

18

11

F1 F2 F3Flag

2 5 9 16

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Extension to Ipv60 7 11

F1 F2 F3Flag

31

Flow Label

2 6 11 19

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Summary

• SCORE Network – Is Scalable– Gives a QoS similar to Jitter Virtual Clock– Extensible to Ipv6– Transparent to the outside network