TTM1 – 2009: Core networks and Optical Circuit Switching (OCS)

1. TTM1 – 2009: Core networks and Optical Circuit Switching (OCS)

2. Overview topics • Short repetition of two important facts • Optical networks (Zouganeli) • Switching architectures (Borella) • AWG based switches with wavelength conversion (Cheyns)

3. Electronic/electrooptical 1 channel pr fiber Earlier WDM: 4-128 channelspr fiber Now Up to Optical amplifier Short repetition of two important facts (1) WDM increases capacity Optical amplifiers simplifies the system

4. Wavelength converter Optical crossconnect Short repetition of two important facts (2) Cross-connection of wavelengths and blocking: Signals inserted into a fibre must be of different wavelengths.

5. Optical networks (Zouganeli) • Increased traffic demands (e.g. from broadband home users/businesses and new services) => Fat pipes needed. • ”IP everywhere” and development in optical technology => Fokus on simplifications:

6. Network element functionality (1) • 70 % of traffic is through-passing in typical node=> Should be able to avoid processing of this traffic. • Simple optical network element • Static Optical Add-Drop Multiplexer (here: ring network): • Fixed wavelengths dropped and added at each node. • Not reconfigurable (inaccessible to control system).

7. Network element functionality (2) • Traffic bypassing intermediate IP routers => Less load on routers (can be smaller and cheaper) • In meshed networks:Used to directly connect node pairs with high traffic between them. • (UNINETT is in the process of doing this now).

8. Reconfigurable (R-)OADM • A flexible add-drop function • Use cross-connect for some wavelength/wavebands Not single wavelength!

9. Alternative R-OADM switch implementations

10. Opaque vs. transparent • Transparent:All-optical transport independent of:- data rate (within limits)- protocols and formats • Opaque: OEO conversion, i.e. signal received/interpreted by electronic receiver/logic • Expected to follow certain speeds/formats.

11. Needed functionality for optical OXC based networks (1) • Opto-electronic or all-optical. • Scalability and flexibility • Handles much higher number of line ports and directions than R-OADM • Higher flexibility than R-OADM • Service provisioning: End-to-end lightpaths should be provisioned in an automated fashion (not necessarily all-optical or same wavelength end-to-end). • Protection and restoration: Must have mechanisms to protect against fiber cuts or equipment failure at nodes. I.e. redirect traffic from failed to backup paths. • Wavelength conversion: Lightpaths can change wavelength to increase flexibility in allocating network resources. Much easier to implement in opto-electronic OXC than in all-optical OXC;3R versus 2R (Mach-Zhender interferometer).

12. Needed functionality for optical OXC based networks (2) • Multiplexing and grooming: Normally done in the opto-electronical add-drop part. • Today mainly opto-electronic solutions. • Many candidate all-optical solutions: - Generic switch architectures (Clos, Shuffle,..) where elements are simple optical switch elements, connected with fibers. - ”Broadcast and select” switching matrixes realized with splitters and Semiconductor Optical Amplifiers (SOAs) (0 – 1 : block or let-through light).- Two- or three dimensional array of micro mirrors (MEMS)- Tunable wavelength converters and Array Waveguide Gratings (AWG)

13. Transparent (all-optical) switches (1) • Micro-electro-machining systems (MEMS) • Complicated, but has received a lot of attention. • Similar production techniques as for electronic chips

14. Transparent (all-optical) switches (2) • Currently widely discussed in research literature • However: Tunable Wavelength Converters (TWCs) are very expensive.

15. Potential future IP router architecture • Aggregation in IP/MPLS switch part • Cross-connection of wavelengths at optical layer • Tunable lasers

16. Switching architectures with wavelength conversion (Borella) • Dedicated converters for each output • Many converters • Flexible, no blocking • Wavelength specific multiplexers minimizes attenuation.

17. Switches with shared wavelength conversion • Shared between all input lines • Access from any input wavelength • Optimal wavelength converter resource utilization • WC may not be available if too few • Extra switch between WC and output MUX required.

18. Wavelength converters shared for input fibre • Less efficient utilization of WC pool than fully shared • Larger probability for blocking with the same number of WC’s • Extra switch not required, i.e. simpler design

19. Switch with add/drop and shared wavelength conversion • If electronic conversion then not transparent • Transparent usually means transparent to bitrate • Other types of transparency?

20. Cheyns: Optical packet switched... AWG • Results from the EU IST-project STOLAS • Optical packet/burst switches requires fast (ns) reconfigurable switching matrixes. • AWG combined with fast tunable wavelength converters is an alternative.

21. Arrayed waveguide Grating • 1 X N or N X N coupler spreads the light in N waveguides with different lengths • Waveguides are merged and create interference • Each wavelength will constructively recombine at only one given output port and cancel out on the others, due to the phase difference

22. AWG switching principle • Cyclic • F fibres , W wavelengths • Same output for lj as for lj + WDl • Table: Given input port and wavelength, the output port is found from the table.

23. Simple AWG node architecture • Internal blocking when two inputs with the same l to the same fibre • No conversion at output • Conversion range at input: l0 to l3 required • Limits which output port the input can be connected to => blocking • Internal blocking may be relaxed by smart choices of output wavelengths for converters and many wavelengths. l0

24. No blocking version • Input converters must be able to convert to seven different wavelength converters: Larger wavelength range. • Fixed wavelength at output converters for multiplexing • Only one wavelength for each output. • Potential problems with scaling, size of AWG.

25. Using smaller AWGs • Future networks have many wavelengths: Scalability • Simple to add an extra input: Add extra input on optical coupler (cheap). • AWG with W input/output ports • Two inputs which is combined can not be converted to the same l: Contention • Couplers at output ports • Same blocking properties as the first design. (Same l setting) • Scales with W rather than F*W (first design)

26. Small AWG, many internal wavelengths • Nonblocking • F*W internal wavelengths • 2F multiplexers with size F*W • Several wavelengths on each output port. • W*F2 TWC’s with conversion grade W • Tunable converters at output

27. Alternative solution (multiport): • Reduced size of muxes and number of converters • Still nonblocking • Still FW internal wavelengths • FW fixed output wavelength converters • W demultiplexers, but F smaller/cheaper Foretrukket!