optical switching switch fabrics, techniques and architectures

Optical SwitchingOptical SwitchingSwitch Fabrics, Techniques and Switch Fabrics, Techniques and

ArchitecturesArchitectures

원종호 (INC lab) Oct 30, 2006

SNU INC lab.SNU INC lab. 2

Outline

Introduction

Optical Switch

Optical Packet Switch

Optical Burst Switch

GMPLS

Conclusion


Introduction

Internet traffic has doubled per year New services like VOD, IPTV DWDM (Dense Wavelength Division Multiplexing) is

developed– Can transport tens to hundreds of wavelengths per fiber

Then, What is problem?– Slow O/E/O conversion.– Electronic equipment is dependent on the data rate &

protocol. (non-transparent) Goal?

– All optical!


Optical switch - OXC

What is Optical Cross-Connect (OXC)?– Set up light paths

Electrical XC, All-optical XC, Opaque XC

Switch

Fabric

Electrical XC

All-optical XC

Process O/E/O (slow)

O/O/O (fast)

Data rate & formatTransparent?

No Yes

Implementation Easy Hard Major difficulties of All-optical XC– The lack of processing at bit level in optical

domain– The lack of efficient buffering in optical domain


Optical switch - Optical Switch Fabrics

Optical Switch Fabrics– Allow switching directly in the optical domain (All-optical)

Important parameters– Switching time (↓)– Insertion loss (↓ and loss uniformity at all input-output

connections)– Crosstalk (↓)– Extinction ratio (ratio of ON-OFF power) (↑ )– Polarization-dependent loss (↓)– Reliability, energy usage, scalability, temperature

resistance



Main optical switching technologies– Opto-mechanical Switch

• Use prisms, mirrors, directional couplers.• Lack of scalability

– Micro-electro-mechanical System Device (MEMS)• Use tiny reflective surfaces to redirect the light• 2D-MEMS(on-off mirror)• 3D-MEMS(movable mirror)• Scalability• low loss• short switching time• Low power consumption• Low crosstalk • Low polarization effect



– Electro-optic Switch• Use a directional coupler• Its coupling ratio is changed by varying the refractive index

– Thermo-optic Switch– Liquid-Crystal Switch– Bubble Switch– Acousto-optic Switch



Optomechanical Switch

MEMS Electro-optic

Switching time

Milliseconds Milliseconds Nanoseconds

Insertion loss Low Low High

PDL Low Low high

Scalability Bad Good Bad


Optical switch – large switches

Main considerations in building Large switch– Number of small switches required– Loss uniformity– Number of crossovers

• cause power loss, crosstalk– Blocking Characteristics

• Blocking vs. non-blocking


Optical Packet Switching

Optical Circuit Switching– Limited circuit– Low efficiency (due to fixed bandwidth)

Optical Packet Switching– Using Packet ( = Header (for routing) + Data )

If Optical Packet Switching is realized, it can– allocate WDM channels on demand (microsecond)– share network resource efficiently– support burst traffic efficiently– offer high-speed data rate/format transparency &

configurability



What is the problem in implementing OPS?– Long Switching time– Buffer is needed

Long switching time is due to– Extracting the routing information from the header– Controlling switching matrix electronically– Performing the switching and buffering functions

Buffer at Optical domain is needed– Data should be buffered while header is processed– When a contention is occurred– When the bandwidth is not sufficient

We don’t have perfect solutions yet.



Contention Resolution– Buffering

• Using FDL (Fiber Delay Line) – bulky, expensive, indefinite, Quality degradation

• Solutions to reduce the number of FDLs, – synchronous manner– Use TOWC (Tunable optical wavelength

converter)

– Deflection routing• Only one packet – desired link, others – longer links• There can be the looping of packets



Architecture

OutputInput

O/E interface: extract the header info.

FDL



Shared Wavelength Converters

Reduce TunableWavelength

converter


Optical Burst Switching

Switch the channels entirely in the optical domain using electronic tech.

Process– Assemble the packets (have same destination) ->

make bursts at the edge– Bursts are assigned to wavelength channels– Switched through transparently without any conversion– Disassemble into the original packets

No need for Optical buffer.



How is it possible?– reservation request

(control packet)– Using offset-time

reservation



QoS Support Bigger offset, lower probability of discard

Optical Composite Burst Switching– Minimize packet loss

Low priority burst

Not discarded


The future of Optical switching


GMPLS - Generalized Multiprotocol Label Switching

Extends common control plane to support various interfaces.

GMPLS can support– Packet switching – Time-division

(SONET/SDH) + – MPλS (wavelength

switching) + – Spatial-switching

(OXC)

It can support integrated control and management


Conclusion

Optical fiber is not fully exploited Switching functions must be executed

optically Two obstacles

– The lack of optical memory – processing capabilities in optical domain

In the future, breakthroughs may counteract the fundamental limitations of optics

Then, current network is completely changed

optical switching switch fabrics, techniques and architectures

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