TTM1 – 2013: Core networks and Optical Circuit Switching (OCS)

Overview topics ● Short repetition of two important facts ● Optical networks (Zouganeli) ● CWDM and DWDM networking (TransPacket white-paper) ● Switching architectures (Borella)

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

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

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:

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).

Course WDM ● Cheaper technology with less scalability than DWDM ● Typically maximum 16 channels 0 0,1 0,2 0,3 0,4 0, Wavelength (nm) Loss (dB/km) 2 dB/km G.652 G.652C nm nm

16 channel CWDM using two multiplexers for two different bands 8 EXT C1 – (8+1) C1 – 8L

CWDM and DWDM hybrid C1-8 D C1–

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).

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

Alternative R-OADM switch implementations

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.

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).

● 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) Needed functionality for optical OXC based networks (2)

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

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

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

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

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.

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

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