1. Towards Dynamic and Scalable Optical Networks  Brian Smith 3 rd May 2005

2. Towards Dynamic and Scalable Optical Networks  What is required to deliver truly dynamic optical networks ?  A Dynamic Control Plane  Technologies for Wavelength Switching  Considerations for achieving higher data rates + capacities.  Issues with 40Gbps  Is 100Gbps achievable ?  Getting maximum spectral efficiency in a dynamic optical network.

3. A Dynamic Control Plane

4. Lightpath Control  To deliver on-demand gigabit lightpaths, a fast and reliable distributed control plane is required  Reliable –transport infrastructure should remain stable during reconfigurations  Fast – otherwise its not on-demand !  GMPLS is one control plane under development for optical networks by the industry.  Based on standard set of IP routing and signaling protocols  UCLP is an example of an R&E initiative (CANARIE)  TL1 interfaces controlled by a distributed service layer based on a web browser and network model.

5. Evolving Towards Dynamic Lightpath Control  Features Required for Light-path Control  Topology discovery and link management.  Operator signaled light-paths (Network should automatically manage its own demand).  Client on-demand light-paths (High end users can individually control wavelengths). An important feature for future R&E networks !  Integration with IP/MPLS control plane for dynamic traffic engineering e.g HOPI / DRAGON.  Dynamic protection – if required

6. Backbone Network On-Demand Bandwidth Capacity Access Network Mesh Network High End Users A B C D Server Farm User Controlled Lightpath (e.g. for nightly data back-up) Available now between routers. Needs to evolve to support high data rates on wavelengths Wavelength Switch Routers

7. Example of need for on-demand wavelengths  4 radio telescopes in an array – 12 hour observation  Assuming 1Gbps per telescope – 0.2 Petabits of data !  How long would it take to back up the data to storage ?  With 100Mbps rate – ~23 days minimum assuming no packet loss.  With dedicated GigE wavelength – ~4 days.  If user can request an on demand 10GigE wavelength – ~5 hours. High-end Research users will require high capacity on demand services

8. Enabling Technologies For Dynamic Networks

9. Enabling Technologies for Dynamic Networks  Electronic ROADM  Optical ROADM  Tunable lasers  Tunable 10G DWDM XFPs will be available in 2006  Integrated optical wavelength converter / tunable laser  Demonstrated in Labs using non-linear cross-talk in Semiconductor Optical Amplifiers – Capable of supporting up to 40Gbps

10. Electronic ROADM NxN Transparent Wavelength Switch (electrical) Trib 1310 Trib 1310 Trib 850 Trib 1550 DWDM West Fiber East Fiber DWDM North Fiber CWDM South Fiber CWDM Native signal transparency with layer 1 performance monitoring Simple Any-to-Any Multi-Degree grid interconnection Simple to Engineer.

11. Optical ROADM – Wave-blocker Splitter Wave-blocker Drop Filter Add Filter Coupler Drop and Add Filters must be tuneable for maximum flexibility. Hitless filter tuning is a problem. Many discrete components so expensive High insertion loss – Limits DCM – Limits reach between nodes for fully transparent networks.

12. Optical ROADM – Wavelength Selective Switch (WSS) Wavelength Selective Switch Add Coupler Drop Channels Optional Expansion Port Fewer discrete optical components Fully flexible colourless add/drop Lower insertion loss Limited number of drop ports – Use expansion port !

13. Comparison - Wavelength Switching FunctionalityElectronic ROADMOptical ROADM Transparency (bit rate and protocol) Yes - wide range of signals Yes Low LatencyYes Single wavelength granularity (I.e. no wavelength stranding) Yes Mesh Support (multi-degree)Yes Yes - Blocking issues Wavelength TranslationYesNo Grid Conversion (e.g. CWDM to DWDM) YesNo Protocol Performance Monitoring EasyOptical power only Wavelength Protection & Hitless Maintenance EasyRing – Easy Mesh – More difficult

14. Implementing ROADM Interfaces Optical and Electronic ROADM complement each other. Trib 1310 DWDM NxN Transparent Wavelength Switch (electrical) West Fiber East Fiber CWDM West Trib 1310 Trib 850 Trib 1550 CWDM East DWDM CWDM DWDM CWDM Pass-through Traffic North Fiber DWDM South Fiber Optical ROADM I/F

