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Optical Networking: Principles, Hot Topics and Future Perspectives November 24

TCOM. Optical Networking: Principles, Hot Topics and Future Perspectives November 24. Sébastien Rumley EPFL – Laboratoire de Telecommunication (TCOM) sebastien.rumley@epfl.ch. Outline. 1. Optical networking : principles Optical transmission (history, rules of thumbs, etc.)

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Optical Networking: Principles, Hot Topics and Future Perspectives November 24

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  1. TCOM Optical Networking: Principles, Hot Topics and Future Perspectives November 24 Sébastien Rumley EPFL – Laboratoire de Telecommunication (TCOM) sebastien.rumley@epfl.ch

  2. Outline • 1. Optical networking : principles • Optical transmission (history, rules of thumbs, etc.) • Optical switching • Context and challenges • 2. Research fields • Components • Network Management schemes • Optical networks design and planning • Routing and Wavelength Assignment (RWA) • Routing and Regenerator Placement (RRP) • Optical Burst Switching • 3. Alternative ideas • All Optical Network Coding • OBS multicast • Ad-hoc wireless optical networks Technological research Academic research

  3. Absorption/Scattering Bending losses Laser + modulation Photodiode Fibre (wave guide) Input data Output data Principles : Optical transmission • An optical fibre is a wave guide. • The light emitted by a laser diode is modulated and injected in this guide • The modulated signal is analysed with a photodiode at the fibre end • The transmitted signal is subject to • Attenuation (bending, absorption, scattering) • Impairments (chromatic dispersion, polarisation, non-linear effects…) Impairments  Noise Attenuation + noise  Signal to Noise Ratio (SNR) !

  4. Raw transmission limits 1. The attenuation is frequency dependent • A fibre is a very good wave guide for given frequencies only • Typically in three “windows” located around 1.4 μm • Outside, light is attenuated by various effects • Modulation speeds • In theory, bandwidth of ~2x20 Thz  ~80 TBaud/s (Nyquist) • Not realisable in practice • Impairments: • Non linear effects • Chromatic dispersion This profile is different for each fibre Image source : http://www.fiberoptics4sale.com/wordpress/optical-fiber-attenuation/

  5. Transmission enhancement : multiplexing • Multiplexing of independent channels (λ), modulated at lower rates WDM (Wavelength Division Multiplexing) Good news : • Capacity multiplied Bad news : • Crosstalk  Noise • Demultiplexing losses  Attenuation Image sources : http://www.imec.be/ScientificReport/SR2008/HTML/1225202.html http://www.harzoptics.de/pof-demultiplexer.html

  6. Trans. enhancement : optical amplification • How to mitigate the attenuation? • How to carry signals over longer distances?  By reamplifying them ! • Electronic amplification Demodulate the light signal with a photodiode, remodulate a new signal + Not only amplification (Resizing), but also Retiming and Reshaping (3R) • Resource and energy consuming • With WDM, demultplexing and remultiplexing is required • One regeneration per signal • Optical amplification Similar principle as the laser + All channels amplified simultaneously • Amplification only • Works only for given frequencies

  7. Historical landmarks for transmission • 1) Point-to-point links with electrical regeneration (70’) • 2) Point-to-point links with multiplexing - WDM (80’) • 3) Point-to-point WDM links with optical amplification (90’)

  8. Recent advances on transmission • QAM modulation • 1.568 Tbit/s with a 16-QAM [1] • Spectral efficiencies > 6 b/s/Hz • More channels • 500 channels (25 Ghz channel spacing) [2] • Faster modulations • 640 Gbit/s [3] [1] Xiang Liu, Sethumadhavan Chandrasekhar, Benyuan Zhu, Peter Winzer, David Peckham “7 x 224-Gb/s WDM Transmission of Reduced-Guard-Interval CO-OFDM with 16-QAM Subcarrier Modulation on a 50-GHz Grid over 2000 km of ULAF and Five ROADM Passes“, ECOC 2010 [2] Chun-Ting Lin, “400-Channel 25-GHz-spacing SOI-based planar waveguide demultiplexer employing a concave grating across Cand L-bands”, Optics Express, Vol. 18, Issue 6 [3] Hao Hu, Evarist Palushani, Michael Galili, Hans Christian Hansen Mulvad, Anders Clausen, Leif Katsuo Oxenløwe, and Palle Jeppesen, “640 Gbit/s and 1.28 Tbit/s polarisation insensitive all optical wavelength conversion”, Optics Express, Vol. 18, Issue 10

