SDN: It’s About Time Tal Mizrahi, Yoram Moses Technion – Israel Institute of Technology

Israeli Networking Day June 2016

Outline • • • • •

Background Timed updates in OpenFlow TIME4: optimal for flow swaps Evaluation Conclusion

Software Defined Networks: It’s About Time

2

Outline • • • • •

Background Timed updates in OpenFlow TIME4: optimal for flow swaps Evaluation Conclusion

Software Defined Networks: It’s About Time

3

at a Glance Controller

data plane control plane

Software Defined Networks (SDN)

• Advantage: Dynamic and frequent updates • Challenge: Minimize disruptions and packet loss

Switches Software Defined Networks: It’s About Time

4

The First Synchronized Clocks

Railway switch

Software Defined Networks: It’s About Time

5

Networks: Communications vs. Trains

SDN Controller

Train Control Center

Network switch

Railway switch Software Defined Networks: It’s About Time

6

Timed

at a Glance TIME4: Time for SDN Controller

A protocol allowing the controller to schedule network updates

Synchronized clocks

Switches Software Defined Networks: It’s About Time

7

Using Time to Coordinate

Updates

This paper focuses on

TIME4

TIME4 Switches invoke update at the same time

Time sequence Switches invoke update according to a scheduled sequence Software Defined Networks: It’s About Time

8

Accurate Synchronization: It’s Already Here Precision Time Protocol (PTP) [IEEE 1588 2008] ~1μsec accuracy

Mobile backhaul

Industrial automation

Power substations

But what about Software Defined Networks?

Open Networking Foundation (ONF) SDN product directory

Financial applications

~70%

~70% of the SDNenabled silicons have native PTP support.

China Mobile: over 1,000,000 PTP-enabled base stations https://mailarchive.ietf.org/arch/attach/tictoc/pdfsY1ADO.pdf Software Defined Networks: It’s About Time

9

Timed

at a Glance

Challenge:

Controller

A protocol allowing the controller to schedule network updates

Synchronized clocks

Switches Software Defined Networks: It’s About Time

10

Outline • • • • •

Background Timed updates in OpenFlow TIME4: optimal for flow swaps Evaluation Conclusion

Software Defined Networks: It’s About Time

11

A Timed SDN Protocol Challenge: defining a generic protocol for timed updates in SDN. 1. Bundle Open

2. A set of OpenFlow commands.

3. Bundle Commit.

reply

reply

e Com Bundl mit

e

N

...

s le Clo Bund

le Add Bund

1

n

le Add Bund

le Ope Bund

reply

controller

switch

Time

Bundle [OpenFlow 1.4] Software Defined Networks: It’s About Time

12

A Timed SDN Protocol: Scheduled Bundles Challenge: defining a generic protocol for timed updates in SDN. Our solution: Scheduled Bundles

OpenFlow 1.5

A generic method to schedule any OpenFlow command. Our solution has been incorporated into OpenFlow 1.5

reply

reply

reply

e

Bundle Discard: [optional] Allows network-wide atomic update.

ard

s le Clo Bund

N

e Disc Bundl

le Add Bund

1

n

le Add Bund

le Ope Bund

...

mit e Com Bundl e Ts) (at tim

controller

switch Ts Time

Commit may include scheduled time Ts Software Defined Networks: It’s About Time

Switch executes bundle at time Ts 13

Timed

at a Glance

Question: do we benefit from using time? Controller A protocol allowing the controller to schedule network updates

Synchronized clocks

Switches Software Defined Networks: It’s About Time

14

Outline • • • • •

Background Timed updates in OpenFlow TIME4: optimal for flow swaps Evaluation Conclusion

Software Defined Networks: It’s About Time

15

Flow Swaps A key benefit of SDN: Dynamic path allocation based on network load

old new

o1

...

controller o2

Software Defined Networks: It’s About Time

16

Flow Swaps A key benefit of SDN: Dynamic path allocation based on network load If O1 , O2 are not updated at the same time…

old new

Temporary congestion.

o1

...

controller o2

O2 is updated first. Software Defined Networks: It’s About Time

17

Flow Swaps A key benefit of SDN: Dynamic path allocation based on network load

TIME4

old new

If O1 , O2 are updated at the same time: No congestion!

