TTM 1 2013 Core networks and Optical

TTM 1 – 2013: Core networks and Optical Circuit Switching (OCS)

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

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

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 2 d. B/km G. 652 C 0, 5 Loss (d. B/km) ● 0, 4 0, 3 0, 2 1271 -1451 nm 0, 1 1471 -1611 nm 0 1200 1300 1400 1500 Wavelength (nm) 1600

16 channel CWDM using two multiplexers for two different bands C 1 – (8+1) C 1 – 8 L 1271 1291 1311 1331 1351 1371 1431 1451 C 1– (8+1) 1471 1491 1511 1531 1551 1571 1591 1611 EXT C 1 – 8 L 1271 1291 1311 1331 1351 1371 1431 1451 8

CWDM and DWDM hybrid C 1 -8 D 1 -52 1535. 82 1535. 04 1534. 25 1533. 47 1532. 68 1531. 90 1531. 12 1530. 33 1471 1491 1511 1531 1551 1571 1591 1611 C 1– 8 1471 1491 1511 1531 1551 1571 1591 1611 D 1 -52 1535. 82 1535. 04 1534. 25 1533. 47 1532. 68 1531. 90 1531. 12 1530. 33

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; 3 R versus 2 R (Mach-Zhender interferometer).

Needed functionality for optical OXC based networks (2) ● ● ● Multiplexing and grooming: Normally done in the optoelectronical 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)

Transparent (all-optical) switches (1) ● ● ● Micro-electromachining 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?