  9. Optical switching and optical regeneration • With these througputs, (< 10 Tbit/s) we have pleanty of leeway at the transmission level • What are the next steps ? • Optical switching • Available • MEMS • Filters • Other • Optical regeneration • Not available (yet?) Image sources : http://www.fiberopticsonline.com/article.mvc/Alcatels-new-OXC-leverages-bubble-technology-0001 https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr200710sp5.html

  10. Optical switching • Per channel (lightpath) switching – Optical Circuit Switching (OCS) After demultiplexing, deflect a wavelength in a particular direction + The easiest way + Can be done manually and statically • Low granularity • More generally… low flexibility • Sub channel switching – Optical Packet/Burst Switching (OPS/OBS) After demultiplexing, deflect a wavelength in a particular direction for a given duration + Finer granularity, more flexibility • Network Control overhead • Switching time overhead - More complex network Management

  11. Optical networks applications • Intra-office communications • Fibre to the home • Application specific (e.g. CERN) • Long-haul networks • Range up to 5’000 km or more • Traffic demands ~ 100 Gbit/s per node pair • Intra domain communications  no more than ~100 nodes • High Availability (six nines  99.9999% 30 sec per year) • One second of unavailability at 1 Tbit/s = 1 Terabit of lost… • High investments Not in the scope of this talk

  12. GOALS : Above all: deliver bits High throughput High availability Low congestions No errors Minimize the costs Energy Investments Maintenance Minimize the risks Network must be under control Capacity must be available CHALLENGES : Improve network utilisation Reduce the cascaded overprovisionning Minimize the frequency « trap » Reduce energy consumption Avoid per bit operations Rationalise the utilisation Improve network management schemes Without adding too much complexity While guaranteeing availability Optical networks – goals and challenges

  13. + 2. Research in optical networks • Components • Fibres • Lasers/modulations • Multiplexers/demultiplexers • Amplifiers • Cross-connects • Network design and planning • Resources provisioning • Network design • Resources allocation • Network planning • Network orchestration • Remote operation • Computer aided management • Configuration automation

  14. Most famous optical network problem Network design version Given: a matrix of demands (# lightpaths required between each source-destination pair) To find: Network capacities a route and a wavelength for each lightpath Constraints: A lightpath must keep the same wavelength all the way long Two lightpaths cannot share a fibre if they use the same wavelength Objective: Minimise the required wavelength Minimise the number of required fibres Network planning version Given: a matrix of demands A list of capacities (fibres and λ) To find: a route and a wavelength for each lightpath Objective: Minimise the rejected demands Minimise the “frequency traps” Minimise the required wavelength inimise the number of required fibres Routing and Wavelength Assignment - RWA

  15. RWA – more variants • In the network planning version, the demands may • Arrive • Simultaneously • At different time points • Begin • Immediately • Later in time (delayed) • Last • Forever (open end) • For a fixed duration • Design + Simultaneous + Immediate + Forever  colouring problem • Planning + Simultaneous + Immediate + Forever bin packing [4] • Planning + Simultaneous + Delayed + Fixed duration  scheduling [5] [4] N. Skorin-Kapov, “Routing and wavelength assignment in optical networks using bin packing based algorithms [5] X. Liu, C. Qiao, et al. “Task Scheduling and Lightpath Establishment in Optical Grids

  16. RWA – event more variants • Impairments constrained RWA • RWA that takes into account the signal quality and inter wavelength perturbations [6] • Protection aware RWA • Both main and spare path must be found • Dedicated or shared protection • Multi priority RWA • Multicast aware RWA • Etc. [6] A. Marsden, A. Maruta, K.-I. Kitayama, “Routing and Wavelength Assignment Encompassing FWM in WDM Lightpath Networks

  17. RWA – Solving methods • ILP / MILP • Constraint Programming • Heuristics • ILP Relaxation • Tabu search • Greedy • Simulated annealing • ….

