DPT-SWFAN-Presentation.pdf

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The Case for Data Plane

Timestamping in SDN

Tal Mizrahi, Yoram Moses

Technion – Israel Institute of Technology

IEEE INFOCOM Workshop on Software-Driven Flexible and Agile Networking (SWFAN)

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Outline

•

Background

•

Timestamp ranges

•

Use cases

•

Discussion

•

Conclusion

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Outline

•

Background

•

Timestamp ranges

•

Use cases

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The

Timed

Project

Controller

4 Data Plane Timestamping in SDN

Switches

Synchronized clocks

A protocol allowing the controller to

schedule network updates

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Using

Timestamps

instead of

Current work: Data Plane Timestamping (DPT) in SDN.

The advantages of timestamping are well-known, e.g., [Lamport ‘78].

ingress switch

vSwitch

Timestamped Domain

External Network

VNF

egress switch

Timestamp is

• Pushed by ingress switch.

• Removed by egress switch.

X

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DPT: Data Plane Timestamping

ingress switch

vSwitch

Timestamped Domain

External Network

VNF

egress switch

What does DPT require from SDN switches?

• Push/remove timestamps.

• Take decisions based on timestamps.

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ingress switch

vSwitch

Timestamped Domain

External Network

VNF

egress switch

DPT: Data Plane Timestamping

What can we gain from DPT?

• One field, can be used for many problems / applications.

• Treated uniformly in the network.

Why is DPT feasible in softwarized environments?

• Network is locally administered.

Adding metadata to header is feasible, e.g., [NSH], [VXLAN-GPE], [Geneve].

• Flexible parsing and header editing

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Outline

•

Background

•

Timestamp ranges

•

Use cases

•

Discussion

•

Conclusion

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Periodic range Extremal range (T≥T0)

Timestamp Ranges

0

... timestamp

value

0

...

T

0

timestamp

value

action

field1 field2 field3 …

Flow Table SDN Switch

packet header

action

timestamp field2 field3 field4 …

DPT Processing

SDN switch (OpenFlow / P4) matchaction procedure

Timestamp-based ranges [TimeFlip, INFOCOM ‘15] Each bit has ternary value: 0 / 1 / *

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32 bits 32 bits

Second Fraction Seconds

Time.Sec Time.Frac

Timestamp Format

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Timestamp Ranges: Examples

Time.Sec

1

Time.Frac

*

…

* * … *

1 _*…

* * … *

0 1 _*…

* * … *

Time.Sec

Time.Frac

Periodic range

0

... timestamp

value

1 second

Extremal range: T≥230

0 ...

230 _timestamp

value

T≥231

231_>T≥230

action

Flow Table SDN Switch packet header DPT Processing action

DPT Processing

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Outline

•

Background

•

Timestamp ranges

•

Use cases

•

Discussion

•

Conclusion

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S2 S1

S3 S4

S2 S1

S3 S4 after

before

Use Case 1: Consistent Updates

•

Two-phase update [Reitblatt et al. ’12].

•

S

₂

attaches version tags to packets.

•

‘

before

’ / ‘

after

’.

•

Indicate distribution tree.

•

Guarantees

per-packet consistency

.

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Two-Phase Consistent Updates

S2 S1

S3 S4

S2 S1

S3 S4

S2 S1

S3 S4

1

2

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DPT-based

One-

Phase Consistent Updates

1. Controller sends the ‘after’ configuration to switches (subject to Timestamp ≥ Tthreshold). 2. Controller updates S2 to start sending ‘after’ version tag.

Switches automatically start using the ‘after’ path when Timestamp ≥ T_threshold

S2 S1

S3 S4

S2 S1

S3 S4

S2 S1

S3 S4

1

DPT

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DPT-based

One-

Phase Consistent Updates

DPT reduces the load on the controller.

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Stateless load balancing:

- Equal Cost Multiple Paths (ECMP)  50% utilization.

- Random Packet Spraying (RPS) [Dixit et al. ‘13].

Stateful methods, e.g., Round Robin.

