TimeFlipInfocomPres.pdf

T

IME

F

LIP

: Scheduling Network

Updates with

Timestamp-based TCAM Ranges

Tal Mizrahi

*

, Ori Rottenstreich

†

, Yoram Moses

*

* Technion – Israel Institute of Technology

† Princeton University

Outline

•

Background

•

Motivation

•

Introducing T

IME

F

LIP

•

Efficient T

IME

F

LIP

s

switch

switch

switch

switch

controller

switch

switch

switch

switch

Software Defined Networks (SDN)

data plane

data plane

control plane

Network updates.

TCAM: Ternary Content Addressable Memory

•

Memory for quick searching

•

Top-down search: first match “wins”

•

Ternary: 0 / 1 / *

•

* = don’t care

action

s

, …, s

TCAM

Network Device

packet’s search

TCAM Ranges

•

How do you represent a range?

•

Example:

–

F is a 3 bit field

–

Range F



1

•

Range

expansion

= the number of entries

required to represent a range.

Outline

•

Background

•

Motivation

•

Introducing T

IME

F

LIP

•

Efficient T

IME

F

LIP

s

TCAM

TCAM

...

TCAM

incoming

packet

outgoing

packet

Network device

TCAM

TCAM

...

TCAM

incoming

packet

outgoing

packet

Network device

Problem 1: Atomic Bundles

Atomic Bundle [OpenFlow 1.4]:

A set of updates that need to be applied atomically (‘all-or-none’).

S

1

S

2

S

3

S

4

S

5

S

1

S

2

S

3

S

4

S

5

S

1

S

2

S

3

S

4

S

5

S

1

S

2

S

3

S

4

S

5

Problem 2: Time-based Updates



A key benefits of SDN:

dynamic path allocation based on network load

Time is a powerful tool in path allocation or reconfiguration.

Our time extension to the OpenFlow protocol – now in OpenFlow 1.5.

Problem: How do we

accurately

apply a time-based update?

Outline

•

Background

•

Motivation

•

Introducing T

IME

F

LIP

•

Efficient T

IME

F

LIP

s

packet’s search

key

action

s

, …, s

TCAM

Network Device

action

s

, …, s

TCAM

Network Device

T

s

, …, s

T



T

TCAM

Network Device

action

T

IME

F

LIP: Timestamp-based TCAM Lookup

The timestamp is used in the TCAM key –

time range

.

COTS switches can synchronize clocks very accurately ~ 1 μsec.

[Using IEEE 1588 Precision Time Protocol (PTP) or GPS]

conventional

TimeFlip

Atomic Bundles Using T

IME

F

LIP

TCAM

1

TCAM

2

...

TCAM

n

incoming

packet

outgoing

packet

Network device

TT0

TT0

TT0

TT0

before

after

Time-based Updates using T

IME

F

LIP

TimeFlip:

switch accurately

starts using ‘after’ at T

₀

.

T

s

u

, …, s

T



T

TCAM

Network Device

search

key

‘after’

T

IME

F

LIP

Use Cases

Timed Installation

Timed Removal

Timed Action Update

TCAM

s

u

, ...,s

,

[

T



T

]

a

TCAM

s

u

, …,s

,

[

T

<

T

]

a

s

u

, …, s

,

*

…

*

TCAM

a

32 bits

48 bits

Nanoseconds

Seconds

What is a Timestamp?

IEEE 1588 Time Of Day (TOD):

Timestamp-based TCAM Lookup

T

s

, …, s

T



T

TCAM

Network Device

search

key

action

Problem:

•

Small number of entries in T



T

₀

.

•

Small number of timestamp bits per entry.

•

Without compromising the scheduling accuracy !

Large # of bits in timestamp field?

Efficient T

IME

F

LIP

s

The Punctual Teacher Problem

•

Afternoon lesson

•

Synchronize watches

The Punctual Teacher Problem

•

Afternoon lesson

•

Synchronize watches

•

Write down

date

time

The Punctual Teacher Problem

•

Afternoon lesson

•

Synchronize watches

•

Write down

date

time

Flexible + punctual !