  18. b a c d g e f Routing and Regenerator placements • Optical signal must be regenerated after a certain journey • Regenerators must be installed • However, regenerators require more power, more space, more complex chassis, more maintenance • They should be placed only in strategic places Problem : minimise the network's critical length (if not fixed) minimise the number of equipped nodes minimise the number of regenerations minimise the routing costs In this example, two solutions to reduce CL: A) Add a regenerator in d B) Reroute e-f-d-g  e-a-c-g

  19. a b a b 10 10 10 10 10 10 S x S x 8 8 8 8 8 8 8 8 c d e c d e (a) (b) 5 5 5 5 a x d a d x 8 8 10 10 8 5 8 5 5 5 S b e y b e S y 8 8 10 10 5 5 5 5 f z c f c z (a) (b) Problem – Conflicting Objectives • Minimize the routing  shortest paths taking no detours • More regeneration sites • Minimize the # of regenerations shortest path… in most cases • Minimize the sites  oblige lightpath to take detours  More regenerations and more routing costs • Regenerations : 3Routing cost : 3x(8+5+5) = 54 • Regenerations : 5Routing cost : 2x(8+5+10) + 18 = 64

  20. Multi-objective optimisation Routing penalty (in %) Relative optical reach

  21. Optical Burst Switching • General problem of Optical Circuit Switching (of circuits in general) : • A customer of a long-haul operator requires capacity for a fixed duration • He measures demand peeks of 60 Gbit/s … whereas the average demand is ~5Gbit/s • He nevertheless orders a 30 Gbit/s connection • Overprovisioning factor : 600% • The operator has many customers • In general, 25% of them ask for connection … but sometimes 75% of them • The operator is required to design its network accordingly • Overprovisionning factor : 300%  Most of the time, a sixth of a third of the capacity is used… ~5%

  22. Optical Burst Switching – Statistical multiplexing • General idea : • With OCS, the operator cannot look “inside” a circuit and fill the voids • Idea: • Offer to the customer to carry its small packet directly (e.g. IP packets) • Schedule them himself in the network • Problems: • IP packets are too small to be inserted independently in the optical network • Reserve a circuit for these packets ? Back to the original problem • Multiplex statistically at network edge ? • Require huge routers (avoid per bit operations ?) • Require to centralise the entering packets (rationalise utilisation ?) • Solution: • Aggregate in edge nodes smaller packet until reaching an adequate size • Let the network node cores multiplex these bursts

  23. OBS – General Assumptions • Burst of about 1mbit – 0.1 ms at 10Gbit/s • Burst are sent in a cut-though manner • No per bit operation along the way • Burst are preceded by a Burst Control Packet (BCP) sent in advance • A dedicated lower bit rate channel is reserved for the BCPs • The BCP “announces” the burst arrival at intermediate nodes • One way reservation • If a node has no resources, the BCP is dropped, and the burst will be blocked [7] C. Qiao, M. Yoo, “Optical Burst switching (OBS) – a new paradigm for an optical internet, Journal of high speed networks, 1999 – IOS Press

  24. OBS Variants • Burst assembly mechanisms (fixed size, fixed delay, hybrid) • Conventional OBS vs. Emulated OBS • In E-OBS, BCP and burst are emitted simultaneously • Burst are delayed at each core node entrance • Reservation protocols • Explicit setup - Explicit release • Estimated setup - Estimated release • Scheduling algorithms • With or without void filling

  25. More OBS Variants • Routing : • In general, try to minimize the resources consumption  shortest path • Sometimes, better to avoid congested zones • Pro-active routing scheme : load-balancing • Re-active routing scheme : deflection routing • Synchronous or quasi-synchronous OBS • Etc.