Use Case 2: Elephant Flow Load Balancing

S

3

10

src

S

₅

dst

S

4

S

2

S

1

10

20

A

B

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DPT-based load balancing:

DPT-based Load Balancing

S

3

10

src

S

₅

dst

S

4

S

2

S

1

10

20

A

B

20 Gbps elephant flow.

timestamp

value

...

A B A B

...

toggle interval

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DPT-based Load Balancing

S

3

10

src

S

₅

dst

S

4

S

2

S

1

10

20

A

B

How does the controller compute the toggle interval?

• L = maximal packet length.

• BW = total bandwidth of the two links.

• Toggle interval = L / BW Independent of the flow rate !

timestamp

value

...

A B A B

...

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Goodput of DPT-based Load Balancing

Toggle interval = L / BW

 1 msec

• Load balancing using 1-bit from the DPT.

• DPT: higher goodput than RPS / ECMP.

timestamp

value

...

A

B

A

B

Time.Sec Time.Frac

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Use Case 3: Network Telemetry

The DPT is the only necessary field for:

•

Delay measurement

•

Loss measurement

S

1

S

2

Ti

m

e

CS1

2

CR1

2

CS0

1

CR0

1

CS1

1

CR1

1

• [Coloring]: All data packets from S₁ to S₂ include a 1-bit ‘color’.

• Measurement is performed separately for each block.

[Coloring] M. Chen, L. Zheng, G. Mirsky, G. Fioccola, and T. Mizrahi, “IP Flow Performance Measurement Framework,”

draft-chen-ippm-coloring-Using the DPT reduces the controller load

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Outline

•

Background

•

Timestamp ranges

•

Use cases

•

Discussion

•

Conclusion

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DPT: is it Worth the Overhead?

Timestamp length / flexibility tradeoff:

64 bits fully flexible

1 bit

often suffices

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ingress switch

vSwitch

Timestamped Domain

External Network

VNF

egress switch

DPT Header Example: NSH Encapsulation

[NSH-Timestamp] R. Browne, A. Chilikin, B. Ryan, T. Mizrahi, and Y. Moses, “Network service header timestamping,” draft-browne-sfc-nsh-timestamp, work in progress, IETF, 2015.

• All traffic is encapsulated with an NSH.

• NSH may include a timestamp [NSH-Timestamp].

Network Service Header (NSH) encapsulation

• NSH is used for Service Function Chaining (SFC).

• Defined by the SFC working group of the IETF.

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Outline

•

Background

•

Timestamp ranges

•

Use cases

•

Discussion

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Conclusion

Load balancing

• Stateless

• High goodput

DPT = Data Plane Timestamping

One header for multiple applications

The

Timed

Project

http://tx.technion.ac.il/~dew/TimedSDN.html

Consistent updates

• Low controller CPU load

• Eliminates management overhead of version tags

Network telemetry

• Low controller CPU load

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Evaluation Method

•

Emulab

testbed.

•

48 Linux-based OpenFlow software switches.

–

CPqD OFSoftSwitch.

–

Dpctl controller.

•

Slightly modified OpenFlow switches

–

Push timestamp into packet’s Ethernet source address.

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The

Project

Why do we need

TimedSDN?

Scheduling

protocol

Accurate scheduling

method

SDN Clock

synchronization

R

EVERSE

PTP

[HotSDN ‘14, ISPCS ‘14]

T

IME

F

LIP [INFOCOM ‘15]

O

NE

C

LOCK [NOMS ‘16] OpenFlow

Scheduled Bundles

[INFOCOM ’16, OpenFlow 1.5]

NETCONF Time Capability

[NOMS ’16, RFC 7758]

Timed Consistent Updates

[SOSR, ‘15]

ONECLOCK to Rule

Them All

[NOMS, ‘16]

TIME4: Dynamic

Path Updates

[INFOCOM, ‘16]

Data Plane Timestamping

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Timestamping vs. Sequence Numbers

ingress switch vSwitch Timestamped Domain External Network VNF egress switch

What if clocks are not synchronized? ==

What if we used sequence numbers [Lamport]?

Controller is synchronized to switches 

controller can plan the schedule of threshold times for network updates.

Controller can sample the counters / timestamps at fixed (synchronized) time intervals.

S2 S1 S3 S4

• Clock synchronization has benefits.

