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WP5: ICCS NTUA

WP5: ICCS NTUA. Wavelength Routing Algorithms for Transparent Optical Core Networks. Outline. Design rules for wavelength routed optical networks Benefits of Analytical Rules Layered Approach for Physical Layer Impairments in TON The layered model

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WP5: ICCS NTUA

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  1. WP5: ICCS NTUA Wavelength Routing Algorithms for Transparent Optical Core Networks IST NOBEL – Plenary Mtg

  2. Outline • Design rules for wavelength routed optical networks • Benefits of Analytical Rules • Layered Approach for Physical Layer Impairments in TON • The layered model • Non-linearities in fibres: Analytical vs. Numerical • Physical Impairment Aware Wavelength Routing Algorithm • Motivation • Description • Preliminary Results • Benefits of the approach IST NOBEL – Plenary Mtg

  3. Design Rules for Optical Networks Empirical Design Rules Analytical Design Rules Numerical Design Rules Time and Resources Consumption Conservatism (higher margin) Accuracy IST NOBEL – Plenary Mtg

  4. Benefits of Analytical Design Rules • Much more accurate and flexible than simple empirical design rules • Can be scalable as far as number of wavelengths, links, nodes etc is concerned • Much faster than Numerical Simulations • For simple cases can fall back to the empirical rules • Depending on application the trade off between accuracy and complexity is adjustable Network Design (static, off line calculations for resource optimisation) WRA (dynamic online calculations for optimised path) IST NOBEL – Plenary Mtg

  5. Transparent Network Physical Impairments • Transmission Impairments • Attenuation -> Amplifiers -> ASE Accumulation • Chromatic Dispersion • Polarisation Mode Dispersion • Nonlinearities • FWM • XPM, SPM • Switching Impairments • Crosstalk • Filtering IST NOBEL – Plenary Mtg

  6. Physical Layer Study Methodology • A “layered” approach has been adopted • Layer 1: OSNR, filter cascade, crosstalk • Layer 2: Fiber non-linearities, dispersion • Layer 3: Real system: combination of the above • A.Stavdas, et al JLT. 21 (2)2003 IST NOBEL – Plenary Mtg

  7. Physical Layer Simulation IST NOBEL – Plenary Mtg

  8. probability i (1) s(1) Optimum decision level i (0) s(0) current Formulae used in analytical modeling (1) Independent noise-like processes, Gaussian statistics assumed • XPM: A. Cartaxo: JLT 1999 • FWM: K. Inoue: JLT 1992 IST NOBEL – Plenary Mtg

  9. Formulae used in analytical modeling (2) Noise accumulation when saturation phenomena are taken into account IST NOBEL – Plenary Mtg

  10. Validation of the XPM Analysis This WDM system has 32 channels of 0dBm average power and 100 GHz channel spacing IST NOBEL – Plenary Mtg

  11. Validation of FWM Analysis This WDM system has 16 channels of 0dBm average power and 50 GHz channel spacing IST NOBEL – Plenary Mtg

  12. Q factor calculation 16 channels, 25 GHz channel spacing, 4 x 40 Km, + 3 dBm per channel, and 2.5 Gb/s. IST NOBEL – Plenary Mtg

  13. Motivation: why use Physical Impairment Aware WRA • Transparent Optical Networks do not offer inherent regeneration • Impairments (noise, nonlinearities etc) are accumulated across the selected paths inducing errors • Wavelength Routing algorithms are traditionally based on minimising the length of the path. • Shortest path does not necessarily ensure best performance since a) the path may not be available! b) adding a new wavelength there might lead to a critical situation. • A request for a connection should be dropped (blocking) when: • there is not an available path • The BER of the signal is expected to be less than a specific value • Hence, the WRA should be ‘Physical Impairment Aware’: • Waste of resource for ‘impaired’ connections will be avoided • Performance tailoring can be achieved for future connections • It can provide QoS classes IST NOBEL – Plenary Mtg

  14. Justification: Physical Impairment Blind WRA IST NOBEL – Plenary Mtg

  15. Connection Set up/Tear Down Connection Requests NMS Route Calc Physical Impairment Calculation Calc Supervisor (decision making) Monitor Component Path/Wavelength Calculation Physical Layer Parameters (e.g fiber plant) Network Topology (graph) Physical Impairment Aware Wavelength Routing Algorithm IST NOBEL – Plenary Mtg

  16. For each of the possible wavelengths: Find the shortest path (min dist) and ensure (continuous) wavelength If No block request If Yes Calculate the Q factor for the all the returned paths - Layered Approach 1. QASE 2. QNLS … If Q<Q thresholdblock request if Q>Q threshold Insert the channel (temp) and check the Q’ of the all the existing paths after reservation if Q’>Q threshold If Q’<Q thresholdblock request Return a table with the acceptable wavelength/paths Choose a wavelength from this table (first fit, etc) Update Monitor with the Power/noise of every channel IST NOBEL – Plenary Mtg

  17. C B Request (A => C) A D Assume a network with nodes ABCD and a request for connection between A and C There are 4 possible wavelengths IST NOBEL – Plenary Mtg

  18. C B A D First step is to find the shortest path for each of the wavelengths: Blue wavelength is available on AC Yellow is available on ADC Green is available on AC Red is not available on any path, i.e. red is blocked IST NOBEL – Plenary Mtg

  19. C B A D The second step is to calculate the Q factor of these wavelengths. Assume that the blue channel has Q<Qthreshold=> blocked Third step is to check the effect of the introduction of yellow wavelength on path ADC and the green wavelength on path AC. Assume that they do not affect the rest of the channels. Final step is to choose from the available wavelengths green and yellow IST NOBEL – Plenary Mtg

  20. Wavelength Routing Algorithm Connection Set up/Tear Down Connection Requests NMS Physical Impairment Calculation Calculation Supervisor (decision making) Monitoring Path/Wavelength Calculation Physical Layer Parameters (e.g fiber plant) Network Topology IST NOBEL – Plenary Mtg

  21. RWA in Optical Circuit Switched Networks • RWAs have to find a path and also assign the same wavelength across this path, i.e. shortest path not always suitable • Thus two problems are separated: • Path calculation • Adaptive • Wavelength assignment • First fit/ Random Fit/ Best Fit IST NOBEL – Plenary Mtg

  22. Physical Impairments Connection Set up/Tear Down Connection Requests NMS Physical Impairment Calculation Calculation Supervisor (decision making) Monitoring Path/Wavelength Calculation Physical Layer Parameters (e.g fiber plant) Network Topology IST NOBEL – Plenary Mtg

  23. Can take into account the impact of the requested connection on the existing connections Can be used to estimate the impact of the connection under investigation on future connections The analytical models utilised are accurate and are being tested against numerical ones Benefits of the specific Approach IST NOBEL – Plenary Mtg

  24. Analytical Design Rules are ideal Layered approach can use accurate analytical models Preliminary results show good agreement with numerical analysis WRA must incorporate physical impairment awareness Conclusions IST NOBEL – Plenary Mtg

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