Optical Packet Switching meets

MythbustersRod Tucker

University of Melbourne

Optical Packet Switching Myths

– Electronic packet switches are power-hungry

– Optical technologies are not power-hungry

– Electronic packet switches have reached their limit of scaling

– Optical packet switches can scale to massive throughput

– The “electronic bottleneck” constrains electronic throughput

– Optical to electronic (O/E) and electronic to optical (E/O) converters need to be eliminated

Packet Switching “Myths”

Reduced bit rate (i.e. parallel processing)

Electronic Packet Switch

Speed (throughput) is not a limitation

Fibers

Optics

Switch Fabrics Buffers

DEMUXsMUXs

Forwarding Engine

J

m x mSwitch

m O/E Converters

Electronics

k:1 DEMUX

1: k MUX

12

k

Optical Packet Switch

Demutiplexers

m x m Wavelength-Interchanging

Switch

Output Buffers

Forwarding Engine

Input SynchronizersMutiplexers

Electronics Optics

Optical synchronization and buffering not viable in practice. See, for example, Tucker JLT, pp. 4655-4673, 2008.

m

m

E/O

12

12

k:1 MUX

k

1

Input wavelengths

(B)Output

wavelengths (B)

Forwarding Engine

m x mElectronic

Switch(B/k)

k

2

k x kElectronic Switches

(B/k)

Forwarding Engine

1:k DEMUX

1

m

2

O/E

2

m

1

Electronic Packet Switch (Wavelength I/O)No buffers

(45pJ/b)

(30 pJ/b/stage)

(20 pJ/b/stage)

(30 pJ/b)

Optical Frequency

Optical Frequency

1 2 3 k 1 2 3 k 1 2 3 k

Wavelength

Waveband

Bit rate per wavelength = B

Bit rate per wavelength = B/k

Aggregate bit rate per

waveband = B

Electronic Packet Switch (Wavelength I/O)

Wavelength (WL)

Waveband (WB)

m

1

E/O

1 k:1 MUX

1:k DEMUX

Input wavebands

(B)

Output wavebands

(B)

O/E

2

m

1

Forwarding Engine

21

k

1

k

1

k

k

m x mElectronic

Switch(B/k)

k

2

Forwarding Engine

k x kElectronic Switches

(B/k)

Electronic Packet Switch (Waveband I/O)No buffers

(30 pJ/b)

(45pJ/b)

Integration: see, for example, R. Nagarajan et al., JSTQE 2010

switch

switches switches switches

1

m

1

m

switch switch

Electronic Switch FabricThree-stage Benes

Power consumption = 21 W 20bitE pJ→ =

Assuming Benes architecture, 22 log 144 1 14 1.4 /bitp E pJ stage= − = → =

10-12

10

2010

100 1000

10-7

10-8

10-9

10-10

10-11Waveband

Ene

rgy

per B

it pe

r Sw

itch,

Ebi

t(J

)

Bit Rate per Wavelength or Waveband, B (Gb/s)

Switch Capacity: mB = 1000 Tb/s

Wavelength

Input-to-Output Energy per Bit

Limited by O/E/O and MUX/DEMUX speed

Excludes Forwarding

Engine

m

m

E/O

12

12

k:1 MUX

Input wavelengths

(B)

Output wavelengths

(B)

1

m

2

O/E

2

m

1

m x mOptical

Switch (B)

Forwarding engine, header replacement (B/k)

1:k DEMUX

Optical Packet Switch

Power off during payload ?

Driver

Optical Packet Switch

Consider four switch fabric technologies:

– Arrayed-waveguide-gratings with tuneable wavelength converters

– Semiconductor optical amplifier (SOA) gate arrays

– Arrays of 1 X N electro-optic switches

– Micro-ring resonator switches

m TWCs m TWCs m FWCsm TWCs1

m

AWG AWG AWG

AWGs

1

m

AWG-Based Switch FabricThree-stage Benes

AWGs AWGs

SOA Gate

FWC

m

1

m3-dB Coupler

1

2

3

2

m x m Benes SOA Gate Array

2Number of stages 2log 1m= − 1024 19 stagesm = →8192 25 stagesm = →

4mlog2 m -1 control lines

R. F. Kalman et al., , IEEE Photonics Tech. Lett., vol. 4, p. 1048, 1992.

1 2

3 dB

3 dB

3 dB 3 dB22 log 1m −

ER ER ER

Crosstalk in SOA Gate Array

22 log 1mCrosstalkSignal ER

−=

Psignal

Pcrosstalk

Idrive ~ 100 mA

Extinction Ratio

Array of 1 X N E/O Switches (Spanke Architecture)

61000 ~ 2 10 control linesm x= →810,000 ~ 2 10 control linesm x= →

n (> m) control lines

FWC

1

m

12

m

n control lines

12

12

m1

m

1 x mswitch

1 x mswitch

m x 1 switch

n control lines

m

12

mm x 1 switch

T. Tanemura and Y. Nakano, IEICE Electron. Express, 2008.

FWCs

m

1

m

2

FWCs

1

2

Crosspoints

Dilated Micro-Ring Resonator Switch

control lines

4 resonance controllers

Lee et al., IEEE Photonics Society Annual meeting, 2010

CMOS driver

10-12

10 100 1000

10-7

10-8

10-9

10-10

10-11

E-WB

O-Spanke

O-Benes/Spanke

Ene

rgy

per B

it pe

r Sw

itch,

Ebi

t(J

)

Bit Rate per Wavelength or Waveband, B (Gb/s)

O-SOA

O-AWG O-Micro-Ring

E-WL

Energy per Bit per SwitchExcludes Forwarding Engine

2010 Switch Capacity: mB = 1000 Tb/s

O- AWG

E-WB

E-WL

O-SOA

O-Benes/Spanke O-Spanke

10-12

10-7

10-8

10-9

10-10

10-11

Ene

rgy

per B

it pe

r Sw

itch,

Ebi

t(J

)

10 100 1000

Bit Rate per Wavelength or Waveband, B (Gb/s)

O-Micro-Ring

Energy per Bit per Switch (2020)Electronics: ITRS Roadmap. Optics: 10% p.a. improvement.

2020 Switch Capacity: mB = 1000 Tb/s

103

107

106

105

104

Sw

itch

Pow

er C

onsu

mpt

ion

(W)

100 1000Switch Throughput, mB (Tb/s)

O-Benes/Spanke

O-SOA

E-WLO-AWG

E-WB

B = 100 Gb/s

2020

Switch Power Consumption(2020)

– Electronic packet switches are power-hungry

– Optical technologies are not power-hungry

– Electronic packet switches have reached their limit of scaling

– Optical packet switches can scale to massive throughput

– The “electronic bottleneck” constrains electronic throughput

– Optical to electronic (O/E) and electronic to optical (E/O) converters need to be eliminated

Packet Switching “Myths”

?

Conclusion: “Don’t underestimate the potential of electronics”

- Optical interconnects

Cascaded m x m Packet Switches

Energy per Bit per Switch

1

i pii

bit

PE

mBp

=

== ∑

m x mswitch

1

m x mswitch

m x mswitch

p1

m

1

m

2

Bit rate per wavelength = B

1P 2P pP