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Load Balancing

S

1

S

2

10

20

A

B

C

timestamp

value

A C B C

...

A C B C

...

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Periodic range Extremal range (T≥T0)

Timestamps Ranges

0

... timestamp

value

0

...

T

0

timestamp

value

action

field1 field2 field3 …

action

DPT Processing

SDN switch (OpenFlow / P4) matchaction procedure

Timestamp-based ranges [TimeFlip, INFOCOM ‘15] Each bit has ternary value: 0 / 1 / *

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Network Telemetry

Delay measurement Loss measurement

T

1

T

2

Ti

m

e

S

1

S

2

One-way delay: T₂-T₁

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S

1

S

2

Ti

m

e

CS1

2

CR1

2

CS0

1

CR0

1

CS1

1

CR1

1

Color-based

Loss

Measurement

• [Coloring]: All data packets from S₁ to S₂ include a 1-bit ‘color’.

• Measurement is performed separately for each block.

Controller can compute:

Packet loss = (CS1₂-CS1₁)-(CR1₂-CR1₁)

S₁ toggles color.

S₁ and S₂ maintain per-color counters.

S₁ and S₂ periodically export counters to central point, e.g., SDN controller.

S₁ inserts 1-bit color into packet header.

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Color-based

Delay

Measurement

T

1

T

3

T

2

T

4

S

1

S

2

Ti

m

e

Controller can compute:

Two-way delay = (T₄-T₁)-(T₃-T₂)

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S

1

S

2

Ti

m

e

CS1

2

CR1

2

CS0

1

CR0

1

CS1

1

CR1

1

Color-based Measurement

Q: How does an SDN switch toggle the color?

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DPT-based Coloring

timestamp

value

...

color

‘1’

‘0’

‘1’

‘0’

Time.Sec Time.Frac

• Each block: a constant time interval.

• The controller is not involved in the color toggling.



• Choose 1 bit from the timestamp.

• Use this bit as the color.

• Each switch has two match-action rules:

• Timestamp bit=0

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DPT-based Coloring

timestamp

value

...

color

‘1’

‘0’

‘1’

‘0’

Time.Sec Time.Frac

A 1-bit timestamp is sufficient.

DPT-based coloring reduces

the load on controller.

DPT allows for both

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References

[1] T. Mizrahi, Y. Moses, “Software Defined Networks: It’s About Time", IEEE INFOCOM, 2016. (http://tx.technion.ac.il/~dew/Time4INFOCOM.pdf)

[2] M. Chen, L. Zheng, G. Mirsky, G. Fioccola, and T. Mizrahi, “IP Flow Performance Measurement Framework,” draft-chen-ippm-coloring-based-ipfpm-framework, work in progress, 2016.

(https://tools.ietf.org/html/draft-chen-ippm-coloring-based-ipfpm-framework)

[3] R. Browne, A. Chilikin, B. Ryan, T. Mizrahi, and Y. Moses, “Network service header timestamping,” draft-browne-sfc-nsh-timestamp, work in progress, IETF, 2015.

(https://tools.ietf.org/html/draft-browne-sfc-nsh-timestamp)

[4] T. Mizrahi, O. Rottenstreich, Y. Moses, "TimeFlip: Scheduling Network Updates with Timestamp-based TCAM Ranges", IEEE INFOCOM, 2015. (http://tx.technion.ac.il/~dew/TimeFlipINFOCOM.pdf)

[5] T. Mizrahi, E. Saat, Y. Moses, "Timed Consistent Network Updates", ACM SIGCOMM Symposium on SDN Research (SOSR), 2015. (http://tx.technion.ac.il/~dew/TimedConsistentSOSR.pdf)

(http://tx.technion.ac.il/~dew/Time4INFOCOM.pdf

(https://tools.ietf.org/html/draft-chen-ippm-coloring-based-ipfpm-framework

(https://tools.ietf.org/html/draft-browne-sfc-nsh-timestamp

(http://tx.technion.ac.il/~dew/TimeFlipINFOCOM.pdf

(http://tx.technion.ac.il/~dew/TimedConsistentSOSR.pdf

http://tx.technion.ac.il/~dew/TimeSDN.pdf)