2015-04-30 15:38

Scheduling Tolerance

T

min

time

T

max

•

Assume: we allow the

controller

to schedule the

update to any time in the range [T

min

, T

max

]

•

It

selects

T

₀

that minimizes the expansion of

T



T

₀

•

Without compromising the accuracy !

scheduled time

T

₀

TOL

Scheduling Tolerance – TOL

controller

switch switch

Optimal Scheduling Algorithm

•

Theorem:

T

SCH

is optimal.

No other scheduling algorithm

produces an extremal range with

a lower expansion.

•

Theorem: the average expansion is:

switch switch

T

T

T

T

TCAM

The Punctual Teacher Problem

time

I know the date.

No need to write it.

2015-04-30 15:38

2015-04-30

15:38

Periodic Ranges

TCAM

controller

switch switch

T

scheduled

time

time

insertion

Assumption: a TimeFlip with

T



T

₀

is present during [T

₀

-Δ,T

₀

+Δ)

For example, if

Δ

=0.5 second:

T

+

D

T

-

D

cleanup

Installation Bounds –

Δ

T



T

₀

TCAM

s

, ...,s

TCAM

s

, ...,s

I know which

second it is.

2015-04-30 15:38:10.251987326

2015-04-30 15:38:10

.251987326

controller

Periodic Continuation Algorithm

A periodic continuation algorithm for

T



T

₀

:

Period=2

The

V

most significant bits are

don’t care

!

Period



2

Δ

Nyquist ?

controller

switch switch

Outline

•

Background

•

Motivation

•

Introducing T

IME

F

LIP

•

Efficient T

IME

F

LIP

s

Resource Consumption

•

Theorem: using S

CHEDULE

and B

OUNDED

R

ANGE:

–

The

expansion

is bounded by:

Example: Efficient T

IME

F

LIP

What can we do with an 8-bit timestamp field?

Switches:

Δ = 8 seconds

Controller:

TOL = 100 milliseconds



The 8-bit timestamp can represent any TimeFlip.

log

(𝟐∆) − log

𝑻𝑶𝑳 ≤ 𝟖 𝒃𝒊𝒕𝒔

action

5-tuple

TCAM

packet’s search

key

metadata timestamp

160 bits

The Cost of T

IME

F

LIP

: 1 Bit / 1 Entry

•

Theorem: if

𝑇𝑂𝐿 ≥ 2

𝑙𝑜𝑔

2

(∆)

, then the

timestamp range requires as little as:

–

1 TCAM entry.

–

1 bit in the timestamp field.

* * * *

*

timestamp

field

* * * * * *

function of

TOL

Timed Action Updates

Using the

complementary action

[Rottenstreich et al.]:

Complementary encoding has been shown to be

optimal for extremal ranges of the form T



T

₀

.

s

u

, …, s

,

*

…

*

TCAM

a

s

u

, …, s

,

[

T



T

]

a’

s

u

, …, s

,

*

…

*

TCAM

a’

s

u

, …, s

,

[

T

<

T

]

a

=

Outline

•

Background

•

Motivation

•

Introducing T

IME

F

LIP

•

Efficient T

IME

F

LIP

s

T

IME

F

LIP

: Would it Work on a Real Switch?

Yes !!

Microbenchmark: TimeFlip was tested on a

TCAM range is

chosen

Conclusion

TimeFlip

Atomic Bundles

Time-based Updates

TimeFlips can be represented

very efficiently

Scheduling Tolerance

Periodic Ranges

Simulation verifies

Microbenchmark:

References

[1] T. Mizrahi, O. Rottenstreich, Y. Moses, "TimeFlip: Scheduling Network Updates with

Timestamp-based TCAM Ranges", INFOCOM, 2015.

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

[2] T. Mizrahi, Y. Moses, "Time-based Updates in Software Defined Networks", the second

workshop on hot topics in software defined networks (HotSDN), 2013.

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

[3] O. Rottenstreich, R. Cohen, D. Raz, and I. Keslassy, “Exact worst case TCAM rule

expansion,” IEEE Trans. Computers, vol. 62, no. 6, pp. 1127–1140, 2013.

http://webee.technion.ac.il/people/or/publications/tc12_exact.pdf

[4] Open Networking Foundation, OpenFlow switch specification, Version 1.5.0, 2015.

https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-switch-v1.5.0.noipr.pdf

[5] Open Networking Foundation, OpenFlow extensions 1.3.x package 2, 2015.