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Lecture: 9 Elastic Optical Networks. Ajmal Muhammad, Robert Forchheimer Information Coding Group ISY Department. Outline. Motivation Elastic Optical Networking Flexible spectrum grid, tunable transceiver, flexible OXC Flexible Optical Nodes Routing and Spectrum Assignment Problem. - PowerPoint PPT Presentation


  • Lecture: 9 Elastic Optical NetworksAjmal Muhammad, Robert ForchheimerInformation Coding Group ISY Department

  • OutlineMotivationElastic Optical NetworkingFlexible spectrum grid, tunable transceiver, flexible OXCFlexible Optical NodesRouting and Spectrum Assignment Problem

  • Research MotivationEmerging applications with a range of transport requirementFuture applications with unknown requirementsFlexible and efficient optical networks to support existing, emerging and future applications

    Courtesy: High performance networklab., Bristol

  • Applications with Diverse RequirementsCourtesy: High performance networklab., Bristol

  • Evolution of Transmission Capacity

  • Spectral Efficiency (SE) ImprovementFixed optical amplifier bandwidth (~ 5 THz)Per fiber capacity increase has been accomplished through boosting SE (bit rate, wavelength, symbol per bit, state of polarization)Bit loading higher than that for DP-QPSK causes rapid increase in SNR penalty, and results in shorter optical reachSE improvement is slowing down, meaning higher rate data need more spectrumOptical amplifier bandwidth (~ 5 THz)

  • Current Optical Networks :: Inflexible

    Super-wavelengthCourtesy: High performance networklab., Bristol

  • Current Solution for Bandwidth-Intensive ApplicationsOptical virtual concatenation (OVC) for high capacity end-to-end connection (super-wavelength)

    Demultiplex the demand to smaller ones such as 100 or 40 Gb/s, which can still fit in the fixed grid (Inverse multiplexing)

    Several wavelengths are grouped and allocated end-to-end according to the application bandwidth requirements

    Grouping occurs at the client layer without really affecting the network

    Connection over several wavelengths is not switched as a single entity in network nodes

  • Elastic Optical NetworkingThe term elastic refers to three key properties:The optical spectrum can be divided up flexibly

    Courtesy: Ori Gerstel, IEEE Comm. Mag. 2012

  • Elastic TransceiversThe transceivers can generate elastic optical paths (EOPs); that is path with variable bit rates

    Tunable transceiverCourtesy: Steven Gringeri, IEEE Comm. Mag. 2013

  • Flexible Switching

    EONsWDM NetworksBandwidth VariableThe optical nodes (cross-connect) need to support a wide range of switching (i.e., varying from sub-wavelength to super-wavelength)

  • Drivers for Developing the EONs Support for 400 Gb/s, 1Tb/s and other high bit rate demands

    Disparate bandwidth needs: properly size the spectrum for each demand based on its bit rate & the transmission distance

    Tighter channel spacing: freeing up spectrum for other demands Reach vs. spectral efficiency trade-off: bandwidth variable transmitter can adjust to a modulation format occupying less optical spectrum for short EOP and still perform error-free due to the reduced impairments

    Dynamic networking: the optical layer can now response directly to variable bandwidth demands from the client layers

  • Elastic Optical Path Network:: Example

  • OutlineMotivationElastic Optical NetworkingFlexible spectrum grid, tunable transceiver, flexible OXCFlexible Optical NodesRouting and Spectrum Assignment Problem

  • Common Building Blocks for Flexible OXCs

  • Reconfigurable Optical Add-Drop Multiplexer (ROADM)Add channelsDrop channelsOptical splitter Wavelength selective switch

  • Multi-Granular Optical SwitchingFXC: Fiber switchBXC: Waveband switchWXC: Wavelength switchBTF: Band to FiberAdd channelsDrop channels

  • Architecture on Demand (AoD) Optical backplane cross-connections for AoD OXCsMEMS switch is used to interconnected all theInput-output ports and switching devicesCourtesy: High performance networklab., Bristol

  • AoD NodeAimed to develop an optical node that can adapt its architecture according to the traffic profile and support elastic allocation of resources

  • Flexible OXC ConfigurationBackplane implemented with 96x96 3D-MEMSFlexibility to implement and test several switch architectures on-the-flySwitching time 20ms

    Courtesy: High performance networklab., Bristol

  • OutlineMotivationElastic Optical NetworkingFlexible spectrum grid, tunable transceiver, flexible OXCFlexible Optical NodesRouting and Spectrum Assignment Problem

  • Routing and Spectrum Assignment (RSA)Spectrum variable (non-constant)connections, in contrast to standardWDM

  • Planning Elastic/Flexgrid NetworksInput: Network topology, traffic matrix, physical layer modelsOutput: Routes and spectrum allocation RSA (RMLSA include also the modulation-level used 2 flexibility degree: modulation and spectrum)Minimize utilized spectrum and/or number of transponders, and/orSatisfy physical layer constraints*

  • ExamplesRMLSARSACourtesy: Ori Gerstel, IEEE Comm. Mag. 2012

  • Cost-Efficient Elastic Networks Planning Using AoD NodesConventional ROADMsAoD ROADMs

  • ***At a fixed optical amplifier bandwidth, typically 5 THz, increases in the per fiber capacity have been achieved through boosting of the spectral efficiency by means of increasing the signal bit rate, wavelengths, symbols per bit, and states of polarization.As a result, a cutting edge transport system employing dual-polarization and QPSK modulation will have a spectral efficiency reaching 2 b/s/Hz.Unfortunately, it is well known that bit loading higher than that for QPSK to further increase the channel capacity causes a rapid increase in the SNR penalty.Under the limited fiber launched power necessary to avoid excessive nonlinear signal distortions, this SNR penalty results in a shorter optical reach. Due to this, despite the potential for more powerful forward error correction, FEC and a lower noise amplifier, we need to concede that the pace of improvement in spectral efficiency will be slowing down in the era beyond 100 Gb/s.*******The aim of the elastic optical path network is to provide spectrum-efficient transport of 100-Gb/s services and beyond through the introduction of elasticity and adaptation into the optical domain.If based on the conventional design philosophy, every optical path is aligned on a fixed grid regardless of the path length, bit rate, and actual client traffic volume.By taking advantage of spectral-efficiency-conscious adaptive signal modulation and elastic channel spacing, elastic optical path networks yield significant spectral-savings as shown in this figure.For shorter optical paths, which suffer from less SNR degradation, we employ a more spectrally-efficient modulation format, such as 16QAM.For client traffic that does not fill the entire capacity of a wavelength, the elastic optical path network provides right-sized intermediate bandwidth, such as 200 Gb/s. Combined with elastic channel spacing, where the required minimum guard band is assigned between channels, elastic optical path networks accommodate a wide range of traffic in a spectrally-efficient manner.******