  26. QS-OBS : Performance analysis [8] O. Pedrola, S. Rumley, et al. “Performance overview of the quasi-synchronous operation mode in optical burst switching (OBS) networks, Elsevier Journal of Optical Switching and Networking, Issue 8, In Press

  27. Contention in OBS • Contention occurs when a burst cannot be forwarded on its natural path • Among all the situations causing contention, one can highlight two extreme cases : Statistical fluctuation – transient phenomenon – short term overload  "bad luck" No fluctuation! - stationary phenomenon – long term overload  "misconfiguration"

  28. Contention avoidance methods Medium term overload Short term overload Long term overload Buffering with FDL Flow smoothing and synchronisation Burst deflection Not viable economically Redimensioning Traffic engineering – load balancing Adaptive load balancing Connection Access Control (CAC)

  29. Our goal Medium Integrate in one single scheme :  perform this scheme directly at the OBS layer Short Long A burst deflection An adaptive load balancing A Connection Access Control (CAC) Adaptive burst Admission and Forwarding [9] S. Rumley, O. Pedrola, et al. “Feedback Based Load Balancing, Deflection Routing and Admission Control in OBS Networks”, Journal of Networks, Academy Publisher, Nov 2010

  30. e1 3 e5 5 1 4 2 1-5:ac OK 1-5:ac OK 1-5:ac OK In more details ID :1-5:ac ID :1-5:ac 1,3 ID :1-5:ac 1 ID :1-5:ac 1,3,4 - Burst Control Packet (BCP) carries an ID - BCP contains a list of visited nodes - When a BCP is dropped… … or arrives at destination a feedback is sent to each node of the list

  31. Pending table node 1 ID Dest Offset Next hop 1-5:ac 5 3 3 e1 3 e5 5 1 4 2 1-5:ac OK In more details ID :1-5:acOff: 4 Dest: e5 ID :1-5:acOff: 2 Dest: e5 ID :1-5:acOff: 3 Dest: e5 ID :1-5:acOff: 0 Dest: e5 ID :1-5:acOff: 1 Dest: e5 Next : 3 ! Dest Offset Next + - - BCP also store the remaining offset time and of course the destination index 2 1 2 0 0 … … … … … - When a core node takes a forwarding decision it adds this decision in a local table (pending table) 5 3 3 0 0 1 … … … … … - When a core node receives a feedback it retrieves the corresponding decision from the table and updates its feedback table

  32. e1 3 e5 5 1 4 2 Dest Offset Next + - 5 3 2 134 5 5 3 3 241 6 Burst forwarding ID :1-5:acOff: 4 Dest: e5 ID :1-5:acOff: 3 Dest: e5 - When a BCP arrives, the core node retrieve the feedbacks corresponding to the destination and offset 96.4 % - The success probabilities are estimated for each possible next hop 97.6 % - Core node tries to make a reservation, starting with the highest probability - If no reservation is possible on the most favorable next hop, other alternatives are successively tried

  33. e1 3 e5 5 1 4 2 Dest Offset Next + - 5 2 3 0 20 5 2 4 156 9 Burst admission ID :1-5:acOff: 3 Dest: e5 ID :1-5:acOff: 2 Dest: e5 In this case, choosing 3 will lead to burst loss :offset is insufficient (2-3-4-5  3 hops) 3 should thus be excluded even there is no other solution CAC Mechanism : We assume a threshold TCACand a minimal number of feedbacks FCAC If the success estimation E is < TCAC while the number of received feedback is ≥ FCAC next hop is excluded

  34. p1,s p2,s p1,s p1+2,s p1+2,s p2,m p1,m p2,m p1,m 3. Alternative research ideas in optical networks • All-Optical Network Coding • For protection purposes mainly [10] E. D. Manley et al. “All Optical Network Coding”, Elsevier Journal of Optical Communications and Networking, Volume 2, Number 4, April 2010

  35. OBS MultiCast • Combine (adaptive) deflection routing with Multicast routing?

  36. Ad-hoc wireless optical networks • Light beams can also propagate in the air (free space optics) • At relatively high speed on short distances • Typically 10-40 Gbit/s < 200m • 1-10 Gbit/s < 10km • Now they have to be manually installed • They might be automated in the future • Beam tracking • Ad-hoc topology organisation • Major problem : almost ON/OFF • Obstacle : OFF • Not as in Wifi, where obstacle only affect SNR • Multicast protection required Image source : http://www.systemsupportsolutions.com/

  37. Comments or questions ? Thank you for your attention

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