on the necessity of time-based updates in sdn
TRANSCRIPT
On the Necessity of Time-based Updates in SDN
Tal Mizrahi, Yoram Moses Technion – Israel Institute of Technology
Open Networking Summit (ONS)
March 2014
Accurate Time in Distributed Applications
• Mobile backhaul
• Power substations
• Industrial automation
• Automotive networks
• Audio/video bridging
• High frequency trading
• Google’s ‘Spanner’
• … On the Necessity of Time-based Updates in SDN 2
Time-based Network Updates
Our approach: switches/routers use accurate time
– Coordinated network updates
– Minimize packet loss / temporary anomalies during updates
3 On the Necessity of Time-based Updates in SDN
Controller
switch
switch switch
switch
Time-based Updates in SDN
• One of the key benefits of SDN: Dynamic path allocation based on network load
• Claim: time is an essential tool in path allocation
4
Controller
switch
switch switch
switch
On the Necessity of Time-based Updates in SDN
The Flow-swapping Scenario
5
A B C D
S1 S2 S3
S4 S5
All links @ 10 Gbps
On the Necessity of Time-based Updates in SDN
The Flow-swapping Scenario
6
A B C D
S1 S2 S3
S4 S5
F1
F2
4 4
On the Necessity of Time-based Updates in SDN
The Flow-swapping Scenario
Problem: add new flow BD @ 2 Gbps
7
A B C D
S1 S2 S3
S4 S5
F1
F2
4 4
F3
F4
5 5
5+4=9
5+4=
9
On the Necessity of Time-based Updates in SDN
10G capacity 9G traffic
The Flow-swapping Scenario
8
A B C D
S1 S2 S3
S4 S5
F1
F2
F3
F4
4+4=8
5+5=
10
4 45 5
After flow-swapping:
On the Necessity of Time-based Updates in SDN
The Flow-swapping Scenario
9
A B C D
S1 S2 S3
S4 S5
F1
F2
F3
F4
5 5 4 4
F5
2
After flow-swapping:
Flow swapping: S2 and S3 should be updated ~ simultaneously. On the Necessity of Time-based Updates in SDN
A B C D
S1 S2 S3
S4 S5
F1
F2
4 4
F3
F4
5 5
5+4=9
5+4=
9
The Flow-swapping Scenario
10
Before flow-swapping:
Flow swapping: S2 and S3 should be updated ~ simultaneously. On the Necessity of Time-based Updates in SDN
The Flow-swapping Scenario
11
A B C D
S1 S2 S3
S4 S5
F1
F2
4 4
F3
F4
5
5+5+
4=14
5
S2 updated first:
Flow swapping: S2 and S3 should be updated ~ simultaneously. On the Necessity of Time-based Updates in SDN
10G capacity 14G traffic
Goal: prove that flow-swaps are inevitable regardless of the controller’s route allocation policy.
12 On the Necessity of Time-based Updates in SDN
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o1 o2 on
q1 q2 qm
c c c
s
The Lossless Flow Allocation Problem
The Lossless Flow Allocation Problem
• Special case of multi-commodity flow (MCF).
• We analyze it as a two-players game.
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...
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d
o1 o2 on
q1 q2 qm
c c c
s
Source • Progressively adds flows. • Goal: force the controller to swap.
Controller • Configures a path for each flow. • Goal: guarantee a path assignment.
On the Necessity of Time-based Updates in SDN
The Swap Theorem
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...
...
d
o1 o2 on
q1 q2 qm
c c c
s
On the Necessity of Time-based Updates in SDN
Theorem: There exists a strategy Ss for the source that forces the controller to perform an n-way swap.
Controller
switch
switch switch
switch
Conclusion
• Flow-swaps are inevitable
– Existing approaches for consistent network updates do not address flow-swaps
• Time and synchronized clocks are optimal for this task
• Time-based solutions are useful for many tasks in SDN
• A time extension for OpenFlow is under discussion by the ONF Extensibility WG
15 On the Necessity of Time-based Updates in SDN
THANKS !
16 On the Necessity of Time-based Updates in SDN
Controller
switch
switch switch
switch
BACKUP SLIDES
17 On the Necessity of Time-based Updates in SDN
C D
S1 S2
after
beforeS3 S4
Example: Multicast Reconfiguration
Time Extension to OpenFlow 18
• Update S3 and then S4 S1 is temporarily disconnected.
• Update S4 and then S3 S1 temporarily receives two copies of each packet.
C D
S1 S2
after
beforeS3 S4
Example: Multicast Reconfiguration
Time Extension to OpenFlow 19
Solution: update S3 and S4 at the same time.
Example: Port Rate Reconfiguration
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Switch Switch
OpenFlow
Configuration
Point
Both switches are configured to change the port rate at time T.
On the Necessity of Time-based Updates in SDN
Physical layer updates with short transition period.
Example: Path Reconfiguration
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Switch 2
Switch 1
Switch 3
Switch 4Flow A
Flow A
path 1
path 2All switches are updated at (T-, T+ ).
On the Necessity of Time-based Updates in SDN