Optical Switching Switch Fabrics, Techniques and Architectures

1. Optical SwitchingSwitch Fabrics, Techniques and Architectures 원종호 (INC lab) Oct 30, 2006

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. Switch Fabric Optical switch - OXC • What is Optical Cross-Connect (OXC)? • Set up light paths • Electrical XC, All-optical XC, Opaque XC • 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 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 TunableWavelength converter SNU INC lab.

15. Optical Burst Switching • Switch thechannels 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 Bigger offset, lower probability of discard • QoS Support Low priority burst • Optical Composite Burst Switching • Minimize packet loss 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 SNU INC lab.