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Challenges in Optically Switched Network Design: Impairment-Aware Solutions

Explore issues and challenges in designing physically-aware optically switched networks. Learn about the DICONET framework and impairment-aware routing. Enhance your knowledge at the Int. Conf. on Photonics in Switching 2009.

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Challenges in Optically Switched Network Design: Impairment-Aware Solutions

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  1. ATHENS INFORMATION TECHNOLOGY “Issues and Challenges in Physical-Layer Aware Optically Switched Network Design and Operation” Yvan Pointurier, Siamak Azodolmolky, Marianna Angelou and Ioannis Tomkos {yvan,sazo,mang,itom}@ait.edu.gr http://www.ait.edu.gr September 15-19, 2009 – Pisa, Italy Session: “Impairment Aware and Reconfigurable Optical Networks” WeII3-1 Int. Conf. on Photonics in Switching 2009

  2. Outline • Introduction • Motivations • Issues and design challenges • DICONET framework • Impairment aware lightpath establishment • Conclusions Int. Conf. on Photonics in Switching 2009

  3. Introduction • Evolution of core optical networks: • Past, Present, Future! Optical-bypass Int. Conf. on Photonics in Switching 2009

  4. Key challenges • Physical Impairments accumulation • Signal impairments accumulate along a transparent optical path, therefore limiting the system reach and the overall network performance • Impairment aware routing and wavelength assignment algorithms • Failure localization • Failure propagate in a transparent network environment and they can not be easily localized and isolated. • Control plane integration • What to monitor and distribute? • What is the best control plane integration model? Int. Conf. on Photonics in Switching 2009

  5. Toward Future Core Optical Networks • The network evolution aims at: • Improved cost economics (less costly electronics) • Cost savings of a transparent solution over an opaque network design of up to 50% could be achieved • Source: M. Gunkel, et. al. “A Cost Model for WDM Layer”, Photonics in Switching Conference, 2006. • Reduced investment and operations Efforts (CAPEX, OPEX) • Scalability (bit rate independence) • Suitability to future services (e.g. Grid computing) • The main drivers for network architecture migration: • High bandwidth and end-to-end QoS guaranteed services • Dynamic (on demand) technology-independent service provisioning Int. Conf. on Photonics in Switching 2009

  6. DICONET framework (1/2) • Cross-layer optimization • Physical layer impairment monitoring/management • Impairment Aware Lightpath Routing (a.k.a. IA-RWA) • The main Idea: • The development of a dynamic network planning/operation tool residing in the core network nodes that incorporates real-time measurements of optical layer performance into IA-RWA algorithms and is integrated into a unified control plane. http://www.diconet.eu Int. Conf. on Photonics in Switching 2009

  7. DICONET framework (2/2) • Physical Layer Impairments modeling • Optical Performance and Impairment Monitoring • IA-RWA (Lightpath routing) • Intelligent Component placement algorithms • Failure localization and resilience algorithms • Control plane integration Int. Conf. on Photonics in Switching 2009

  8. DICONET NPOT: Key building blocks • Network Planning and Operation Tool (NPOT) Int. Conf. on Photonics in Switching 2009

  9. Physical layer performance evaluation • In the context of transparent optical networks impairment can be categorized into “static” (e.g. ASE noise, PMD, filter concatenation) and “dynamic” (network-state dependent: e.g. node crosstalk, XPM, FWM) impairments. • We utilize a “Q-Tool” to assess the QoT of a lightpath. Q-Factor for a lightpath is a QoT indicator that is related to the signal’s BER. Int. Conf. on Photonics in Switching 2009

  10. Inaccuracy of the Q-Tool (1/2) • Practical QoT estimators (including our Q-Tool) is a combination of analytical models and/or interpolations of measurements and simulations. • Practical QoT estimators should be fast in order to support quick lightpath establishment. • Inaccuracy of Q-Tool • Imperfect physical models (by nature) • Optimization for speed • Incorrect QoT estimation has a direct impact on lightpath establishment • Q overestimate  accept LP with inadequate QoT • Q underestimate  block LP with adequate QoT Int. Conf. on Photonics in Switching 2009

  11. Inaccuracy of the Q-Tool (2/2) 40% (η=1) Int. Conf. on Photonics in Switching 2009

  12. Online “Rahyab” (1/4) • The main idea behind online Rahyab algorithm is to design a multi-constraint IA-RWA algorithm that considers QoT inaccuracy through optical monitor availability information in routing decisions, in order to alleviate the inaccuracy of the QoT estimator (i.e. Q-Tool). • “Rahyab” building blocks • Multi-Constraint Path (MCP) computation framework • Link cost vector and Single Mixed Metric Mapping • Online “Rahyab” flowchart Int. Conf. on Photonics in Switching 2009

  13. Online “Rahyab” (2/4) • Considering a network topology G=(V,E), each link ‘e’ is characterized by M additive non-negative weights, wm(e), m=1,2,…,M. Given constraint Cm,m=1,…,M, the MCP problem is to find a path p such that: • Single Mixed Metric (SMM) (insight: can meet all Cm with high prob. using simple shortest path alg. on weighted graph): Int. Conf. on Photonics in Switching 2009

  14. Online “Rahyab” (3/4) • Link cost vector (2 costs, can be extended): • Metric: link length L(e) Constraint: max lightpath length: L<LMax • Metric: impact of inaccuracy (on QoT estimator) based on monitor availability (mi) for a given link e: Θ(e). Constraint: max inaccuracy over a lightpath: η<ηmax Int. Conf. on Photonics in Switching 2009