15. Multi-Degree ROADM Interfaces First step towards full NxN photonic wavelength switch. Optical Pass-through channels North Fiber South Fiber Optical ROADM I/F NorthW Fiber DWDM NxN Transparent Wavelength Switch (electrical) West Fiber East Fiber DWDM Optical ROADM I/F SouthE Fiber Optical ROADM I/F DWDM

16. ~17 Cost Comparison – 2.5G Traffic

17. ~6 Cost Comparison – 10G Traffic

18. Wavelength Switching - Cost sweet spots 4 8 12 16 20 24 28 32 Pass-through Channels Optical ROADM Electronic ROADM Optical ROADM Electronic ROADM 10G 2.5G Channel Rate Note: For 2-degree metro ring applications. Also applies to 4-degree mesh architecture

19. The Future of 40G/100G

20. 40Gbps/100Gbps  40Gbps  40Gbps DWDM trials and demonstrations becoming more common.  Ability to overlay on existing 2.5/10G links – a key driver !  40Gbps router interfaces have been demonstrated.  Dispersion must be controlled within ± 62 ps/nm.  PMD is an issue. Cannot exceed 2ps (outage < 3min/year)  100Gbps  Can 100Gbps be achieved over DWDM ?  Dispersion tolerance even tighter - ± 25 ps/nm.  PMD more of an issue. Cannot exceed 1ps (outage < 3min/year)

21. 40Gbps Dispersion Tolerance 6x80kmx26dB - 32 100GHz spacing SPM, XPM and FWM effects included Range of possible net dispersion Tunable Dispersion Compensation Required for 40Gbps.

22. 100Gbps  Several published examples of single wavelength 100Gbps+ transmission.  Spectral width ~ 150 GHz for NRZ so won’t fit into a 100GHz spaced DWDM pass-band (~85GHz) !  Dispersion limit for NRZ is ± 25ps/nm.  If we use non-binary coding – Spectral width reduced to 75GHz – Just fits within 100Ghz spaced DWDM band.  Needs tight control of laser + filter wavelengths.  Using >1 bit per symbol coding technique such as duo-binary or QPSK improves tolerance to dispersion and PMD. 100Gbps is achievable. Needs sophisticated coding!

23. Polarization Mode Dispersion  Using 6x80kmx26dB with 6 EDFA and 6 DCM, the calculated average DGD (assuming fiber is post 1995) = 2.5 ps  The PMD tolerance (and expected outage) for various data rates is: Rate pmd tolerance system outages/yr 2.5G30ps insignificant pmd outages/yr 10G7.6ps insignificant pmd outages/yr 40G(NRZ)2ps~ 3 minutes/year assuming FEC 100G(NRZ)0.9psRequires PMD compensation

24. How Much Capacity ? 100Gbps Duo-binary Wave-locker++ 1b/s/Hz 16 symbol levels – 4 bits per symbol required. 256 symbol levels – 8 bits per symbol required. 40Gbps NRZ/CS-RZ/ Wave-locker+ 10G overlay  0.4b/s/Hz Duobinary Wave-locker+ 0.8b/s/Hz 16 symbol levels – 4 bits per symbol 10Gbps No issue NRZ 0.1b/s/Hz Reduced reach Wave-locker NRZ 0.2b/s/Hz Reduced reach No ROADMs Wave-locker+ 0.4b/s/Hz 100GHz50GHz25GHz

25. Summary  On-Demand Light-path Control Enabled by:  Distributed, Intelligent Light-path Control (UCLP, GMPLS)  Electronic and Optical ROADM.  Widely Tunable Laser Sources.  40Gbps/100Gbps  40Gbps can be deployed over existing 10G infrastructure with appropriate dispersion control + FEC.  100Gbps will a challenge requiring sophisticated coding schemes and components for PMD mitigation.

26. Thank You

27. Impact of Tighter Channel Spacing  Four Wave Mixing (FWM) Increased FWM Impact – Reduced Reach.

28. Impact of Tighter Channel Spacing  Cross Phase Modulation distortion (XPM) Increased XPM Impact – Reduced Reach.