Optical Switching Switch Fabrics, Techniques and Architectures 원종호 (INC lab) Oct 30, 2006

SNU INC lab. 2 Outline  Introduction  Optical Switch  Optical Packet Switch  Optical Burst Switch  GMPLS  Conclusion

SNU INC lab. 3 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!

SNU INC lab. 4 Optical switch - OXC  What is Optical Cross-Connect (OXC)? –Set up light paths  Electrical XC, All-optical XC, Opaque XC Switch Fabric Electrical XCAll-optical XC Process O/E/O (slow)O/O/O (fast) Data rate & format Transparent? NoYes ImplementationEasyHard  Major difficulties of All-optical XC –The lack of processing at bit level in optical domain –The lack of efficient buffering in optical domain

SNU INC lab. 5 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

SNU INC lab. 6 Optical switch - Optical Switch Fabrics  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

SNU INC lab. 7 Optical switch - Optical Switch Fabrics –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

SNU INC lab. 8 Optical switch - Optical Switch Fabrics Optomechanical Switch MEMSElectro-optic Switching timeMilliseconds Nanoseconds Insertion lossLow High PDLLow high ScalabilityBadGoodBad

SNU INC lab. 9 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

SNU INC lab. 10 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

SNU INC lab. 11 Optical Packet Switching  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.

SNU INC lab. 12 Optical Packet Switching  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

SNU INC lab. 13 Optical Packet Switching  Architecture Output Input O/E interface: extract the header info. FDL

SNU INC lab. 14 Optical Packet Switching  Shared Wavelength Converters Reduce Tunable Wavelength converter

SNU INC lab. 15 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.

SNU INC lab. 16 Optical Burst Switching  How is it possible? –reservation request (control packet) –Using offset-time reservation

SNU INC lab. 17 Optical Burst Switching  QoS Support Bigger offset, lower probability of discard  Optical Composite Burst Switching –Minimize packet loss Low priority burst Not discarded

SNU INC lab. 18 The future of Optical switching

SNU INC lab. 19 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

SNU INC lab. 20 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