  15. Flow diagram of Rahyab Int. Conf. on Photonics in Switching 2009

  16. Hamburg Bremen Berlin Hannover Essen Dortmund Düsseldorf Leipzig Köln Frankfurt Nürnberg Stuttgart Ulm München Simulation Setup • DTNet • Number of nodes:14 • Number of links:23 • Average node degree:3.29 • Diameter: 800 km Int. Conf. on Photonics in Switching 2009

  17. Results (1/3) • Blocking rate vs. load Int. Conf. on Photonics in Switching 2009

  18. Results (2/3) • Blocking rate vs. channels/link Int. Conf. on Photonics in Switching 2009

  19. Results (3/3) • Required channels/link to reach 0% blocking rate Int. Conf. on Photonics in Switching 2009

  20. Fast lightpath establishment • Different approach: incorporate additional (“historic”) probing data to make better QoT estimation • Setup: when demand arrives: a) estimate QoT using past monitoring data (probes), b) send probe • Problem: wrong QoT estimation leads to additional LP establishment attempts, which should be decreased for fast lightpath establishment • Proposed solution: • Perform QoT estimation for LPs - use monitoring data of LPs already established • Use “end-to-end” estimation framework (“network kriging”): leverage correlation between LP QoT, induced by topology • Lightpaths using common links sustain similar physical effects Work with Nicola Sambo et al., ICTON 2009 (BONE) Int. Conf. on Photonics in Switching 2009

  21. Principle Of Network Kriging • End-to-end estimation framework [Chua, Kolaczyk, Crovella, JSAC 2006] • Solves the following problem: • Given additive metric y s.t. y=Gx • =end-to-end (lightpath) metric, =routing matrix, x=link metric • OB: observed lightpath/metric, UN: unobserved • Typical example: x=link delay, y=route delay, G(i,j)=1 if link j is on route i, G(i,j)=0 otherwise • Given the observed (with probing) end-to-end metrics (for some of the routes) yOB • Compute the end-to-end metric y for all routes (and in particular for yUN) • We will exhibit the real physical meaning of y soon Example • Suppose LP1, LP2, LP3 established and monitored • LP4 demand arrives: QoT>QoTthreshold? • Can estimate ŷ4 given y1, y2, y3 and determine QoTLP4 • Estimation technique = “network kriging” [JSAC 2006] ŷUN=GUNGOB(GOBGTOB)+yOB Int. Conf. on Photonics in Switching 2009

  22. QoT model • Use QLP=f(OSNR(LP), CD(LP), PMD(LP), φ(LP)) • QoT model account for ASE, PMD, CD, SPM (φNL) • OSNR: OSNR-1 is additive 1/OSNR(LP)=1/OSNR(l1)+1/OSNR(l2) • CD: dispersion is additive (in ps/nm) • PMD: PMD2 is additive (in ps2) • φNL: nonlinear phase is additive (in rad) • Can use power monitor to measure it • Need 4 types of monitors (OSNR, CD, PMD, φNL)  Perform estimation on y={1/OSNR, CD, PMD2, φNL} Int. Conf. on Photonics in Switching 2009

  23. Support through PCE architecture • Assume all 4 kinds of monitors are available at all nodes • Existence of a centralized measurement database MD where measurements from all previous monitored LPs is recorded • LP establishment: source queries MD to estimate QoT of candidate • If QoT acceptable: • probing • destination updates MD LP1: (OSNR1, CD1, PMD1, φ1) LP2: (OSNR2, CD2, PMD2, φ2) LP3: (OSNR3, CD3, PMD3, φ3) LP4: (OSNR4, CD4, PMD4, φ4) MD LP4 QoT(LP4) Update MD: LP4= (OSNR4, CD4, PMD4, φ4) s Establish LP4 d Estimated QoT>QoTthreshold Int. Conf. on Photonics in Switching 2009

  24. Simulation results: Reduction in setup attempts • Pan-European topology, 17 nodes, 2x32 links, 40 W/direction • C-NKS: with network kriging; C-MDS: without • n=number of attempts to establish a lightpath • For same blocking rate, gain 1 attempt in average Same blocking rate ≈2x10-3 Without estimation (MDS): 2 attempts to establish lightpath With estimation (NKS): 1 attempt needed to establish lightpath Source: Nicola Sambo, et al., ICTON 2009 Int. Conf. on Photonics in Switching 2009

  25. Simulation results: dynamic behavior x-axis: time With end-to-end estimation: faster convergence of blocking rate  hints at a higher resilience of the technique to network changes (failure, etc) Source: Nicola Sambo, et al., ICTON 2009 Int. Conf. on Photonics in Switching 2009

  26. Conclusions • Next Generation Core Optical Networks • Many studies around • Many problem addressed • Not many integrated and comprehensive works • DICONET  Integrated Network Planning and Operation Tool • Presented here: Lightpath establishment with consideration for Q-Tool inaccuracy, fast lightpath establishment • Future work/Work in progress: • Fault detection/management • Control plane design and implementation • Integrated planning and operation tool • FPGA acceleration of Q estimator • Validation with test-bed Int. Conf. on Photonics in Switching 2009

  27. Thank you! • Question & Answers • Acknowledgements • This work is partially funded by the European Commission (FP7) Dynamic Impairment Constraint Networking for Transparent Mesh Optical Networks http://www.diconet.eu Building the Future Optical Network in Europe http://www.ict-bone.eu Int. Conf. on Photonics in Switching 2009

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