Can updates occur at the same time? o1

...

controller o2

1. Clock synchronization. 2. Accurate scheduling, e.g., [TimeFlip, INFOCOM ‘15]. Software Defined Networks: It’s About Time

18

Existing Network Update Approaches Description

Order [Dionysus ‘14] [zUpdate ‘13] [Vanbever et al. ‘11] [Francois et al. ’07]

Two-phase

Flow swaps

Sequentially update switches in specific order

Use version tags

Version tags do not avoid congestion

[Reitblatt et al. ’12]

SWAN [Hong et al. ‘13]

B4 [Jain et al. ‘13]

TIME4

No order avoids congestion

Spare capacity for rerouting Temporarily reduce flow bandwidth

Requires resource overhead

...

Avoids congestion without resource overhead J Software Defined Networks: It’s About Time

19

Can Flow Swaps be Avoided? Problem: controller has to reroute two flows at the same time.

...

controller

Solution (?): don’t reroute. Leave flows in current paths.

Question: maybe a smart controller routing policy can avoid flow swaps?

Answer: NO! Theorem: flow swaps are inevitable. Software Defined Networks: It’s About Time

20

The Lossless Flow Allocation (LFA) Problem Goal: Prove that flow-swaps are inevitable regardless of the controller’s route allocation policy. d c

c

q1

o1

Directed graph. A special case of the unsplittable flow problem.

c

q2

... ...

o2

qm

on

s Software Defined Networks: It’s About Time

21

The LFA Game A two-player game d c

c

q1

o1

c

q2

... ...

o2

qm

on

Controller • Configures a path for each flow. • Goal: guarantee a path assignment.

Source • Progressively adds flows. • Goal: force the controller to swap.

s Software Defined Networks: It’s About Time

22

The Swap Theorem Theorem: There exists a strategy Ss for the source that forces the controller to perform an n-switch swap. d c

c

q1

o1

c

q2

... ...

o2

qm

n switches on

are updated in the flow swap

s Software Defined Networks: It’s About Time

23

The Cost of Not Swapping

Oversubscription = 100%

o1

Software Defined Networks: It’s About Time

...

controller o2

24

The Cost of Not Swapping Theorem: There exists a strategy Ss for the source that forces the controller to perform a swap with an oversubscription of 50%.

The oversubscription is 50% of the edge capacity o1

Software Defined Networks: It’s About Time

...

controller o2

25

Example: Consistent Path Update before after

Sequential update approaches: [Dionysus ‘14] [zUpdate ‘13] [Vanbever et al. ‘11] [Francois et al. ’07]

0. 1. 2. 3.

The ‘before’ configuration. Controller updates S1. X Controller updates S2. Controller updates S3.

S3

S4

S3

S4

S2

S1

S2

S1

0

1

wait…

S3

S4

S2

S1

2

Software Defined Networks: It’s About Time

wait…

S3

S4

S2

S1

S3

S4

S2

S1

3 26

Simultaneous Updates? En-route packets run into a ‘black hole’. Not consistent!

S3

S4

S3

S4

S3

S4

S3

S4

S2

S1

S2

S1

S2

S1

S2

S1

1

2

Software Defined Networks: It’s About Time

3 27

Timed Multi-phase Consistent Updates [SOSR ‘16] - The controller sends timed update messages to S1, S2, S3. - Scheduled updates occur at times T1, T2, T3. Controller does not need to wait between steps! Timed update  Lower update duration. S3

S4

S3

S4

S3

S4

S3

S4

S2

S1

S2

S1

S2

S1

S2

S1

T1

T2

Software Defined Networks: It’s About Time

T3

28

Outline • • • • •

Background Timed updates in OpenFlow TIME4: optimal for flow swaps Evaluation Conclusion

Software Defined Networks: It’s About Time

29

Prototype Design Controller SDN application using time-based updates

OpenFlow controller Time-based update

supports Scheduled Bundles

offseti

Open source

Time extension

OpenFlow switch supports Scheduled Bundles

OpenFlow Agent Dpctl

Clock

PTPd Slave i

OpenFlow protocol using time extension OpenFlow Switch CPqD OFSoftswitch Switch scheduling

REVERSEPTP

Synchronization using ReversePTP [ISPCS ‘14]; customized for SDN.

PTP PTPd Master Clock

REVERSEPTP

Black building blocks: open source Timed . https://github.com/timedsdn

Switch i Software Defined Networks: It’s About Time

30

Evaluation Method • 70 nodes (Linux machines). • DeterLab testbed. • Three types of nodes: – OpenFlow switch – Controller – Host

d q2

q1

• Measured the packet loss during flow swaps.

o1

o2

H1

H2

Software Defined Networks: It’s About Time

...

controller on

Hn

31

TIME4 vs. Other Update Approaches Packet loss during a flow swap

SWAN: slightly lower packet loss than TIME4. TIME4: less resource overhead (scratch capacity). Software Defined Networks: It’s About Time

TIME4+SWAN → Low packet loss with low resource overhead. 32

TIME4: Scalability Packet loss during a flow swap Untimed: packet loss increases with the number of switches.

