Advanced Computer Networks 1
Providing Guaranteed Services Without Per Flow Management
By: Ion Stoica, Hui Zhang
Presented by: Sanjeev R. Kulkarni
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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
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b
c
d
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How it works
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b
c
d
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How it works
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b
c
d
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How it works
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b
c
d
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How it works
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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
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b
ea1 da
1
eb1 db
1
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Example
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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