TIME4 is scalable!

Software Defined Networks: It’s About Time

33

Outline • • • • •

Background Timed updates in OpenFlow TIME4: optimal for flow swaps Evaluation Conclusion

Software Defined Networks: It’s About Time

34

Conclusion Why do we need Timed ?

TIME4: Dynamic Path Updates Flow swaps are provably inevitable

Scheduling protocol

OpenFlow Scheduled Bundles [OpenFlow 1.5]

The Timed

Project

http://tx.technion.ac.il/~dew/TimedSDN.html Software Defined Networks: It’s About Time

35

Thanks! The Timed

Project

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

The Why do we need time in SDN? Scheduling protocol Accurate scheduling method SDN Clock synchronization

Project

Timed Consistent Updates

TIME4: Dynamic Path Updates

ONECLOCK to Rule Them All

Data Plane Timestamping

[SOSR, ‘15]

[INFOCOM, ‘16]

[NOMS, ‘16]

[SWFAN, ‘16]

OpenFlow Scheduled Bundles

NETCONF Time Capability

[INFOCOM ’16, OpenFlow 1.5]

[NOMS ’16, RFC 7758]

TIMEFLIP

ONECLOCK

[INFOCOM ‘15]

[NOMS ‘16]

REVERSEPTP [HotSDN ‘14, ISPCS ‘14] Software Defined Networks: It’s About Time

37

References [1]

T. Mizrahi, Y. Moses, "Software Defined Networks: It's About Time", IEEE INFOCOM, 2016.

[2]

T. Mizrahi, Y. Moses, "OneClock to Rule Them All: Using Time in Networked Applications", IEEE/IFIP Network Operations and Management Symposium (NOMS), 2016.

[3]

T. Mizrahi, E. Saat, Y. Moses, "Timed Consistent Network Updates", ACM SIGCOMM Symposium on SDN Research (SOSR), 2015.

[4]

T. Mizrahi, E. Saat, Y. Moses, "Timed Consistent Network Updates in Software Defined Networks", IEEE/ACM Transactions on Networking (ToN), 2016.

[5]

T. Mizrahi, O. Rottenstreich, Y. Moses, "TimeFlip: Scheduling Network Updates with Timestamp-based TCAM Ranges", IEEE INFOCOM, 2015.

[6]

T. Mizrahi, Y. Moses, "Time-based Updates in Software Defined Networks", workshop on hot topics in software defined networks (HotSDN), 2013.

[7]

T. Mizrahi, Y. Moses, "On the Necessity of Time-based Updates in SDN", Open Networking Summit (ONS), 2014.

[8]

T. Mizrahi, Y. Moses "Using ReversePTP to Distribute Time in Software Defined Networks", International IEEE Symposium on Precision Clock Synchronization for Measurement, Control and Communication, (ISPCS), 2014.

[9]

T. Mizrahi, Y. Moses, "ReversePTP: A Software Defined Networking Approach to Clock Synchronization", workshop on hot topics in software defined networks (HotSDN), 2014.

[10]

T. Mizrahi and Y. Moses, "ReversePTP: A clock synchronization scheme for software defined networks", International Journal of Network Management (IJNM), under minor revision, 2016.

[11]

T. Mizrahi, Y. Moses, "Time4: Time for SDN", arXiv preprint arXiv:1505.03421, 2016.

[12]

T. Mizrahi, Y. Moses, "The Case for Data Plane Timestamping in SDN", IEEE INFOCOM Workshop on Software-Driven Flexible and Agile Networking (SWFAN), 2016.

[13]

T. Mizrahi, Y. Moses, "Time Capability in NETCONF", RFC 7758, 2016.

[14]

T. Mizrahi, Y. Moses, "Serving Time in the Cloud: Why Time-as-a-Service?", IEEE INFOCOM, 2016.

[15]

T. Mizrahi, Y. Moses, "On the Behavior of Network Delay in the Cloud", IEEE INFOCOM, 2016.

[16]

Open Networking Foundation, OpenFlow switch specification, Version 1.5.0, 2015.

[17]

Open Networking Foundation, OpenFlow extensions 1.3.x package 2, 2015. Software Defined Networks: It’s About Time

38